anesthes

iTrader: (12)

Hello,

So. On my '68, which currently has a stock low hp 350 with a quadrajet. I'm planning on putting a 412" small block that I have on a stand collecting dust in it. This is a 4 speed 3.70 car, weighs about 3,000lbs. Naturally aspirated, the engine makes a little over 450hp.
(9.5:1, afr 210 heads, nx276hr cam).

I have a 1206 ported intake on it. I got a brand new Holley 0-4779C 750 double pumper. I was originally going to put a sniper EFI on this car, but I decided for a couple of reasons to leave it carbureted.

Carb has 70 primary main jets, 80 secondary main jets, 6.5 primary pv, 28 primary nozzle, 31 secondary.

I have no idea how to 'size' a Holley carb, honestly. Like, when you build an EFI car you can mathematically select your injects based on what you will make for power. On some powersports that I mess with, there is charts for starting
point on jets and then you go up or down to fine tune. It seems this is not as straight forward with a Holley 750 as it is a single bore Mikuni.

Two questions:

1) What would a good jet combination be for a 450-500hp big inch small block such as this? This is a STREET CAR. Think car shows and back roads. Absolutely no strip use. Skinny 8" tires.
2) Is there a way to retrofit this "manual choke" body carb to an electric choke? I have zero interest in running a cable under the dash.

As far as EFI swapping this, that was my original "plan" but I just decided for the purpose of the car, it's age, I want to keep it basic and use parts I have in the shop.

Thanks.

sofakingdom

iTrader: (1)

1. Go to the Holley web site and look at the Carb Listing pdf. Put whatever size jets in it that the sheet says. Then read and follow the Holley Tuning sticky at the top of this forum. Tuning a carb isn't really any different from tuning EFI, except that you have to go off of different (physical, not computer-generated) indicators of engine "happiness". While you can use a WB O2 to great advantage, most other parameters aren't available to log. Carb jets don't work the same way as injectors, where they feed a fixed amount of fuel; rather, they feed in proportion to air flow. In that sense they are self-sizing. If the engine is flowing xxx CFM of air, the jets allow yyy fuel molecules in. If the air flow doubles, the fuel also doubles, all by itself. As opposed to, each rev of the engine gives zzz molecules of fuel, independent of air flow or anything else, except fuel pressure. Using a WB O2 you can easily enough get to somewhere near stoich at cruise and tune from there for driveability, and get 12.7:1 or near there at WOT and tune for best trap speed or other max HP indicator from there.
2. Generally so, yes. Holley offers EC kits for most of their popular carbs, and I think they have one for that series.