When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am currently working on my dads 408/S485 Yukon Denali and having some issues making boost. I currently have 26psi springs in the WG and the truck will not make over 12 psi. I pressure tested the cold side and found that there was some air escaping from the Turbosmart Race port BOV. I pulled it apart and it has a blue spring in it which im assuming is "race" level of boosts. Im not sure how to read the attached chart but i figured it would be better than for 12 psi.
I'm utilizing a Huron speed T6 kit and have now plumbed all of the lines in different ways and still not having any luck. I currently have a line running from the back of the intake manifold that T's. One goes to a distribution vacuum block, one goes to the 3 port mac valve into the right hand side. It goes through the mac valve out of the left hand side and goes to the top of the wastegate. The bottom line from the WG returns to the vacuum block. I then have another port in the vacuum block that goes to the top of the BOV, and another port on the vacuum block goes to the fuel pressure regulator. and t's off into the boost gauge on in the truck.
Huron speed said this kit would work with boost reference to hold the gate shut and pressure on the BOV so i would not have to utilize 2 mac valves or onboard air/CO2.
I also included a picture of how i routed everything. Please excuse the clutter and zip ties. I've had everything together and apart so many times i haven't tidied it up till it will work.
My next plan of attack was to completely remove the mac valve from the system and see if the truck will make any more boost.
Are you using the Mac valve at all to get it to 12psi or is that just on the spring? What size is the intercooler? I would try to bypass the intercooler to rule it out if it's not that difficult. You can also use a boost gauge or any pressure gauge to check the preintercooler pressure, shouldn't be losing much across the intercooler.
The reference to the top can only add pressure, and if the bov is still leaking you could block it off and retest. I would also take some of that spring out of it, whenever you find the leak or restriction the boost will be high.
"My next plan of attack was to completely remove the mac valve from the system and see if the truck will make any more boost".
Any progress?
I'd start with LSXford's suggestion.
"I would also take some of that spring out of it, whenever you find the leak or restriction the boost will be high."
Have you tried to use, say a 10# spring in the gate, disconnect all the other plumbing and block the bov, so it runs on the gate spring only?
If I were to block the bov, I'd make a plate to replace the valve.
Might you have plumbing available to check turbine back pressure?
I just had a similar issue on my car. It wouldn't build any boost past 9 psi. Turned out to be my wastegate. Replaced it and everything worked as it did before
Figured it out guys. Ended up being the shitty 4" downpipe to 3" to 2.5" connector pipe to the full exhaust that was holding everything back. Wouldn't even allow the truck to get up near boost control territory. After I uncapped the exhaust I took it out and it spooled up and hit boost cut so fast at 19lbs I didn't even have time to lift. It's gonna be rowdy.
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Slideshow: From wobbling harmonic balancers to failed EBCMs, these are the issues that define long-term C5 ownership and what repairs typically involve.
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Slideshow: A modern Camaro transformed into a retro icon, this limited-run "Bandit" build blends nostalgia with brute force in a way few revivals manage.
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Slideshow: Cadillac didn't just crash the high-performance luxury vehicle party, it showed up loud, supercharged, and occasionally a little unhinged...
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Slideshow: A one-off sports car that looks like a vintage Italian exotic-but hides a C6 Corvette underneath-just sold for the price of a new mid-engine Corvette.
Turbo Denali - no boost issue 
