4 bbl intake 273
Everything about the car seems stock, so the 273 is bolted to a torqueflight 3 speed 1st is 2.45:1 2nd is 1.45:1 3rd is 1.00:1, also the car is a small block, I'm not overly mechanically inclined yet however comma I can definitely figure stuff out. So you recommend some change to gearing a torque converter stall converter thing?
I do yes.
If you want more jump off the line, and if you cannot spin both tires;then, the absolute best, and probably cheapest thing that you can do for the littlest LA, is a looser TC.
The factory low-stall is a nod to economy. I'm guessing the factory tires were about 24 inchs tall. With a 2.73 rear gear, and 1750 stall TC, this might put down 100ftlbs x 2.45x2.73=669 ftlbs to the pavement. That is a pretty mellow take-off. I think street-performance starts around 1200ftlbs. So there is a lot of improvement to be had right there.
1200 is 79% more than what you might currently have, and 1200 will spin both 245s; so maybe that is more than you need.Perhaps you would be happy with 30%,or 40% more. That would be say 669 x 1.35=903 ftlbs
To get that, you would need some combination of more power and gears. Since the factory TC is about 1750, the fastest way to more power is to rev the engine up a little higher. To get the 903 with 2.73s would take 903/(2.73x2.45)=135 ftlbs, about 35 more than she might currently be putting out. I'm guessing a true 2250 would get you there.
But my math says your current hi-way cruise rpm is 2485 at zero slip, so depending on the wind,or terrain, and chassis, it could be up to say,150 rpm either way. So then if the rear gear is staying,and hi way fuel mileage mattered to me, then, a 2400 would be my logical pick. This will put your engine up nearer to or even at the torque-peak,which I can't recall offhand but I would guess it to be over 200 by 2400. If it was, then 200 x 2.45 x 2.73 =1337 ftlbs, and magically you are in tire-spinning power; both of them, with a 2bbl. So don't be spinning just one all the time, you will wear out the spider gears in no time.
You could achieve similar results with more gear and less TC,and it may cost about the same but is more labor intensive,IMO.
For instance, upping the rear gear to say
3.23s is a 20% improvement.
The engine torque now required would be ;
1337/(3.23 x 2.45) =169 ftlbs. This might be doable at
2200 say. Your cruise rpm would rise to
2940=65 tho, at zero slip.
However 3.23s will rip through the rpm band at a much faster rate, and your car will be way quicker in zero to 60 times. So which method, or both, is kindof dependent on what you want from the car.
and she's still a 2bbl.
With 3.23s and the 2500 rpm from my earlier post, this is now 19ish mph, about where the 2bbl starts running into a problem passing air. So NOW the 4bbl will start earning it's keep. This does not mean that at 2500 your 273 will hit a wall. Not at all. I have taken that carb to 5500 many a time, and in second gear as well,and on 318s, and on a 340 even!
If you really want to get to 60 in a hurry, then 3.23s are the ones to install. 60mph will be; 1/{(60x1056x3.23x1.45)/tire rollout} x 1.05TC slip= about
4130rpm. And, the 4bbl will be a little quicker.3.55s will also be quicker, but may require a shift into Drive, before 60, to stay out of lifter pump-up.
So, to recap,
if it was my project, I would stick a 2250 in there with 3.23/3.55 gears and call it done.
A 4bbl might add 15ish hp, and would work better with,optional dual exhaust and large-dump iron manifolds. I would strive to find a small port dual-plane and a very small 4bbl.
Alternatively, I might (cuz I have one) try a 360 2bbl van set-up (carb and large-port intake), with the big Holley 2 bbl. I have had good success modding them. The slow-jet may have to be increased, as they are pretty lean from the factory.
Just FYI;
At 4100 your 273 might be looking for
(273x4100)/3450 x .65VE =211cfm.
I guessed at the .65VE. If the engine was able to pull a .75VE, then she would want 243cfm. I think the smallest 4bbl out there is a 390 Holley.Which is probably getting close to double what you need.
Again that doesn't mean it is waay too big.It will be just fine.
A 650 tho, at 8/1 compression, might be a bit of a bear to tune,
A 500AVS could be made to work pretty good. Just tighten up the airdoor until the bog goes away,lol.
Keep in mind tho that the hp increase with the 4bbl is a gradual increase beginning at 2500 ish and continuing to build with rpm. So you might get an increase of 1hp@2550@18mph/first gear,building to around 15@4000@34mph,still in first gear.Unless you spin the tires, and the engine gets into the rev-limiter,lol. Then you can have full power at like 2mph. If that happens you really need to do something about it, especially if you are peg-legging it!
As for me, I would probably just stay with the 2bbl, if it's in good shape.
