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Old 09-27-2012, 01:13 AM   #36
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Quote:
Originally Posted by JDF

Sadly Whipple doesn't make a kit for them either, at least that I know of. Kennel Bell is the only twin screw I've heard of for the 2V
Well that sucks. Eventually I want to get the whipple 4.0 crusher. $$$$
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Old 09-27-2012, 06:24 AM   #37
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Sts kit never really thought of that cause i want to pop the hood and have that little wow factor
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Old 09-27-2012, 12:48 PM   #38
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Originally Posted by sam minnick
Sts kit never really thought of that cause i want to pop the hood and have that little wow factor
Gives you that nice sleeper factor.
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Old 09-27-2012, 02:29 PM   #39
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Quote:
Originally Posted by sam minnick
Sts kit never really thought of that cause i want to pop the hood and have that little wow factor
They may not see it, but the minute you get on it they will definitely hear it

---------- Post added at 01:29 PM ---------- Previous post was at 01:28 PM ----------

Quote:
Originally Posted by frank07stanggt

Well that sucks. Eventually I want to get the whipple 4.0 crusher. $$$$
That is one monster blower
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Old 09-27-2012, 02:36 PM   #40
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Quote:
Originally Posted by JDF

They may not see it, but the minute you get on it they will definitely hear it

---------- Post added at 01:29 PM ---------- Previous post was at 01:28 PM ----------



That is one monster blower
Oh yeah. Gotta do some work on the motor and cooling system first. Lol
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Old 09-27-2012, 02:42 PM   #41
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Quote:
Originally Posted by frank07stanggt

Oh yeah. Gotta do some work on the motor and cooling system first. Lol
Don't you need a new hood for one of those?
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Old 09-27-2012, 02:47 PM   #42
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Don't you need a new hood for one of those?
I haven't really looked too much into it cause I'm not even close money wise. But I might since its so gigantic.
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Old 09-27-2012, 03:10 PM   #43
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What do you have again frank is it a 03 cobra you running 450 hp
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Old 09-27-2012, 03:15 PM   #44
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Quote:
Originally Posted by sam minnick
What do you have again frank is it a 03 cobra you running 450 hp
An 04 cobra and its somewhere around there. Haven't been on a dyno but that's what others with my mods are getting. Mods are jlt high boost cai, 2.76 upper pulley, and a tune.
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Old 09-27-2012, 03:36 PM   #45
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Did the 04 come charged
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Old 09-27-2012, 03:46 PM   #46
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Did the 04 come charged
Yeah 2003-2004 were s/c from the factory. After I port the blower this weekend I'm going to paint it black. Gonna look sweet. I'll post a pic after I do it.
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Old 09-27-2012, 03:48 PM   #47
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Quote:
Originally Posted by frank07stanggt

Yeah 2003-2004 were s/c from the factory. After I port the blower this weekend I'm going to paint it black. Gonna look sweet. I'll post a pic after I do it.


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Just put the jlt intake in last night. Going to look better when the blower and throttle body are black.
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Old 09-27-2012, 04:24 PM   #48
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That looks bad *** man i wish i could have gotten a supercharged car but the funds didn't allow that... i got a super clean car it has 101 thousand miles on it but the speedo is off so my guess is the odometer is too i only paid 6 for it
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Old 09-27-2012, 04:30 PM   #49
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Quote:
Originally Posted by sam minnick
That looks bad *** man i wish i could have gotten a supercharged car but the funds didn't allow that... i got a super clean car it has 101 thousand miles on it but the speedo is off so my guess is the odometer is too i only paid 6 for it
Yeah I traded an 07 gt with 95k on it for this cobra with only 82k on it. There are deals out there you just have to look for them. I got lucky cause a guy traded it in on a gt500 like 3 days before I saw it.
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Old 09-27-2012, 08:59 PM   #50
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Thats awesome i put new wheels on mine tonight ill try to upload a pic but its hard to see cause its dark out
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Old 09-27-2012, 09:01 PM   #51
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The wheels look good
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Old 09-27-2012, 10:38 PM   #52
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Quote:
Originally Posted by taylor98gt
Hellion twin turbo kit. Lol
X1000
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Old 09-30-2012, 07:19 PM   #53
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Are vortech worth the money
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Old 09-30-2012, 10:33 PM   #54
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Quote:
Originally Posted by frank07stanggt

Just put the jlt intake in last night. Going to look better when the blower and throttle body are black.
All finished. Painted the blower and valve covers. If you ever want to paint your cobra valve covers just stop......and don't cause the drivers side valve cover was a biotch to get out.
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Old 09-30-2012, 11:46 PM   #55
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Quote:
Originally Posted by frank07stanggt

