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-   -   Rear end gears (https://www.airforums.com/forums/f311/rear-end-gears-191583.html)

davejay 01-28-2019 02:57 PM

Rear end gears
 
Hey,
Our 325 has I think4:56 gears. Stock tranny behind a 454. If I go with a differant ratio, any suggestions. I'm thinking 3:73 s maybe 3:54s that may be a little rough on heavy grades. DJ

Isuzusweet 01-28-2019 06:57 PM

Maybe think about a GV overdrive. This way you get the higher top end with lower rpms, but retain the lower gearing when the going gets tough.

Cheers
Sidekick Tony

Smartstream 01-28-2019 11:36 PM

Last I checked a GV costs about 3 times what a gear change would cost. My Isuzu is so slow that the extra gears of the GV made more sense. If you are comfortable that you have enough power to handle the taller gears, you will save money up front. Also consider the amount of time you spend in low gears from a stop light vs how much time you spend in top gear on the highway. If you don't think you could handle the loss of power then go for the GV.

davejay 01-29-2019 06:33 AM

Hey,
Yah, we were talking about a GV the other day. Having a lot of gears is nice. But, I can have the whole rear end set up with a new ring and pinion for about 650.00 I got a pretty mild cam in this thing, I should be making about 350 hp. And a little more low end torque. Taking off fast doesn't concern my, (to much),big hills. That is where the drive line takes the most beating mainly the Ujoints. So I'm still thinking. A GV would be easier to install, and this 325 only has 5420 miles on it. It would be a shame to tear out a perfectly good set of OE gears. The more I ponder this thing, the closer I get to putting in a GV. Thanks guys. DJ
You guys both have diesals, so I can't get a good comparison of the mileage differance between gas and diesal. With a GV in yours, how much better is your mileage when using it as to when not using it.

panamerican 01-29-2019 08:11 AM

Gearing IIRC really amplifies torque. Diesels don't need any torque amplification as they have such high torque already at low RPMs. This may also be why if you try to get a 2500/3500 truck with a diesel engine, most won't go any higher than 3.73s, while their same vehicles with gas engines can get 4.10s or sometimes larger.

Gas engines are a different story. Though my exp is with consumer grade trucks, 2500/3500, the same physics apply. Gas engines can greatly benefit from gears in the 4.10 or larger range because gas engines don't have anywhere near the torque of it's diesel counterpart.

In my exp, there is a small MPG hit between 4.10 and 3.73, could be a bit more of a MPG perk going from 4.56 yo 3.73 but going up hills and mountains the 4.10s or larger would prove far more useful than 3.73. What is your thinking in going to 3.73s from 4.56?

Smartstream 01-29-2019 01:07 PM

As mentioned above gearing and torque effects are different with gas and diesel. Gearing also depends on power available. Low power benefits a lot with more gears.

My fuel economy didn't change much with the GV because you are still pushing the same vehicle weight against the same wall of air at cruising speed. It just made driving a whole bunch gooder. :lol:

tjdonahoe 01-29-2019 01:18 PM

Quote:

Originally Posted by panamerican (Post 2204491)
Gearing IIRC really amplifies torque. Diesels don't need any torque amplification as they have such high torque already at low RPMs. This may also be why if you try to get a 2500/3500 truck with a diesel engine, most won't go any higher than 3.73s, while their same vehicles with gas engines can get 4.10s or sometimes larger.

Gas engines are a different story. Though my exp is with consumer grade trucks, 2500/3500, the same physics apply. Gas engines can greatly benefit from gears in the 4.10 or larger range because gas engines don't have anywhere near the torque of it's diesel counterpart.

In my exp, there is a small MPG hit between 4.10 and 3.73, could be a bit more of a MPG perk going from 4.56 yo 3.73 but going up hills and mountains the 4.10s or larger would prove far more useful than 3.73. What is your thinking in going to 3.73s from 4.56?

.......newer diesel 3/4 ton pickups are 3:54...ram6.7..the transmission is double over...near .73....

davejay 01-29-2019 07:33 PM

Hey,
A GV may be in the future, but for now, we'll just run her down the road at 65.that puts the rpm around 3300. With a new engine and trans and some internal mods to the 454, I may pull 10-12 out of it. That would be good. Realistically, I'm thinking we'll get about 8-9 mpg. I can live with that. I got a hydrogen kit a while back. I may throw that on, and see if it does anything. They say 25-30 percent gain in mileage. We'll see. Thanks guys for the suggestions. DJ


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