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Planning for more HP

3K views 13 replies 6 participants last post by  medwards 
#1 ·
Hi everyone. I bought my 2015 GT Premium PP 6 months ago. I'm finally getting to drive it more consistently, and am looking forward to future performance mods when timing and budget are right (warranty considerations, bang for buck, etc.). So far I've done some basic appearance mods and added an H-pipe. I'd like to put together a plan to get to 500, 600 or even 700+ HP over the next 5 years, but doing it in a way that lets me build upon each mod logically, primarily with bolt-ons.

For example, I know a supercharger will be in my future someday. But in the meantime, what mods can I be doing to move toward that goal while seeing incremental improvements that will also stay relevant with a supercharger? Should I plan for headers before then? Does it make sense to do anything with a CAI prior? I'm sure a tune will be in order at some point, but which one? When? Will my choice of supercharger dictate what I should or should not do as I'm building?

This car is my partial daily driver during good weather, and I don't have any plans to track it. I'm mostly interested in experiencing the performance modding process and feeling the improvements during some spirited driving. I want to learn.

I appreciate your experience and expertise! Thanks!


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#2 · (Edited)
CAI is going to get you some HP gain. A tune will help as well. However, be careful. If you get up to 500HP+ and put on slicks you may break a half shaft. I would strongly recommend the first thing you do is install Ford Racing halfshafts.

The thing that will reach your "spirited" driving goal would be putting lower gears in the car. You have 430HP. That's a lot if you put in lower gears. If it's an auto then 3.55's will do wonders. If it's a standard, then 3.73's will be nothing short of a ton-of-fun. And since you have 6 gears in a manual transmission you will still have highway cruising abilities. If you switch the gears you will need to update the computer but it is really simple to do with the Whipple Flare tool (it connects to the computer of your car with a laptop to update settings).

A set of headers would add some power but make sure you are a patient person as they are a ***** to install and they aren't cheap.

A supercharger is a lot of fun, but is going to set you back $$$'s and they are quite complicated to install. But, if you're mechanically inclined and take your time it won't be hard.

I would go in the following order:

1. Differential bushing inserts by Steeda (no HP gain but stops wheel hop)
2. Half shafts (no power gain but no breaking things later)
3. Lower gears (no power gain but damn will that thing take off out of the hole)
4. CAI and a tune (I would go to a local tuner instead of buying one of the canned tunes). Research the CAI to see if you can get one that is compatible with the future supercharger install
5. Exhaust (I like Borla)
6. Headers...I would recommend Kooks...expensive but awesome (this will also help you when you finally install the super charger)
7. And lastly a supercharger (and all the ancillaries that go with it...new radiator, new CAI, throttle body, tune, etc). You likely will be installing a new CAI unless you did your homework on step #4

Through this process, at some point, you are going to want to do things to improve handling and braking. That gets expensive but isn't hard to do (just following directions and turning bolts). Once you start hitting 650HP+ you really are going to want to look at suspension and brakes.
 
#3 ·
Thanks for the great response! I knew you would have some valuable input given your current build (which I've been following).

The car is a 6 speed and already has 3:73 gears. Regarding some of the other mods, I plan to do some of the easier ones, but will likely leave the complex ones to the pros (although it will hurt the wallet a bit!)


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#4 · (Edited)
If you have the 6 speed and the 3.73 gears, you are likely experiencing the wheel hop issue that occurs during hard acceleration from a full stop. That is caused by all the rubber bushings in the rear end. There are 8 rubber bushings that all contribute to wheel hop. 4 bushings connect the subframe to the car. 4 connect the differential to the subframe. Each of these locations can flex up to 1/2 an inch. So, there is a total potential 4" of movement of the subframe/differential/rear wheel combination relative to the alignment of the car in addition to the normal travel of the rear suspension (8 x 1/2 inch = 4"). This causes all sorts of weird things including the dreaded wheel hop.

The bushings that connect the subframe to the car I would recommend ignoring. If you change them out to something harder or install the Steeda collars you will create NVH (noise, vibration, harshness).

The ones on the differential (two in front, two in back) are easily addressed with the Steeda differential bushings (https://youtu.be/id8onLo7zuo). That will go a long way to stop the hopping. This kit is bolt on and adjustable for ride and can be completely removed back to stock.

I WOULD NOT LOOSEN THE SUBFRAME BOLTS AS SHOWN IN THAT VIDEO.

There is no reason to loosen those four subframe bolts. All 4 differential bolts are easily accessed without loosening the subframe. Loosening the subframe bolts may cause your subframe to become misaligned with the car! This is a bad thing. Keep the stock bolts in a bag in case you want to completely remove the steeda bushing kit and go back to stock (this would get you back to the nice cushy stock ride...but the wheel hop will return). If you do find you want to loosen those bolts, only loosen the front and not the back ones so that the subframe cannot move relative to the body. Also, watch that video and see how the subframe is supported so that when you drop the front of the subframe while the back is still fully bolted, you are only dropping it to the point where the rear subframe rubber bushings are flexing. You don't want to drop below that point as you don't want to risk damaging the rubber bushings on the back or bending the subframe tabs where the back is bolted on.

As you saw in my post, I completely removed the subframe. It's not hard to do and it's not hard to reinstall. But, aligning it for reinstalling would be almost impossible unless you used the Ford Racing aluminum bushings (or you had the dealer alignment rack). As I show in a video, the stock rubber bushings are much wider than the bolts and you can move the subframe around the bolts. So...I realize at this point I'm beating a dead horse...but be very careful if you do loosen any of those 4 bolts that you have at least 2 of them fully tightened so that subframe cannot become misaligned.
 
