I just got my 2.2 motor back, fully built, and was tuning it the other day, and I adjusted my 1.6 rocker rollers a little. The ones that were a little loose, i just slightly tightened until they were not loose again, but only a very small turn of the socket. Anyways, before i did that, I could get about a -18 in Hg reading on my boost gauge at idle, now the lowest it goes at idle, is like -13 in Hg, maybe -14. The camshaft is a higer lift JBP turbo version camshaft. I'm thinking after I adjusted the valves, I am now opening the valves a bit more, letting more air in, and that somehow lowered the vacuum level..??? Anyone know for sure why it might be lower? The car is still running pretty strong, but it sounds a bit more like a rumbly V8 or something at idle. I was thinking if the valves are letting in more air, i don't see how it would affect the vacuum level. if the piston is pulling more air into the engine(valve open longer), the vacuum should be just as high, maybe higher. because of the longer duration of pull from the piston.

I don't think i have the rockers so tight that the valve isn't closing all the way, I would think that would make the car run pretty bad. Anyone have ideas?

not all cams will keep the vacuum high like stock


either you went to tight , or you now have the correct idle vacuum

could be a lose vac line somewhere or maybe the TB or intake mani isnt bolted down all the way, thats usually what causes vac leak



1989 Turbo Trans Am #82, 2007 Cobalt SS G85

I suppose it could be a loose vacuum line, but I didn't take off anything vac lines, or the throttle or anything when I adjusted the valves. The intake manifold and TB is bolted all the way down. They were all just installed like 500 miles ago, but i'll double check them. I think it's just the cam, the car is running a bit better then it was before i adjusted it, so, I think it's probably just the profile of the cam. Does anyone know why the valve staying open longer, or opening further would cause this? I guess that's getting into cam design, but i'm just thirsty for knowledge.

Well, I found out what was happening, the stud that the rocker arm is on was pulling the threads out of the head. and thereby reducing the distance and duration that the exhaust valve on cylinder 1 was opening. As a consequence, the vacuum level started to drop. Then, today the whole stud came out far enough for the rocker to slid off the valve, and pushrod all together. So, when that happen , the car ran like crap. And i immediatly found the problem. I think it must have pulled out the threads just a little a few days ago, and today when i got on it some, it pulled it out even further.
Time to order a timesert and repair the threads. Once I get it all running again, I'll try and update this thread to confirm if that was the original problem.

just a note, aftermarket cams usually change your vac reading so it may be like that even after you fix your other threadin issue


|Forged 8.9:1 Wiseco Pistons|Forged Eagle Rods|HPTuners|60trim|Tial Wastegate|
|Precision Intercooler|2.5" Exhaust|2.5" Charge Pipes|630CC Mototron Injectors|
|Stock: Fuel Pump, Transmission, Manifold, TB, Head, Head Gasket, Ignition, Suspension...|

ya, I've thought about that, and i understand it may still be lower even after i fix the rocker roller stud.