TBSS low power issues with 370/LS3 heads
07-09-2013, 03:36 PM
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TBSS low power issues with 370/LS3 heads Guys,
I have been chasing a low power problem in my Trailblazer SS since I put the rebuilt motor in. It's a 370/4L80E ls3 pro comp ported heads, ported l92 intake by peak speed shop. Lt1z custom cam, 11.3:1. It dynoed at 388 RWHP. It is slower than stock now and I am running out of ideas and things to check. So far i have checked cam timing. Compression tested every cylinder which are all 150 PSI. Not sure if that is too low or not? Some people say its normal for a good size cam. Changed the torque converter. checked pushrod length. The tune was done by Justune and then sent to a couple other reputable tuners and looked over.
Looking for someone local in Kansas City to help me out. I'm willing to pay. This thing wont even do a burnout
Thanks Brent!
I have been chasing a low power problem in my Trailblazer SS since I put the rebuilt motor in. It's a 370/4L80E ls3 pro comp ported heads, ported l92 intake by peak speed shop. Lt1z custom cam, 11.3:1. It dynoed at 388 RWHP. It is slower than stock now and I am running out of ideas and things to check. So far i have checked cam timing. Compression tested every cylinder which are all 150 PSI. Not sure if that is too low or not? Some people say its normal for a good size cam. Changed the torque converter. checked pushrod length. The tune was done by Justune and then sent to a couple other reputable tuners and looked over.
Looking for someone local in Kansas City to help me out. I'm willing to pay. This thing wont even do a burnout
Thanks Brent!
07-09-2013, 07:22 PM
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I felt like 150psi was low. i was thinking the guy that milled the heads may not have milled them enough and I'm like at 10:1 or something. I should have had them cc'd. In your opinion what should my compression be per cylinder?
Thanks for your help,
Brent
Thanks for your help,
Brent
07-09-2013, 07:37 PM
#7
How much timing are you able to run?
I would expect a compression test to my 185 and better. BTW: I've never like a wide lsa with these heads. It makes them soggy on the bottom. I've run a bunch of cams and best results are with an ICL in the 111 range.
I would expect a compression test to my 185 and better. BTW: I've never like a wide lsa with these heads. It makes them soggy on the bottom. I've run a bunch of cams and best results are with an ICL in the 111 range.
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07-09-2013, 07:39 PM
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had a similar experience a year ago we checked the engine and found it all was in spec and correct. We pulled heads It was only running on 6 max, two heads were not firing very, oily, wet and fowled .Tore it down and put it back together twice. Same thing no power. It ended up being in the harness. check the wiring start over there. I bet its electrical bad pin bent pin improper connection.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
07-09-2013, 07:50 PM
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had a similar experience a year ago we checked the engine and found it all was in spec and correct. We pulled heads It was only running on 6 max, two heads were not firing very, oily, wet and fowled .Tore it down and put it back together twice. Same thing no power. It ended up being in the harness. check the wiring start over there. I bet its electrical bad pin bent pin improper connection.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
07-09-2013, 09:19 PM
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had a similar experience a year ago we checked the engine and found it all was in spec and correct. We pulled heads It was only running on 6 max, two heads were not firing very, oily, wet and fowled .Tore it down and put it back together twice. Same thing no power. It ended up being in the harness. check the wiring start over there. I bet its electrical bad pin bent pin improper connection.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
Good luck electrical stuff can be hard to find . We did not start there because the car would fire up idle fine just no good power numbers it sounded fine.
07-11-2013, 05:53 AM
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The electrical problem we chased only showed up as the ecu advanced ignition timing at start up the engine fired on all 8 presumably. We use wd-40 for the smoke and sizzle test. We did not have the option for codes the engine ran a race car the computer was re configured and not odb compliant.
We were running most of the ls-1 harness and hp tuners. Even at 10:1 you should be making 420 at the wheels.
Good luck
We were running most of the ls-1 harness and hp tuners. Even at 10:1 you should be making 420 at the wheels.
Good luck
07-11-2013, 10:25 AM
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Hope u fix ur problem, iam fixing to do something similar but on a forged 365 aluminum block tbss as well. I did some work and found out not to port the oem l92 truck intake. I have mine their with no use. If its any help
07-11-2013, 04:04 PM
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Something isn't right at that low of cranking psi even with that cam, maybe the heads aren't milled meaning the static is much lower as you stated which would hurt low end along with the ported heads that aren't helping port velocity. That 4L80 has a lower first gear than the 4L70 and eats up more power with it's beefier internals, is this the first time running it and what stall is in it?