[Railcop094]

Could someone help me out with the formula to figure what my rpms or speed would be with different gear ratios? Muchos gracias.

 

[llama_boy]

If this doesn't answer your question try http://www.corral.net under the technical link.



70 mph indicated
2037 rpms

3.27
70mph actual

3.73
61mph actual

4.10
56mph actual

____________________

70 mph actual

3.27
2037 rpms

3.73
2324 rpms

4.10
2554

___________________
various speeds
Assumes stock tires

3.27

50=1455
60=1746
70=2037
80=2328
90=2619
100=2910
110=3201
120=3492
130=3783
140=4074
150=4365
Theoretical maximum speed:209

3.73
50=1659
60=1992
70=2323
80=2655
90=2987
100=3319
110=3651
120=3983
130=4315
140=4647
150=4979
Theoretical maximum speed:183

4.10
50=1824
60=2189
70=2554
80=2919
90=3284
100=3649
110=4014
120=4379
130=4743
140=5108
150=5473
Theoretical maximum speed:167

 

[Railcop094]

That was quick! Thanks.

 

[llama_boy]

The fact that at 80mph the rpms are still under 3,000 made the 4.10s my choice.

Besides I can always put bigger tires on ;-)

 

[llama_boy]

On 2002-01-17 19:22, Railcop094 wrote:
That was quick! Thanks.

Us "geeks" are quick with are formulas

 

[Railcop094]

I am leaning more toward the 3.73s. I am not too wild that Dallas Mustang wants $80 to reburn my chip for the speedo adjust.

 

[Pony XTC]

Hey llama_boy, I decided to go with 4.10s myself after a lot of reserch. I figure we should gain about a half second in the quarter, and should be some great pull when going thru the gears. How do you like yours? And is it a lot of work when crusing around compared to the stock ones?

 

[llama_boy]

Wish I knew.. I'm still waiting to get them in the mail, I just placed the order today throught the group purchase I set up.

1/2 a second sounds great, that prolly includes better rear tires?

 

[Micah]

Does changing out for 4.10 gears do anything to your gas mileage? I don't know much about all of this, but it seems to me that lower RPMs at higher speed would equal better gas mileage, yet you're getting "more power" out of the switch, and conventional wisdom says "more power" means worse gas mileage.

What does the gear switch really do?

 

[Railcop094]

The 4.10s produce higher RPMs at lower speeds. According to the chart listed above, there is a 500 RPM increase at 70 MPH with 4.10s over the stock gears. So yeah you will see a bit of a downslide in the MPG.

 

[llama_boy]

I have done ALOT of research on this.. but the following info IS second hand.

Burning fuel = power. It doesn't equal RPMs. This means that running out car @ 70mph will require the same HP with 3.27, 3.73, or 4.10 gears therefore the MPG is the same. The added RPMs do take a little extra fuel therefore the MPG change a little, very little. I have seen posts that put the amount aruond 5% or 1-2MPG.

What are you worried about MPG for?? Gas is cheap! It's the car payment, insurance, and mods that will get ya! :wink:

 

[Micah]

Heh, good point. Thanks for the info, folks!

 

[Mid Life Crisis #388]

to make it easy to compare I made up some charts comparing 3.27 3.55 3.73 and 4.10's

http://www.quicksurf.com/ths/bullitt/Misc/Gears/

 

[Railcop094]

Very nice charts Mid-Life. Makes me almost wish I had gone with the 4.10s instead of the 3.73s.

 

[Pony XTC]

Great chart 388. Thanks