Weird issue on fresh build
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Weird issue on fresh build Here is the issue
2009 Pontiac G8 with stock L76
Installed Texas Speed Bald Eagle cam NA
Beefed internals with head studs, ZL1 Head Gaskets, ZL1 Lifters, Double Spring Valve Springs, Titanium Pushrods. To get it ready for 10 psi of boost from a centrifugal supercharger.
First start up working with a tuner it was running at 1.2 lamda and would not accelerate under no load. I added some fuel just to circulate the cooling system out then send him a log. He said something does not look right so I checked vacuum and we have 5 in/hg. I proceed to smoke test for vacuum leaks, pull the intake and inspect, remove supercharger belt and intake hose and pull from ambient air, hose the vehicle down with flammable brake cleaner watching pids for a spike in fuel trims, pull rocker arms and measure pushrods and they are .025 too long so I order correct length pushrods, I check Overlap on TDC of Exhaust stroke and the cam degree seems to be good and no timing chain issues (Not sure how anyone could mess up an ls timing chain but hey I am human).
The right length pushrods was the only thing that made a difference and that got me to 7 in/hg of vacuum.
So my tuner said lets just see if we can tune it to make a couple runs and we got it running pretty well around .8 lamda but still terrible vacuum assist for the brakes and it lopes like a sun of a gun. I find out from my tuner it is common for Texas Speed and BTR both to misbox cams and I could have gotten a stage 4 or some humongous cam so I researched and their is virtually no ls cam that would make less than 15 in/hg of vacuum. Then I get the thumbs up from my tuner to push it into boost and see what happens.
We got 1/2 a pound of boost at 5500 rpms. I should have been around 7 psi at that rpms. The supercharger peaks at 10 psi at 6800 rpms with the pulley I have. Something is wrong, here is a couple things I noticed none of which tell me anything but maybe someone can shed some light.
When I replace the pushrods all the valves opened instead of the lifters bleeding down, however I have 150 psi of compression at 5k above sea level and a leak down test proved it must just be very stout lifters.
If the valves where staying open that seems like boost would not be affected as compression would be going back into the intake and honestly the car should not even run.
The vehicle runs awesome, still only about 400 hp based on some simple math and this combo should be 600+ at the crank and be capable of 10 psi and we got 1/2 a psi.
I am stumped, my techs with 30 years combined are stumped, my Dad with 30 years is stumped, the tuner with 20 years is stumped. What could possibly be going on? It seems like a massive vacuum leak, how and where if so. I followed instructions and ran a T from the Vacuum booster to the blow off valve. The PCV system is intact and the vent on the passenger side is vented directly back to the air cleaner. It has the EVAP system intact but the purge valve is closed and operating correctly.
Any Ideas?
The car runs amazing, pulls just like a healthy cammed engine should but the no boost from the vacuum booster for the brakes and virtually no boost from the supercharger at the rpm levels I have tells me I got a serious problem, but I cannot explain what the heck.
2009 Pontiac G8 with stock L76
Installed Texas Speed Bald Eagle cam NA
Beefed internals with head studs, ZL1 Head Gaskets, ZL1 Lifters, Double Spring Valve Springs, Titanium Pushrods. To get it ready for 10 psi of boost from a centrifugal supercharger.
First start up working with a tuner it was running at 1.2 lamda and would not accelerate under no load. I added some fuel just to circulate the cooling system out then send him a log. He said something does not look right so I checked vacuum and we have 5 in/hg. I proceed to smoke test for vacuum leaks, pull the intake and inspect, remove supercharger belt and intake hose and pull from ambient air, hose the vehicle down with flammable brake cleaner watching pids for a spike in fuel trims, pull rocker arms and measure pushrods and they are .025 too long so I order correct length pushrods, I check Overlap on TDC of Exhaust stroke and the cam degree seems to be good and no timing chain issues (Not sure how anyone could mess up an ls timing chain but hey I am human).
The right length pushrods was the only thing that made a difference and that got me to 7 in/hg of vacuum.
So my tuner said lets just see if we can tune it to make a couple runs and we got it running pretty well around .8 lamda but still terrible vacuum assist for the brakes and it lopes like a sun of a gun. I find out from my tuner it is common for Texas Speed and BTR both to misbox cams and I could have gotten a stage 4 or some humongous cam so I researched and their is virtually no ls cam that would make less than 15 in/hg of vacuum. Then I get the thumbs up from my tuner to push it into boost and see what happens.