All finished. Painted the blower and valve covers. If you ever want to paint your cobra valve covers just stop......and don't cause the drivers side valve cover was a biotch to get out.
That looks oh so nice......
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Old 10-01-2012, 05:26 AM   #56
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It looks good though so id say it was worth it
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Old 10-01-2012, 06:57 AM   #57
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Quote:
Originally Posted by frank07stanggt

All finished. Painted the blower and valve covers. If you ever want to paint your cobra valve covers just stop......and don't cause the drivers side valve cover was a biotch to get out.
Can't be worse than on my 04 f150
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Old 10-01-2012, 07:12 AM   #58
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Originally Posted by 2002VertGT

Can't be worse than on my 04 f150
Drivers side is under the hydro booster= me upside down taking out bolts behind the pedals. Took 4 hours to get the drivers side out. Had to move everything.
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Old 10-01-2012, 08:54 AM   #59
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Wow that sucks i think you should take them back off and paint them yellow leave the charger black but the covers paint yellow hahaha jk
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Old 10-01-2012, 11:20 AM   #60
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Quote:
Originally Posted by frank07stanggt

Drivers side is under the hydro booster= me upside down taking out bolts behind the pedals. Took 4 hours to get the drivers side out. Had to move everything.
My 04 f150 is under the firewall....and smack dead next to the hydro booster....literally, enough room for a 1/4 in extension with 8mm socket to get to bolts behind the cover..best pic I have atm
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Old 10-01-2012, 11:21 AM   #61
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Originally Posted by 2002VertGT

My 04 f150 is under the firewall....and smack dead next to the hydro booster....literally, enough room for a 1/4 in extension with 8mm socket to get to bolts behind the cover..best pic I have atm
Notice how I didn't even try to take them off in this pic...I had done wiggled them out 3 times at this point and didnt want the hassle
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Old 10-01-2012, 11:51 AM   #62
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Originally Posted by 2002VertGT

My 04 f150 is under the firewall....and smack dead next to the hydro booster....literally, enough room for a 1/4 in extension with 8mm socket to get to bolts behind the cover..best pic I have atm
I would have set my car on fire and beat the person who designed it that way. What did u have to do. Pull the motor?
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Old 10-01-2012, 12:17 PM   #63
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Originally Posted by frank07stanggt

I would have set my car on fire and beat the person who designed it that way. What did u have to do. Pull the motor?
I had to replace timing stuff, seals on the tentioners blew and f'ed everything up...even the timing cover. Put it back to together and it didn't run right...took it back apart and put it back together and it ran right. Drive for a lil while and had to replace pass side manifold, bolt broke in head so I had to strip the motor down again. Once back together found out timing had been set wrong so apart it came again....now it runs right but I thing the tq converter is bad...all this since February.
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Old 10-08-2012, 12:19 PM   #64
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If i have automatic whats better
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Old 10-08-2012, 12:28 PM   #65
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If i have automatic whats better
A manual. Lol jk. I had to
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Old 10-08-2012, 03:24 PM   #66
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Originally Posted by sam minnick
If i have automatic whats better
Well it still depends on what sort of boost you want. A turbo would benefit from an automatic because you don't lose the boost by shifting.
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Old 10-08-2012, 04:29 PM   #67
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Manual is more fun but its nice having a automatic and just go...
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Old 10-09-2012, 12:26 AM   #68
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Here's research results loosely compiled into a paper I collaborated on a while ago on turbo vs SC. (it's incredibly long, but I feel that it is very informative) my sincerest apologies for the length. I don't feel like cutting it down and losing info. (Additional Note: it does not account for TVS or twin screw models.) (Additional ADDITIONAL note: excuse the typos, I was sleepy when it was compiled)

Here are some arguments for use of waste energy and parastic loss. So I used a Honda engine but I am too lazy to find my SR20 notes.

As stated before, turbos are driven by the wasted 30% of fuel energy dumping out of the exhaust stream without parasitic losses on the crankshaft. This use of waste energy is the main reason why turbochargers have a tremendous power advantages over superchargers.

Here is the long and boring nerd way to add some validity to the power debate. Lets figure out how much power it takes to compress the air to make serious engine power. We will do this two ways; we will figure the differences in intake air temp for a turbo, a roots supercharger and a centrifugal supercharger. Then we will show how much power it takes to turn the supercharger. It should all make sense once it’s laid out.

First lets calculate Delta T for the various compressors. Delta T is the change in the intake air temp after it is compressed.

Delta T= Intake Absolute Temperature x (Pressure Ratio to the .238 power –1)/ Compressor Efficiency

Lets assume our engine is going to run 20 psi of boost or a pressure ratio of 2.36.
Pressure ratio= boost pressure+14.7/14.7

The temperature scale engineers use for absolute temperature is the Rankin Scale. On the Rankin Scale Zero degrees is absolute zero. So assuming our intake air temp is 85 degrees, lets call that 545 degrees Rankin.

