i have the turboheaders that have the t3 built on the header . i'm gonna use 2.5 " pipe to combine the two sides . i'm pondering on wether ishould stay 2.5"an use a t3 or go 3" an use a t4 turbo .

 

Feed pipe to the flange? For a milder 305, 2-2.5" feed to turbo flange would be great. Id do a t4 p trim sized wheel and depending on rpm range .68 or .96 a/r. It would spool a .96 pretty quick tho. .68 would choke top end unless you have a tpi or similar with 4500 rpm limit. Then you would have a diesel truck like setup. Lol torque out your ears

There are 1000 hp cars using 2.5" feed pipes to single turbos although most use 3" for big flanges since it fits better.

 

i was looking at a .84 exhaust i was just wondering if a t3 would be better or if it would choke it sum .

 

There is a lot more to it than just that, if you have an idea what your engine is making naturally aspirated it would be easier to explain for you, as well as where you plan on capping your RPM at full throttle...

 

ok i'm about 220 hp right now , rpm's will be no more than 5800 . i just ordered a t3 t70 with a .84 ar exhaust housing . i'm gonna go ahead an put a lt1 cam in it so i'm guessing my hp will be around 250 bhp . the rest of my mods are in my sig. in the first post .i want a quick spooling turbo with little lag ...

 

Sure its a true t70? What size is the turbine wheel. I dont like to see a turbine wheel too much smaller than compressor wheel. T4 p trim is 64/74 mm on turbine wheel and i wouldnt go much larger than 70 mm on compressor or else it will not spool as quick.

A .84 t3 should be sorta close to a .68 t4 so it will spool fast unless turbine is alot smaller. Then it will struggle to drive the large compressor

 

Then in my opinion you picked a good turbo, although make sure the turbo is true to its' specs by measuring it. Be sure to take the time and port the exhaust housing while your at it (disregard the wastegate porting, obviously)...

 

thanks for your input . how doyou like that t72 on yours ?

 

Spools very fast even with the current stall speed, but that is because I paid so much attention to the head work that I did, the camshaft I went with, and a few other things in which many Turbo Buick guys went over and over and over with me. Must have driven those guys crazy over the years. The new stall will finalize everything, but I have been too damn lazy to install it, just don't feel like dropping the trans. But yeah, your going to spool pretty quick with your setup, and it's going to be quite addictive for you, so make sure your tuning is precise the higher you raise the boost... and you will, trust me.

 

i know how addictive boost is . i had a 400 whp srt4 before this car . i'm looking at a 2500 stall converter an i have the 3.23 posi rear to redo the brakes on an installed still . i have a good safe tune right now with no knock at all an i plan on a very safe tune to start out at 6 lbs of boost an work my way up to 12-14 at the most . thanks for the advise i been follow your build an orrs an fasteddi build for awhile now .