Help: I am losing BOOST!
Thread Starter
Burning Brakes
Joined: Sep 2004
Posts: 812
Likes: 20
From: www.shockerracing.com
Help: I am losing BOOST!
I have a 1998 Automatic Corvette. Last winter I forged the bottom end of my motor with Eagle Forged H Beam Rods and Mahle Pistons. The car has AFR Mongoose 205cc heads 66cc, 226/234 .598 .599 117 lsa blower cam, Procharger P-1sc-1 ho kit with a 3.70 pulley on it. I took it to Straightline Performance for tuning and we found that the boost is jumping up to about 4lbs and then dropping off to 2lbs. I have ruled out belt slip as I had a new tensioner made to give me a lot more belt wrap. I also went through and rechecked all of my hose fittings from the supercharger to the intake manifold. Any ideas or suggestions as to what to do next?
Here are some screen shots from the dyno:
Here are some screen shots from the dyno:
Last edited by ShockerRacing; Sep 22, 2009 at 03:22 PM.
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
Rule #1 don't ever rule out belt slip.
Rule #2 refer to rule #1
Belt slip doesn't always occur at the charger. It can also occur at the balancer.
If it is absolutely not belt slip, do a pressure check. Cap off the inlet and pressurize it. Listen to your bypass valve. It's a common point for leaking in some systems.
After that, it's anyone's guess. Balancer not pinned and spinning on the crank or who knows what.
Rule #2 refer to rule #1
Belt slip doesn't always occur at the charger. It can also occur at the balancer.
If it is absolutely not belt slip, do a pressure check. Cap off the inlet and pressurize it. Listen to your bypass valve. It's a common point for leaking in some systems.
After that, it's anyone's guess. Balancer not pinned and spinning on the crank or who knows what.
Burning Brakes
Joined: Sep 2005
Posts: 1,218
Likes: 0
From: Temple TX
Rule #1 don't ever rule out belt slip.
Rule #2 refer to rule #1
Belt slip doesn't always occur at the charger. It can also occur at the balancer.
If it is absolutely not belt slip, do a pressure check. Cap off the inlet and pressurize it. Listen to your bypass valve. It's a common point for leaking in some systems.
After that, it's anyone's guess. Balancer not pinned and spinning on the crank or who knows what.
Rule #2 refer to rule #1
Belt slip doesn't always occur at the charger. It can also occur at the balancer.
If it is absolutely not belt slip, do a pressure check. Cap off the inlet and pressurize it. Listen to your bypass valve. It's a common point for leaking in some systems.
After that, it's anyone's guess. Balancer not pinned and spinning on the crank or who knows what.
You prob found the limit of your 6-rib belt.
I would also concur about doing a pressure check as Bret has stated as he is one of the most knowledgeable people on this board!
Thread Starter
Burning Brakes
Joined: Sep 2004
Posts: 812
Likes: 20
From: www.shockerracing.com
"Balancer not pinned and spinning on the crank"
Also, if this was the case wouldn't the engine not run properly? Wouldn't there be other more obvious signs if the crank was spinning?
Also, if this was the case wouldn't the engine not run properly? Wouldn't there be other more obvious signs if the crank was spinning?
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
The balancer spinning on the crank was a way-off statement. More b.s. than anything. The other 2 are the main issues. Have also seen intake leaks, broken rings and pistons causing the loss of boost.
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Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
Which manifold do you have?
FAST are notorious for leaking and cracking, especially under BOOSTed conditions!
It is quiet possible you have a crack in the manifold even if it is the stock LS1/LS6 - time for a close inspection
Other than that I'd seriously inspect the belt at the crank and do a WOT pull and watch the Volt gauge to see if it drops which will = Belt slip @ Crank (This is a tried and true method to see whether you have belt slip indeed - ARUN's Method is waht we shall call it
)
Thanks,Matt
FAST are notorious for leaking and cracking, especially under BOOSTed conditions!
It is quiet possible you have a crack in the manifold even if it is the stock LS1/LS6 - time for a close inspection
Other than that I'd seriously inspect the belt at the crank and do a WOT pull and watch the Volt gauge to see if it drops which will = Belt slip @ Crank (This is a tried and true method to see whether you have belt slip indeed - ARUN's Method is waht we shall call it
)Thanks,Matt
Race Director
Joined: Apr 2009
Posts: 10,581
Likes: 252
From: SE TEX
4lbs is not very much even for a P1. Like the others have said never rule out belt slip. As far as other possibilities, it would help to pressurize the entire system and see if there is a leak somewhere, especially at the valve.
Good luck!
Good luck!
Team Owner
Joined: May 2006
Posts: 21,473
Likes: 356
From: Palmdale, Ca----- 2009 Cyber Gray 4LT A6 F55 452 RWHP 422 RWTQ- RIP 1998 C5 734 RWHP & 585 RWTQ-----
If it is a BPV then VACUUM holds it open and BOOST closes it!
If you have a MityVac Vacuum/Pressure tester you'll be set and you can test the diaphram in the BPV's POD!
Thanks,Matt
Tech Contributor
Joined: Apr 2007
Posts: 10,924
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From: Forney Texas
Advanced
Joined: Jul 2009
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^^^ lol yeah man its all natural smoke man.
Im the same problem. i have a vortech v1 t trim and with a 6' crank pulley and the 3.33 vortech pulley i only made about 1.5 psi so i bought a 2.95 vortech pulley and it made 5 psi.
Im the same problem. i have a vortech v1 t trim and with a 6' crank pulley and the 3.33 vortech pulley i only made about 1.5 psi so i bought a 2.95 vortech pulley and it made 5 psi.
Last edited by toofastlt1; Sep 24, 2009 at 09:53 PM.
Thread Starter
Burning Brakes
Joined: Sep 2004
Posts: 812
Likes: 20
From: www.shockerracing.com
Mine was making 6.5 psi with a 3.85 pulley before I forged the motor.
Drifting
Joined: Feb 2008
Posts: 1,765
Likes: 2
From: St. Clair Shores Mi
6" crank pulley? sounds like a hella under drive pulley!