Lets say our match car is a hot Acura GSR with a B18C motor. By using standard compressor matching equations , we figure that the B18C can flow about 45.3 lb/min going full tilt at 20 psi.

So here we go. Lets figure out Delta T for our good turbo first. Lets assume an efficiency of 78% as there are many turbos that can do that at the given flow and pressure ratio.

Delta T= 545 x (2.36 to the .238 power –1)/ 0.78
Delta T= 158 degrees

A 4-cylinder sized Centrifugal Supercharger is probably much less than 70% efficient at this point but lets be kind to it and assume that, Plugging and chugging gets us a temp of 177 degrees.

Now there are not any current roots blowers on the market that can support this sort of boost pressure on a small 4 cylinder car but lets suppose there is and lets be very kind, assuming it will get 60% compressor efficiency at 20 psi and 45.3 lb/min of flow. This is not likely, but lets be nice to the poor roots. Plug and chug and we get a Delta T of 206 degrees. In reality the efficiency would be closer to 50% at 20 psi and the numbers much worse.

Now Delta T is the difference in temp after being compressed. What would our intake charge temp be for the roots assuming an intake temp of 85 degrees? 85+206= an egg frying 291 degrees with no intercooler!

Now lets figure out the power required to make the boost from these three compressors.

The equation for compressor power needed is.

Power in BTU per minute= Mass Flow x Cp (a coefficient) x Delta T/ Compressor Efficiency

To convert BTU per minute to horsepower divide by 42.4

Power = 45.3 x .242 x 158/78 = 2220 BTU min/42.4 = 52 hp recovered from the exhaust.

So here is the Horsepower that won’t be taken from the crankshaft but recovered from the exhaust stream by the turbocharger on our vapor GSR.

If you check out the gas power cycle in a thermodynamics book, the PV diagram for you engineers, you need to correct the power equation a little for a supercharger. Since a supercharger adds pressure to one side of the motor and the turbo adds it to both, we need to do an estimation of the power recovered by the supercharger on the intake stroke.

The equation is:

((Boost Pressure x Engine Displacement in cubic inches x RPM)/2)/12 x 60 x 550

So for our B18C:

(20psi x 110 x 8500 rpm/2)/396000 = 24 hp

To figure out how much power the Centrifugal Supercharger takes from the crankshaft, lets plug and chug again, getting a 65 horsepower, subtract 24 hp and you get a crankshaft power loss of 41 hp

Repeating for the Roots Blower gets us a loss of 65 horsepower stolen from the crank.

So simply reducing our meager data, if you calculate the potential hp of our turbocharged B18C we will get about 453 hp. Thus well might be around 412 hp from our centrifugally supercharged version of the same motor and 388 hp from our roots equipped motor. Now this is vastly oversimplified and does not take into account differences in VE, air density differences for intercooler effectiveness or lack thereof, dynamic matching to compressor maps and engine tuning variable that have to be different between the types of compressors. Of these variables, all of them except for VE differences will be in favor of the turbo. This shows that all other things being equal, the turbocharger does have an advantage when it comes to sheer power output. The compressor efficiencies we used for the superchargers were very conservative. In real life the superchargers would probably be much worse at 20 psi. If we upped the boost higher, to higher pressure ratios where turbochargers really shine, the calculated differences would be even greater.

Again, a 4-cylinder sized Centrifugal Supercharger is probably much less than 70% efficient at this point but lets be kind to it and assume that, Plugging and chugging gets us a temp of 177 degrees or a hellish 262 degrees at the intake. Let me remind you that to my knowlege there are no centrifugal superchargers that can even reach 20 psi on a small engine on the market besides maybe Procharger, which is a horrible design, and I dispute that it can be much more efficient than 65% no matter what Procharger claims due to thick impeller blades, no diffuser and a raidial non-curved vane impeller blade, ie, 1950's technology.

Staying in the Compressors Sweet Spot:

As we stared before a lot of how a turbocharger behaves is dependant upon how it is matched to the engine. Turbos come in many sizes and can be precisely tailored to the engines displacement and the owners desire in power characteristics. Since the turbo is not directly coupled to the engines crankshaft, there is some latency in the throttle response, described as turbo lag. As explained before this lag can be largely tuned out but it will always be there to some degree. Since the turbo is free floating from the crankshaft, creative sizing and wastegating enables the turbo to be kept in a more efficient range of operation over a wider band of the engines operating range.

