downpipe pix
#22
7 Second Club
iTrader: (11)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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.
#23
TECH Junkie
iTrader: (17)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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
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
#24
TECH Apprentice
Thread Starter
iTrader: (1)
Join Date: Jan 2010
Posts: 362
Likes: 0
Received 0 Likes
on
0 Posts
![](https://ls1tech.com/forums/images/ranks/ls1tech10year.png)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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
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
#31
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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 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.
#33
7 Second Club
iTrader: (11)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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 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.
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".
#34
TECH Fanatic
iTrader: (22)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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.
This is on a 365c.i. Forged LS2, LS6 Heads/Intake/Stock ported TB with E85.
#38
TECH Regular
iTrader: (2)
Join Date: Nov 2007
Location: OK,Elk City
Posts: 434
Likes: 0
Received 0 Likes
on
0 Posts
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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..
#39
7 Second Club
iTrader: (11)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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".
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".
#40
7 Second Club
iTrader: (11)
![Default](https://ls1tech.com/forums/images/icons/icon1.gif)
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..