IMHO; 2.76s will never fly with dual 2bbls, it's gonna be hard enough to tune with the stock TC.
IMHO, even a 4 bbl is not gonna fly... because
I'm guessing your 318 at a 4000 power-peak and 75% efficiency, will mathematically want 286cfm
So with a 600,Firstly; if you start to bring the secondaries in any sooner than ~3000, you're likely to have a bog. And 3000 will be 33mph, so the reason for the 4bbl is what again? Ok but say you are a magician, and get the secondaries to start coming in at 2800. Hang on a sec; the 318 at 2800 and 100% efficiency, will need (318 x2800)/3450 =258 cfm... but at say 50% efficiency more like 129cfm....and you have a theoretical 600cfm available. So hang on; lets do the math backwards; and I get 600cfm is good to 8680 rpm at 75%efficiency. Hmmmmmm. And 75%, IMO, is very generous.
I'm guessing your 318 at a 4000 power-peak and 75% efficiency, will mathematically want 286cfm
Soooo the point is; what are the primaries good for. Well firstly your 318 is never gonna drag the primaries down to 1.5 inches so lets just re-rate the 300cfm primaries to 3 inches and call them a 212. So 212 is good to 3300. Ok so 3300 is where the primaries may top out at 3" mercury. So 2800 is a reasonable start point.
But hang on, peak power in a stock 318 is at about 4000 rpm and the secondaries let's say in your combo are good for 14hp... at 4000, and you are running out at 3300 so we can throw this out there; from 3300 to 4000 we are expecting 14 hp, so that is about
2hp per 100 rpm, beginning at 3300.
I think this is pretty generous. And 3300 with 2.76s is 36mph in 2.45 low gear with 26.1" tires.
The point of this exercise is to see that the secondaries even if the are wide open at take off, the engine will not pull 1 cfm more thru them, than it could thru the primaries alone, until after 3000 rpm@33mph, probably closer to 3300/36mph. Course if it spins the one tire, you could get to 4000 in a hurry. But the rear end is not gonna take that for very long.
But it's worse; What if the 318 never pulled the vacuum down to even 3" Oh my.
You say those 2bbls are 285s@3" mercury............... each. Ok I'm just messing with you now.
If the math is right, then your engine will be pulling ~128cfm thru each of those 2bbls, and I bet it could do that with the butterflies somewhere around half closed. So what jets are you gonna start with? IDK either,lol.
What about the jets in the 600? IDK that either.
There are exactly three or four cures for this; supercharging, a higher stall, plus gears, or a manual trans.
My go-to would be a hi-stall and at least 3.23s. The hi-stall lets your engine wind up to where the power might be. The bigger rear gear, multiplies that power out the back door. Together they are a very fine 1-2 punch. Even if you only find plus 80 ftpounds with the hi-stall; switching from 2.76s to 3.23s multiplies those meager 80 another 3.23/2.85=plus 17%, to 94. But something else happens with gears; the engine spools up quicker between shifts. So now you are accelerating quicker with more power per unit of time. NOW the 4bbl has a chance to work... but with the stock engine, shifting at 4500, the Rs drop to 2655 on the 1-2 shift, and then you wait, and wait, and wait, to get back up on the cam with the secondaries again open.
With a stock LA318, I'd sooner have a hi stall and gears than a 4bbl. and a free-flowing exhaust before the 4bbl too. I'd probably be happy with a big 2bbl. Or a really really, really small 4bbl.
IDK
But I always wanted to try a pair of deuces.
I always wanted to say; I got a 323 with a pair of deuces, and a three on the tree.. with a 3.23............ It's late, I'm off to bed;lol.
