I was wondering what are the advantages and Disadvanges for TURBO in going to a larger downpipe to a 3 inch.
What im trying to say is if there any low end power loss when doing this on BOTH Stock and LOW compression motors.
Thanks!

 

From the turbo outlet you want to keep it at 2.5" till you get to the flex section. Afterward running 3" pipe is ideal. That's my $0.02.

 

Hmmm, well all I know is stock for us is 2.5" and the HKS downpipe that I have are 3". It provides nice power higher up in the powerband. I don't notice much loss in the lower end though.

 

yeah in a ideal world we wouldn't have dump pipes! lol! you would want it free straight after the turbo as to create no back pressure what so ever (unlike N/A) to allow the turbo to spin as freeley as possible. on the rex's over here exhaust mods can make a fair big HP gain going a full 3" system. you don't loose much down low as the turbo can spool up much faster with hardly any restrctions. the moral here is the bigger the better with turbo cars!

 

Using a 3" pipe straight from the turbo outlet is not very beneficial since the velocity of the exhaust gases will slow down. Using a smaller pipe (relative to the rest of the exhaust) upstream helps maximize flow of the "hotter" exhaust gases.

 

all the turbo guys up here run the 3" downpipe with a 3" exhaust. none have problems with low end and all have some pretty sick cars

 

Thanks for the input guys.The reason why im asking is because i have a choice between a 2.5inch and a 3 inch Downpipe which im custom making from my Friends shop.Its gonna cost me the same price so i was just wondering which would be better considering i dont loose bottom end!

 

it doesn't matter if the velocity of the exhaust gasses slow down as it would of already passed through the turbine! If a smaller diameter pipe is used it creats back pressure which slows down the turbine its as simple as that! some supra's are using 4" all the way with no cat or muffler.

 

It matters..

.and if you guys read my earlier post carefully you will notice that the DP is 3", just the small section upstram should be slightly smaller RELATIVE to the rest of the DP & exhaust.

UNIQ...Do what you feel best. RRE are very famous for building fast DSM's and they say the same thing, here is a quote from their website....

"Our DPs have a 2 1/2" stainless steel first bend with a 2 1/2" stainless steel flex section. They then expand to 3" right after the flex section right under the oil pan area. Why start out at 2 1/2"? If you are running on the stock O2 sensor housing, even ported it is 2 1/2" inside diameter. When the exhaust gasses are hot, they flow better, 2 1/2" is plenty for the first 12". As the gasses cool , bigger helps. By going to 3" after the flex section...."

 

heres a web site from HiTech (very well known exhaust company in aus) showing some pretty good gains using a 3" dump, all the way through, its for a 2L turbo WRX same as a turbo tib. I was just sayin

HiTech

[ August 27, 2002, 03:47 PM: Message edited by: Scrud1 ]