Transmission gearing questions

[Slither]

OK guys and gals, so after the cruise on Saturday I was picking Butch's brain on rear-end gear ratios and transmission options. He suggested the close ratio toploader with either 3.31 or 3.54 rear gears. I had been thinking that the wide ratio box with a 3.08 gear would be a better option, and here's why.

If you run the numbers with a gearing calculator (I used the SecondStrike version), it appears that first and second gear with the wide box and 3.08 rear would perform almost exactly the same as the close box with the 3.54 rear, i.e. the overall ratio (end to end) for first/second gears is 8.56/5.94 and 8.24/6.00 for the wide/3.08 and close/3.54 respectively (interestingly, first gear in the wide/3.08 combo, 8.56, is lower than first in the close/3.54 combo, 8.24!).

Next, if you look at third and forth, third in the wide/3.08 setup is identical to a close ratio box with the 3.31 gear set, while fourth is equivalent to the rear end ratio in each of the setups, since it is a one-to-one ratio in the tranny. This gives a little lower cruise rpm for the 3.08 over the 3.31, and even more difference in rpm over the 3.54 gear set.

The engines you all are running are more than capable of pulling in any of these combinations, as I witnessed (quite impressively) over this last weekend. I plan to run either the 408 Windsor or the 427FE engine, so no problem here with torque/power. The only issue I could see is that the split between second and third or third and fourth might be a bit tall for the wide box, but it doesn't seem that large from the numbers at 1.42 and 1,36 for the wide box versus 1.36 and 1.29 for the close box.

So is there any flaw in this logic? I realize that this is more of a clinical approach rather than the seat of the pants feel needed to really make a good choice. However, you can't just go and drive a bunch of Cobras of all different combinations to help you make a choice. Besides, it's the engineer in me that wants to see the numbers.

Additionally, I found a potential replacement for my lost toploader, and I suspect it is for a small block application... price is right and right now I can't be choosey. Let me know what you think. Is this too much of a compromise?

[Brent]

Quote:
"However, you can't just go and drive a bunch of Cobras of all different combinations to help you make a choice. Besides, it's the engineer in me that wants to see the numbers."

If you can't drive every Cobra with every combination then you should listen to someone that has driven every Cobra with every combination.

It would be even better if that person had not only driven every Cobra with every combination but also built transmissions and rear ends every day for a living.

Butch Capps!

As far as cars go, in the battle of clinical vs. experience I would always lean toward experience.

[chris knueven]

paul,

i will second the comment brent made.....listen to mr. capps.....

chris

brent...if you see this i am sending you a p.m.........gots a question for ya...

[brfutbrian]

paul, butch`s advise is right on ( it always is). imo, if youre going to run posi go with the 3.54, if youre going with an open rear the 3.31 would give you a little better traction with only half the rubber having power put to it. any higher ratio than that, youll never see anything near the top end of that combo cause the front end will have too much high speed lift before you get there (unless you have a death wish). i went with the 3.31/ posi / cr trans and wish i had gone with the 3.54 instead. later, freakin`brian

[Slither]

Right, great answers, but to the wrong question. Butch has a world of experience... thats why I was discussing it with him. I just could not tap into all of that experience in such a short period of time. In our discussion, we did not have time to cover all of the subtleties and nuances of different combinations. He did not say this was a bad combo (maybe he was just being polite). As you know, he is a busy man and I don't want to keep bothering him (maybe every once in a while). And collectively, you all have good experience, as well.

I asked David Kee about it and he said it is a great combo, and that there is a 428FE/wide ratio topoader car there in San Antonio that is delightful to drive.

Rick mentioned trying a 3.54, so I wonder why, and if a 3.54 with effectively a taller 3rd and 4th would be advantageous or not... pros and cons.

Chris, I thought you said you have a 5-speed??? - which I understand is a wide ratio box. What rear gearing, and would you rather have something different, and why?

Brent, you mentioned doing a taller rear gear if you were to do it ever again... so...?

Thanks!

[juanone]

Paul:

When are you getting your car? Have you ordered it already? I know you wrote me some e-mail middle of last year during my build and I got the impression you already had ordered yours.

What did you finally decide to order from Unique? When will you be driving it?

Juan

[Justin Upchurch]

Paul,

My car has a TKO 600 w/ .64 OD and 3.54 axle ratio. If you go with the small block I do not think I would go taller than a 3:54. A BB car, maybe the 3:31. Both Chris and I have a 5 speed trans, and if you are going to be on the highway that may be the best way to go.

Justin