I've been reading a lot on how to design a custom exhaust system, seen a lot of threads and also how different designs fit different engine setups/goals better... but well, obviously I am no expert, and would love to get some help from more knowledgeable members

Here's what my setup is going to look like:

- 6-Port S4 NA Engine
- Pineapple Racing 6-PI Large Streetport
- Pineapple Racing EP2A Exhaust Porting
- IDA Weber Intake Manifold
- EFI Hardware Individual Throttle Body kit, tapered bode 55/53/50mm (these)
- 4x 650cc Injectors
- Turbo2 Ignition Coils
- Jacob's FC1000

The car itself is a S5 FC

Well, that's it... I look forward to any feedback you guys can provide.

If you happen to need any more information or I missed something, please let me know

Thanks in advance

 

what are you looking for? max power? a broad power band? noise?

 

I'm looking for a broad powerband.

Noise and emissions aren't a problem.

 

Anyone?

 

Go with an RB streetable header and presilencer and then create a custom cat-back using
2.5" 14 guage mild or stainless steel pipe to two Magnaflow race mufflers. Don't go larger than 2.5" pipe.

 

Is the RB header that good? How long are the primaries?

Why shouldn't I go larger than 2.5"?

 

As much as I don't like the sound, the RB true duals would work fine with your setup. In your case it will make more power than an RB header with a cat back. For other porting styles that may not be so though.

If you stick to a conventional system, you won't make enough power to justify larger than a 2-1/2" collected pipe. The key in making power is to size everything right around what you need with little excess capacity. If you go larger you may end up hurting your powerband.

 

So... I should look into a true dual system instead of a collected one? Why?

 

That would be a very long technical response and in the end it doesn't always apply. There is no exhaust system that works well with every porting style. A true dual works great with stock or streetport engines but becomes worthless garbage on bridge or peripheral port engines. Simple put it all has to due with tuning and for the milder forms of porting it works pretty well. If you can get over the exhaust tone that is. There is far more to exhaust design than just flow and it gets complicated when weighing the pros and cons of collected (and where collected) vs non collected. This isn't to say that there isn't a collected design that will make more power. There isn't an off the shelf retail one that I know of but it would be possible to design one if you really knew what you were doing and had lots of time for trial and error. Since you have a 2nd gen, I am thinking about what is easiest to do, what is available and what would fit. The RB true dual while not the cheapest or best sounding (in my opinion) is a direct fit for your car and will give a wide power gain over the entire rpm range. I have always felt that average power is more important than peak power and for your setup I feel this would be the way to go to accomplish that.

 

Thanks a lot

 

Since you are running ITB's, I'm assuming you have a standalone ecu. You'd better! There is absolutely NO reason whatsoever to use larger injectors. There isn't a streetported engine on the planet that needs them. This is misinformation spread around based on 30 year old technology. Modern fuel injectors are a far cry from those on the FC and ahead of most current options out there. Everyone uses the same old thing because it's what they know. It's old tech though. Look into injectors from Injector Dynamics. They have a website. For the ITB's, you only need 2 injectors. Keep it simple. You don't need 4. Look at their ID725's. These are rated at 725cc at 43.5 psi. That may not sound like much injector but you need to upgrade the rest of the fuel system too. Get a better pump and an adjustable regulator. Run the fuel pressure up at 60 psi. Using only these 2 injectors, you'll have plenty of fuel but the fuel metering will be far smoother than anything you've thought of before and definitely better than 4 larger injectors! Ignore the numbers on paper. Only concern yourself with performance in the real world. Sometimes it requires a different way of thinking.

 

I plan to run a Haltech PS1000 EMS, and a Walbro 255 fuel pump.

So I should get 2x 725cc instead of 4x 650cc? Doesn't like much, especially considering that the stock ones are 4x 460cc -- Shouldn't this limit the performance in any way?

 

Stop thinking according to numbers on paper. You don't need 4x650cc. You don't even have a need for more than 4x460cc as you won't max those out. It's all about pressure, tuning, and a quality injector. Use only Injector Dynamics injectors. Those are the most modern out there. All the others that people use are of a design from the 70's.

 

I see I see... so, having a pair of bigger injectors would be better than 2 pairs of smaller, sequential ones?


Thanks a lot for your advice

 

Not just any injectors. What I'm getting at is that the ID injectors are 2 generations better. They are 25 years more advanced. That makes them more linear with a very fine spray pattern with excellent atomization. That is something that normally suffers with going larger. Their 725 cc injectors have better atomization than the stock 460 cc injectors. If you can retain good atomization and get the amount of flow that you need, why not use them? They cost $115 a piece but you need 2 of them not 4 so it is even cheaper. You also don't need to worry about injector staging. It all stays very simple. If you were to just go out and get 2 larger injectors but they were the same style as the stock ones, you would lose low end atomization ability and performance might suffer. Not with these.

No, I'm not affliated with them btw in case you were wondering.

 

Thanks a lot for the explanation

 

I personally run 2 x 750cc injectors at 55psi on my 12a, just came back from the dyno yesterday and pushed out 165whp. My duty cycle peak at around 90% so it cutting it close. That would be at 8500 rpm

 

Injector Dynamics injectors?

I was also wondering... should I go for a IDA or DCOE manifold?

 

no just regular siemens

 

If 2-750's wouldn't be enough fuel, he could run 2-1000's instead. Provided of course the ecu used can control it effectively. 4 injectors is always an option of course and with a Weber style manifold wouldn't need them to transition if so desired but could instead batch fire them all together. It doesn't matter. I'm just a fan of keeping things as simple as possible.

 

here is my exhaust, similar setup to yours.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/racing-beat-exhaust-dyno-compairisons-823229/

 

So... you would reccommend a collected setup?