What size downpipes?
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Teching In
Joined: Jun 2005
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What size downpipes? I'm installing a pair of Garrett GT42 turbos on my lt1 and can't decide on which downpipe size would be best 2 1/2" or 3". The pipes will have to merge to 2 1/2" under the car and it will be dual exhaust with no converters.
Originally Posted by americanlt1
I'm installing a pair of Garrett GT42 turbos on my lt1 and can't decide on which downpipe size would be best 2 1/2" or 3". The pipes will have to merge to 2 1/2" under the car and it will be dual exhaust with no converters.
In my opinion both of the sizes you posted are way to small..... **** twins GT42's...... with my single GT42 76MM wheel im running a 5" stepped to 4" and 4" all the way down........... why choke them like that???
Staging Lane
Joined: Jul 2004
Posts: 62
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Originally Posted by americanlt1
I'm installing a pair of Garrett GT42 turbos on my lt1 and can't decide on which downpipe size would be best 2 1/2" or 3". The pipes will have to merge to 2 1/2" under the car and it will be dual exhaust with no converters.
2 1/2 pipe imo is to small for the 42's. 3" or larger for each if you are going to be using the realistic powerband of a pair of 42's.
dont choke 'em!! To start with, what size is the exhaust outlet on the turbine?? (aka the diameter of the exducer bore) That should give you a good idea or where you want to start.
Don't forget, any restriction on the downpipe means the turbine wheel has to work harder, which means unnecessary backpressure through the headers which means higher cylinder temperatures... and that equates to LESS POWER because you have to run more timing to avoid the higher risk of detonation!
Those are big-a$$ turbo's... I'd say 3" minimum.
Don't forget, any restriction on the downpipe means the turbine wheel has to work harder, which means unnecessary backpressure through the headers which means higher cylinder temperatures... and that equates to LESS POWER because you have to run more timing to avoid the higher risk of detonation!
Those are big-a$$ turbo's... I'd say 3" minimum.
Originally Posted by americanlt1
I'm installing a pair of Garrett GT42 turbos on my lt1 and can't decide on which downpipe size would be best 2 1/2" or 3". The pipes will have to merge to 2 1/2" under the car and it will be dual exhaust with no converters.
have to agree...im running twin t-70's and im going with 3 inch with dual 3 inch cutouts before the y into my 3 inch catback...so i can just open it up at the track and have basically stait dual 3 inch DP's
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Verdad Gallardo Wow... how do you keep the pressure ratio so low? Is it intercooled? Just a real high volumetric efficiency??
Originally Posted by JZ 97 SS 1500
Twin 2.75 or 3" are more then enough. Our Viper runs twin 2.75 DP's and is making well over 1000rwhp and the pressure ratio is 1.3:1 
Don't mean to pry or be a pain, but what kind of features make the kit so efficient? Seems to me like that's a really low pressure ratio! Not that I doubt it, because I don't..... just want to take home some pointers for my own kit design. 
Originally Posted by JZ 97 SS 1500
The kit is very efficient and requires fairly low pressure to make big #'s.
Jose
Jose
