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Background: I have a 2005 Colorado that I swapped a 5.3L from a Trailblazer into. Stock heads, stock cam, LS2 intake/tb. Soon after, I got the idea to make my own supercharger kit from another member on LS1tech. I used an M112 off of a Jaguar XKR. Anyway, I tuned it myself and had it running great for a stock 5.3L on about 7-8psi. Decided I wanted more power and got a 6.0L for basically free. This is where my problems start. When I got the 6.0L I installed a 'small' blower cam as well. Mid 220's duration, .580 lift. Used the LS9 head gaskets, new comp 918 springs and hardware. Stock heads. New oil pump, timing set. With the blower installed, A/C off, the engine was pulling only about 12-13in hg. Would idle fine, but would stall on decel (automatic) or sometimes after a quick rev. I messed around with the tune (A LOT) and finally gave up realizing that the low vacuum was the cause of the symptoms. It drove ok under load, didn't seem to have as much power as I was expecting, but I also didn't have a chance to properly tune it either since I could never nail down the idle. With the A/C on, it dropped to about 10in hg vacuum. With the 5.3L, it would pull about 18-19in hg A/C off and 16-17in hg A/C on. I know with the (slightly) larger cam it will pull less vacuum but something else is not right. I removed the blower, and left the belt off. With no blower, no accessories, and the booster capped the most vacuum I can pull is 15in hg. I've checked the MAP sensor values vs. the boost/vac gauge, and used a second vacuum gauge. They all agree on the numbers. I've removed the intake, checked all gaskets, removed TB, checked all hoses. I pressure tested all of my charge piping (since it is under vac as well) and then completely bypassed it all by running the TB right off of the intake. I pulled the timing cover to confirm cam/crank timing. It was correct. Finally tonight I just did a compression test. All cylinders were 150psi+/- 5psi after 3 bumps. Plugs looked fine. I'm at a loss. Only thing I can think of is that the cam is ground off and needs to be degreed in? Either that or there is a massive crack in my intake. No hissing sound from a vac. leak though. PCV is a fixed orifice type, no moving parts to get stuck. Anything I've overlooked? I'm almost tempted to swap cams since I still have my 5.3L sitting on the stand and don't have a degree wheel sitting around. I've never degreed in a cam before either. That would rule out the cam being the issue but I almost feel like I am grasping at straws here. Not sure what else to check. Any ideas? TL;DR New engine/very mild cam can only pull 15in hg with no accessories, no booster, no blower. 12-13in hg with blower. Old engine, stock cam would pull 18-19in hg with blower. 
FuzzKill fucked around with this message at 12:32 on Jun 26, 2014 |
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Jun 26, 2014 02:51
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Can the cam be off a tooth and the motor still run? That's what it sounds like to me.
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Jun 26, 2014 04:22
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mafoose posted:Can the cam be off a tooth and the motor still run? If the cam timing is a tooth off it'll idle like poo poo, run like poo poo, and not have all that much power. but it should have a crank/cam sync within the ecu.
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Jun 26, 2014 04:26
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I came to that conclusion as well, I pulled the timing cover and verified timing marks. They were fine.
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Jun 26, 2014 12:33
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Same intake manifold that you had on the 5.3? There isn't anything like the coolant crossover tubes preventing the manifold from seating properly on the 6.0, is there?
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Jun 26, 2014 19:47
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