FI engine manifold vacuum?

[Bruce B.]

I have a 327 with a Corvette 151 (327, 3650 HP) cam in it which I choose for it's 114 LSA and its resultant high manifold vacuum.
I also have a rebuilt stock 1957 283 CI 283 HP FI engine. My question is what amount of manifold vacuum can I expect from the FI engine?
Also can someone tell me the LSA of the stock FI cam?
Thanks.

[Jim L.]

Re: FI engine manifold vacuum?

Bruce, you can reasonably expect to see about 14" Hg manifold vacuum on that '57 engine if it has the 097 cam.

Jim

[Bruce B.]

Re: FI engine manifold vacuum?

Jim,
Thanks.
I am thinking of using the original 283/283 in my Gasser with my Hilborn EFI and I need a good MAP signal.
So it should be fine.
Bruce B

[Duke W.]

Re: FI engine manifold vacuum?

L-79 cam 14-15" @ 750... Duntov cam about 12" @ 850-900. Both have about the same effective duration, but the Duntov LSA is 110.5 degrees, which means greater effective overlap and a more "lopey" idle. Thus the lower idle vacuum and higher necessary idle speed for reasonably stable idle behavior.

For reference-

LT-1 cam: about 12" @ 850-900 (about the same as the Duntov)

30-30 cam: about 10" @ 900

Base engine cam: 18-19" @ 500 (manual trans idling in neutral, a few inches less for an auto idling in Drive @ 500)

The Duntov cam has been "obsolete" for a long time - symmetrical lobes, harsh dynamics, and insufficient lift for big port heads. For a road engine having it ground with the inlet POML at 110 deg. ATC and a 114 LSA would make it essentially a mechanical lifter version of the L-79 cam (except for the lower lift), which will improve low end torque without sacrificing top end power. Crane has Duntov lobe masters and can do the job.

Also, as a reminder to everyone, specifying idle vacuum without including idle speed is meaningless because for any given cam, the higher the idle speed, the higher the manifold vacuum.

Duke

[Bruce B.]

Re: FI engine manifold vacuum?

Duke,
Very good info.
Thanks,
Bruce B

[John D.]

Re: FI engine manifold vacuum?

Bruce, With a Duntov O97 cam my '63 has 16" at 900 RPM. As you know the same cam was used from '57 to '63. John

[Bruce B.]

Re: FI engine manifold vacuum?

John,
Thanks.
Bruce B