i understand, but he has an mpt70. the turbo has (i hope) a .96 AR with a 70 something mm turbine wheel. its tiny.

whos tracy? does he have a build thread?

 

See post #13...

If your using off the shelf parts thats one thing but if your taking the time and effort to fabricate it than do the research and figure out exactly what your combo needs vs using what joe blow says. Sure a 2.5" crossover pipe will work as it works on my 2000hp motor. Doesn't mean its optimal and if your going to take the time to build it yourself why not maximize it? Now if you dont have the skills to fabricate the specific components than its a different story.

 

im not an expert in turbo fabrication but from first hand experience i dont think youll have an issue

my setup is 2.5" cross over and 3" downpipe just like yours and there is no lag or issues with spool. my crossover also isnt wrapped or coated and neither is the turbine side of the turbo. im also in the 560-580 rwhp range as well with the 3" dp and 11#'s

 

when do you start to spool and when do you see full boost thanks for your input.

 

not sure if it matters but from what I've read tracy rr has a rear mount set up and I have a front mount.

 

Looking good. I say try it. Take your hotside and coat it or wrap it. That will help spool.

 

I'm using flipped c6 maniflods and the outlet on them is 2.5". If I were to reduce down to 2" wouldnt that restrict the flow? Just a thought I had

 

C6 manifolds were build for a N/A motor.... Cone engineering sells 2.5 to 2" reducers.

 

Thanks phil I'll check it out

 

crossover is fine, leave it. ppl have used this same setup thousand and thousands of times!

 

This is an interesting thread, and the other linked one as well. While I don't claim to know anything about turbo systems building, I do have a question. What is to be said about backpressure, detonation and heat?

I had a buddy who had too small of a cross over pipe (2.5") and too small of a exhaust housing on his turbo (t4 flanged T76 I believe) and was making over 800 RWHP and the tuner (Job from The Turbo People) had to throw tons of fuel at the car to keep the detonation down due to the heat not escaping. He ended up swapping the turbo to a GT4788 (much bigger exhaust housing) and a 3" crossover and the car is on the money now. Spools faster and needs LESS fuel, and makes more power.

 

i doubt it was the crossover. what was the A/R?

 

A GT4788 wont make more than 1200 on a v8, we use a 2.5" crossover and make somewhere in the 2100-2300hp range. Our setup spools faster, we run a tighter converter than anyone on the planet and the car flat out flies. Maybe we just got lucky with the combo but it was probably the fact we spec'd out the parts to work at maximium efficiency.

So the fact that the cars run and drive ok classifies the setup as "works fine". So if you put the correct size tubing on it and the spool was 1000rpm quicker, would it still work fine since a million people have done it with 2.5" and it "works fine". If your going to take the effort to build a system, take the time to figure the correct size piping, turbine compressor, and intercooler. Don't just go with "what works".

 

I'm looking to do a flipped manifold kit with a Precision T76GTS. Looking for 800-850rwhp. The plan was to run 2.5" crossover with a 3" DP. I've been told by several people that 3" DP is fine for that hp level. I personally want to run 4" or at least a 3.5" DP but was worried about clearance. I'm running a BMR turbo K-member but I'm also trying to keep A/C.

This is on a 365c.i. Forged LS2, LS6 Heads/Intake/Stock ported TB with E85.

 

too small. its going to limit your hp and slow spool.

 

Is your kit optimal for your set up?........No..

Will it spool fast and make the power you want?......Yes..

 

3 in dp is too small, I'd go 3.5 at least. As far as the Turbo you'll be pushing it pretty hard to reach 850 rwhp. It'd be much easier with an 80 or 88mm.

 

It seems like a teeter totter... Finding the sweet spot between retriction and velocity... But it also seems like 2.5" is the norm. What about 2.25? 2.25" crossover pipes have less area then the 3.5" Downpipe. You would think you'd want it pretty much equal area. But velocity make sence..

 

As far as downpipes on a turbo car they can't be too big. Generally 1.10 - 1.25 x the exducer size and external wastegate vent tubes help a bunch. For example on our setup we run twin 4" downpipes and twin external 44mm wastegates.

3" is a good tube for up to 350rwhp with an external gate so if you plan on making 650 to 700 twin 3" would work but I'd rather see twin 3.5".

 

2.25" is not too small for a crossover tube on any of the street cars on this forum, honestly I think 2" or 2 1/8" would work very very nice. Its all about heat retention and velocity. We plan on making over 2500hp and still will use a 2.5" crossover if that tells you anything, if you want to talk about restriction, how much restriction is in a 2.5" pipe and 2500hp.