We got 1/2 a pound of boost at 5500 rpms. I should have been around 7 psi at that rpms. The supercharger peaks at 10 psi at 6800 rpms with the pulley I have. Something is wrong, here is a couple things I noticed none of which tell me anything but maybe someone can shed some light.
When I replace the pushrods all the valves opened instead of the lifters bleeding down, however I have 150 psi of compression at 5k above sea level and a leak down test proved it must just be very stout lifters.
If the valves where staying open that seems like boost would not be affected as compression would be going back into the intake and honestly the car should not even run.
The vehicle runs awesome, still only about 400 hp based on some simple math and this combo should be 600+ at the crank and be capable of 10 psi and we got 1/2 a psi.
I am stumped, my techs with 30 years combined are stumped, my Dad with 30 years is stumped, the tuner with 20 years is stumped. What could possibly be going on? It seems like a massive vacuum leak, how and where if so. I followed instructions and ran a T from the Vacuum booster to the blow off valve. The PCV system is intact and the vent on the passenger side is vented directly back to the air cleaner. It has the EVAP system intact but the purge valve is closed and operating correctly.
Any Ideas?
The car runs amazing, pulls just like a healthy cammed engine should but the no boost from the vacuum booster for the brakes and virtually no boost from the supercharger at the rpm levels I have tells me I got a serious problem, but I cannot explain what the heck.
TECH Apprentice
Joined: Feb 2010
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You said the pushrods were .025 to long. Most makers can only get the actual rod length within +/- .025.
Was extra .025 holding the valves open?
Not sure why more people don’t switch to a hydroboost system. They are absolutely great.
Was extra .025 holding the valves open?
Not sure why more people don’t switch to a hydroboost system. They are absolutely great.
Last edited by jasons69chevelle; Jul 16, 2022 at 12:11 PM.
Thread Starter
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I agree but after smoke testing, pulling the intake and inspecting, and housing the intake down with flammable fluid with no change on short trims. I have to say no dice.
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Bleeding the hydroboost is easiest if you have tire turn tables. Make shift one can be made with 4 thin sheets of plastic.
I did the first round with the engine off second with engine running. My Chevelle has a steering box though.
To bleed hydroboost you turn the steering wheel about a 1/4 inch to the right then to the left increasing 1/4 inch with each turn until full lock. Slow and smooth. So the last turn will be full lock right then full lock left. It does take time but will work perfectly. Make sure the Reservoir stays full. May need this done twice. Don’t use the brakes to bleed the booster. You may get a pedal kick back on the first pump after the first bleeding go around.
slow to return will speed after a few hundred miles. Return isn’t as fast a vacuum setup/ but release is instant and assist is 100 times better.
I did the first round with the engine off second with engine running. My Chevelle has a steering box though.
To bleed hydroboost you turn the steering wheel about a 1/4 inch to the right then to the left increasing 1/4 inch with each turn until full lock. Slow and smooth. So the last turn will be full lock right then full lock left. It does take time but will work perfectly. Make sure the Reservoir stays full. May need this done twice. Don’t use the brakes to bleed the booster. You may get a pedal kick back on the first pump after the first bleeding go around.
slow to return will speed after a few hundred miles. Return isn’t as fast a vacuum setup/ but release is instant and assist is 100 times better.
Last edited by jasons69chevelle; Jul 18, 2022 at 04:31 PM.
Teching In
Joined: May 2021
Posts: 45
Likes: 30
Bleeding the hydroboost is easiest if you have tire turn tables. Make shift one can be made with 4 thin sheets of plastic.
I did the first round with the engine off second with engine running. My Chevelle has a steering box though.
To bleed hydroboost you turn the steering wheel about a 1/4 inch to the right then to the left increasing 1/4 inch with each turn until full lock. Slow and smooth. So the last turn will be full lock right then full lock left. It does take time but will work perfectly. Make sure the Reservoir stays full. May need this done twice. Don’t use the brakes to bleed the booster. You may get a pedal kick back on the first pump after the first bleeding go around.
slow to return will speed after a few hundred miles. Return isn’t as fast a vacuum setup/ but release is instant and assist is 100 times better.
I did the first round with the engine off second with engine running. My Chevelle has a steering box though.
To bleed hydroboost you turn the steering wheel about a 1/4 inch to the right then to the left increasing 1/4 inch with each turn until full lock. Slow and smooth. So the last turn will be full lock right then full lock left. It does take time but will work perfectly. Make sure the Reservoir stays full. May need this done twice. Don’t use the brakes to bleed the booster. You may get a pedal kick back on the first pump after the first bleeding go around.
slow to return will speed after a few hundred miles. Return isn’t as fast a vacuum setup/ but release is instant and assist is 100 times better.
