327 vacuum question

[DonSSDD]

I figure you guys could answer this question posted on the Cdn Poncho site. What kind of vacuum would be normal with this setup?

327 .040" over, forged crank and rods
flat tops with small valve reliefs
59-60 cc double humps, 2.02/1.6" 461 heads
.040" quench with .016" in the hole and .024" composite head gasket
10.3 static and 8.0 - 8.1 dynamic compression
280 comp cam, 230 @ .050". .480" lift 110 lsa
L79 intake and dual snorkel air cleaner, 600 Holley
1 5/8" long tube headers
small body distributor with pertonix module and coil
timing is 16 initial and 38 with centrifigual
Idle is set at 750-800 RPM
Ive got 9.5 to 10" Of vacuum. Just discovered my vacuum can is wrong. Vacuum advance should be all in at idle. From what ive read I need a can rated 2" below the below idle vacuum. I have a B1 can rated all in at 16". I need the B28 or Vc1810 which is rated at 8" of vacuum to give 16 degrees of advance. My can isnt giving me nearly enough advance at idle.
Im sure my vacuum will go up and become more stable once I can source the right canister and add more advance at idle.
Anyone have a source for a VC1810 can?

Does 10" at 750-800 with low vacuum advance(presently) sound right for this engine build?

 

[Don Jacks]

I've ran that little Comp Magnum 280 in several 350's and the vacuum at idle was always was right around 14-15 inches and steady.I think that he may be on to something as to the vacuum advance can.

 

[DonSSDD]

Thanks Don, I figured you'd have the answer to this one.

 

[Mearl]

Can't go wrong with a L79 in a Nova!! OOPs Acadian?

 

[models916]

Is your timing 16 at idle no vacuum advance? Total with no vacuum advance is 38? At what RPM are you seeing total come in?

 

[Don Jacks]

Don Show Cars carries a vacuum advance that's adjustable for those points style distrubitors that he may be able to find easier than those cannisters that he listed.

 

[DonSSDD]

Don, I passed that on. Models he said: Only 4 degrees advance from vacuum at idle. About 16 off idle when the vacuum comes up.

 

[Don Jacks]

He's definitely on the right track about the vacuum can.That engine package needs to see at least 10-12 degrees at idle from the vacuum advance.

 

[La Hot Rods]

I have tuned most engines with an after market cam with just mechanical advance and no vacuum.

 

[models916]

I would run all mechanical. Use one of the aftermarket curve and weight kits. 18 at idle and 36 total all in at 2500-2800 and be done with it.

 

[DonSSDD]

He seems to know what he is doing, he posted this:

Not a ton of options out there for mechanical advance kits. Bought the one from Mr Gasket. OMG. TOTAL GARBAGE.
Spent hours trying to make their springs work...every imaginable combination and nothing that resembled a performance curve. Even with their heavy springs they are advancing the timing at idle.
The weights are another story!
Ended up taking my springs, putting a bend in the hook to shorten them up and add voila! 15 degress at idle, 36 at 2800 RPM.

Ill check this in a few weeks to make sure it hasn't changed. Then ill start playing around with the vacuum can to see if it can take more advance from idle up...

 

[models916]

You need the high advance at idle when you don't use the can. My kit was from Crane. My timing light says it is perfect. I run 18 idle and 36 total at 2800.

 

[427John]

Don, I passed that on. Models he said: Only 4 degrees advance from vacuum at idle. About 16 off idle when the vacuum comes up.

Are you saying his initial timing with vacuum advance hooked up is 16 if so has he tried bumping initial timing with with no vacuum advance to 14 to see if his vacuum comes up?If necessary he can recurve his mechanical to keep his total at 38.