ARCguy

Hello again folks. For those of you who haven’t read my introduction in the new member area (and I think that’s probably all of you) I recently picked up a ’69 Ford Torino GT that I’ll be working on for a good long time to come. Right now my problem is with the 351W that is sitting in the engine bay. Sadly I don’t have receipts for anything that’s been done to engine, nor have I pulled it apart and inspected every square inch of it, as for the moment it runs fine and that’s good enough for me.

But here’s what I do know about the engine. It’s a 351W that was rebuilt a few thousand miles ago. At some point in its travels it picked up tubular headers (sorry, I don’t know the diameter) and a three-inch exhaust. It also has a Weiand Stealth intake manifold and a cam. Sadly, I know next to nothing about the cam. The guy I bought the car from said that the previous owner had put in a cam that was “a little bigger than stock”, but it honestly sounds more aggressive than “a little bigger than stock” to me. Maybe that’s the headers and the exhaust doing it, but either way it’s something of a question mark there. From what I’ve seen the heads look like they’re stock, but then again I haven’t pulled them out and searched for casting numbers or checked for porting/polishing either, but I’d be surprised if they were anything other than stock. The carb is a 750 CFM Demon with no choke.

Frankly, getting the car to hold idle when I first start it is something of a chore. Not to mention that having the car literally spitting fuel out the exhaust for the first minute or two while it warms up can’t be doing my engine any favors… To that end I’ve decided to go with a Holley Street Avenger carb with one of those oh-so-convenient electric chokes. But then my issue becomes, for what little I know has been done to my engine, what size carb should I be getting?

While the 750 CFM carbs are very nice for a properly built engine, on my car it’s going to be doing nothing but killing low RPM performance and causing me to run pig-rich. So really I’m looking at either the 670 CFM or the 570 CFM carbs and trying to decide which would be best for me? Higher peak HP is nice and all, but there’s something to be said for low-end torque and a broader power curve, yanno?
So anyway, sorry for the phone-book masquerading as a question, but I’d really appreciate some input as to what would give me the best combination of low end torque and usable upper end HP on what is a mostly mild engine.

THUMPIN455

Wanna mail me the Demon? If it isnt set up right, it wont run right. If its dripping gas from the boosters at idle, the floats are too high. If the floats dont change the fuel level, then the needle valve is sticking. Tunning is more than just turning the idle mix screws.

If its a mechanical secondary carb it is probably too much, especially if it isnt set up right. Too much cam will also make it a dog down low, if the timing is retarded in an attempt to make a high compression engine run on cheap gas, it will be a pig.

If you are looking for a new carb suited for daily driving, pretty much anything with vacuum secondaries will work, 500-750 CFM, but the 650 and 600 Holleys seem to work well..

Seriously I will take that Demon off your hands..

67mustang302

Haha, I can't blame you for trying to get the Demon [8D]

+1 though on the carb being set up right. A poorly tuned carburetor, no matter how properly sized, will never run right