hey guys, i currently have a TH400 with a GV overdrive on it. that makes my final ratio .78:1. i have 3.90 gears in the rear and run a 26" tire. i turn about 3100 rpms going 70 mph.

i have been contemplating swapping out the transmission (sometime way down the road) with a richmond 6 speed manual, because they come with real low first, second, and third gears, which would allow me to run a real high rear end, like a 2.73 ratio. my question is this: the final ratio in the transmission i was looking at was .62. can you guys calculate (or tell me how to calculate) what my engine speed would be at 70 mph, with say a 2.73 or a 3.31 rear end? (same tire)

Richmond gear ratios:
First 3.01:1
Second 2.13:1
Third 1.57:1
Fourth 1.24:1
Fifth 1.00:1
Sixth 0.62:1

TH-400 gear ratios:
First 2.48:1
Second 1.48:1
Third 1.00:1
OD 0.78:1

with this Richmond setup, would i still be running about the same amount of gear with a 2.73 rear as i am with a 3.90 rear and a TH-400?

thanks for the input...

With a .62:1 and 2.73 rear gear 1500rpm's@66 mph,with a rear gear of 3.31 would be 2000rpm's@72 mph. web site with calculators (http://www.smokemup.com/)

The only thing I can say is make sure you dont put the cam too far out of its intended cruise rpm. It sounds like you want awesome out of the hole performance, but at the same time, nice cruising manners and mileage. Youve got some numbers to look at so far, but if you do gear it so that the engine rpms are well below the cam/motor combo's happies cruise rpm, you could end up with worse mileage than if you were running a few hundred more rpm. This is cause, depending on your overall combo, the motor might not be very efficient at lower rpm and trying to push a car 70 miles per hour at those rpm takes a little heaver foot that it does if you bring your rpm up enough so that the motors power starts to come on and it feels like you barely even have to touch the pedal to keep it moving. Thats why cams have reccomended cruise rpm, cause depending on the whole combo, your best, most efficient cruise rpm should fall somwhere around those guidelines.

good point greg. just to let you know, my cam is a 244/252 & .612/.616 Comp hydraulic roller. i'll have to look into the exact recommended cruise rpm. those #'s sure look a lot more enticing than running 3 grand @ 70. it's just killin' the drivability of the car (for long distances anyways) graemlins/clonk.gif

i don't think it would take a lot of pedal to keep the car crusing @ 70 mph at around 1500 rpm, but you never know. the engine i have just dyno'd 557 hp @ 6186 rpm and 540 lb-ft @ 4700 rpm, 440 of that comes in at 1400 rpm. :D

a 6 speed would be so nice - but there comes the issue of "cutting up" a #'s matching SS car. some of the purists get mad when i talk about it, but i don't look at it that way. if i ever did do a swap, i would be sure to do a real nice job or not do it at all.

I would keep the rpm's up more than 1500@70 mph.I have a 5 speed 0.74:1 and 3.73 rear gears @55mph i'm around 2000 rpm's @70 i'm around 2400 rpm's.Took the chevelle on a 240 mile trip 3 weeks ago and averaged 15 mpg highway and city driving.I run 255/263@50 612/630 solid,comp 10.7,with an 850DP. graemlins/waving.gif