Best bang for the buck, off the line, is a higher stall convertor.
Hands down on a low-compression tiny-cammed engine, it will beat a 4bbl every time.
Second best, is to mod the trans or the linkage, whatever it takes, so it will actually allow the engine to wind up to where the power is.
Third best; is gears, that will allow your handicapped engine to get to shift rpm quicker. and
Fourth; is more intake airflow, which will almost invariably also require more exhaust flow, so you kindof need to do those together.
If you're planning ONLY a 4bbl upgrade, do your self a favor and
FIRST
do some TIMED first-gear speed runs to whatever mph you would like to see an improvement in. then do the swap, then repeat the tests. It is all too easy to be fooled by the 4bbl sound, into thinking your car is so much faster, when in reality, it is only sounding like it.
Then, later, when you figure out that the 4bbl with factory stall/hiway gearing, is almost no quicker in any first gear speed contest nor even below about 50 mph; and you decide to put a 2800 convertor in it, repeat the tests again. After you get thru that, disable the secondaries and repeat the test again.
now you have some data to process; and not some seat of the pants bs.
How does it work?
Well lets say your 2bbl-273 is able to muster a whopping 150 hp at 4000 rpm and let's say at a stall of 2000, the power is just 50. I chose these numbers cuz I can do the math in my head. and so can you, so you can follow along.
Ok so let's say the power is linear. Thus, the power of this 2bbl engine will be, from 50 to 150= 100 hp over 2000 rpm = 5hp per 100 rpm. So then you can predict the power increase at any rpm. At 2800, we can predict an increase of 8 x 5=40 hp; woohoo! that's almost double.
Let's compare that to the 4bbl, with no other changes.
At 2000 rpm, your 2bbl is still adequately sized, so the 4 bbl even WFO will get you zero hp. even at 2800 that stinking 4bbl carb is barely adding any power. Let's be generous and say that at the power peak, it generates IDK say 20 hp, and at 2000 zero. so we can predict 1hp per 100 rpm. So then, when you take off, with the 4bbl screaming, at a stall of 2000 rpm, if it doesn't bog, you will be taking off at par with the 2bbl. If yur lucky, that 4bbl will add 1 hp per 100 rpm so by 4000, yur looking at plus 20 hp.
Sounds great right. Well , yes and no.
If you have 2.76 gears, then 4000 rpm will be about 40 mph. When the trans shifts, the rpm will drop to about 59%= 2360 which will be 3.6 hp over 50=53.6 hp, and that's that.
If you have 3.23 gears, then 4000 will be about 34mph, and again, on the shift, the Rs will fall to 2360, and again adding just 3.6 hp.
But; no matter what gear you have in it, if you have a 2800 stall, then; when it shifts at 4000, the Rs are not likely to fall below 2800,
which is (5hp x 8) plus the base50 =90 hp.
Now, 90/53.6= 1.68, so,
with the 2800 convertor, your 273 is likely to send 68% more hp into the driveshaft at every take off .
a 4bbl can't touch this.
Now recall that, the numbers I chose, were for ease of calculating and ease of understanding and may not reflect your engine at all; nor do I know what gearing you currently have. But;
the principle is still the same.
Happy HotRodding
