AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,071
- Reaction score
- 12,413
the A833 has ratio splits of .73,
so a full gear difference would be
2.76/.73=~3.78s, or
2.94/.73=4.03, or
3.23/.73=4.42
In these instances you would be trading away exactly one low gear for one higher gear.
In other words; if you had 3.78s, and you swapped to 2.76s, then your second gear with 3.78s would feel exactly the same as first with the 2.76s
The standard TorqueFlite has a 1-2 split of 1.45/2.45= .59, so the gear spread is wider and hurts more. So
2.76/.59=4.68 for exactly one gear difference
2.94/.59=4.98.. So you don't have the same flexibility.
But you do have the A998/999 which can be had with ratios of 2.74/1.54/1.00 which have splits of .56/.65 which are worse than the A904 splits of .59/.69, because they have to be,lol.
But, that 2.74 is 11.8% lower than the 2.45 which is about the same as 2.94s to 3.23s, or about the same as any one gear swap from 2.76 to 3.73 skipping 3.55s which is the beginning of the half-steps.
What that means is this;
2.45x3.23=7.91, and
2.74x2.94=8.06, basically the same to your engine. So now you have the same starter gear.
The bonus of the 2.94s is the 11.8% slower rpm at any given cruising speed. but
The penalty is the wider gear splits, with the further rpm drops.
The cure for that is the next smaller cam, or a wider LSA, or more cylinder pressure, or some combination of those. This is to pull up the low rpm torque difference. And I found the 2800TC very helpful together with the small-cam/high-pressure package. I'm no fan of wide LSA cams .
And the best part is that A998/low-gear trans are dirt cheap cores. You can even transfer the entire geartrain from a slanty box into a V8 case . And if you have a performance VB, you can use that. And the TC from the 904 will drive the 998Non-loc-up. These slanty 998s are almost give-aways.
So, for a streeter, you can have your cake pretty cheaply.
And one more thing, the difference from a 28" tire to a 26.5 tire is 5%, or about a half gear change. Combining this with the above, you can have more first gear performance with the 2.94/2.74 combo and small tires, than the 3.23/2.45 tall tire combo. Here are the numbers corrected to a 24 inch tire;
3.23x2.45x24/28=6.78
2.94x2.74x24/26.5=7.29
that is a 7.6% improvement to the 2.94s That's actually almost the same as
3.55x2.45x24/28=7.45
But don't get too excited,the 5% tireswap is only worth 120rpm at 65mph.
so a full gear difference would be
2.76/.73=~3.78s, or
2.94/.73=4.03, or
3.23/.73=4.42
In these instances you would be trading away exactly one low gear for one higher gear.
In other words; if you had 3.78s, and you swapped to 2.76s, then your second gear with 3.78s would feel exactly the same as first with the 2.76s
The standard TorqueFlite has a 1-2 split of 1.45/2.45= .59, so the gear spread is wider and hurts more. So
2.76/.59=4.68 for exactly one gear difference
2.94/.59=4.98.. So you don't have the same flexibility.
But you do have the A998/999 which can be had with ratios of 2.74/1.54/1.00 which have splits of .56/.65 which are worse than the A904 splits of .59/.69, because they have to be,lol.
But, that 2.74 is 11.8% lower than the 2.45 which is about the same as 2.94s to 3.23s, or about the same as any one gear swap from 2.76 to 3.73 skipping 3.55s which is the beginning of the half-steps.
What that means is this;
2.45x3.23=7.91, and
2.74x2.94=8.06, basically the same to your engine. So now you have the same starter gear.
The bonus of the 2.94s is the 11.8% slower rpm at any given cruising speed. but
The penalty is the wider gear splits, with the further rpm drops.
The cure for that is the next smaller cam, or a wider LSA, or more cylinder pressure, or some combination of those. This is to pull up the low rpm torque difference. And I found the 2800TC very helpful together with the small-cam/high-pressure package. I'm no fan of wide LSA cams .
And the best part is that A998/low-gear trans are dirt cheap cores. You can even transfer the entire geartrain from a slanty box into a V8 case . And if you have a performance VB, you can use that. And the TC from the 904 will drive the 998Non-loc-up. These slanty 998s are almost give-aways.
So, for a streeter, you can have your cake pretty cheaply.
And one more thing, the difference from a 28" tire to a 26.5 tire is 5%, or about a half gear change. Combining this with the above, you can have more first gear performance with the 2.94/2.74 combo and small tires, than the 3.23/2.45 tall tire combo. Here are the numbers corrected to a 24 inch tire;
3.23x2.45x24/28=6.78
2.94x2.74x24/26.5=7.29
that is a 7.6% improvement to the 2.94s That's actually almost the same as
3.55x2.45x24/28=7.45
But don't get too excited,the 5% tireswap is only worth 120rpm at 65mph.
