Hello everyone, I installed my STS(t4 60-1 turbo w/ intercooler) on my 04 Yukon XL Denali 6.0L. I am having not getting the full boost what I have on my WG spring(5.80psi) There is no exhaust leak, all couplers and clamps checked. Vacuum lines checked. My guage at first and second gear reads only 3.5 psi and falls to 1 psi during these gears. After it shift to 3rd gear the neeedle shoots to 4 psi and still there all thru redline. Could the psi drop is cause by slippage in transmission? This is my first auto tranny and not had any experience on tranny slippage compare to a 5 speed. I do not see the revs shoot up like a clutch slippage. The truck still pulls and swift like normal but the boost power on the truck seem laggy. Also does anyone have an idea why im not hitting the 5.8o psi? Thanks in adavance.

Richard

 

I'm not sure where your sense line for your wastegate is at on the STS,but your probably measuring boost loss from the intercooler. The wastegate sees 5.8 psi at the compressor outlet and your seeing what boost you have in the intake manifold.

 

The wastegate bottom side port line is hooked up directly to the turbo compressor.

From experience from building import turbo cars usually dont get much pressure lost usless you use a crappy restrictive intercooler. I assume the STS uses a quailty intercooler core. Our turbocharged S2000 see less than one psi drop using a PWR core. This also doesnt explain the boost drop during the first 2 gears. and holds steady on 3rd and plus gears.

Richard

 

Just run your boost reference to the intake and see what you get. There will be pressure drop with the intercooler.
Also, wrap your exhaust all the way back to the turbo. I will make a difference in how fast it spools and help your "low boost in 1st and 2nd" issue.
A Yukon XL in long and there is alot of heat loss back to the turbo. Spend $100.00 on wrap and you wont be sorry.

 

The boost reference is taken from the intake manifold. I already have all my exhaust pipes wrapped with thermal wrap. Im not having problem with turbo lag. Just having problem maintaining and building boost. I will refenece boost pressure from the turbo to compare it to intake manifold. But this doesnt explain the change in boost drop during 1st and 2nd gear.

 

One thing you have to be aware of is the diffrence in air density at the diffrent temps. You are seeing the diffrence in pressure from the temps of the intake charge. I would "t" into your Intake manifold for the wastegate signal and i think you will be a lot happier.

 

I will use another boost guage to compare the two on turbo side and intake manifold. However, the lost in boost during the gears is still a mystery.

Richard

 

^Bump