Cam vacuum question

[Dartfan71]

I'm in the process of tuning a fresh 360. At idle in gear with the engine warm I am only pulling about 6" of vacuum at the intake. Does that sound about right? I knew that my vacuum would be pretty low the the amount of overlap in this cam. I have order a new power valve #3 and secondary spring set, because I'm sure that my secondaries aren't opening and my 6.5 power valve is ineffective with this low of vacuum.

Here are the specs

KB107's zero deck'd
Holley 750 vacuum secondaries
LD340
Cam is Howards Hyd Flat Tappet 277 283 230 236 .531 .547 108 104

Timing is set at 18 degrees inital
Idle is set at about 800 and idles decent for the cam.

Just curious if the vacuum sounds about right?

Here is the motor.

[ame="https://www.youtube.com/watch?v=RIZW4mxXCBs"]First fire up of fresh Mopar 360 - YouTube[/ame]

 

[rumblefish360]

A lot will depend on how that can is ground and where it is installed. You could bump up the initial. Did you Use a vacuum gauge to help tune it?

 

[mguner]

In gear that is probably about right. Time to get a weaker power valve. Gonna have to see what it pulls at WOT on a run so you don't lean out on top.

 

[Dartfan71]

A lot will depend on how that can is ground and where it is installed. You could bump up the initial. Did you Use a vacuum gauge to help tune it?

I installed the cam straight up and I did use a vacuum guage. Will bumping up the timing effect vacuum?

 

[mguner]

I installed the cam straight up and I did use a vacuum guage. Will bumping up the timing effect vacuum?

More advance should improve your vacuum yes but also make it harder to start warm and you will need to shorten the advance curve.

 

[Woods74]

^Vacuum advance could help too. Total 48-52. 42-48 Magnum heads.

 

[mguner]

^Vacuum advance could help too. Total 48-52. 42-48 Magnum heads.

Great idea! In your case to improve vacuum at idle you will want to use manifold vacuum. This would keep you from having it crank against the starter. Not sure how much timing 6" of vacuum will pull but worth a try.

 

[Woods74]

10-12 out of the VA seems to do well most of the time up to 16 for crusing, most of the time it's going to be a trade off between initial, mechanical advance, and in your case manifold vacuum, to get your best curve, all VA adjustable via the nipple and a 3/32 allen.

That cam probably likes a ton of initial 18-20, VA 10-12 gets us 28-32, mechanical is usually 10-16, 34-36 total. Something to play with! Plug the vacuum advance, set total timing and see where you are from there.

A Timing and vacuum advance 101 could be in order on google..

http://www.chevelles.com/forums/showthread.php?t=392066