druckle

I'm considering changing from Muncie 4 speed to Keisler RS400/500 5 speed with a 3.37 1st gear. I have 3.36 rear gears and 410hp at the flywheel, 425tq. It is used for street only and like to do shows now and then. I am concerned about first gear being too low. With the keisler speed analyzer it says I would have the same performance as a 4.49 rear gear ratio in 1st, but I have neve driven anything that low. It comes out to a final drive ratio in 1st of 11.3-1. I know 10-1 is considered ideal and I have 8.46 now. I don't know how low is too low, I don't want a first gear I can't use. Any thoughts on this?

Vette5.5

Think a big part is your engine, and how high the redline is. Have a buddy with a 79' L-82 3.70 axle car, that did the Keisler TKO 500 conversion. I've ridden in it a few times, and didn't seem to bad to me. I have a BB car with 3.73 axle and a 700R4 with 3.05 1st gear, and seems fine. Nice thing about both these cars, is the 0.70 od highway cruising, as quite an improvement. The low 1st gears, are getting to be quite the thing on newer cars. My daily Pontiac GXP 3.6 DOHC 6 speed auto has a 2.77 axle, with 4.50 1st gear. You can do the math on that one, and thing really launches.

Gordonm

Not a problem. I drove my TKO 500 with a 3.27 1st gear and a 3.70 rear for years with no problem. I was around 500 HP with this setup. It really jumps out of the hole. You will get used to it very quickly.

rponfick

Should be ideal. I have the Keisler TKO 500 in my '69 L71, and I just went up from a 3.08 to a 3.55. It is about perfect now. The L71 I have originally came with a 4.11, and that was too low. I went overboard on the 3.08, but now am happy with the 3.55.

Ralph

tsw71

I'm running a Richmond 5 speed with a 3.27 1st gear with 3.36's in the rear. It is a perfect combination. Having had an M20 previously, it seemed quite low at first, but I got used to it very quickly. Now I could not imagine going back.

Priya

Why is 10-1 considered ideal, and by whom? It would seem to me that the ideal final drive ratio would vary considerably depending on car weight and rpm the motor produces the most power at with a small block car or heavier car perhaps needing more than 10 to 1 and a big block car or lighter car perhaps needing less than 10-1. Since when does one size fit all?

druckle

Thanks for the replies and support. I am going to order one for a winter project. Also Priya, I don't know who made that determination, but I know a final of 8.47 is too high so 10 or 11 seems to be about right. Thanks for all responses.

Priya

I wasn't really directing my question towards you in particular, but rather to the Corvette Forum membership in general many of whom often repeat this idea but never provide a rationalization for it (that I've seen).

TheSkunkWorks

As with any "rule of thumb", there's plenty of wriggle room for debate, and there are several factors not accounted for in the 10:1 theory which affect just what gearing should prove optimal for a specific car and purpose. That said, having driven C3's with quite a few gear combinations (from 8.95:1 to 14.14:1), IMOE it's a pretty good reference point from which to work in lieu of more thorough analysis for most street C3's (assuming more or less stock diameter tires).

Is 11.3:1 too deep? If you otherwise like the transmission in question I don't see any glaring reason not to ahead and pull the trigger on it. Personally, I'd draw the line at ~12.5:1 on the street, and doubt I'd care for anything any taller ~8.5:1. YMMV

Vette5.5

I recall seeing mention of the 10:1 ratio, but really think it's more dependant on vehicle weight, engine rpm and low end torque. I have a 3100 lb C6 ZO6, and the LS7 makes torque everywhere. 1st gear is 2.66, feeding a 3.42 axle, making total 1st gear ratio 9:1. This thing will boil the large rear tires anywhere in 1st gear. Some even change the axle on these, but don't know why.

Priya

Nicely explained, Skunkworks. My 70 Torino had 3.89 rear end with 22 inch tall rear tires which is the equivalent of 5.00 rear end with 31 inch rear tires. I don't know what the first gear ratio was but if it was around 2.5 it had a 12.5 final drive ratio which I LOVED - perfect for the 351 Cleveland's 6000 rpm redline in the 3700 lb Torino. My Corvette has a 3.70 rear and the Keisler five speed waiting to be installed has a 3.37 first so based on that the 12.5 final drive in my 3700 pound 6000 rpm redline Corvette ought to be exactly right.

druckle

Thanks guys and gals. I'm sold, I will be ordering one for a winter project. Much appreciated!

Phil Zell

I have the Richmond 5 speed with 308 rear gears and a first gear of 327, all I can say is be prepared to shift from first to second in a hurry.

Gale Banks 80'

Well I'm going to go along with your original concern of 1st being to low. If You have a small CI Engine with a lot of Cam and all You do is Drag Race I wouldn't have any concern. However You don't decribe this at all. You might go to Randys Ring and Pinion web site, I consider his the best RPM Calulator I have found and play around with the numbers. I'd bet that the second gear is probably not much diffrent than the 1st gear in your Muncie. A freind of mine has a Richmond with 3.27 1st Gear, installed 2.87 Rear Gears to be close to the 10 to 1 Ratio, has a 465 CI Built Motor and has run 11 second times being very Traction limeted. The last thing He needs is a lower gear.