Vaccum Low. Please Help
Vaccum Low. Please Help Hi guys, I just finished installing my new heads 7 days ago and when it was all said and done the car has very low vaccum. 
My gauge before that usually showed between 17-21 hg and now it only shows 9-11 hg. I tried torquing the manifold bolts down, and made sure all vaccum lines are connected. I sprayed starting fluid all around the manifold, throttle body and pcv areas and i hear no difference in the way the motor revs. Is it possible that the intake didnt seat properly. I had the headers welded to the y pipe. When I punch it, it backfires and may sound like the welder may have missed a spot. Any ideas?
What else could cause the vaccum to be low? The car drives fine and idles okay, but every now and then it pings or surges.
My gauge before that usually showed between 17-21 hg and now it only shows 9-11 hg. I tried torquing the manifold bolts down, and made sure all vaccum lines are connected. I sprayed starting fluid all around the manifold, throttle body and pcv areas and i hear no difference in the way the motor revs. Is it possible that the intake didnt seat properly. I had the headers welded to the y pipe. When I punch it, it backfires and may sound like the welder may have missed a spot. Any ideas?
What else could cause the vaccum to be low? The car drives fine and idles okay, but every now and then it pings or surges.
Last edited by trans_am_31; Jul 23, 2006 at 11:14 PM.
On The Tree
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did you change the cam too?
my only thought is maybe your new heads are a *hair* shorter than your old ones and maybe the valves are opening earlier and closing later, therefore increasing the duration of the intake (and exhaust) valves.
That would decrease vacuum, right?
common sense tells me you would have a tiny bit less-than-optimal compression also.
my only thought is maybe your new heads are a *hair* shorter than your old ones and maybe the valves are opening earlier and closing later, therefore increasing the duration of the intake (and exhaust) valves.
That would decrease vacuum, right?
common sense tells me you would have a tiny bit less-than-optimal compression also.
mmmchickenboy
Thanks for your reply, No, I didnt replace the cam, its still stock. I also forgot to mention that the heads are 853 catings ported with dual springs and that they were milled .030. Thanks for your reply.
Thanks for your reply, No, I didnt replace the cam, its still stock. I also forgot to mention that the heads are 853 catings ported with dual springs and that they were milled .030. Thanks for your reply.
mmmchickenboy,
Yes, I changed them to Thunder Racing Hardened Pushrods 7.350 .
I was all freaked out about cracking the block with the head bolts. I put a lot of compressed air on them and also did the towel thing and the bolt cleaning procedure. Car drives decent there are no leaks and the car doesnt overheat and also no milky stuff inside the oil dipstick and the car doesnt blow any white smoke. I would have heard the block crack, right?
Yes, I changed them to Thunder Racing Hardened Pushrods 7.350
.I was all freaked out about cracking the block with the head bolts. I put a lot of compressed air on them and also did the towel thing and the bolt cleaning procedure. Car drives decent there are no leaks and the car doesnt overheat and also no milky stuff inside the oil dipstick and the car doesnt blow any white smoke. I would have heard the block crack, right?
Last edited by trans_am_31; Jul 23, 2006 at 11:15 PM.
Now that I think about it. I dont think its a vacuum leak. Because if it was a vacuum leak the gauge would go up higher and the idlewould go crazy. Does that sound correct? 
