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Old 02-20-2012, 05:06 PM   #1
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Here Comes EXHAUST!!

Ok, so I believe I've narrowed down my equation with help from people here for what my stock valve lift is. Based on the valve lift formula (lobe lift x roller or rocker arm ratio) for the exhaust side which I've tried to be conservative with (.295" x 1.8 = .531" valve lift).. I've come to the conclusion that if I use .531" of valve lift for the Header Primary Tube Size formula: √(valve lift x valve diameter) x 2, it will have given me a very close size of primary tube size for my headers. So here goes:
√(.531" x 1.417") x 2 =
√.752427" = .687425501"
.687425501 x 2 = 1.73485----" or basically 1.75" primary tubes. I was taught that you always go to the nearest size whether up or down, but if using a power adder, it's always better to go to the larger size or even one size larger than that. So with a 50-100 shot of NOS, I figure that 1.75" (1 3/4) primaries should be accurate right? Anyone know if this is a good size to run? I was set on 1 5/8" primaries but now I'm not so sure. My reason for being set on 1 5/8" primaries was due to the following math:

Let's say we take 1 5/8" primaries (1.625").. this is the outer diameter (OD) of the pipe. Let's assume a wall thickness of 0.040" for most common pipe, this means we have to take off 0.080" total when calculating cross sectioal area of the pipe. So 1.625" - 0.080" = 1.545". To find the cross sectional area of a circle we use this equation:

diameter squared x Pi /4 or 1.545" ^2 x 3.1416 / 4
2.387025 x 3.1416 / 4
7.49907774 / 4 = 1.874769435" or basically 1.875"

To find peak torque RPM with these primaries, we use the following equation:
Primary Pipe area x 88,200 / displacement of one cyl or 35.125 so..
1.875 x 88200 / 35.125 = 4708 RPM

Using the same math for a 1 3/4 (or 1.75") primary gives us a peak torque RPM of 5520 RPM. I've read that stock Rev limit is right around 5750 +/- 50 RPM and using the shiftpoint formula:
1265 x intake CFM / one cyl. CID we get the following for max Redline:
1265 x 165 CFM / 35/125 = 5942 RPM

So here are my questions: Which primary tube size on a set of full length long tubes would you use or have you used and what were the results? 1 5/8 or 1 3/4?

I should be able to keep my stock exhaust pipe diameter of 2.5", however I will be using an O/R H pipe and then mufflers. I have (estimated 50 shot but could be 75??) of NOS when the switch and MSD RPM box and all that works. I have MSD coil over plug Coils, NGK Iridium 9 spark plugs, and a K&N FIPK cold air kit. I also run Amsoil Signature Series 0W-20 synthetic oil and use 91 Oct fuel. When I get the exhaust on my car, I also plan on going with an SCT tuner with a custom tune. At some point as well, 3.73 gears are in the works and a centerforce clutch but that's another thread.. Anyways, help with this would be great!!! Thanks for making it through this if you're still reading, and any advice/experience would be great!!

---------- Post added at 05:06 PM ---------- Previous post was at 04:39 PM ----------

Just got an update.. looks to be like lobe lift is closer to being .2594" taken from a Haynes manual, but not sure the year of the 4.6L it was mentioning or if it was from the truck or mustang or whatever. But using that info brings valve lift down to around
.466" to .470" using a rocker ratio of 1.80:1 to 1.81:1. This would be much closer to needing 1 5/8 primaries according to the math. Still could use some help deciding though!!
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Old 02-20-2012, 05:23 PM   #2
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Wow that's quiet in depth. What's your occupation?
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Old 02-21-2012, 02:53 AM   #3
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Re: Here Comes EXHAUST!!

LMAO.. I like to say I'm a Senior Vacuum Truck and Fluid Management Specialist (aka Oil Field Truck Driver).. But I have a degree in automotive technology and High Performance Engineering. It's just before I could really get into the automotive field as a career or profession after I graduated, I was offered a job for my current occupation as a truck driver in the oil field making far more than I would starting out in the automotive industry.. hence my free time on here setting things straight and tinkering around with my own projects. It's my hobby when I'm not out hauling water around to various oil field locations or entertaining the wife and family.
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Old 03-24-2012, 07:37 AM   #4
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Re: Here Comes EXHAUST!!

Let us simplify all that math. If you want better low end power go with the 1 5/8" tubes.
Better high end flow, go with the 1 3/4".


