427 sbc cam vacumn

[ebert]

have a sbc 427 street engine. compression is 11. to 1. the cam is 236 in 256 ex with 580 lift on a 108 sep, I am wanting to run fuel inj. I am looking at fast and also holley. my question is how much vacumn will this engine make at idle and also which system will work best for this application.

[user-612937456]

That's an unusual cam are you sure it isn't for turbo application with the wide in/ex split it's hard to say what your vacuum will be without some more specifics For fuel injection and higher vacuum readings you might want to consider a different cam

[ebert]

main thing I was looking for was a nasty cam sound

[user-612937456]

Get your vacuum storage canister are you going to have to compromise between nasty sounding and a drivable vacuum number you could also consider an electric vacuum pump

[wyrmrider]

was this a blower/ nitrus cam?

[ebert]

no I just wanted a wicked sounding cam then decided on fuel injection. I guess I could of had it ground on a 110

[mag2555]

A nasty Exh sound produced by a Cam does not in any way shape or form guarantee maximum power being durived from the rest of the parts in the motor build up!
Your stated need for such is making me not comment on your post any more than what I have!

[ebert]

B. This is not a race engine it is a street car. I would be glad to give up horsepower for a wicked sounding cam. I am just looking for the best combo for this application.m

[turdwilly]

Holy 20 degree split!! Unfortunately this is one of those "you can't have your cake & eat it too" deals - the overlap that causes your desired "wicked sounding cam" effect is also what causes low idle vacuum. That's why self-learing EFI cams are ground on a wider LSA so that they will have enough idle vacuum signal to satisfy the MAP sensor, which also smooths out the idle.

[Orr89rocz]

It should get near 10" if good sealing rings and proper tuning.

I ran a 246/252 113 cam on a 400" which has 23 deg overlap at .050, to your 30 deg, and it was 12-13" at 1000 rpm idle. Not quite same but its 27 cubes less so that cam will act a touch smaller

I also ran a 230/245 on a 109 lsa on a 383 sbc. Ran fine, estimated 10" vacuum from the maf tune readings. Wasnt a map car but power brakes worked without a canister. Sounded wicked tho lol

Holley hp system will run well for the money and use a efi single plane

[lefty o]

id trash the cam.tighten up the separation a good bit, and have it ground on a 106 lc, it'll sound bad, and actually run well, instead of sounding likes its missing on 3cyls and running like a turd. just my opinion.

[RevTheory]

For what it's worth, many moons ago I did some valve lash tests and every time I increased the lash on the exhaust side, manifold vacuum came up a little. Oddly enough, a similar reduction in intake lash had very little effect on manifold vacuum.

Don't ask me for specifics because that was back in '03 and I'm quite certain that I've bumped my head since then but keep that in mind with regards to your pretty-massive exhaust duration bias.

[thedynoguy]

I've run a bunch of FAST EZ EFI setups on my dyno and the one thing I can tell you is that they don't like wild cams with a ton of overlap. Nothing but idle/low speed drivability issues. Good luck...

[Seanh832]

I've run 248 254 @.050 on a 110 in a 11 to 1 406 sbc with Fast EZ EFI without issue. 50 psi fuel pressure and target 13.5 target cruise air fuel ratio and it runs great. Best 60' of 1.31 and 9.70's in the 1/4 on 93 octane pump gas. Idle set at 1100.

[My427stang]

have a sbc 427 street engine. compression is 11. to 1. the cam is 236 in 256 ex with 580 lift on a 108 sep, I am wanting to run fuel inj. I am looking at fast and also holley. my question is how much vacumn will this engine make at idle and also which system will work best for this application.

That cam looks very Thumpt-like. It should sound very healthy and I'd guess 8-10 inches of vacuum, assuming you have enough initial timing and it is installed early (generally those Thumprs are on 103)

As far as EFI, it depends. If you have a kit that you can adjust for open loop idle, meaning it doesn't use the O2 sensor data specifically, then it'll be fine. You just tweak idle and then when you are higher RPM, and lighter load, it goes back to closed loop. In those cases, it's also common to run open loop at WOT

The reason to open in both of these situations is that you don't want the computer to try to correct for a richer mixture due to unburnt fuel going out the pipes during overlap. As long as your system allows you to trick it, and you are willing to take the time to tune, it'll run well.

If you want to do a "bolt on and learn" TB EFI without programming it with very specific behavior, expect that it'll be very fussy and never run as good as it could because of all the overlap