Aluminum cylinder heads

If the car already runs, then,
for improved off-idle to low-speed/low-rpm, performance,
the best bang for the buck, is a higher-stall TC , and/or higher rear gears, (the 4bbl and free-flowing exhaust is assumed).
Think of it this way;
>suppose your 318 makes 200ftlbs at 2000rpm, the probable current stall speed. That would be 76hp., jus saying
> now suppose your 318 makes 220ftlbs at 2800. That would be 117hp.
> from 76 to 117, is an increase , coming out of the TC of 54%; and there is nothing short of supercharging your 318, that can touch that.
> now suppose your current gears are the typical 2.76s. And at 200 ftlbs at the crank, going thru the 2.45 first gear, that would be 1352 ftlbs to the road. But with 3.23s and 220 ftlbs, that would be 1741#, an increase of 29% ; again only supercharging can touch that.

A2800TC really woke up my smogger-teen, and 4.30s sealed the deal. Later, I got me an A998 with the 2.74 low gear in it, and with 3.55s, that took off like 3.97s
With 27" tires;
2.76s will cruise at 65=~2230rpm at zero-slip. your tach could say more or less depending on the load
3.23s will cruise at 65=~2610@ zero-slip.
But here's the deal;
with 2.76s and a 2800TC and traveling at 65mph; as you slam the gas pedal down,but before the downshift, the rpm will rev up to 2800 OR MORE, whereas the 2000 stall may slip 8%, so 2400.
Passing gear at 55mph;
with 2.76s. the Rs will jump to about 2740 plus slip, so say 3014@10% slip.
with 3.23s, the Rs will jump to about 3210 plus slip, so say 3530@10% slip.
Where would you rather be?
I'm sure Rumble is about to put his gums in gear, so here's the final deal;
I'm not assuming anything, and I'm not leaving anything out.
I'm merely giving examples, for your perusal, so you can wrap your head around how this all works.

Furthermore, you need to understand something else;
Suppose you currently had 3.23s and a 2000stall. And using the above 318 example that made 200ftlbs at 2000rpm; to the road, this is 1583 ftlbs in first gear.
Now suppose you installed a 2800TC and swapped out the 3.23s for 2.76s. Again in first gear but at 220 ftlbs crank, this is 1488 ftlbs . So even tho you gave up 15% gear multiplication, you only gave up 6% torque delivery.

Now swap out the A904 for the A999, and get the 2.74 low gear (compared to the 2.45), and the latter example becomes 1664ftlbs, a GAIN of 5% over the A904/2000stall. Of course your hi-way cruise rpm changes from say 2610@0% slip, to 2230 in loc-up mode, yes with the 2800TC.

If this is a dedicated city car, with an A904; I would be tempted to gear it for peak-power at say 55mph in Second gear, which, with an A904 would take 4.56s. and thus 55= about 5000@10% slip, in Second gear.
With an A999 this would take 4.30s hence why I ran them.

Be advised tho;
once the Rs have climbed to past the stall-rpm, any performance gain after that, has to come from Torque-multiplication, or motor.
With the A904, 2.76s, and a 2000 stall, this comes at about 22mph.
with the A999, 3.23s, and a 2800, this comes at about 23mph
At this point, with the engine unchanged, the 3.23s will out-accelerate the 2.76s....... until you increase the cranking pressure, or the cubic inches, or the valve-timing events..

Finally; suppose you installed better flowing heads and a bigger cam to let them work, but did not increase the compression ratio, nor made any changes to the chassis or the rest of the powertrain; if you did this, your low rpm power is almost guaranteed to suffer, as will your low-SPEED performance.
But say the net result of the smaller combustion chambers and later-closing intake valve angle, sets your engine up for the same before and after cranking cylinder pressure, so then, your low rpm power is likely to be the same as it was in the earlier iteration, namely; below about 3000 to perhaps as high as 3500, there will be NO perceptible performance gain. Ok hang on a sec;
Without tirespin; in first gear with an A904 and 2.76s, 3000rpm will get you 36mph, and 3500 is 42mph. (Yes Rumble, with 27" tires, and at 10% slip@WOT.)

So I ask you; where should you spend your money?
Well, where do you want the performance increase?
And that takes us back to the top of the page.

Happy HotRodding