WARNING! SBC RELATED!! One More Time...Dist Vacuum Question

[Homeresque]

Getting close to the rebuild stage for my 283/060over. Im using a 450cfm Holley and a chevy cast-iron Holley-pattern intake. The carb only has the timed-port vacuum tit, no full-time tit. Can I run a vacuum line off the boss on the manifold runner?? Id rather have cooler running full-time vacuum instead of off-idle vacuum.
I thought this was discussed before and someone said that either it wont work because that runner wont have enough vacuum as it sucks only 4 of the 8 cylinders, or too much vacuum as the usual full-time port on a carb is TINY. Anyone know??
The super-secret project its going in should be ready for shakedown Nov 1(Super Secret,yeah...its a '32 roadster,bleh. If anyone cared, I sold my '32 3W for a bazillion dollars and now only wipe my ass with hundreds. Twentys were chafing a little). Id get some pictures up if Chopped50Norm would come over with his camera!

[Scotch]

Why not run a small (half-inch) carb spacer drilled and tapped for a vacuum port? Base of the carb is best vacuum source and a carb spacer will keep heat from the carb. Hood clearance should not be an issue.

I'm not you, but I'd run a 600 cfm vacuum-scondary Holley on that engine. I dig the 450s...as half a dual-quad setup. The 450 will limit your acceleration potential, and that's not normally what hot rodders want. The 600 would be primo for a built 283.


Scotch~!

[Homeresque]

I plan to use a 1" wooden/phenolic spacer, but the 4-hole type. I considered tapping a fitting into it but thought it would be back to the same problem, fitting too big.

I liked the 450 because its new not used, mech secondary, and side-hung/single feed. I dont know if they make a new mech side-hung 600, definitely be special order.

[Louie]

no more coupe?......

[DrJ]

Stock Chevy intakes had one carb mount bolt hole drilled all the way thru and ran a special drilled bolt with a nipple on it to plumb the advance on. You can get the drilled bolt at most Chevy resto parts stores.
If you have a bib for a transmission vacuum modulator you can T it off there. After all, the Trans must be getting accurate vacuum readings from a "good" source, right?

[Model A Vette]

You can run the dist vac off the manifold. Are you sure there isn't a port on the holley down near the manifold?
Some 60's Fords had plastic carb spacers that came with a little vac port tube built onto them. You might run into one of them at a swap meet.

[Homeresque]

No more coupe, waved goodbye at the LARS. It now reclines on its own little pedestal in an LA warehouse next to an unrestored 2-owner 427 Cobra and about 25 other heaps. But the $ really put the roadster on the fasttrack.

I thought about a hollow stud but it brings the same problem, vacuum out of one runner.

Nope, only one tit midway up the metering block, the off-idle port. I was a little perturbed when I opened the box and saw that.
I think I got it now though. Im gonna drill and insert a tit on the phenolic spacer and vee it into the two primary bores.

[38Chevy454]

Manifold vacuum off one runner is fine. Remember you are not using flow, but rather the vacuum level. Vacuum is vacuum in the manifold, it will not matter if you have a small or large port, or if you tap off carb or manifold. Vacuum is essentially constant. Unless you tap off a single runner near the head, then it can fluctuate a bit at idle. But if that is a stock manifold, I am sure the vacuum tap is into a common plenum area and will be just fine. Tee off it and go.

[skipperman]

What 38 chev said ....................

Jersey Skip