I just gotta say something here.
To make good use of the Overdrive models, as pertains to fuel economy, with a modest cam; you are sorta married to a final drive of 3.91 x .69=2.77s for 65=2240, which is as low as you dare go and still be able to at least almost give the engine the ignition timing it wants. With this, and the A518, your Roadgears are
9.58- 5.67-3.91-2.77 Whereas with the A999 and 2.76s, they are
xxxxx -7.56-4.25-2.76 So, you get the same ~cruise rpm.
Now check out those numbers. For acceleration;
7.56 is a way better gear than 5.67, as is 4.25 compared to 3.91. So then, the only thing you are loosing is ALL of First gear. But the two next gears are better.
But you can get around some of that first-gear handicap, to some degree, by setting up your engine for more low-rpm torque. And/or you can compromise.
Say you increase your cruise rpm by 10% (to 2460) with a new rear gear of 3.23s. Your new road gears are
*** 8.85-4.97-3.23 , compared to
9.58- 5.67-3.91-2.77
Now, 8.85 is better than half way in between The first two A518 gears. You can easily make up the starting-line difference with stall and or cylinder pressure. From 9.58 to 8.85 is only 8.2% which equates to say 20ftlbs
IMO
this is a reasonable compromise, and is way cheaper, and you don't have any fabrication to do..
Another good compromise is say just 5% more gear (than 2.77) and a higher than factory stall.
From a stall of 2000, to 2800, the 318 might make an extra 20 footpounds, and lets go with 2.94 (cruises at 65=2380 in LU, perhaps 2450 without. Your new Roadgears with the A999 ratios are
xxxx8.06-4.53-2.94 compared to
9.58- 5.67-3.91-2.77 with the A518;
But, the extra 20 ftlbs found by the highstall, are worth perhaps the same 5% so if you factor that in, you get the equivalent performance of;
8.46-4.76-3.09 still not
9.58- 5.67-3.91-2.77, but a reasonable compromise, IMO
BTW, that 8.46 starter gear is with the 2.74 Low gear of the A999. Compared to the A904 with only a 2.45 First gear, this would math to 3.45s in the back...... which, being between 3.23s and 3.55s, is not really all that slow..........
Food for thought; and
we never even talked about cylinder pressure yet.
