When is a 3.5-4" dp needed?

[sbcxtreme]

Just curious when a 3" downpipe becomes somewhat of a restriction. Thanks guys.

 

[1bad92awd]

Well a 3" downpipe is a significant upgrade. Once your talking hp numbers over probably 500-600 it may be a "restriction" but for most applications a 3" would be sufficient.

 

[talonz27]

I would say when the exit on your turbo is bigger than 3in and you have over 500hp you would need some 3.5in to 4in downpipe.

 

[kspharris]

I would say when the exit on your turbo is bigger than 3in and you have over 500hp you would need some 3.5in to 4in downpipe.

Ditto

 

[inneedof]

According to maximum boost it is about 650-700 you will need the 3.5 inch and around 950 for a 4 inch, the book is pretty dated but still extremely useful.

 

[1bad92awd]

According to maximum boost it is about 650-700 you will need the 3.5 inch and around 950 for a 4 inch, the book is pretty dated but still extremely useful.

Thats even higher than what I would have expected but makes complete sense. Personally I only know 1 person who has a downpipe that large and his setup is over 800awhp. Good info

 

[sbcxtreme]

The plan is around 600whp on race gas. Just seeing if i needed to go bigger than a 3" for an open dp. Thanks guys.

 

[2gAWDTalon]

The plan is around 600whp on race gas. Just seeing if i needed to go bigger than a 3" for an open dp. Thanks guys.

eh... I think 3" will be alright.
On my 6776 Full T4 the V band outlet is only 3" so I figure a 3" DP to my 3.5" catback will be alright.

 

[assault187]

If your running an open downpipe, I dont see it as a restriction @ 3".

I also have a quick question while were on the subject of downpipes. Does anyone know who would make a FULL 3" downpipe that will also delete the cat. for a 2G front wheel? I can't seem to find any on the vendor websites, or on the internet...

 

[1bad92awd]

If your running an open downpipe, I dont see it as a restriction @ 3".

I also have a quick question while were on the subject of downpipes. Does anyone know who would make a FULL 3" downpipe that will also delete the cat. for a 2G front wheel? I can't seem to find any on the vendor websites, or on the internet...

Check Slowboy racing, they have a lot of different options for O2 and cat delete downpipes. Check Road Race Engineering too, they might also have something..

http://www.slowboyracing.com
http://www.roadraceengineering.com

Also, I forgot to mention, Apexi makes cat-delete downpipes as well.

 

[fulanititoo8198]

Punishment racing has very nice pieces also.

 

[wishihadatalon]

Jake M. ran a 2.5" down pipe when he was running his fp3575 and made 692 whp found here http://dsmvideo.vidiac.com/category/evil_eagle/0/e130f530-730b-4385-b1ed-983000abcd09.htm

 

[sbcxtreme]

Jake M. ran a 2.5" down pipe when he was running his fp3575 and made 692 whp found here http://dsmvideo.vidiac.com/category/evil_eagle/0/e130f530-730b-4385-b1ed-983000abcd09.htm

Any idea if he dyno'd it after a larger dp was installed? Curious what the difference would be at that power level.

 

[wishihadatalon]

Any idea if he dyno'd it after a larger dp was installed? Curious what the difference would be at that power level.

You could pm him and ask. I think he switched to a t67 after that but I am not sure.

 

[CanadianTSi]

Jake M. ran a 2.5" down pipe when he was running his fp3575 and made 692 whp found here http://dsmvideo.vidiac.com/category/evil_eagle/0/e130f530-730b-4385-b1ed-983000abcd09.htm

According to that Video he was running a 3" Turbo back, 2.5" o2

 

[wishihadatalon]

According to that Video he was running a 3" Turbo back, 2.5" o2

eh they are the same thing j/k

I just remember him saying 2.5" 02 housing. I guess his numbers are a great example of how far you can go with 3"

 

[JWoodley]

I'm running a 3" turboback (3" ATR 02, 3" ATR DP w/ cat delete, and an Apexi N1). I'm around the 360awhp mark and it made a huge difference upgrading from the stock 02/dp. I figure if you're flowing enough air that the 3.5 or 4 inch downpipe would make an equal improvement in hp/trq and especially spoolup.

 

[sbengineering]

I'm running a T67 with 3.5dp. i think for the sharp turndown usually in DSM dp's, anything in T4 size, 650hp, something over 3inch is well worth it. for exhaust, bigger is always better. 4inch is not needed for anyone here.