Found this while cruising on the net to figure out which diameter exhasut to get for a turbo tc. http://www.nsxprime.com/FAQ/Miscella...austtheory.htm


Any opinions on this? Would a lowered tc be able to handle a 3 inch piping?

 

ive read that before

props to nsxprime

 

hehe yeah nice article but now iam curious weather i should get a 2.5 inch exhaust or a 3inch becuase i will be turboing eventually and want the best exhaust for performance.

 

Good article.

 

I have Hotchkis springs on my car, I removed my TRD exhaust last week and noticed some scraps on the piping. That was on 2.25" piping.
If you can find a better way to route the piping, it might be do'able.

 

This article is a great foundational article for those who know little or next none about exhaust systems, however with respect to diameter of the exhaust, I think they failed to mention some crucial points like the role of exhaust A/R on back pressure and exhaust size. Just because 3000 Turbo Civic owners putting down 300whp each decide to run 3" exhaust does not mean it's correct.

Ok. Let's start here.....Exhaust A/R on the turbo is like a light beam that you can focus on how large or how narrow and fine you want the overall beam. The wider you want the beam, the less FOCUSED power in range you will have (like a lower A/R, .48 or .63 compared ro a 1.08 A/R). Be aware of an excessively low A/R because it will cause a jumpy and touchy throttle response that might be hard to control. It will spool quick, but die after a short RPM span. So lower A/Rs are a double edged sword and must be treated with a lot of importance for selection of the sized turbo, with goals and how the car is used.......[taken from Maximum Boost]


Higher A/Rs are focused on top end, maximum power and generally have short lives with respect to power bands. Like say 1500 RPMS of power, great for drag racing, but not practical for street. Perfect example, 1.8L Turbo Civic H/B. Not the most ideal street set-up but a great drag set-up.:

But note, this set-up has a large turbo with a small A/R (to aid spool ups) to put down massive top end. Some people have taken the opposite approach like using a T3/T66 turbo on a 3.0L with a large A/R like 1.08 A/R to help focus the smaller exhaust housing's potential on the higher RPM portions.

Anyway, the lower the A/R, the more back pressure it will choke on in the RPMS thus making less top end power, but better mid-range let's say. That .48 A/R will choke it'self to death in back pressure on the top end because that wheel can not shuffle the air fast enough past it to get into the exhaust system. So several pulses may go by, and in event, clusters of air are given a bit more time to cool requiring more effort to expunge from the system. Add a larger diameter piping, which slows exhaust velocity down, and viola! Bad news.

Turbos create back pressure and hate it as well. As minimal restriction as possible with respect to turbo is the best. However exhaust gas can only move a certain speed and is generally lazy as well. Hence why Mandrel bends are better than Crush Bends in exhaust systems. Crush flow like crap and are very restrictive. Exhaust gases don't want to jump through firing hoops....They just want to get out of there as easy as possible....So Mandrel bends are an attempt to keep the exhaust gas flowing in a staright line as much as possible with still having optimal flow. (No dimished diameters in piping through bends and curves either!) So here Corky Bell has a guide to help deciding some exhaust diameters based upon HP.


I hope this helps too.

 

Fortunately all(that I am aware of) turbo kit manf are using some common sense in exhaust sizing, 2.5 is more than enough, bigger is not always better, especially for us moderately powered(or still building, planning, etc) FI folks

3" exhaust on a 10PSI tC is RICE!

Sure, no exhaust is best on a turbo but that means when you litterally have no exhaust, as in no piping at all. Since we are all going to run piping out the back of the car we need to keep the diameter inline with what will promote the velocity. Bigger in our circumstance can very well me just more noise and less usable power.

Rick

 

Hm thanks guys for all the posts Iam starting to understand a little bit more but definitly need to read up some more. Should buy maximum boost I guess.

 

Thanks for all the great info Mr Dezod! Better than just generalities like I posted even though I have studied alot of the same material to understand this, just to lazy to do as much work as you did, thanks!!!

Rick

 

Your welcome!

 

Very nice info paul!

I think a lot of people, as rick brought up, think huge exhaust is analogous to no exhaust, which is untrue.