Better Compressor Efficiency, More Flexibility:

Another advantage that most turbochargers have is improved compressor efficiency over superchargers. Compressor efficiency is the thermodynamically calculated temperature rise of compressing intake air a given amount via the ideal gas law divided by the actual temperature rise of air compressed to the same pressure by the compressor in question. This is also known as the adiabatic efficiency. When talking about compressor efficiency, it is given as a percentage with the higher the percentage, the better. The higher efficiency means that the intake charge will be heated less while it is being compressed. A centrifugal compressor like the one found on a turbocharger is very efficient. Typically the efficiency is at least 70 percent over a broad range of engine operation for most turbochargers with state of the art examples having efficiencies around 80 percent. Typical good turbo compressors found in the aftermarket, like the Garrett TO4E have efficiencies ranging in the mid 70’s. Newer designs like Garrett’s GT series can have efficiencies of up to 80 percent. The more efficient the compressor, the cooler the intake charge air will be. In the case of an old school, less than 50% efficient, roots blower vs. a state of the art turbo, the difference in compressor discharge air temp can be over 100 degrees F at the same boost pressure!

Good turbocharger compressor efficiency is important for reducing engine backpressure on a turbocharged car as well. A more efficient compressor requires less power to compress the air, thus the turbine has to recover less energy from the exhaust stream. With less of a pressure drop required to recover the energy, the exhaust backpressure is reduced and the volumetric efficiency goes up. A more efficient compressor also has less turbo lag for this very reason.

The latest designs of turbos like the Garrett GT series and the latest offerings from IHI have highly efficient compressor and turbine wheels combined with low friction ball bearing center sections. The IHI compressor also features an abradeable lining to the compressor housing. This Teflon like coating is abraded away by the compressor wheel to allow the tightest possible housing to wheel fit. This significantly improves compressor efficiency. These high tech features reduce turbo lag to a large degree without sacrificing flow.

In contrast, some newer roots blowers like the Eaton, have improved designs and higher efficiencies in the low 60% range, a vast improvement from the old 50% efficient bus supercharger, but still much less than the typical turbocharger compressor. The roots design is less efficient because it has a lot of internal leakage and does not have internal compression, relying instead of external compression in the manifold. The Eaton’s improved efficiency over prior roots superchargers comes from its having some internal compression due to changes in its port timing and rotor geometry over old style roots blowers. Modern CNC machining techniques also allow the Eaton to have tighter tolerances and less internal leakage then the older designs had.

You might have heard of a Lysholm supercharger, which is very similar to a roots blower but has two rotating screws with a varying pitch to compress the air instead of 3 lobed impellers like the roots. Whipple makes a blower of this design. The Whipple should have superior adiabatic efficiency because of the designs internal compression. Whipple claims 75% although they do not publish compressor maps to validate this claim. The only Import Whipple application that we know of is the Comptech NSX kit, which produces 367 hp to the wheels.

Centrifugal supercharger compressors like the Vortech are much more efficient. The V-5 supercharger used in their Civic Si kit can reach efficiencies of 73% over a fairly broad band. Unfortunately this efficiency is achieved at fairly low-pressure ratios, which would limit the engines swallowing capacity if you were to try to go to a full race high boost application. With small motor, the way to increase the swallowing capacity is to run more boost and higher pressure ratios. Higher boost means more air stuffed into the engine. With high flow and good efficiency at lower pressure ratios, centrifugal superchargers now on the market, seem better suited for large capacity V-8 engines.

Even with the Vortech superchargers broad (for a centrifugal blower) peak efficiency island, the turbo will still dwell in a higher efficiency zone of operation longer than the centrifugal supercharger will. This is due to the turbo’s wastegating allowing the turbocharger to operate in an efficient zone longer.

The inability to operate with good efficiency at high pressure ratios on small engines seems to be a major limiting factor for centrifugal superchargers when it comes to making race winning levels of power with 4-cylinders. Most centrifugal superchargers of the proper size for a 4-cylinder are out in the 65% or less Efficiency Island of the compressor map at a pressure ratio of over 2.4:1 or just a tick under 20 psi. The bigger centrifugal superchargers that can get into the higher-pressure ratios are in the surge zone with smaller 4-cylinder motors like ours. It takes more than 20 psi to win in the quick and outlaw classes these days.

At 2.4:1 the centrifugal supercharger is nearly off the map, close to the surge line on a small 4-cylinder motor and operating in an inefficient part of its operating range where it is heating the air and eating a lot of crank power. This is just not enough boost pressure to make serious quick sixteen winning power with a small displacement 4 cylinder. Many turbochargers are capable of efficiently (easily over 72%) operating at pressure ratios of 3:1 (30 psi) and higher on small engines without surge.

The final negative supercharger issue is the lack of tuning flexibility. On a turbo, you can drastically alter the boost levels by tweaking the wastegate pressure signal with a boost controller. Are you at 15 psi and dump in some race gas? You can crank her up to 20 psi and enjoy the power in a second. Are you racing, running 23 psi and the track starts to hook up better? No problem, turn her up to 27 psi to take advantage of it. With a supercharger, you have to change drive ratios, which is not very practical between rounds.

