Hypothetically; if I were to run a 3" Downpipe to a 3" high-flow cat and out to an Apexi N1 exhaust (2.75" -> 3"), will/could this limit possible horsepower compared to a complete 3" exhaust.?

 

Yes, it could, but there could be a difference between the N1 mufflers and whatever you would use instead that could give you better or worse performance.

 

Ok, I was wondering because I already have an N1 on my N/A S4 and I plan to turbo it in the near future. So I'm basically asking what the best set-up would be while still utilizing the cat-back

 

3" is big for an N/A.

If you are changing to turbo soon it will depend on how big a turbo you plan on using. If you are going to throw on a stock S4 or S5 turbo than there will be minimal if any ill effects from that setup.

 

I'll probably go with the stock S4 for a while. What's the biggest turbo I could run?

 

That depends on your budget, purpose for the car, what you're doing to the motor... the list goes on, and searching is very helpful on this subject...

 

3 inch to 2.75? hmm proabably just fine. N/A then way more than you will ever need. Turbo? Stock s4 turbo? Then should be fine. My 2cents

 

I'm sure it would be 'just fine'. Ultimately the best flowing exhaust for a turbo will be open to the atmosphere immediately after the turbo, you'd probably still want a large downpipe to get the hot exhaust out of the engine bay, but that'd be about it. 3" vs 2.75" isn't a big difference, but assuming the mufflers and pipe bends performed the same, the 2.75" pipe WILL have a measurable reduction in performance compared to the full 3". It may only be 3hp difference at 12psi of boost, it could be 15hp difference at 12psi of boost, but a difference will exist.

 

Ok, makes sense. As to your previous question, the car is my DD and occasional drift car. My budget is kinda tight because I'm High School student but Im getting a part-time to full time job this summer.

 

I imagine a stock turbo would be a good option then. Anything bigger and you will have to deal with a lot more supporting upgrades.

 

Not so much...

By the time your exhaust gas hits the muffler it's already (by comparison) WAYYY more dense than it first was due to cooling, making it harder to deal with already. Then you're trying to channel it all through a smaller opening... Not so much with the good flow...

With the Rotary in our cars it may not matter at all because it's so much hotter already than a piston motor. But If I were going turbo, I'd probably just go with a 3" exhaust all the way back...

 

yeah, i say if your running about 8lbs or more, go "3 from the turbo back, if its 2.75 at the end, all that "3 piping was a waste, because its all going to built up on the 2.75 part.

but if your n/a 2.5 is the MOST you ever wanna go period.

2.75 is nice for factory boost =] good quick spool and a good gain in power.

but yeah if your over factory boost go 3inch *all the way back*

and i assume your not running the kinda power/boost to go with a 3.5 or 4inch =]

 

To be truthful though, wouldn't a 4" system perform better than a 3" for even the stock turbo? Granted, the gains may not outweigh the physical weight added by the 4" system versus a 3", but it should flow better.

I've always wondered, what kind of power, boost, or motor displacement would see the greatest gains from a 3.5" or 4" exhaust?

 

It MAY, but again, you run into the cooling thing. It's just too gosh darn big to get it all out before it cools to much. I'd never really consider running anything bigger than 3.5... But as you said before, everyone's exhaust of CHOICE would be an open down pipe...

 

awwww, but what size dp lol??? =D

 

I'm looking to hit at least 250hp. Maybe 300.

 

As big as your face. :P


300hp available on a daily basis with a stock turbo will not happen. 250hp daily driven I think is doable, but difficult and that's around the limit I've read about for the stock turbo.

 

I figured 300 is a lot and not do-able on the stock turbo. This is a bit of a ways off but thanks for all the info