Ignition timing can greatly affect idle vacuum, not sure it can boost though. I'd drop the blower belt off and try some different tunes just to see if you can get the idle vacuum back up. I've seen a lot of YouTube vids of start ups on stock calibrations (tunes) with an aftermarket cam, and they can sometimes start and run half way decent, at least enough for just comparative diagnostics.
You may also have a bad or disconnected sensor from the swap. Check your fault codes diligently. Something that has a lot of authority which is reading out of rational could drag the whole show down.
Also check airflow in and out of the engine. This one sounds like a rag was left in an intake hose or the exhaust is plugged. Check compression, check leakdown, check fuel pressure, confirm no cold cylinders as mentioned, etc....Were the timing gears confirmed to be in alignment?
You may also have a bad or disconnected sensor from the swap. Check your fault codes diligently. Something that has a lot of authority which is reading out of rational could drag the whole show down.
Also check airflow in and out of the engine. This one sounds like a rag was left in an intake hose or the exhaust is plugged. Check compression, check leakdown, check fuel pressure, confirm no cold cylinders as mentioned, etc....Were the timing gears confirmed to be in alignment?
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Ignition timing can greatly affect idle vacuum, not sure it can boost though. I'd drop the blower belt off and try some different tunes just to see if you can get the idle vacuum back up. I've seen a lot of YouTube vids of start ups on stock calibrations (tunes) with an aftermarket cam, and they can sometimes start and run half way decent, at least enough for just comparative diagnostics.
You may also have a bad or disconnected sensor from the swap. Check your fault codes diligently. Something that has a lot of authority which is reading out of rational could drag the whole show down.
Also check airflow in and out of the engine. This one sounds like a rag was left in an intake hose or the exhaust is plugged. Check compression, check leakdown, check fuel pressure, confirm no cold cylinders as mentioned, etc....Were the timing gears confirmed to be in alignment?
You may also have a bad or disconnected sensor from the swap. Check your fault codes diligently. Something that has a lot of authority which is reading out of rational could drag the whole show down.
Also check airflow in and out of the engine. This one sounds like a rag was left in an intake hose or the exhaust is plugged. Check compression, check leakdown, check fuel pressure, confirm no cold cylinders as mentioned, etc....Were the timing gears confirmed to be in alignment?
Thread Starter
Teching In
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Reason I'm asking is i've seen ECU's use a ton of air to keep a motor running with a dead cylinder, and it results in extremely low vacuum at idle. Doesn't explain the lack of boost, though.
Another thought I've had is perhaps the heads are cracked in one or more of the intake runners. This would cause both vacuum and boost leaks without showing up on a smoke test, since the smoke would go into the crankcase. Have you perhaps noticed any buildup of crankcase pressure? This would also result in oily plugs ont he affected cylinders, so the condition of your plugs could help indicate this as well.
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Thanks. Did the plugs look good when you pulled them to do the compression and leak down tests?
Reason I'm asking is i've seen ECU's use a ton of air to keep a motor running with a dead cylinder, and it results in extremely low vacuum at idle. Doesn't explain the lack of boost, though.
Another thought I've had is perhaps the heads are cracked in one or more of the intake runners. This would cause both vacuum and boost leaks without showing up on a smoke test, since the smoke would go into the crankcase. Have you perhaps noticed any buildup of crankcase pressure? This would also result in oily plugs ont he affected cylinders, so the condition of your plugs could help indicate this as well.
Reason I'm asking is i've seen ECU's use a ton of air to keep a motor running with a dead cylinder, and it results in extremely low vacuum at idle. Doesn't explain the lack of boost, though.
Another thought I've had is perhaps the heads are cracked in one or more of the intake runners. This would cause both vacuum and boost leaks without showing up on a smoke test, since the smoke would go into the crankcase. Have you perhaps noticed any buildup of crankcase pressure? This would also result in oily plugs ont he affected cylinders, so the condition of your plugs could help indicate this as well.
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My tuner told me too, says everything on the data log points to a perfect running motor. Frankly after 3 weeks of messing with this I don't care. I got 3 5.3's sitting around with a cast iron block that will take way more power than this all aluminum block. I don't want to hurt my engine but I have also spent probably 30+ hours researching and 30+ hours tinkering with no answers. 2 psi of boost is barely enough to add 50 hp. If someone could give me some ideas or answers I hadn't already tried I am all for it. So far 0/alot on the tests that will give me a result I can use. No offense to anything people have suggested I really appreciate it and keep it coming I just really want to be able to finally enjoy instead of screw around with it.