#6 · (Edited)
I was thinking...I didn't address options for people that don't want to put on a super charger (S/C's are expensive and complicated to install).

From my perspective....more air into the engine allows for more fuel to be dumped in while maintaining the proper fuel to air ratio. More air + more fuel = more power. This is an old school view to increase power and still applies even to today's complicated computer controlled engine bays.

So...we want to increase air supply which also allows us to pump in more fuel at the same time.

So...let's look at non-mechanical ways to increase air (and fuel!) into the combustion chambers.

1. One way to increase air in is to make it cooler since cooler air is more dense than warmer air. Hence CAI's taking air from as far away from the engine as possibly. These do work, but are limited...since we drive during the summer the air is still relatively warm and therefore their usefulness often doesn't meet the claims. But, they do help.

2. Another way to increase air into the combustion chamber is to exhaust all the air that was put in during the prior intake stroke and ignited during the combustion stroke. The way we exhaust more air is to reduce the restriction on the exhaust. Hence....headers and more free flowing mufflers. These again will help but the gains are limited if everything else is stock. Combined with a CAI, they are useful. IMHO putting on a set of headers, less restrictive mufflers, a CAI, and a throttle body (as described below) followed by a tune is the most economical way to get HP and easy to install. Long tube headers are best. With this said, the stock GT exhaust is actually pretty good at exhausting gas and if you look, they actually are a set of headers...but remember that production cars consider cost and mileage...so they aren't optimized for power.

3. A very useful way to increase air into the combustion chamber is to increase the size of the opening at the front of the air intake. This is throttle body area. Oh boy is this an area. You have to research what you are looking to accomplish when looking at throttle bodies. Do you want low end torque or high revving power or mid range power. This is going to require research on your part. If you have a daily driver, mid range power and fuel economy may be primary concerns...etc etc.

4. Intake manifolds will allow air to travel more efficiently to each cylinder. As air is bent through different tubes or channels it creates resistance. That resistance reduces the amount of air able to be sucked into the combustion chamber on the intake stroke. Putting on a new manifold with a different design changes the flow of the air and improves efficiency. These manifolds are as diverse as throttle bodies and you have the same considerations (low range, mid range, or high revving HP goals).

5. Injectors....this is how you get more fuel as you add more air. Research will get you the right size injectors depending on how much extra air you are pumping in.

6. A crossover pipe helps equalize exhaust pressure and is quite useful for that purpose. However, I'm not certain the claims are as real as stated in benefits for a car that is not boosted.

7. Larger radiator and perhaps an extra fan or two. Don't forget, as you increase HP you increase heat within the engine block which both robs power and can damage the engine. We want heat in the compression chamber but then we want to remove it from the engine block and heads as quickly as possible.

8. And lastly the "tune". Us old timers used to have it easy. We'd change out plugs to get hotter or colder and literally rotate a rotor with our hands to advance or re tard (had to break the spelling as the message board doesn't like the word r e t a r d....that's odd) the timing (mostly advancing for more power). Depending on how hot we wanted the compression burn (with the consideration we didn't want to 1) melt a spark plug electrode 2) burn a hole in the piston 3) crack a head) in order to burn as much gas as possible, we would turn the rotor clockwise/counter clockwise. Nowadays that is all done with the computer. Even with a stock motor, you can play with these settings and increase power if you increase the octane of the fuel you are burning. But...this is best left to someone who knows what they are doing. As you change anything on the car you likely will have to change the computer settings. WISE PEOPLE change one thing at a time and retune the car with each change. It may cost more money, and certainly takes more time, but saves in headaches (changing multiple variables at once is never a good idea because it makes chasing problems infinitely harder).

So, if you want 650HP+ you can do it with a naturally aspirated motor. And it will costs thousands of $$$ LESS than slapping on a S/C, but it will take a lot of research. If you install a S/C properly you end up with the best of everything....lots of extra air in those cylinders at low, mid and high range. If you install a turbo its a bit trickier but still a lot of power (maybe even more since you don't have the scavenger loss of power from running the super charger impellers using the belt drive off the engine crank shaft).

If you do decide to go the naturally aspirated route and start working with the items above, you need to do your research very carefully as everything needs to work in harmony with the RPM/HP goals you are trying to achieve. But, if you do it right you can get a ton of power without the maintenance of mechanically forced induction and do it for a lot less $$$$.

Phew....time to go to bed.
 
#8 ·
An appreciated post. Thank you for your time and knowledge. You answered a lot of questions that are asked daily here.

I am a fan of naturally aspirated engines. Maybe I'm old, or finally getting there? I keep sketching out the idea of a naturally aspirated chiller box to hide in the fender for hot and humid days at the drag strip. Cost and complications do not make my ideas feasible yet.

It would be nice to use the A/C compressor as an air chiller and dehumidifier to pre cool air in the fender. A cooling coil stretching down the intake tube could keep this newly cooled air a fee degrees cooler, but I doubt it would be enough to make a reasonable difference.

I have spent too much time in the music industry. For for low fog effects, fog emitted from a scorching hot machine has to be chilled. Cold air is dense, or heavy and settles below the hot ambient air. In regard to fog a nice low level effect is made. I keep wondering how to apply this same idea to a naturally aspirated intake.
 
#10 ·
It came direct from Shelby. I'm certain they didn't make it. I'll have to unwrap it and reply (maybe tomorrow night). It is only a 4 point with a cross bar so it won't meet full NHRA requirements below 9.99s. I was going to contact the manufacturer to see if they have the front bars to turn it into a 7 point cage to meet NHRA requirements. It's fully bolt in. Your question may get me to actually contact the manufacturer next week
 
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