straw1628

OK, I have 11" of vacuum at idle in park. Is that the time to test vacuum, in park? I still think, according to all of you guys, and Summit, that I should have more vacuum. I shot car cleaner around the base gasket of the carb, and no change, (by the way, it doesnt work well with the semi gloss black under the hood, man was I pissed until I got fixed) any way, I heard one of the guys on here say something about checking the vacuum line at the tranny, that they are prone to leak, can anyone expand on that? What should I look for. I want to tune the carb (670 holley) but I want to make sure I have vacuum solved. For you guys that have been helping me along, I'm sorry it is taking me so long to solve, I just have so much going on I cant work on it as much as I would like. Three kids, old lady, full time job and side jobs. Im sure you guys know all about it. Anyway thanks for all the help, I didnt mean to get so long winded.

urban_cowboy

Idle quality should be checked and tuned with auto cars in drive. As I said in your other post, 11" is low, but not out of the range for a rowdy cam. Bump your car against something that will not move or get a buddy to stand on the brake, put it in gear, and tune your idle. Set the idle speed to start and then work the idle screws to maximize your idle vacuum. Too much fuel or not enough fuel will lower vacuum. Then reset your idle speed for your desired idle. Idle speed and vacuum are going to depend on what your cam specs are.

straw1628

OK, but when people talk about 18-22 inches of vacuum, is that in park? I'm only asking because I hope that is what it is. The guy who built the motor for me, says the 11 is ok because of the cam I have, so maybe I should quit trying to be so ****. Thanks

urban_cowboy

Ok, higher vacuum is created when the throttle plates are closed. RPMs can also increase vacuum. A car running 70mph at 4000 with the throttles closed will have a high vacuum. A car running WOT will have low vacuum. Quickly opening the throttle will also drop the vacuum because there is a drop in velocity. My 383 has a vacuum of about 4-5" at WOT, 12" at idle, and 17"+ at light cruise with the throttles basically closed. It is much more complicated than that, but I have over simplified it to help get you looking in the right direction. All engines will idle at different vacuum levels b/c the cam, intake, carb, timing, and tuning dictate what the vacuum is. Lot of variables, but 11" is on the low side for idle, but about right for a race cam.

kalli

i have 15" with edelbrock rpm heads and cam. and yes the more radical the cam the less the vacuum. The edelbrock is well known for pulling a lot of vacuum for such a performance cam. So this can be easily used with power brakes (which I don't have).

I guess you already have adjusted your idle for highest vacuum (idle mixture screws). If you end up with 11" and your engine is running fine, then I wouldn't be too much concerned.
What cam is it you're running?
Maybe call the manufacturer of cam if they have any reference. The engine byuilder of yours seems to agree that it's normal

MIL1ION

get yourself a small propane torch and point it all vacuum hose joints with the valve open and unlit .....way cleaner way to find leaks

HTH'S


http://good-times.webshots.com/photo...ost=good-times

Starfury

That chart doesn't necessarily apply all the time (and actually, I don't like that chart; it's too vague). A cam with lots of valve overlap will show a low and erratic vacuum reading because it actually is misfiring at idle. All the valve overlap reduces dynamic compression at idle, causing sporatic misfires which throw the vacuum reading off.