The Stovebolt Site Forums The Shop Area Engine Shop too many rpm's

im currently running a 350 trans with 355 gears in rear. took it to a gear shop to have them changed to a better highway gear. the man said he could do me no good. at 70 he figured by a chart that i would be turning 3100 rpm way too high. By putting 308's it would only drop 500 rpm. he then suggested the best thing to do was put an overdrive tranny in it. have any of you run into this? By the way dont plan to be hitting the 70 mph mark often just want myself and my truck to be comfortable. Oh it has a 350 motor.

I've got a 350ci th400 and 3.08's and 28" tires in the '74 and i run 80 on the freeway no problem. Even get 17-18 mpg.

I worked some figures for you.
Without overdrive and with 28"tires and 3.08 rears
70-2500
80-2900
90-3325
100-3695
110-4025
these are the figures with a .75 overdrive
70-1950
80-2210
90-2495
100-2772
110-3326
these should be close but if you want to figure it out for yourself go to www.randysringandpinion.com Click on calculater then on engine rpm's Hope this helps Keith

He probly said that cuz he does trannies too, and would make more off the tranny. BUT, just putting an Overdrive tranny in would benefit 2 ways, the 700R4 has a lower first gear, which would give you better take off, and the od will help at speed, and give you an effective 30% reduction in rear gear. So with OD, your 3.55 is effectively 2.49 rear gears in OD, It might not work for towing, but would be great for just a driver. This post has some info in it too 700r4
It should give you about 2100 rpm cruising.

How about a turbo 350 with lock up torque converter. It should help and you wouldn't have to change the driveline or mounts. Switch shouldn't be a problem. If he builds transmissions ask about converting yours, may save some money. Joe

Thanks for the info guys. Keith you said no problem but do you have a tach and how many r's are you turning at 70 mph? Rob, this man does gears only and said putting 308's would only drop me 500 r's. I will ask the trannie guy about a torque converter in mine. I plan to do no hauling with this truck. Again I appreciate the info.

Go to Randy's Ring and Pinion and use his calculator. You do the math, then you will know for sure.

http://www.ring-pinion.com/home.html

Rick