Final Drive Calculations

[WatchmaN]

Originally Posted by wootwoot

No one else?

Yeah me too, probably have to do the shifting in an another rpm range and he did'nt adjust to it.

[wootwoot]

Could be. I was hoping someone that has this upgrade in their FRS would chime in. From all accounts it gives power throughout the RPM band and through each gear. Which makes the most sense to me. Maybe racecomp or robi could give us a few words on their experience with this product?

[evilconcarne999]

Originally Posted by wootwoot

No one else?

I dont get it either? If your in a higher rpm band against the same or similarly powered car with similar or less modifications in a lower rpm band, your going to pull on it just for the sure fact that you would be able to accelerate faster due to being in that higher rpm range and having more usuable power. I know even with all the lightweight modifications i have if im cruising at 35 in 6th and a similar car whether it be stock or not is sitting at 35 in 2nd or third it will pull on me just like I said above because its in a higher rpm band thus more usuable power. So I dont understand how with a final drive modification which would have you cruising in a higher rpm range and thats supposed to increase torque throughout the gears, and a noticeable torque increase, a stock car would pull on it? Especially considering you wouldnt have to downshift since you would already be at a higher rpm than the similar car. Maby im missing something...?

Im planning on getting the mfactory 4.67 final drive down the road.

[Sonolin]

All I know is @robispec is using 4.7 final drive in his track car. It posted a very good time at Willow Springs (1:35), which is a high speed track. Lots of 3rd & 4th gear turns, with a large bank to a straight at the end of the track.

Based on that and that 4.7 final drive is going to give more torque, I'd say highway pulls would be faster with 4.7 final drive. Again this is all speculation.

[FT-86 SpeedFactory]

We have the Mfactory 4.7 in our silver car now, and our red car is stock. We have some good comparisons and videos coming soon on this very subject.

[evilconcarne999]

Originally Posted by FT-86 SpeedFactory

We have the Mfactory 4.7 in our silver car now, and our red car is stock. We have some good comparisons and videos coming soon on this very subject.

Sweet looking forward to viewing the different comparisons between the 2

[arghx7]

Every application is different, but remember that there's a reason why drag racers with muscle cars carefully spec out their final drive ratio and transmission.

Also, here's formulas to consider...

(Engine torque in newton-meters) * transmission ratio * final drive) / (tire radius in meters) = driving force in newtons . You can calculate that easy enough if you have the engine torque curve.

Driving force - running resistance = acceleration power . You can't easily calculate that in a useable way at home. If you change the final drive, your final drive multiplier increases. However, at a given vehicle speed you are now at a different engine rpm so torque might change. It's not that straightforward to predict which would be faster.

[mrk1]

I have changed many a BMW diff to a higher ratio. I know its a bit apples to oranges but it was often a hard sell to customers but everyone came back smiling.

For me its a debate between 4.55 or 4.44, I drive highway more then I'd like to admit so I need to keep that mileage in check.

[WatchmaN]

I've got my mfactory 4.67 sitting on shelf, waiting for my friend silverdub to install it, i'll surely make video and virtual dyno pull to show the differance. Simply can't wait to try that.

[OrbitalEllipses]

Originally Posted by mrk1

For me its a debate between 4.55 or 4.44, I drive highway more then I'd like to admit so I need to keep that mileage in check.

Samesies. Don't want to be turning 4-4.5K at 80mph, nahmean?

[evilconcarne999]

Originally Posted by WatchmaN

I've got my mfactory 4.67 sitting on shelf, waiting for my friend silverdub to install it, i'll surely make video and virtual dyno pull to show the differance. Simply can't wait to try that.

That would be awesome to see considering im planning on getting the same exact final drive looking forward to the videos after the install.

[evilconcarne999]

Originally Posted by OrbitalEllipses

Samesies. Don't want to be turning 4-4.5K at 80mph, nahmean?

Luckly I dont do as much highway driving as I use to but I know that I will be again soon, ill just have to adjust to it. