1987 carpenter F156s 5.57 ratio swap to 4.33

[Condormfg]

And the pain is setting in. Just bought a drop in reman gear box for the 87 carpenter. I was tacking @32k at 60mph. Anyone know what I can expect with the 4.33? 20" wheels. 7.3 idi. Also I havent pulled the axles yet but truck shop said 95% have 36 splines. Can't wait to find out I'm in the other 5%..any help here wld be great.

[ns9987]

I hope your bus has a manual tranny, because 4.33's are going to suck ass with a 7.3L AND an Automatic... you will lose a hell of alot of power on the highway. But, if you do have a manual trans, with some deep starting gears, it won't suck AS bad... And, I'd turn up the fuel a bit to that 7.3L too, so you can crank a few extra horses out when you're flooring it to climb a steep hill. lol You never want to gear a 7.3L, even if it has a manual trans with anything higher than 4.78's and that's pushing it the limit there. I know because my bus has a 6.9L IDI and an Allison AT-545 auto trans, with 5.38 gears. I can do 45mph @ 2500RPM's, Yes, and that sucks as well. But, remember there's a reason they gear buses low, because some engines just don't have the horses to turn anything higher.... I seriously would try to find a 4.78 if I were you.

Don't think I'm hating on you or anything, I'm just telling you from experience. I'd hate to see you spend all that money to swap it and then you wish'd you hadn't. lol =D

[crazycal]

Originally Posted by Condormfg

And the pain is setting in. Just bought a drop in reman gear box for the 87 carpenter. I was tacking @32k at 60mph. Anyone know what I can expect with the 4.33? 20" wheels. 7.3 idi. Also I havent pulled the axles yet but truck shop said 95% have 36 splines. Can't wait to find out I'm in the other 5%..any help here wld be great.

You can expect to buy a new engine running around at 32,000 rpms. Sorry , couldn't resist.

[chev49]

you are safe up to 31.5...

[Jarlaxle]

Originally Posted by Condormfg

And the pain is setting in. Just bought a drop in reman gear box for the 87 carpenter. I was tacking @32k at 60mph. Anyone know what I can expect with the 4.33? 20" wheels. 7.3 idi. Also I havent pulled the axles yet but truck shop said 95% have 36 splines. Can't wait to find out I'm in the other 5%..any help here wld be great.

With 9.00-20 tires and 4.33 gears, 60MPH will be about 2200RPM.