I have a question for those of you who make your own feed pipes. Have you ever tested or compared how the turbo responds to different feed pipe diameters? For example a 2.5" vs. 3". In my understanding/logic I assume it would take longer to fill the volume of a 3" pipe vs. 2.5", therefore taking longer to start spooling the turbo, however once its spooled up the engine will exhaust more and produce more power.

 

It all depends on your setup. Some people have run 2.5 and switched to 3 and saw some gains on the dyno. What are your goals?

 

well i currently have 2.5" from engine(collector at the ypipe) to the turbo, so was curious if 3" would yield more power. But there is just too much physics/math behind figuring it out, so wanted to see if anyone had tried different diameters.

 

For your 3.5 I would say go for it, you could sell your old feed no problem if you decide to go for the 3". There is a new thread in 4th gen on that obx 3" y for an rmt, but I don't think anyone tried it yet.

 

Well I was talking to Kevlo about it, and I think ill stick to my 2.5". I dont think we have enough RPM range to benefit from 3", id have to do something about having a better spooling turbo, smaller housing, quick spool valve or something. With about 10' worth of piping, going from 2.5 to 3", there is a big difference in volume to fill and pressurize, so I dont wanna spend all the money doing 3" to find out my spool up curve moved more to the right lol. I already get late boost (full boost at high 4k and shift at 6k)

 

That is probably right. The 2.5" is not likely choking it up enough to offset the reduced spool time. Are you using a dual scroll turbocharger? If so, there's no reason not to use a quick spool valve... They can be kind of expensive or difficult to fabricate, but I see tons of good reviews about them.

 

the only way it would be worth switching from 2.5 to 3inches is the following:

1.
you plan to extend your rev limiter

2.
the new feedpipe will be shorter and to make the total volume between the two setups the same. If not your turbo will spool slower

 

I have a twin scroll, fabing one up is actually pretty simple but no time, and i REFUSE to pay $500 for a SP spool valve, they have it patented and no one else can produce/sell it so they charge insane amounts.

 

Yeah, im sticking with what i got

 

well my feed pipe went is FULL 2.5 until it crosses the front motor mount then as it get to the t4 flange it is a large as 3.25 oval bent...

Maybe that was my problem with boost in first gear, on my little old 3.0

 

you ever think about running two seperate exhaust pipes from each bank into the turbo.

 

That's certainly doable, but probably wouldn't do anything more than Y-ing them together into the turbo and no ability to use a spool valve.

 

it would if he has a twin scroll turbo which most holsets are, remember that divider is there for a reason

 

whats a spool valve

 

From what I know, 350Z guys were losing power when they went to 2.75 primary pipe for headers. The 2.5 were the best for power.

Ferhan

 

you guys are funny

 

make a forwared feedpipe!!! shorter and better flowing. say what you want, on my old car i made full boost 1st gear on a 3.0... lol yes still hating just a little lol come tune 2 cars and put some cash in the y-pipe fund