Vortech is the most efficient of the centrifugal superchargers on the market. Other brands struggle to get their efficiency into the mid 60’s.One of the reasons why some aftermarket centrifugal Supercharger compressors are not as efficient as turbochargers is that typically a small aftermarket company usually engineers them where as most turbochargers are designed by big OEM automotive supply companies and their product is highly engineered. OEM development sinks a lot of costs into optimization of the compressor design, especially in the long haul diesel and stationary engine market where every bit of efficiency is desired as every bit helps improve fuel consumption. Where Garrett has a whole building full of engineers and a multimillion-dollar test facility, an aftermarket company cannot muster anywhere near that level of engineering resources when it comes to design, testing and manufacturing. Buying a turbo from Garrett, Mitsubishi or IHI means that you are buying a unit with lots of engineering time and optimization, way more than what a typical aftermarket centrifugal supercharger will ever hope to have.

Better Matching to the Engine:

Another reason why turbochargers are such kings of power is that turbochargers are used heavily in the long haul diesel and commercial stationary engine market. This market covers a wide variety of applications from small 4 cylinder Japanese panel trucks to huge Caterpillar earthmovers. As stated before, fuel economy is very critical to commercial operators as is precise engineering of the engines power characteristics. This diversity in application engine size and output plus the market demands for efficiency on a large commercial scale ensures that much R&D money is spent on turbocharger optimization, which means that there are literally hundreds of different sizes of turbochargers optimized for a great deal of different applications. This makes it easy to come up with some very nice turbo combinations for most automotive performance users. The supercharger aftermarket tends to be of the one-size fits all variety with perhaps about 3 to 9 size applications to cover the performance car market.

So which is best for you? If a very broad powerband and very linear throttle response is paramount and you are happy with about a 40% power increase, then a roots blower is for you. If you don’t care about low-end power but want lots of peak power in the order of nearly a 50 to100% gain with a predictable throttle response then a centrifugal blower might float your boat. Do you want a CARB E.O.? Again a supercharger system has more choices. Superchargers are my choice for V8 motors. Turbos are more efficient, but a Garret GT V8 just doesn't have that raw, menacing off-the-line power as a Kenne Bell Mammoth or Whipple Crusher V8.

A turbo system can be tuned anyway you want, from a responsive, lots of low-end system to a screaming insane, race only power monster. The only drawback is that disconnect from your throttle foot, which can be tuned to be either somewhat unnoticeable, to somewhat significant. There are less CARB approved options with a turbo.
How to calculate your potential HP output with a turbo
Once you have figured out your engines airflow at the boost you plan on running you can estimate your hp output pretty easily. To estimate your potential power output, you can do so easily with this formula:

HP= Airflow x 60/Air Fuel Ratio x BSFC

Airflow is in lb/min like we just calculated, 60 is to convert minutes units to hours, Air fuel ratio is self explanatory, BSFC is Brake Specific Fuel Consumption as measured in lb of fuel per hp per hour.

For guidelines, a highly boosted turbo engine running on street 92 octane unleaded pump gas might run an AF ratio of 10.5:1 to hold down detonation. Conversely, a highly massaged drag motor running a specialized high specific gravity turbo fuel might run an AF ratio as lean as 13:1. For estimations on BSFC, a rich tuned pump gas motor might run a BSFC of 0.60. A massaged, tuned to the edge drag race motor on specialized gas might run at 0.45.

So lets pick a crisp state of tune (conservative on race gas) for our hypothetical B18C.

Lets pick a conservative, on race gas air fuel ratio of 12:1 and a reasonable BSFC of 0.50, this is a very safe state of tune where you won’t be close to burning down any motors.

HP= 45.3 x 60/ 12 x 0.50
HP= 453

So our hypothetical B18C will put out around 453 hp @ 20 psi of boost. If you take the time to play around with the equations, the things the tuner has the most control over are the VE, through different size turbines, turbine housings, exhaust systems, headwork cam combos, etc and the tuning factors which include AF ratio and BSFC. The intake manifold temperature can be fiddled with different intercoolers or better yet, go and measure your cars post intercooler intake temp. You can play around with these numbers mathematically and see how they can affect your power and what you can do to extract more power.
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Old 10-09-2012, 03:58 AM   #69
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Nice! Very informative!
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Old 10-09-2012, 08:40 AM   #70
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Quote:
Originally Posted by BackPressure
Here's research results loosely compiled into a paper I collaborated on a while ago on turbo vs SC. (it's incredibly long, but I feel that it is very informative) my sincerest apologies for the length. I don't feel like cutting it down and losing info. (Additional Note: it does not account for TVS or twin screw models.) (Additional ADDITIONAL note: excuse the typos, I was sleepy when it was compiled)

Here are some arguments for use of waste energy and parastic loss. So I used a Honda engine but I am too lazy to find my SR20 notes.

As stated before, turbos are driven by the wasted 30% of fuel energy dumping out of the exhaust stream without parasitic loses on the crankshaft. This use of waste energy is the main reason why turbochargers have a tremendous power advantages over superchargers.

