4.10s or 4.56s ?

[ajd89]

Ok guys so I've got both dually rearends according the codes the 89 is a 4.10 open diff and the newlly acquired 88 is a 4.56 open maybe cause it used to be a diesel but before i go trying to sell the whole truck I want to be sure I don't want it in the 89. It will be 454 4l80e and a 241 tcase. Plan on 6inchs of lift and 35s. Mostly a daily but I want to be able to play in the mud and sand and tow if needed I mean it is a 1 ton! I did the calculations so what do you think.

The 4.10s in overdrive at 70mph is 2066 rpm think that is where I want to be. The 4.56s is 2298. Maybe 300rpms don't make a diffrence and im just crazy?

Also at somepoint way down the road I can see doing a l29 7.4 or maybe a even a 8.1. Can't see putting a 12valve in it. If that makes any difference in ratio.

 

[bucket]

If sticking with a gasser, 4.56 for sure without a doubt.

 

[shiftpro]

4.56 is still too high for 35s and overdrive. Maybe consider 33s. For overdrive and 35s you need 4.88s.... or lower even.

 

[Rusty Nail]

4.56 without question.

 

[74 Shortbed]

4.56 is still too high for 35s and overdrive.

At 70mph he'd be running 2145rpm, what's wrong with that???..

 

[Rusty Nail]

The closer you cruise to the torque peak, the higher the mileage. Ain't nothin wrong with that.

 

[74 Shortbed]

Exactly...

 

[ajd89]

At 70mph he'd be running 2145rpm, what's wrong with that???..

Maybe I did it wrong I got like 4300rpms on crawlpedia

The closer you cruise to the torque peak, the higher the mileage. Ain't nothin wrong with that.

Where would the peak torque peak be at? I know they say you can' rev a stock big block to high or you float valves and bend pushrods right?

 

[74 Shortbed]

Maybe I did it wrong I got like 4300rpms on crawlpedia

Try this one.

http://project33.com/tiresize.cfm#trans_rpm

Where would the peak torque peak be at? I know they say you can' rev a stock big block to high or you float valves and bend pushrods right?

That goes for any engine stock parts are not meant to rev high, BB will rev 5500-6000 if it's not tired but don't do any good since you're out of the power range on a stocker anyways.

 

[ajd89]

4.56 is still too high for 35s and overdrive. Maybe consider 33s. For overdrive and 35s you need 4.88s.... or lower even.

That would put it at 2460rpms

 

[ajd89]

Try this one.

http://project33.com/tiresize.cfm#trans_rpm



That goes for any engine stock parts are not meant to rev high, BB will rev 5500-6000 if it's not tired but don't do any good since you're out of the power range on a stocker anyways.

Yeah that one shows the rpms lower. So where is the power range on a big block? I' thinking I seen 1800 to 2200 but that might be wrong

 

[ajd89]

I just want to have a good all the way around gear. Lol

 

[74 Shortbed]

Yeah that one shows the rpms lower. So where is the power range on a big block? I' thinking I seen 1800 to 2200 but that might be wrong

If you have peanut port heads it'll be down there, depends on the cam too.

 

[74 Shortbed]

I just want to have a good all the way around gear. Lol

All depends what you're going to do with the truck too, if you're going to haul heavy loads you need a lower gear, no loads a higher gear.

 

[shiftpro]

At 70mph he'd be running 2145rpm, what's wrong with that???..

Because at 60 mph anything that looks like a hill or even a head wind and the 700r4 will be hunting back and forth between overdrive and third gear... and this creates nuclear meltdown in these transmissions.
Think about an overdrive transmission's final gear as 1 to 1. Set your final drive/tire height gear ratio in those terms.
And just because a BBC has the torque to lug a bit on the highway and get by with it... it can make matters worse as these overdrives (700 or 4l80)
don't like to be lugged.
Also the lock up converter if hunting back and forth makes big heat too.