No vacuum at idle after cam/intake swap
10-22-2009, 01:24 PM
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No vacuum at idle after cam/intake swap I've got an LS4 with GMPP Hot cam, GMPP lightweight lifters, heads shaved .050", LS2 intake, and TB. Everything is new including the base engine. I did put this together but I wouldn't call myself an engine builder. It starts and runs (poorly) on a basically stock tune. It's making very little vacuum at idle, about 80 kpA on the HPT dashboard, not enough for the power brakes. Cranking compression is about 150psi. Could this be a cam timing issue, like maybe I have it a tooth off? It seems to run fine at higher RPM, but I haven't tried to drive it.
10-22-2009, 05:49 PM
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A little more info, I've hooked up a vac gauge to confirm the MAP reading, getting approximately 5" Hg at idle. I checked for leaks at the manifold, none detected. Checked and double checked pushrod length, I've got about .040-.050" preload with the lifters on base circle.
10-22-2009, 09:30 PM
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I would double check everthing changed or touched during the swap.
If I remember the Hot Cam had about 48 KPA in the LS3 on the dyno and my 2010 Camaro.
Robin
If I remember the Hot Cam had about 48 KPA in the LS3 on the dyno and my 2010 Camaro.
Robin
10-22-2009, 09:34 PM
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My ls1 with a 224 cam had 200 psi and now my bigger cam tv.2 in my ls2 has 260 psi, check to make sure the cam timing is right, and/or make sure none of the valves are open on the compression stroke. maybe the pushrods are to long for some reason with your new setup.
10-24-2009, 09:32 AM
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My ls1 with a 224 cam had 200 psi and now my bigger cam tv.2 in my ls2 has 260 psi, check to make sure the cam timing is right, and/or make sure none of the valves are open on the compression stroke. maybe the pushrods are to long for some reason with your new setup.
10-24-2009, 01:16 PM
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I pulled the intake to do a visual check, found no problems. I set it back on the engine without the gaskets, it sits nice and flat on the heads with no gaps. I put it back together and still only 5" vacuum.
I dropped the engine to check the cam timing... it's installed straight up, dot to dot. I degreed it with a makeshift degree wheel and dial indicators on the pushrods, it matches the spec card for the cam, so no problem there.
I attribute the low cranking compression to the engine not being broken in. It has a total of 7 miles on it since it left the assembly line.
Still no idea what the problem is.
I dropped the engine to check the cam timing... it's installed straight up, dot to dot. I degreed it with a makeshift degree wheel and dial indicators on the pushrods, it matches the spec card for the cam, so no problem there.
I attribute the low cranking compression to the engine not being broken in. It has a total of 7 miles on it since it left the assembly line.
Still no idea what the problem is.
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10-24-2009, 05:14 PM
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I checked compression again, this time with all plugs removed and the throttle body wedged open which I failed to do last time. All cylinders hit 150 on the first revolution and top out at 210-230 psi after four compression strokes.
I don't know what else to look for. I think I'm going to stick the LS4 intake back on and see what happens.
I don't know what else to look for. I think I'm going to stick the LS4 intake back on and see what happens.
10-06-2014, 05:23 PM
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I was never able to figure it out. The car has been sold and I don't know exactly what was done with it after it left here. I heard from the new owner a few months ago and if I recall correctly he said it was running fairly well, but it sounded like he didn't know exactly what was done before he got it. I don't think it was a mechanical problem, I believe it had something to do with the ECU/tune.
