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Marv D · 02-28-2011, 10:44 PM

Surely was not trying to offend, Sounds like I touched on a nerve and DEFINATELY was not the intent. Just thinking that is a very mild cam for the cubes. If it makes it's steam in the mid low RPM say 600 pound feet at 3000rpm,, that is only 350HP,, it will have to make some massive torque to 5250 to make 450. A 262 @ 0.050 I would think would fall short of making steam high enough in the RPM band to be an honest 450 HP with that many cubes. I would think it noses over around 4800-5000, but sounds like you know the ins and outs of the BBC much better than I. Been wrong many many times before and this surely would not be the first :-) But that has nothing to do with what yuo asked.

as far as gear.....
the simple formula for rpm and combination is
rpm =
MHP x gear ratio
divided by tire diameter (in inches)
times 336

So a 4.11 gear with the 31" tires is going to be only 2000rpm at 45mph in city traffic.

out on the highway at 65 it will only be 2900 plus any losses thrpough the converter (5-8% for a real efficient tight converter)

If your sticking with a 31" tire I'd consider a 4.56 gear
It would put you at 2200 at 45, and 3200 at 65. Would take advantage of the motor a little better than a taller gear,

But again,,, just an opinion.

02-28-2011, 10:44 PM	#6
Marv D Registered Truck Offender Join Date: May 2008 Location: hells training ground (aka Ariz) Posts: 3,118	Re: what gear ratio to run ? Surely was not trying to offend, Sounds like I touched on a nerve and DEFINATELY was not the intent. Just thinking that is a very mild cam for the cubes. If it makes it's steam in the mid low RPM say 600 pound feet at 3000rpm,, that is only 350HP,, it will have to make some massive torque to 5250 to make 450. A 262 @ 0.050 I would think would fall short of making steam high enough in the RPM band to be an honest 450 HP with that many cubes. I would think it noses over around 4800-5000, but sounds like you know the ins and outs of the BBC much better than I. Been wrong many many times before and this surely would not be the first :-) But that has nothing to do with what yuo asked. as far as gear..... the simple formula for rpm and combination is rpm = MHP x gear ratio divided by tire diameter (in inches) times 336 So a 4.11 gear with the 31" tires is going to be only 2000rpm at 45mph in city traffic. out on the highway at 65 it will only be 2900 plus any losses thrpough the converter (5-8% for a real efficient tight converter) If your sticking with a 31" tire I'd consider a 4.56 gear It would put you at 2200 at 45, and 3200 at 65. Would take advantage of the motor a little better than a taller gear, But again,,, just an opinion. __________________ Still playin with trucks, even at my age! When you're dead, it's only a problem for the people around you, because you don't know you're dead. .....It's kinda the same when your STUPID. I just did my taxes and reviewed my SS statement. Thanks to the current administration it looks like I will only have to work till noon on the day of my funeral.