I'll be installing my 3.73 this week probably and was wondering if it would help or hurt my 1/4 times? Of course it would seem like I would get there quicker but I also have to shift sooner. What do you guys think?:dunno

Do you have to shift to 4th in the 1/4 mile with your stock gears? I know I do,but if so, then I think the 3.73 will still leave you in 4th by the end of the 1/4, so I think you will def. pick up some faster times.

Yes I do shift into 4th already. I did have that in mind too...I guess you're right. Thanks.

As long as it doesn't create an extra shift on your run, you should pick up a couple tenths or so.

Ideally, in a drag car, you want to be maxed out in high gear at the end of the quarter mile. Nothing left. So, if you drive a 5-speed with a 6800rpm rev limiter, you'd want to be in 5th gear at 6500rpms + when you cross the finish line.

Unless you have tire/traction limitations, go for the gear that will put you there. I'm sure that would be lower than 3.73.

On the other hand, if you still drive on the street/freeway, you may want to set the gearing up so you max out in 4th at the end of the track.

Go to diffsonline.com to look at speed/rpm charts for different gear sets. Then talk to Dan (forum sponsor) for your new diff.

Jay

I don't know about the maxing out in fifth gear thing for all cars. Do the Zs and Ms (or any modern BMW for that matter) have overdrive gears? I know my Mustang did and if I were to hit fifth in that car, I could kiss my race goodbye, even with lower gears because of its huge jump in gearing from fourth to fifth. Just a thought. I guess that if the Bimmers are geared right in the tranny, like my Z3 seems to be, then fifth gear's redline wouldn't be a bad place to finish. :buttrock

but changing out the rear drive ratio changes the effective ratio of ALL the gears, so you would be getting to those higher gears faster and you would have more mechanical advantage than you would with stock gearing. That indeed is ideal, but as he stated, only if traction isn't an issue. Alot time, when someone wants to deriously drag, they can't do really tall gears like that because they are pushing too much power to get traction.

Alot of guys with big power will shorten them which will help with the launch and also have lees shifts.

but changing out the rear drive ratio changes the effective ratio of ALL the gears, so you would be getting to those higher gears faster and you would have more mechanical advantage than you would with stock gearing. That indeed is ideal, but as he stated, only if traction isn't an issue. Alot time, when someone wants to deriously drag, they can't do really tall gears like that because they are pushing too much power to get traction.

Alot of guys with big power will shorten them which will help with the launch and also have lees shifts.

Exmple of this: A 400 RWHP with Ford Lightning runs its best time with 4.1 gears, a 550 RWHP Lightning likes 3.73s (both are near the top of third at the traps) but the 720 RWHP Lightning that JLP drove to a 9.8@133 has 3.55s.

also remember that if you drop into an overdrive gear, you just pissed away a lot of energy into friction loss.

In your M Coupe 5th gear is 1:1. you want to hit redline in 5th gear just after you cross the line.

If you want to know exact gearing details, post your redline and your rear tyres sizes.