Here is the long and boring nerd way to add some validity to the power debate. Lets figure out how much power it takes to compress the air to make serious engine power. We will do this two ways; we will figure the differences in intake air temp for a turbo, a roots supercharger and a centrifugal supercharger. Then we will show how much power it takes to turn the supercharger. It should all make sense once it’s laid out.

First lets calculate Delta T for the various compressors. Delta T is the change in the intake air temp after it is compressed.

Delta T= Intake Absolute Temperature x (Pressure Ratio to the .238 power –1)/ Compressor Efficiency

Lets assume our engine is going to run 20 psi of boost or a pressure ratio of 2.36.
Pressure ratio= boost pressure+14.7/14.7

The temperature scale engineers use for absolute temperature is the Rankin Scale. On the Rankin Scale Zero degrees is absolute zero. So assuming our intake air temp is 85 degrees, lets call that 545 degrees Rankin.

Lets say our match car is a hot Acura GSR with a B18C motor. By using standard compressor matching equations , we figure that the B18C can flow about 45.3 lb/min going full tilt at 20 psi.

So here we go. Lets figure out Delta T for our good turbo first. Lets assume an efficiency of 78% as there are many turbos that can do that at the given flow and pressure ratio.

Delta T= 545 x (2.36 to the .238 power –1)/ 0.78
Delta T= 158 degrees

A 4-cylinder sized Centrifugal Supercharger is probably much less than 70% efficient at this point but lets be kind to it and assume that, Plugging and chugging gets us a temp of 177 degrees.

Now there are not any current roots blowers on the market that can support this sort of boost pressure on a small 4 cylinder car but lets suppose there is and lets be very kind, assuming it will get 60% compressor efficiency at 20 psi and 45.3 lb/min of flow. This is not likely, but lets be nice to the poor roots. Plug and chug and we get a Delta T of 206 degrees. In reality the efficiency would be closer to 50% at 20 psi and the numbers much worse.

Now Delta T is the difference in temp after being compressed. What would our intake charge temp be for the roots assuming an intake temp of 85 degrees? 85+206= an egg frying 291 degrees with no intercooler!

Now lets figure out the power required to make the boost from these three compressors.

The equation for compressor power needed is.

Power in BTU per minute= Mass Flow x Cp (a coefficient) x Delta T/ Compressor Efficiency

To convert BTU per minute to horsepower divide by 42.4

Power = 45.3 x .242 x 158/78 = 2220 BTU min/42.4 = 52 hp recovered from the exhaust.

So here is the Horsepower that won’t be taken from the crankshaft but recovered from the exhaust stream by the turbocharger on our vapor GSR.

If you check out the gas power cycle in a thermodynamics book, the PV diagram for you engineers, you need to correct the power equation a little for a supercharger. Since a supercharger adds pressure to one side of the motor and the turbo adds it to both, we need to do an estimation of the power recovered by the supercharger on the intake stroke.

The equation is:

((Boost Pressure x Engine Displacement in cubic inches x RPM)/2)/12 x 60 x 550

So for our B18C:

(20psi x 110 x 8500 rpm/2)/396000 = 24 hp

To figure out how much power the Centrifugal Supercharger takes from the crankshaft, lets plug and chug again, getting a 65 horsepower, subtract 24 hp and you get a crankshaft power loss of 41 hp

Repeating for the Roots Blower gets us a loss of 65 horsepower stolen from the crank.

So simply reducing our meager data, if you calculate the potential hp of our turbocharged B18C we will get about 453 hp. Thus well might be around 412 hp from our centrifugally supercharged version of the same motor and 388 hp from our roots equipped motor. Now this is vastly oversimplified and does not take into account differences in VE, air density differences for intercooler effectiveness or lack thereof, dynamic matching to compressor maps and engine tuning variable that have to be different between the types of compressors. Of these variables, all of them except for VE differences will be in favor of the turbo. This shows that all other things being equal, the turbocharger does have an advantage when it comes to sheer power output. The compressor efficiencies we used for the superchargers were very conservative. In real life the superchargers would probably be much worse at 20 psi. If we upped the boost higher, to higher pressure ratios where turbochargers really shine, the calculated differences would be even greater.

Again, a 4-cylinder sized Centrifugal Supercharger is probably much less than 70% efficient at this point but lets be kind to it and assume that, Plugging and chugging gets us a temp of 177 degrees or a hellish 262 degrees at the intake. Let me remind you that to my knowlege there are no centrifugal superchargers that can even reach 20 psi on a small engine on the market besides maybe Procharger and Procharger is a horrible design and I dispute that it can be much more efficent than 65% no matter what Procharger claims due to thick impeller blades, no diffuser and a raidial non-curved vane impeller blade, ie, 1950's technology.

