JGT

I see a lot of posts about people worrying about losing MPG with a gear swap, but I find myself more worried about the increased wear and tear on the engine.

I forgot the exact way to calculate it, but I have heard something like going to a 3.73 from the stock auto gear will increase your highway RPMs by 200-300. Are you going to reduce the life of your engine by running at higher RPMs? I do a pretty reasonable amount of highway driving, which is why I am concerned. I think I'll probably hold on to this car for awhile and maybe even supercharge it down the road, so I would like to take care of the engine. Any thoughts?

redass02gt

(new ratio/old ratio) * old gear's rpm = new gear's rpm

05ROUSHER

Yes you will raise your rpms but not enough to worry about. But remember that every engine has so many revolutions in it before it wears out. But what the heck, we bought these cars to have fun with so go for it. My $0.02

wmtheflash

Yeah, I was worried about exactly the same thing. It's true, the higher the RPM, the more wear you're going to get. It doesn't seem like that much more to be, though.

Maybe this will make you feel better, it's relates RPM to vehicle speed:

http://tech.oldsgmail.com/axle_RPM.php

I did some quick calculations for my automatic. I should be getting the same wear at 65 mph with the new gears as I do at 73 mph now. The new 80 mph should give about the same RPM as the old 90 mph, etc.

3.31 gears @ 65 mph = 1895 RPM
3.73 gears @ 57.65 mph = 1894 RPM

3.73 gears @ 65 mph = 2136 RPM
3.31 gears @ 73.3 mph = 2137 RPM

3.73 gears @ 80 mph = 2629 RPM
3.31 gears @ 90 mph = 2624 RPM

Plug in a few numbers in the calculator and you'll see what I mean.

As far as other variables due to the increased acceleration, I have no idea.

Isn't the Mustang's engine a bit over engineered, anyway? I understand that you can add something like 100 hp with no internal engine modification at all, right? It seems to me that Ford designed the engine to take some modifications without much worry. Gears aren't that radical, it's a very basic modification that Ford knew people were going to do.

If you are really concerned about it, then here are the only things I could think of:

1) Switch to a fully synthetic motor oil like Mobil 1 if you haven't already. You'll probably gain a couple of HP, too.

2) Consider an aluminum driveshaft with your gears. An aluminum drive shaft is almost 30 lbs lighter than stock. Reducing rotational weight mass is much more beneficial than static mass. It will greatly reduce the amount of force it takes to rotate the driveshaft, which should improve power at the wheels, reduce wear and tear, and should increase gas mileage (that is, if you can control your right foot!), especially when accelerating.

3) Slow down or do the speed limit.

Daniel06GT

I don't think this is something to worry about, I had an 5.0 '89 GT with 3.73 gears on it, they've been on for at least 70,000 miles and the engine was still running strong the car had well over 200,000 miles on it. If it does "wear" your car more it's an insignificant amount, if you take care of your car and your engine getting any 4.10's or 3.73's or whatever the case is don't worry about it IMO.
Just my .02

-DG