4.10's or 4.56's? Read what AirRam has to say..
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Record Breaker
Joined: Apr 2008
Posts: 1,612
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From: Indiana
4.10's or 4.56's? Read what AirRam has to say..
I went from 3.55's to 4.56's and gained only 300 RPMs at 60MPH. With that 300 RPM's I also gained 3-4MPG at that same 60MPH speed. My tire height at the time was 32" tall... So it all depends on your tire height and transmission overdrive gear. I tend to advise my customers to chose a rear gear that will offer them 2100RPM@60MPH for the best overall performance to include MPG.
If you obtain the 2100RPMs@60MPH then you will be well on your way to being able to have your cake and eat it too.
Here is the SIMPLE MATH:
___________________________
Find your OVERALL GEAR RATIO (OGR)
TRANSMISSION GEAR RATIO X REAR GEAR RATIO = OGR
___________________________
Find you RPM's at any SPEED:
SPEED X OGR X 336 / TIRE HEIGHT = RPM
Math has only one right answer. Use the math when selecting your gears.
EVERYTHING ABOVE IS WORD FOR WORD AIRRAM'S.
If you obtain the 2100RPMs@60MPH then you will be well on your way to being able to have your cake and eat it too.
Here is the SIMPLE MATH:
___________________________
Find your OVERALL GEAR RATIO (OGR)
TRANSMISSION GEAR RATIO X REAR GEAR RATIO = OGR
___________________________
Find you RPM's at any SPEED:
SPEED X OGR X 336 / TIRE HEIGHT = RPM
Math has only one right answer. Use the math when selecting your gears.
EVERYTHING ABOVE IS WORD FOR WORD AIRRAM'S.
Grand Champion
Joined: Apr 2009
Posts: 5,293
Likes: 3
From: Kekaha, HI
Baracis, Airram has been trying to talk me out of 4.10s but I'm doing them anyway. He thinks I'm producing too much HP to effectively use them. But I say "Too much HP, is that possible?" Lol.
Veteran
Joined: Oct 2006
Posts: 383
Likes: 1
From: Raleigh, NC
Well, if AirRam believes in the simple math his RPM change should be double from what he said.
http://www.4lo.com/calc/geartable.htm
Here's a site that gets mentioned a lot on the jeep forum I'm on. There's a helpful chart plus the same formulas.
I added in one of Eric's posts awhile back using the online calculator that if he goes with 4.56s should he ever do 80mph down the highway for long trips the tach will read +4K. That's pretty high...
http://www.4lo.com/calc/geartable.htm
Here's a site that gets mentioned a lot on the jeep forum I'm on. There's a helpful chart plus the same formulas.
I added in one of Eric's posts awhile back using the online calculator that if he goes with 4.56s should he ever do 80mph down the highway for long trips the tach will read +4K. That's pretty high...
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Grand Champion
Joined: Apr 2009
Posts: 5,293
Likes: 3
From: Kekaha, HI
Baracis, this is what Airram told me about gears in my setup.
You should have the Chrysler 9.25 rear end... so all your parts you order should be specifically for the CHRY 9.25 rear axle.
I honestly would just keep the 3.55's and make it a POSI traction going with either an Eaton or a Detroit true trac... Since you will be Supercharged you will be making tons of low end torque... so you will be able to take advantage of the 3.55 gear ratio.... With the supercharger the highest I would recommend would be a 3.92... and honestly I would wait till you hit the track with the 3.55's to make that call. You may find out that the 3.55's are better suited for SUPERCHARGER DUTY then 4.10's.
Either way I can set you up with what ever you need... just let me know. Im just trying to save you money... I dont think you need 4.10's with 400+HP
SPEED SAFE, NICK
I honestly would just keep the 3.55's and make it a POSI traction going with either an Eaton or a Detroit true trac... Since you will be Supercharged you will be making tons of low end torque... so you will be able to take advantage of the 3.55 gear ratio.... With the supercharger the highest I would recommend would be a 3.92... and honestly I would wait till you hit the track with the 3.55's to make that call. You may find out that the 3.55's are better suited for SUPERCHARGER DUTY then 4.10's.
Either way I can set you up with what ever you need... just let me know. Im just trying to save you money... I dont think you need 4.10's with 400+HP
SPEED SAFE, NICK
Record Breaker
Joined: Dec 2005
Posts: 2,147
Likes: 0
From: Winter Garden, Fl
I can see his point blown but I think that he has it confused with turbos. with turbos you need load on the engine to run the turbos faster, the more load on the engine the faster the turbos spool to an extent. Superchargers work off engine speed so as long as you dont reach a point you are overspeeding the superchargers efficient rpm level then I think you will be ok.