Big Cam Really Low Vacuum?
Hi All,
I've been having an intermittent bogging problem with the Firebird while racing so I've been looking to see if I can tune it out (I know the real solution to this problem is a looser converter but I'm trying to get by for now). :whacked:
First step was going to make sure idle circuits were tuned then go from there with the power valve and maybe larger pumps.
So I hook up my vacuum gauge to the rear vacuum port on the carb (which I'm pretty sure is manifold vac) and found I was only at 4-5 inches at 800rpm idle (whether in gear or not). Vac didn't change hardly at all until I leaned out enough to kill the motor.
4-5" seems incredibly low (I was expecting at least 8-10ish). Should I expect vacuum to be this low with a large cam?
I'm running a 427++ BBC with:
.630/.630 lift
255/264@.050 duration
110 LSA and 104 ICL solid roller
and 850cfm Holley double pump 4150 race (0-9380 list) carb.
I'm running a 6.5 power valve, so this also has me concerned that it will always be open at idle :confused:
If that's all the vac I get, it doesn't bother me much because I don't need it for brakes or trans just wondering if this is abnormal and I should look closer for leaks. BTW: vac comes up into the teens when I rev it in neutral.
I'll start another thread on the bogging problem...
Thanks in advance,
-Chris :D