2.5" DOwnpipe with 3" Exhaust?

[TurboBlue]

I currently have a 3" ATR Exhaust on my car with a High Flow Cat. My question is, would putting a 2.5" downpipe on my car be benneficial with the 3" or should all the pipe diameters match?

 

[StarCraftLover]

I've wanted to know the answer to that also.

My friend has a buddy with a shop, and he owns a older bodied 240sx. He has ordered a turbo kit for the 240 and has 4" exhaust. Now what I don't get is the 4" exhaust...

Wouldn't 3" be more than suitable? I think that 4" would actually hurt performance wouldn't it?

Thanks all

 

[jim97gst]

My question is, would putting a 2.5" downpipe on my car be benneficial with the 3" or should all the pipe diameters match?

The pipe diameters don't need to match. Actually, the diameter doesn't need to be as large the closer you are to the turbo. The exhaust gas close to the turbo is a hotter and flows better than when it is further downstream.

2.5" will definitely be an improvement over your stock downpipe, especially if it is mandrel bent. The decision between 2.5" or 3" depends on how far you want to go with performance. 2.5" is probably fine with a 16G/T28. If you're planning on going with a bigger turbo, you might want to consider a 3".

Wouldn't 3" be more than suitable? I think that 4" would actually hurt performance wouldn't it?

Again, it depends on the turbo he's using, but he should have a REALLY big turbo to justify a 4" exhaust. It won't hurt performance, just your ears and your wallet. You can't have the exhaust too big on a turbo, the turbo provides backpresure.

 

[TurboBlue]

Im not plaiing a 4inch exhaust, but anyways, thanks for the help. ANd for now im probably not going to go any bigger then a 16G. SHe's my daily for a while so its not going to be too insane. Just a stage 1 upgrade for the whole car. Thanks a lot though

 

[Silent2g]

im running a 2.5 inch dp to a 3inch dp back
runs pretty good. might want to keep an eye on the boost gauge. mine slowly creeps above 5500 rpms {even with the EBC}
stock 1g o2 housing, unported turbo

 

[RaysTsi]

Ive heard that since the exhuast gasses are at thier hottest at the Dp that it helps to have a 2.5 bacause the gasses will move faster into your 3" exhuast

 

[Grizzly Racing]

i had a full 3" on my car with a big 16G.....

all i did was replace the downpipe with a 2.5" one and kept the 3" catback.

i gained 2mph in the 1/8th mile and 4mph in the 1/4

boost creep was totally eliminated and my boost held rock solid all the way to redline. with the 3" i was getting bad creep and tried about everything to remedy it. o2 dump, porting, etc.