Staying in the Compressors Sweet Spot
As we stared before a lot of how a turbocharger behaves is dependant upon how it is matched to the engine. Turbos come in many sizes and can be precisely tailored to the engines displacement and the owners desire in power characteristics. Since the turbo is not directly coupled to the engines crankshaft, there is some latency in the throttle response, described as turbo lag in the previous section of this article. As explained before this lag can be largely tuned out but it will always be there to some degree. Since the turbo is free floating from the crankshaft, creative sizing and wastegating enables the turbo to be kept in a more efficient range of operation over a wider band of the engines operating range.

Better Compressor Efficiency, More Flexibility
Another advantage that most turbochargers have is improved compressor efficiency over superchargers. Compressor efficiency is the thermodynamically calculated temperature rise of compressing intake air a given amount via the ideal gas law divided by the actual temperature rise of air compressed to the same pressure by the compressor in question. This is also known as the adiabatic efficiency. When talking about compressor efficiency, it is given as a percentage with the higher the percentage, the better. The higher efficiency means that the intake charge will be heated less while it is being compressed. A centrifugal compressor like the one found on a turbocharger is very efficient. Typically the efficiency is at least 70 percent over a broad range of engine operation for most turbochargers with state of the art examples having efficiencies around 80 percent. Typical good turbo compressors found in the aftermarket, like the Garrett TO4E have efficiencies ranging in the mid 70’s. Newer designs like Garrett’s GT series can have efficiencies of up to 80 percent. The more efficient the compressor, the cooler the intake charge air will be. In the case of an old school, less than 50% efficient, roots blower vs. a state of the art turbo, the difference in compressor discharge air temp can be over 100 degrees F at the same boost pressure!

Good turbocharger compressor efficiency is important for reducing engine backpressure on a turbocharged car as well. A more efficient compressor requires less power to compress the air, thus the turbine has to recover less energy from the exhaust stream. With less of a pressure drop required to recover the energy, the exhaust backpressure is reduced and the volumetric efficiency goes up. A more efficient compressor also has less turbo lag for this very reason.

The latest designs of turbos like the Garrett GT series and the latest offerings from IHI have highly efficient compressor and turbine wheels combined with low friction ball bearing center sections. The IHI compressor also features an abradeable lining to the compressor housing. This Teflon like coating is abraded away by the compressor wheel to allow the tightest possible housing to wheel fit. This significantly improves compressor efficiency. These high tech features reduce turbo lag to a large degree without sacrificing flow.

In contrast, some newer roots blowers like the Eaton, have improved designs and higher efficiencies in the low 60% range, a vast improvement from the old 50% efficient bus supercharger, but still much less than the typical turbocharger compressor. The roots design is less efficient because it has a lot of internal leakage and does not have internal compression, relying instead of external compression in the manifold. The Eaton’s improved efficiency over prior roots superchargers comes from its having some internal compression due to changes in its port timing and rotor geometry over old style roots blowers. Modern CNC machining techniques also allow the Eaton to have tighter tolerances and less internal leakage then the older designs had.

You might have heard of a Lysholm supercharger, which is very similar to a roots blower but has two rotating screws with a varying pitch to compress the air instead of 3 lobed impellers like the roots. Whipple makes a blower of this design. The Whipple should have superior adiabatic efficiency because of the designs internal compression. Whipple claims 75% although they do not publish compressor maps to validate this claim. The only Import Whipple application that we know of is the Comptech NSX kit, which produces 367 hp to the wheels.

Centrifugal supercharger compressors like the Vortech are much more efficient. The V-5 supercharger used in their Civic Si kit can reach efficiencies of 73% over a fairly broad band. Unfortunately this efficiency is achieved at fairly low-pressure ratios, which would limit the engines swallowing capacity if you were to try to go to a full race high boost application. With small motor, the way to increase the swallowing capacity is to run more boost and higher pressure ratios. Higher boost means more air stuffed into the engine. With high flow and good efficiency at lower pressure ratios, centrifugal superchargers now on the market, seem better suited for large capacity V-8 engines.

Even with the Vortech superchargers broad (for a centrifugal blower) peak efficiency island, the turbo will still dwell in a higher efficiency zone of operation longer than the centrifugal supercharger will. This is due to the turbo’s wastegating allowing the turbocharger to operate in an efficient zone longer.

The inability to operate with good efficiency at high pressure ratios on small engines seems to be a major limiting factor for centrifugal superchargers when it comes to making race winning levels of power with 4-cylinders. Most centrifugal superchargers of the proper size for a 4-cylinder are out in the 65% or less Efficiency Island of the compressor map at a pressure ratio of over 2.4:1 or just a tick under 20 psi. The bigger centrifugal superchargers that can get into the higher-pressure ratios are in the surge zone with smaller 4-cylinder motors like ours. It takes more than 20 psi to win in the quick and outlaw classes these days.

