Boost Issues
Boost Issues I'm having issues with achieving and holding 20 psi with my 346.
I broke a rod in my 383, so I went with a new 346 short block and am trying to get the bugs worked out. The only changes other than the short block is I went with a Speed Inc. TU1 cam in place of the Comp LSR 281 that was in the 383. I also dropped compression from 10.9 down to about 9.5.
Here's the abridged version: I have a Turbonetics billet 7575 on a Huron Speed kit and made 750/750 rwhp at 15 psi on the 383. So far the 346 has spiked 700/750 at 18 psi, but boost is tapering to 16 psi. We have swapped the 9 psi spring for a 13 psi spring and it peaks at 19 psi and still tapers to 16. The wastegate is a Precision PW46, BTW.
Running strictly off the wastegate with the 13 psi spring, boost hits 10 psi and tapers to 6. I'm at a loss here, but will admit that I'm the opposite of a turbo guru.
Please chime in!
I broke a rod in my 383, so I went with a new 346 short block and am trying to get the bugs worked out. The only changes other than the short block is I went with a Speed Inc. TU1 cam in place of the Comp LSR 281 that was in the 383. I also dropped compression from 10.9 down to about 9.5.
Here's the abridged version: I have a Turbonetics billet 7575 on a Huron Speed kit and made 750/750 rwhp at 15 psi on the 383. So far the 346 has spiked 700/750 at 18 psi, but boost is tapering to 16 psi. We have swapped the 9 psi spring for a 13 psi spring and it peaks at 19 psi and still tapers to 16. The wastegate is a Precision PW46, BTW.
Running strictly off the wastegate with the 13 psi spring, boost hits 10 psi and tapers to 6. I'm at a loss here, but will admit that I'm the opposite of a turbo guru.
Please chime in!
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Where are you taking the reference signal from for the gate ?
And there is never any guarantee with gate only that boost control will be perfectly stable, there are may other factors at play.
That's why many like a good electronic control as it gives you flexibility to make...or have it make adjustments to help maintain boost etc if fighting against mechanical limitations.
And there is never any guarantee with gate only that boost control will be perfectly stable, there are may other factors at play.
That's why many like a good electronic control as it gives you flexibility to make...or have it make adjustments to help maintain boost etc if fighting against mechanical limitations.
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
I have a huron speed kit on my 346 using a PW46 just on spring. I have 3 springs in mine the 9 lb green one, the 6 lb red one and the 1.5 lb one. I also have a T series, but the 7875 turbo. My boost is as flat as a table top from about 4000 rpm, it varies less than a 3 kPa, on my HPTuners log all the way up to 6700. This is only at 15 lbs though, and by the springs that would equate to 16.5 lbs. Considering that there is some boost loss going from the compressor housing through the intercooler, the charge pipes, and the throttle body all the way back to the back of the intake manifold where I'm measuring the 15 lbs that would make good sense. What spring do you have in your PW46 that would equate to 13 lbs? I'd try putting the big blue spring in the gate and see what it does? What are you running for a boost controller besides the spring?
Where are you taking the reference signal from for the gate ?
And there is never any guarantee with gate only that boost control will be perfectly stable, there are may other factors at play.
That's why many like a good electronic control as it gives you flexibility to make...or have it make adjustments to help maintain boost etc if fighting against mechanical limitations.
And there is never any guarantee with gate only that boost control will be perfectly stable, there are may other factors at play.
That's why many like a good electronic control as it gives you flexibility to make...or have it make adjustments to help maintain boost etc if fighting against mechanical limitations.
I have a huron speed kit on my 346 using a PW46 just on spring. I have 3 springs in mine the 9 lb green one, the 6 lb red one and the 1.5 lb one. I also have a T series, but the 7875 turbo. My boost is as flat as a table top from about 4000 rpm, it varies less than a 3 kPa, on my HPTuners log all the way up to 6700. This is only at 15 lbs though, and by the springs that would equate to 16.5 lbs. Considering that there is some boost loss going from the compressor housing through the intercooler, the charge pipes, and the throttle body all the way back to the back of the intake manifold where I'm measuring the 15 lbs that would make good sense. What spring do you have in your PW46 that would equate to 13 lbs? I'd try putting the big blue spring in the gate and see what it does? What are you running for a boost controller besides the spring?
Last edited by gixxer9; Feb 16, 2017 at 06:51 PM. Reason: Forgot to mention boost controller
Trending Topics
I keep hearing about back pressure, but I'm confused by this because this setup was able to move enough air on a 383 to produce 750 rwhp at 15 psi -- why would there be more back pressure on a 346? There should be less..
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
Actually there should be about the same back pressure on it at a given HP level. More boost on the 346, which offsets the displacement difference,should equalize it. It takes a certain amount of air, fuel and exhaust for a given HP level. You would be forcing the same amount of air, about 70 lbs/minute into either engine to make 750hp. The same amount of intake air will make the same amount of exhaust. It is somewhat independent of engine displacement.
Actually there should be about the same back pressure on it at a given HP level. More boost on the 346, which offsets the displacement difference,should equalize it. It takes a certain amount of air, fuel and exhaust for a given HP level. You would be forcing the same amount of air, about 70 lbs/minute into either engine to make 750hp. The same amount of intake air will make the same amount of exhaust. It is somewhat independent of engine displacement.
The wastegate was pressurized with air and begins to open at 11.5 psi and fully opens at 13 psi.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Any leaks on the line, which there almost always will be with a wastegate and absolutely with any controller that is bleed off controlled will skew the readings on that line.
It may not be the cause of your issue, but it is very bad practise.
I was running 15 psi on the 383, and it held that without taper to the tune of 750/750. I could turn it up to 18 psi and it would still hold boost. I was on the 9 lb spring at that time. I am now running 13.5 lbs of spring pressure with the 346. The boost will hit 18-19 psi, but then tapers to 16 psi.
At this point is where we ran straight wastegate to see what it would hold -- it hits 10 psi and tapers to 6 psi. We tested the gate with compressed air with it beginning to open at 11.5 psi and fully open at 13 psi.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
The gate only was for testing purposes. I have a TurboSmart manual boost controller tee.
I was running 15 psi on the 383, and it held that without taper to the tune of 750/750. I could turn it up to 18 psi and it would still hold boost. I was on the 9 lb spring at that time. I am now running 13.5 lbs of spring pressure with the 346. The boost will hit 18-19 psi, but then tapers to 16 psi.
At this point is where we ran straight wastegate to see what it would hold -- it hits 10 psi and tapers to 6 psi. We tested the gate with compressed air with it beginning to open at 11.5 psi and fully open at 13 psi.
I was running 15 psi on the 383, and it held that without taper to the tune of 750/750. I could turn it up to 18 psi and it would still hold boost. I was on the 9 lb spring at that time. I am now running 13.5 lbs of spring pressure with the 346. The boost will hit 18-19 psi, but then tapers to 16 psi.
At this point is where we ran straight wastegate to see what it would hold -- it hits 10 psi and tapers to 6 psi. We tested the gate with compressed air with it beginning to open at 11.5 psi and fully open at 13 psi.
Connect the gauge to a manifold source that does not have any air leaks on it and start again.
But you probably just need a better controller and I would always prefer taking the reference line for the gates from the compressor housing or close to it.
Whilst many do, I would never take this from the intake manifold
If you feel your IC/plumbing is crap and there may be large pressure loss across it...either fix it or take the reference after the IC but before the TB so it never sees intake vacuum.
i ditched my air filter on the turbo and added cutouts just after the DP and boost appears to only drop .5-1psi now from my street logs.