to all the ppl who have big cams what is your vacuum @ idle??

i gauged mine and it's 13. now, i dont know if that makes a difference if it's for a stock motor or a cammed motor...any help?


when i hit the gas, it goes to ~18hg, and then goes down to ~6, and then comes up to ~13.

 

come on....anyone??????

 

Mine is 11inchs at idle and 19 cruising. My cam is 228/236 511/533 112 LSA. It will fluctuate when on and off the throttle, As long as you have 10 inchs at idle your fine

 

I have about 9.5 inches at idle with a 234/242 575/595 112.

 

I have about 8.5 inches at idle. Ahh, this sucks.

 

13" here with hot cam

 

great, thanks guys!

one more question: after your car's warmed up, when you put it into park and then put it back into drive, does your rpm go down by about 500rpm and then jump back up to what it's supposed to idle at?

for example, when my car's warm, i put into park and then back into drive, and right as it shifts, the rpm goes from the 1000 idle to ~500, and then jumps back up to 1000 idle.

 

11-12in Hg at 950rpm with a 224/236 XE cam.

Rich Krause

 

So if you have a low vacuum at idle, how do you fix it, provided the obvious (I.E. leaks and blockage) showed no problems? Tuning?

 

The computer has a different idle setting for when the car is in neutral or in gear the difference is about 200 RPM when cold and 100 rpm when hot (A4 only)

 

Yes, Tuning. By adjusting the spark advance at idle, you can improve the vacuum. At the right timing, the vacuum will be at its best. That is when your engine is running most efficiently. If you have low vacuum because the spark is too retarded you will notice that the engine gets bogged down easily while idling. Such as wneh your A/C kicks on the engine may seem like it's going to stall for a moment.

 

Bingo. I just had a stock bottom end 236/242 car here the other day. After about 20 minutes of fiddling the idle was much smoother.With 32* closed TPS spark advance we were getting 12-13" of vacuum. Seemed pretty good to me.
Had another stock bottom end car here a couple weeks ago that had the 230/236 in it. That car seemed to like 31* best. Didn't put the vacuum gauge on it, but map seemed at it's lowest right there.
Both idles were smooth as silk at 1000rpm in park and 950 in gear. TPS and IAC counts were approx .65 and 30.
Hope this helps somewhat.

 

The larger the cam, the more the overlap. The larger the cam, the more the high rpm efficiency is improved, at the expense of low rpm efficiency. That is why low rpm operation is not as smooth/efficient as oem. Yes, timing will improve a larger than oem overlap cam. Is it a cureall? NO! Don't expect miracles with timing mods when using a cam with more overlap than oem. This is not to state improvements can not be made. BTW Rich, you could have mentioned, (even though it is in your sig.) the stroke of your engine. We both know it makes a diff when stating cam timing specs. Some may not be aware.