The modular engines like to rev more than what I'm used to, so were the choice up to me I would probably go with the slightly bigger tubes and maybe even go with a stepped tube header depending on future modification plans.
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Old 03-24-2012, 07:56 AM   #5
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Re: Here Comes EXHAUST!!

Honestly that all went right over my head. I think whatever you choose will be more correct than anything I would choose.. Hah.
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Old 03-24-2012, 08:27 AM   #6
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Re: Here Comes EXHAUST!!

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Honestly that all went right over my head. I think whatever you choose will be more correct than anything I would choose.. Hah.
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Old 03-24-2012, 02:27 PM   #7
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Given your math I definitely would do the 1 5/8. Its the closest by far and will net the best curve. Also, switching away from the math, opening up the midpipe is going to free the flow up and could net you a bit of back pursue issues at cruising rpm. I'm 99% sure stock midpipe and catback are 2.25" my 96 gt didn't respond great to the addition of a catback and offroad H and started smoking. On a race application with little cruising I think it would be fine... But on a car that sees street idle duty... A little conservative decision making in the exhaust is a good thing.
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Old 03-24-2012, 08:47 PM   #8
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Re: Here Comes EXHAUST!!

I should update this.. I've decided I will be going with the 1 5/8 inch primaries. I'm going with the BBK Ceramic coated long tubes with exhaust wrap, a BBK offroad H pipe with exhaust wrap, and then a Magnaflow magnapak cat back set up. All mandrel bent and all 2 1/2 inch piping from headers back. Should be just fine for where the engine is at right now.. Total cost of parts is gonna be around $1452 on AM before taxes and S+H. Currently though, I'm doing all drivetrain upgrades. Then it'll be suspension, and then finally at the end of the summer I'll be getting exhaust and wheels/tires. It's a little bass ackwards but it's just how it's falling for what I really need first with the way the car is currently set up. All in all, this summer is costing around $5215 in parts. Over the winter will be coming Corbeau racing seats, rear seat delete, brakes, interior upgrades (gauges, painting, carpet, etc.), braided lines on everything. After that it'll exterior cosmetic updates.. The list never ends..
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Old 03-24-2012, 08:49 PM   #9
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Would not bother wrapping ceramic. Wrap holds moister.
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Old 03-24-2012, 09:03 PM   #10
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Re: Here Comes EXHAUST!!

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Would not bother wrapping ceramic. Wrap holds moisture.
I agree. I ruined a good set of Hooker headers using exhaust wrap.
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Old 03-24-2012, 09:18 PM   #11
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Quote:
Originally Posted by deadsp0t
Would not bother wrapping ceramic. Wrap holds moister.
What if you were to paint the wrap with a high temp exhaust paint?..
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Old 03-24-2012, 09:19 PM   #12
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If they are ceramic coated there is no point.
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Old 03-24-2012, 09:27 PM   #13
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Re: Here Comes EXHAUST!!

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What if you were to paint the wrap with a high temp exhaust paint?..
It would not help. The wrap will still hold moisture.
The ceramic coating provides protection and a thermal barrier, so wrap really isn't needed.
I would only consider the wrap on a car that would never see rain and was kept inside in a temperature controlled environment to minimize condensation.
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Old 03-24-2012, 09:31 PM   #14
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Originally Posted by deadsp0t
If they are ceramic coated there is no point.
Ok so for the sake of argument, shouldnt the high temp paint hold out the moisture?.. Just asking because I'm looking at getting a set of headers that are not ceramic coated!.. But if I'm possibly going to still get some moisture then I'll just shell out the extra cash and get the ceramics!..
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Old 03-24-2012, 09:45 PM   #15
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Re: Here Comes EXHAUST!!

Although Ceramics does keep underhood temps down, the headers do still get pretty hot. i will be wrapping them to help keep even more heat in the exhaust to help keep exhaust velocity up through the system. Although it 'can' keep moisture in, a lot of times I've found people don't wrap their headers or exhaust components correctly. Besides, I never drive when it's wet anyways. It never see's the rain. It's definately not a daily driver.. And when it is running, it's hot enough to evaporate all the moisture anyways.. I'm pretty sure I'll be fine, but thanks guys!!
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Old 03-24-2012, 09:46 PM   #16
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Quote:
Originally Posted by Trojan Horse

It would not help. The wrap will still hold moisture.
The ceramic coating provides protection and a thermal barrier, so wrap really isn't needed.
I would only consider the wrap on a car that would never see rain and was kept inside in a temperature controlled environment to minimize condensation.
Ok cool thanks Bro!.. And ya my ride is my DD and will be for the foreseeable future!.. Lol.
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