Rear End Gears
Any and all comments appreciated
I think it depends on your engine and performance requirement.
I have run a combo that put my cruising rpm at less than 65-1600; which is really comfortable. But your engine will have to be built to support that.
But then, it will be pretty sucked out to about 30 mph. To combat that, you need a bigger engine.
So; round and round it goes. Pretty soon you get to thinking about a stroker, or a V10.
So I no longer have that trans.gears combo.
I found that cruising in the 2200 to 2400 @65 was a reasonable compromise.
In your case, that would require a rear gear of 3.91s to 4.10s with the .69od and loc-up. So with a 273 I would go 4.10s, and with a 360 I'd go 3.91s.
But if the 360 is warmed up, it might like the 4.10 better.
In your case, you don't have a big range of tire sizes available, and will probably end up in the 24 to 26 inch range, so about 8% from the smallest to the largest. After 3.55s each next bigger gear size is about 5%.
So my numbers reflect the taller tires. If you have really small tires then the gear range should likewise be reduced one size.
That is to say;
4.10s will cruise 65=2377 with 26s, and 2584 with 24s
3.91s will cruise 65=2267 with 26s, and 2464 with 24s
3.73s cruise 65=2163 with 26s, & 2351 with 24s
3.55s cruise 65=2058 with 26s, & 2237 with24s
As to first gear performance;
a starter gear of 9/1 is usually plenty, with a smaller engine liking a lil more and a bigger a lil less.
In your case, 9/2.74= calls for a minimum of 3.23s in the back. So you ain't got much to worry about there!
The other thing is that much over 12/1 is not really all that great, so
12/2.74=~4.30s is getting to be on the big side, so
3.55/3.73s go right up the middle.Which is why I included them above.
3.73 x 2.74=10.30, plenty of starter gear to spin the tires in first gear and what's not to like about 65=~2240 I've been cruising there since 2004.
And finally the kickdown into first at 30mph will get you 4300 rpm@8%slip with 26s..... already too high for a factory cammed engine, to be much good. 3.91s or 4.10s would only make it worse.
3.55x 2.74=9.73. a 360 will have no problem breaking the tires loose with this. But a low-stalled 2.73 is gonna struggle.
Kickdown at 30mph is now 4074@8% slip, still high for a stock-cammed SBM, excluding the 340 of course,lol.
I'm not saying
you should run 3.55s or 3.73s.
I am saying here are the numbers, choose for yourself.
