Thread: 454 3spd w/4.68 gear rpm on highway...

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I figure you hotrod guys know your motors, so I have a quick question...

I have a 78 GM Chassis motorhome with a 454 w/4barrel carb and 3spd auto trans (turbo400 i think) with 4.68 gears (dana 11?).

At normal throttle, it will shift into 3rd at about 25mph. 60mph is a long way away from 25mph and i'm all out of gears! At 60mph it is rev'ing about 3200rpm.

I've been contemplating throwing a set of 4.10 or even 3.73 gears to improve mileage, but I'm curious as to if it is even worth it?

Is 3200+rpm ok for these old 454's? I have a 12hour drive planned in a few weeks, and I know 3200rpm is ok for a little 4cylinder, but a big 454 seems a bit high.

Thanks for the advice!

It sounds like you have a front-motor, rear-drive arrangement. I have taken an interest in the front-motor, front-drive '73-'78 GMC Motorhome and have begun researching it. I ran across this link to Applied GMC that lists 3.07, 3.21, 3.55, 3.70 and 4.10 gearsets. These are to fit the TH425 Toronado transaxle, but will show that these are the most popular sets. I'm pretty sure the Motorhome came from the GM Pontiac plant originally with 3.42 gears, so if you have a good, strong motor, 3.42 might be the best all-around ratio to use.
http://www.appliedgmc.com/level.itml/icOid/482

I'm pretty sure I'm gonna buy one of these classic motorhomes and do a little fixin' up. Maybe get Pat to put a rotund rat motor together for me.

why not install an o/d trans???

put in a 4l80e trans----

I had a 1984 Chev 454 with 4:10 gears---ran around 3300 at 70----course with you guys using kilos---your rpm will be less at 70

you can get a trans guy to work on the govner and adjust shift points---sounds like your throttle/trans link is set correctly if it shifts that soon---does it ship hard or smooth??