c1 270 hp low vacuum

[Daniel R.]

I have a fully restored 1959 270 dual quad car that I cant seem to be able to get to idle. When I hook up a vacuum guage it reads 5.5 ", Does anybody know what the stock reading should be with the 097 cam??

[Jim L.]

Re: c1 270 hp low vacuum

I've got a '60 with the same cam, but different induction. Manifold vacuum is around 12" Hg at idle, as I recall.

Jim

[Duke W.]

Re: c1 270 hp low vacuum

11-12" Hg @ 800-900 is a good ballpark figure for a 283 with the Duntov cam.

Burned/leaking valve? Bad vacuum leak? Some aftermarket cam with higher overlap than the Duntov?

...could be any of the above.

Duke

[Daniel R.]

Re: c1 270 hp low vacuum

Thanks Guy's I believe that I just found the problem or at least one big problem. The heat riser is stuck closed. The engine couldn't breath so I'm thinking that is it. Any thoughts ??

[Duke W.]

Re: c1 270 hp low vacuum

A stuck closed heat riser will plug up the top end and likely result in severe fuel percolation. Open it up, wire it full open and see what happens. With current fuel percolation problems and driving in warm weather a closed heat riser is not necessary at any time.

Duke

[Clem Z.]

Re: c1 270 hp low vacuum

i have seen the heat riser valve installed upside down and yes the engine does not run well that way.

[Daniel R.]

Re: c1 270 hp low vacuum

Well I fixed the heat riser issue but still have low vacuum. I'm going to check the valve lash today and timing to see what happens.

[Duke W.]

Re: c1 270 hp low vacuum

Download the valve adjustment paper by John Hinckley and me:

http://www.lbfun.com/warehouse/tech_info/valvetrain/SBvlvadj.pdf

Of the several instances of this paper on the Web, the above is the only one that is the latest 9-23-08 revision. Earlier versions have errors.

Use the 30-30/LT-1 indexing scheme and the recommended clearances for a 283 with the Duntov cam.

Once you are finished setting the clearances, check a few cylinders' valves at TDC, which is an optional indexing scheme for the Duntov cam, only. If the measured clearances are less than what you set, you do not have a Duntov cam.

[Daniel R.]

Re: c1 270 hp low vacuum

well, opening up the heat riser helped alot but the cars idle goes away once its warmed. do you think that its in a vapor lock. The carbs are really hot under the hood?