..i was wondering how much of a spool improvment was reducing the hot side from 3" to 2.5"???...anyone go smaller,2.25"?? or 2"??

 

bump...any info appreciated!!

 

2.5" ID will get you to 900 HP, I would not go any smaller.

 

Zombie,thanks for the reply....would it spool much faster with a smaller diameter pipe but lose the top end???

 

possibly, but why go smaller than 2.5" ?

 

is there much of a difference between 3" and 2.5" when it comes to spool?

 

well its less area to fill with pressure .. so yes im sure the lag will be less .. but im sure there is a point of being too small..

 

..i was thinking the smaller the diameter would keep up the velocity,pressure and heat feeding the rear turbo....seems it[2"] would be benificial??

 

the reason I went 2.5" over 3" was to reduce overall surface area for heat retention. Heat is what is the most important. Volume of the pipe, velocity and pressure are minor compared to heat retention. 2.5" pipe has 15% less surface area than 3" pipe.

How large the exhaust pipe is doesn't really matter as long as you can keep the heat in.

 

Since a couple of questions are similar, I was wondering since the manifold outlet is 2" i.d. wouldn't 2.25" pipe from both sides into a single 2.5 be sufficient to the turbo? As you have preached to many, heat retention is key so, the outlet is 2" and my theory is going bigger than 2.25 from each manifold to the y just wastes the heat energy through more surface area. Yes? No? These manifolds support 400 hp from the factory with that small exit opening. Thanks for any input.

 

Just try it and let us know if it works. I had mine done in 2.5" all the way, so I know how that works. Most of what has been tried on my car was done because no information could be found on how changes affect a setup. I would have gone with something I knew worked well had someone else tried it before me and shared the results.

It was fun to experiment, but it certainly wasn't cheap (well it was sorta cheap because I have a good fabricator who likes to experiment too). My car has had around 10 different configurations.

 

my application is much different, but the heat properties are the same. I used a 2.5" pipe for the Y-pipe, then a Flowmaster y into 3 inch, all the way to the turbo. The whole hot side is wrapped in DEI header wrap, then used their black silicone coating on it. My engine displaces 6.5L but only spins to 3400 rpm. I have no problem hitting 18 psi under WOT. The turbo is rear mounted, and had a front mount intercooler. Cold side charge pipe is 2.5" all the way. There is about 16 feet of cold piping.

I agree with Zombie. If I had to do it again I would prob go with 2.5" all the way to the turbo. But I am not sure if my EGT's would be ok. I am sure with a gas engine and the right turbo, the 2.5" setup would be great. hope this helps. car is in sig.


Cody

 

Zombie, whatt kind of backpressure are you seeing with the ST80 vs the 76GTS?

 

Mine is 2.5 custom Y to a 2.75 I stock f body I to the turbo.

 

mine is stock diamiter y that goes into what once was my 3" SLP LM set up...so from y pipe back is 3"...seems to work pretty good for when i drive it....