Am I getting enough Vacuum??
Thread Starter
Racer
Joined: Nov 2005
Posts: 410
Likes: 1
From: Amherst NH
Am I getting enough Vacuum??
Im Finishing up a TT home build and I am concerned with the vacuum numbers I'm getting. Keep in mind this hasn't seen the tuner yet and the idle is rough if barely there. But with a little pedal work I can hold an idle and I'm only seeing 10-11 in/hg @ 900 rpm. I've checked for leaks. Ran 10psi into the manifold with air compressor and no leaks from the back (or anywhere else). All air lines have been checked as well with no leaks. I'm running 317 heads and a custom grind TT cam. Thoughts??
Last edited by nightman06; Oct 12, 2015 at 03:47 PM.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
If the engine isn't properly tuned,, you will NOT have all the vacuum that is on the table.
You could be excessively rich and the PCM will add extra THROTTLE BLADE opening to compensate. When you work the throttle, your OPENING the Throttle blade THUS changing the MANIFOLD VACUUM reading.
If the engine is running, and it hasn't been tuned, I wouldn't worry much about initial readings. Good oil pressure, proper engine temps and no weird noises, are all you need for now.
See what it is after the TUNE!!!
Like previously stated, A BIG CAM with a lot of overlap will have lower than OEM idle vacuum readings.
What CAM specs did you install??
BC
You could be excessively rich and the PCM will add extra THROTTLE BLADE opening to compensate. When you work the throttle, your OPENING the Throttle blade THUS changing the MANIFOLD VACUUM reading.
If the engine is running, and it hasn't been tuned, I wouldn't worry much about initial readings. Good oil pressure, proper engine temps and no weird noises, are all you need for now.
See what it is after the TUNE!!!
Like previously stated, A BIG CAM with a lot of overlap will have lower than OEM idle vacuum readings.
What CAM specs did you install??
BC
Thread Starter
Racer
Joined: Nov 2005
Posts: 410
Likes: 1
From: Amherst NH
Definitely am excessively rich!! I can barely get my wideband to drop onto the scale right now so if that's a contributor than I'd say that is probably my explanation. Bill, sent you a PM. Thanks guys, nice to have some confirmation to my suspicions.
