low vacuum
12-13-2006, 01:39 PM
#1
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low vacuum ok still trying to figure out whats wrong with my car after the cam install. ive narrowed it down to vacuum problems. i put a vacuum guage on and im reading only 5 to 10 at idle. a coworker is telling me that it should be more...less with a bigger cam but more than than. normal stock is 17 to 22. i checked the vacuum straight off the intake and at one of the lines. its the same reading.
ive had problems with it running rich and every time i take it to tune he tunes it and it goes back to rich at idle.
it looks like with the less vacuum its dumping more fuel in.
another coworker thinks i used the wrong size pushrods. i used hardened 7.4s same as stock. he is saying the valves are too tight, because of the pushrods being too long, and not opening right and as a result less vacuum.
any input on this? comp 236/244 .580 on a 112. mods are in the sig. should i have gone with 7.3s?
ive had problems with it running rich and every time i take it to tune he tunes it and it goes back to rich at idle.
it looks like with the less vacuum its dumping more fuel in.
another coworker thinks i used the wrong size pushrods. i used hardened 7.4s same as stock. he is saying the valves are too tight, because of the pushrods being too long, and not opening right and as a result less vacuum.
any input on this? comp 236/244 .580 on a 112. mods are in the sig. should i have gone with 7.3s?
12-13-2006, 01:57 PM
#2
Low and steady vacuum can be caused be retarded (cam or ignition) timing. That's a lot of duration on your cam, which will cause a low vacuum reading. With the valves being open longer, and more lobe separation, it won’t pull as strong of a vacuum.
What does the needle look like? Steady, fluctuating…
What does the needle look like? Steady, fluctuating…
Last edited by 2002 SS #476; 12-14-2006 at 10:03 AM.
12-13-2006, 02:45 PM
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Originally Posted by 2002 SS #476
Low and steady vacuum can be caused be retarded (cam or ignition) timing. That a lot of duration on your cam, which will cause a low vacuum reading. With the valves being open longer, and more lobe separation, it won’t pull as strong of a vacuum.
What does the needle look like? Steady, fluctuating…
What does the needle look like? Steady, fluctuating…
12-14-2006, 10:26 AM
#6
Alot of your reading is going to depend on RPM, what rpm was the car idling at? Was it a steady RPM or a back and forth RPM (like at my house)? Seems like people with cams around 750-900 rpm read anywhere from 9-11. When bone stock I think its around 15-20. I dont see how he can tune it, then it just goes back rich. that just doesnt make any sense to me.
Get a PR length checker and try that, Make sure you dont have any leaks, Maybe the TB is cracked to far open, or the hole isnt drilled to large. Just a couple things to check...
Get a PR length checker and try that, Make sure you dont have any leaks, Maybe the TB is cracked to far open, or the hole isnt drilled to large. Just a couple things to check...
Last edited by Z'mnypit; 12-14-2006 at 10:38 AM.
