What is the issue w/ runnin straight pipes on turbo cars? I've been researching but haven't found a straight answer, I think its somethin about how it won't give sufficient back pressure.

 

On a stock turbo car the wastegate is an enteral type, generally very small.

Stock cars have smaller diameter pipe and a catalyist systems that are flow restrictions.

Remove these systems and incress flow increases.

This incress in flow allows the turbo to spine more freely.

The small enteral wastegate generally cannot keep up, as the restrictions were keeping flow down in the first place and you can no long control boost pressure.

 

Yea I read that so thats why it'd need to be tuned to compensate that extra flow...I also read somethin about losin bottom end torque, that's my main question, or any loss of power.

 

It sounds like you need to do somemore research. This topic has been covered at great length many times in the past. You should really use the search function on this site. There is a vast amount of information out there about this. Read Read Read...

I am guessing you have a turbo II with a stock turbo. I am unsure what the limits are with one of those, as to what size pipe is safe to use to incress flow but avoiding overwhelming the stock wastegate. I would suggest you SEARCH/ask this question in the 2nd gen section, as this section is more for aftermarket( not stock) turbos and you won't get much feed back.

If you are concerned with low end torque, you are playing with the wrong engine.

 

" thats why it'd need to be tuned to compensate that extra flow" No, you can't tune the engine to avoid boost spikes cause by an exhaust thats too large. Your only two choices are a bigger wastegate( ported or add an external) or put a restriction in the exhaust.

You also don't want to over speed the turbo as it will not last long, allowing boost to spike unchecked can cause this. You want to control the boost, not try to tune for the spike, though you could do this, I wouldn't, but do as you will.

" losin bottom end torque, that's my main question, or any loss of power. " The power gains that can be made at medium/high rpm, generally outweight any loss in low end TQ, I wouldn't even worry about it. On a turbo car, FLOW is what you want, unless it is more than the WG can handle.

Again man, read and research... This fourm is full of good information

 

I've learned a lot about rotary and turbos in general by reading through lots of FAQs so search and read is good advice.

However, I understand how frustrating it is when you can't seem to figure out the correct search terms and everyone just tells you to search so here's a short answer.

As you probably know, turbos work by using the exhaust flow to spin an air compressor to provide high pressure air for the engine's intake. Turbos are typically chosen for the engine in such a way so they will provide the full desired boost early in the revs. As you can probably imagine or already know, this means the turbo is capable of producing too much boost when the engine is producing the most exhaust. A wastegate solves this problem by diverting exhaust away from the turbo and straight out the exhaust so that it won't spin the turbo as much as it possibly could. The exhaust will choose the path of least resistance which normally would be an open wastegate but if you remove resistance from the entire exhaust system then the turbo will spool better while the wastegate does not become more effective. Now the turbo will spool up more than it used to even with the wastegate fully open so now you have too much boost, exactly what the wastegate is designed to prevent.

Now you could increase fuel to compensate for the extra boost and make more power but most cars are only built with the parts they need and not much more so the fuel can't keep up with requirements and the engine explodes. The ignorance of the fuel limits are a big reason why rotaries have a bad rap for reliability, especially since newer cars having electronic boost controllers built in too keep this sort of problem at bay.

 

Exactly, I couldnt find a straight answer to my questions so I jus made thus thread, appreciate it, I plan on using an s366 tho instead of a stock turbo. As far as low end torque, as I mentioned, I jus wanna make sure im not losing any bc there's not an abundance of it w/ the rota.

 

If you want to make low tq run a small turbo with a small hotside and a lot of boost pressure. Boost pressure makes Torque. Here is a wonderful example of it. I

https://www.rx7club.com/single-turbo...d-dyno-956766/

This has nothing to do with the size of the after turbo exhaust, and everything to do with the size of the turbo. Look at the TQ curve, see how it peaks around 4000 rpm, You won't seen this out of a 366, the power will come on later, as its a bigger turbo.

Now there are 3 big down sides to this, high outlettemps on the turbo, High exhaust manifold back pressure and he is running 110 octane so it is not nessessarily streetable.

But the car was also 3rd fastest in its class in the entire scca, so it has its place.

 

Aiight appreciate it, I planned on runnin that turbo but I wanted to know if there was any real power loss anywhere bc that's what I read somewhere during my research.

 

To answer your original question, the ideal (max power) exhaust setup after a turbo is no exhaust at all. The backpressure theory applies between the engine and the turbo only. So as long as your wastegate can keep the boost where you want it, the less backpressure you have after the turbo, the better.

thewird

 

With the 366 you will have a properly sized external wastegate so u shouldn't have boost creep issues and want the exhaust off the turbine as free flowing as possible.

I was assuming you were taking about a stock turbo with an enternal wg. In the orignal question add a little information about the set up and your goals. Good luck with it man.

 

Aiight appreciate it