18,000 orig. mile 318 build
Don't think 600 cfm is to big , I used an 850 thermoquad off a 440 and my 318 ran great . All it had was holley intake , heads shaved , headers a with dual exhaust and a mild cam , forget the number . All I can say about the carbs is Holley is super easy to fix side of the road , if it breaks down , TQ not so much , but the TQ is super reliable , never had a problem with mine .
Nope...600 cfm is about right--even for a stock/mild 318. I've personally had better luck with Edelbrocks for mild engines...but I've never had ANY carb strand me on the side of the road...fuel filter on the other hand...well, that's another story.
Going back to Kurt's comments:
Also a good option if you find them.
And on that used carb note - don't try it. Too much of a headache potential.
I'd suggest the new Summit 600cfm carb which has fantastic reviews (and a bowl design that won't leak like a Holley) and no reports of loose throttle shafts out of the box due to poor castings.
However, I think a 600cfm might be a bit over the top for a smog-era 318 with minimal mods. You don't want your engine budget getting sucked through the venturis with no purpose other than to score your cylinder walls prematurely.
302 castings are no better or worse than any other 318 LA casting...the only advantage to using them really is the small combustion chambers to bump the compression, but if you're trying to keep things simple, buying a new set of heads only increases cost.
I'll stand by my statement of using a used carb; it's OK to use one, just be a picky buyer...not every one of them can be brought back to reliable service unless you want to make "my grandfather's axe", in which case, you won't save much (if any) money.
As far as the Summit carbs-I have used one of them on my stock 5.2. It worked fairly well...by that I mean it ran great when WOT; idle and putting around town was a little fat. It can be a fine carb (regardless of who thinks it's ugly or not), especially for a mild build, but that doesn't negate the likelihood for fine tuning via swapping out squirters, idle or air restrictors, pump cams, jets, power valves, etc. The DVD that comes with the carb does allude to it in skimming detail. In a nutshell, if you were to decide to purchase the Summit carb, do yourself a favor and buy the tuning kits to go with it
I elected to pull that Summit carb off in favor of a rebuilt Edelbrock 600 sitting on my bench. After filling the bowls and making some minor idle and mixture adjustments, it was running like a sewing machine.
Again, I think a correctly tuned 600 would be a good match...downsizing the cfm rating says nothing about how the carb is jetted...an overjetted 500 will waste more fuel (potentially scoring cylinder walls) compared to even a correctly tuned 700 cfm carb.
