vacuumlevel with Crower 60240

[Marx3]

I installed a Crower 60240, 210/221@.050, 112 lsa in my otherwise stock lowcompression Pontiac 400 ( well, heads have been milled so CR is about 8.4 ). Engine completely rebuild. stock converter
I have been having some problems getting it to idle strong.
tubes are .038
DCR is .058
IAB both in body are .070
bypass is .116
holes are .090.
I must admit I havent had a vacuum gauge on there yet, but right now if idle is 900 it will be just about to stall when I put it in drive.

Cliff, you suggested the cam and followingly wrote that it would make about 12" of vacuum in idle. 12" is not that much, if this is normal I will stop searching for stronger idle ?

[77cruiser]

What's your timing look like?

[Marx3]

had it at 22 in idle ( without vacuum ) to hit 35 total.
Right now it is stock 16 in idle. plus vacuum.
The advance mechanism ind the distributor moves fine, everything about the HEI seems good and it at stock settings right now.

I just bought a quality vacuum gauge. 20" hg at 800 rpm is the best I can pull out of it.
what I heck.. I had actually expected that idle vacuum would be kind of low... But no!
When I put it in gear id tends to drop off a bit but then stabilize at 600 rpm.
None of this sounds like something is wrong... I know!

[Jeff K]

Sounds like a timing issue, disconnect the vacuum advance and go from there..

 Frankly I don't like vacuum advances and prefer 16-20 initial with 34 total..... I find it much more stable then to have my timing going up and down due to the wims of a vacuum advance... On my 462 with 041 cam, I find no difference is gas mileage without a vacuum advance so long as I'm running a healthy initial...

By the way, I only use points distributors so I have no experience with the HEI but doesn't the HEI have a 10 degree start retard feature so you can run a nice fat 18-22 degree initial?

[Cliff Ruggles]

Timing at idle effects vacuum with any cam.  We see about 12" or so with those cams in low compression 400's with about 12-14 degrees initial timing.  More timing would increase vacuum some, but too much timing will cause the rpm's to fall off to much when a slight load is placed on the engine.  If you are using MVA it can cause all the VA timing to fall out, and the engine may slow WAY down or even stall.....Cliff

[Marx3]

sorry, just saw your post's...
I like having vacuum advance for a mild engine in a stock driver.
I remember you said it would make about 12" in idle when you suggested it to me Cliff. That's why I was surprised to see it actually making up to 20" at 800 rpm and on stock 18 degrees initial plus vacuum...
I upped compression to about 8.5 on this particular 400 and the carb is calibrated per your advice ofcourse.

what is MVA short for? I don't get it...

[77cruiser]

Manifold vacuum advance

[Marx3]

ohhh ofcourse :-)

I get the picture now... I never tried ported vacuum. I just didn´t think it could be the issue with an engine that made so much vacuum in idle.
I'll look into it!