At 2.4:1 the centrifugal supercharger is nearly off the map, close to the surge line on a small 4-cylinder motor and operating in an inefficient part of its operating range where it is heating the air and eating a lot of crank power. This is just not enough boost pressure to make serious quick sixteen winning power with a small displacement 4 cylinder. Many turbochargers are capable of efficiently (easily over 72%) operating at pressure ratios of 3:1 (30 psi) and higher on small engines without surge.

The final negative supercharger issue is the lack of tuning flexibility. On a turbo, you can drastically alter the boost levels by tweaking the wastegate pressure signal with a boost controller. Are you at 15 psi and dump in some race gas? You can crank her up to 20 psi and enjoy the power in a second. Are you racing, running 23 psi and the track starts to hook up better? No problem, turn her up to 27 psi to take advantage of it. With a supercharger, you have to change drive ratios, which is not very practical between rounds.

Vortech is the most efficient of the centrifugal superchargers on the market. Other brands struggle to get their efficiency into the mid 60’s.One of the reasons why some aftermarket centrifugal Supercharger compressors are not as efficient as turbochargers is that typically a small aftermarket company usually engineers them where as most turbochargers are designed by big OEM automotive supply companies and their product is highly engineered. OEM development sinks a lot of costs into optimization of the compressor design, especially in the long haul diesel and stationary engine market where every bit of efficiency is desired as every bit helps improve fuel consumption. Where Garrett has a whole building full of engineers and a multimillion-dollar test facility, an aftermarket company cannot muster anywhere near that level of engineering resources when it comes to design, testing and manufacturing. Buying a turbo from Garrett, Mitsubishi or IHI means that you are buying a unit with lots of engineering time and optimization, way more than what a typical aftermarket centrifugal supercharger will ever hope to have.

Better Matching to the Engine
Another reason why turbochargers are such kings of power is that turbochargers are used heavily in the long haul diesel and commercial stationary engine market. This market covers a wide variety of applications from small 4 cylinder Japanese panel trucks to huge Caterpillar earthmovers. As stated before, fuel economy is very critical to commercial operators as is precise engineering of the engines power characteristics. This diversity in application engine size and output plus the market demands for efficiency on a large commercial scale insures that much R&D money is spent on turbocharger optimization which means that there are literally hundreds of different sizes of turbochargers optimized for a great deal of different applications. This makes it easy to come up with some very nice turbo combination for most automotive performance users. The supercharger aftermarket tends to be of the one-size fits all variety with perhaps about 3 to 9 size applications to cover the performance car market.

So which is best for you? If a very broad powerband and very linear throttle response is paramount and you are happy with about a 40% power increase, then a roots blower is for you. If you don’t care about low-end power but want lots of peak power in the order of nearly a 50 to100% gain with a predictable throttle response then a centrifugal blower might float your boat. Do you want a CARB E.O.? Again a supercharger system has more choices.

A turbo system can be tuned anyway you want, from a responsive, lots of low-end system to a screaming insane, race only power monster. The only drawback is that disconnect from your throttle foot, which can be tuned to be either almost unnoticeable, to somewhat significant. There are less CARB approved options with a turbo.
How to calculate your potential HP output with a turbo
Once you have figured out your engines airflow at the boost you plan on running you can estimate your hp output pretty easily. To estimate your potential power output, you can do so easily with this formula:

HP= Airflow x 60/Air Fuel Ratio x BSFC

Airflow is in lb/min like we just calculated, 60 is to convert minutes units to hours, Air fuel ratio is self explanatory, BSFC is Brake Specific Fuel Consumption as measured in lb of fuel per hp per hour.

For guidelines, a highly boosted turbo engine running on street 92 octane unleaded pump gas might run an AF ratio of 10.5:1 to hold down detonation. Conversely, a highly massaged drag motor running a specialized high specific gravity turbo fuel might run an AF ratio as lean as 13:1. For estimations on BSFC, a rich tuned pump gas motor might run a BSFC of 0.60. A massaged, tuned to the edge drag race motor on specialized gas might run at 0.45.

So lets pick a crisp state of tune (conservative on race gas) for our hypothetical B18C.

Lets pick a conservative, on race gas air fuel ratio of 12:1 and a reasonable BSFC of 0.50, this is a very safe state of tune where you won’t be close to burning down any motors.

HP= 45.3 x 60/ 12 x 0.50
HP= 453

So our hypothetical B18C will put out around 453 hp @ 20 psi of boost. If you take the time to play around with the equations, the things the tuner has the most control over are the VE, through different size turbines, turbine housings, exhaust systems, headwork cam combos, etc and the tuning factors which include AF ratio and BSFC. The intake manifold temperature can be fiddled with different intercoolers or better yet, go and measure your cars post intercooler intake temp. You can play around with these numbers mathematically and see how they can affect your power and what you can do to extract more power.
2012 best seller. Turbo vs sc. By. Back pressure Lol
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