1bad lad

Hey guys, need a little input. so i have a 2001 yukon denali original block and crank, 4th gen rods with flat tops from a gto. square port heads and truck intake. ls9 head gaskets. so its about 10.5 compression.
So i installed forward facing headers and precision t3 .82ar vband flange turbos. 3" pipes to the axle with straight through mufflers.
so with 7.5psi in the manifoldi am seein about 25psi backpressure at 5500rpm.
My question is i keep reading all over the interwebs of people with similar sized stuff but i know there is no way 25psi backpressure is correct. needs to be under 2:1 has anyone else had any experience with these things?

svslow

Where are you taking the back pressure measurement and what are you using to take it?

1bad lad

welded in an o2 bung before the turbo in the collector. drill/tapped a o2 plug 1/8npt. screwed in fitting with a nipple. run vac hose to a boost gauge. its a little bouncy but definitly makes it way over 25psi.

jordoza

What turbine size on the turbos. T3 is just a flange size turbine size effect back pressure alot. What compressor size. In my opinion size ratio between compressor and turbine can effect backpressure also.

kbracing96

iTrader: (25)

Is 25 the peak of the pressure or the average? I'd put a small restrictor inside the fitting, like .062 to knock out the "noise" from the pulses and show you the actual average pressure.

1bad lad

ya sorry. precision 6266s .82 ar exh housings

kbracing96

iTrader: (25)

You should not have a back pressure issue at only 7.5psi with those turbos on a 6L...

slowride

iTrader: (3)

Yeah I have cheap old 6265 .82 v band in/out t04b turbos on my old 383 turd. You turbos will make a ton of power.

jordoza

I agree backpressure shouldnt be an issue with those turbos.

gnx7

iTrader: (28)

let's see some pics/video of this beast