You are going to ruin the motor running 14.2 A/F at WOT. You need to get this down to at least 12.5:1.

Mitch

I'll agree on the A/F comments. Rule of thumb that I've worked with in the past is 14.5 at idle, 14.5 at cruise, 12.5 in power mode (power valve operating) and 12.5 at WOT. I'm not suggesting those numbers are the best for every combination but they seem to be fairly common dyno tune targets to shoot for.

The carb choice is a little more difficult. They Holley design works great for drag racing since you can dump a lot of fuel into the manifold in a hurry with the big accelerator pumps. But that design can be very difficult to coax a fuel curve out of since there is no easy way to change the power valve restriction area. (plug and drill operation) Most drag racers don't care about part throttle fuel mileage but many people who drive their cars on the street do.

Given enough time and money a Holley can be dialed in very precisely, but if you have access to a small Carter type carb then it will dial in a lot faster. Maybe with your manifold you need the big pump shot to cover a lean bog on acceleration? If so, a Holley might be the way to go.

On Slants, I have found the Holley 600 4bbl took much more fiddling to get it to be bog free than the Edel 600 on a built motor. The Holley 600 got worse mileage by about 3-4 MPG as well. I like the Edel 500 even better. Never tried the Holley 390 so I can't comment on that.

Lou

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Home of Slant6-powered fun machines since 1988

last record of my Volare was 22.5MPG with 50/50 city/hwy driving. it went down from 25 with the Supersix. not to shabby saying i have a foot the size of the car.

Justin

I agree with all the numbers except cruise. I've read that best fuel mileage during cruise is obtained at 16:1, although it typically increases NOx emissions to run that lean... (although with excellent ignition control, some modern vehicles are running even leaner, in the 18:1 range.)

But at the very least, I would think overall you'd want to be a little on the lean side of stoichiometric (14.7) than a little on the rich side. In other words, I'd shoot for 15.0-15.5 rather than 14.5 on cruising.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

If you have near perfect fuel distribution as you would with port fuel injection, then you can run lean during low power demands. With carburation and wet manifold flow, you will be lucky to get the engine to run well at stoichiometric. Working against you further is the lack of significant quench in the slant head which affords little mixture turbulence.

Mitch

When in doubt, er on the side of rich. All it'll cost you is gas. Lean can cost you a motor or head.

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Brett

1963 Valiant Vert(225 /6)
1964 Dart GT Vert(225 /6)
1965 Dart GT (273)
1966 Barracuda (273)
1966 Dart (225 /6)
1970 Charger R/T (440)
1972 Satellite 4 door (318)
1974 Valiant 4 door (318)
1981 Ramcharger (318)
1987 RamVan (225 /6)

Oops. Sorry, forgot which thread I was reading... I thought you were talking about multiport.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

I've been running my EFI slant on the lean side for cruise - around 16:1 based on my O2 sensor readings. If your advance curve (and vac) is set up right, there should be no ill effects whatsoever. Pinging is only really damaging when you are under load, and the mixture should be richer there anyway.

Lou

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Home of Slant6-powered fun machines since 1988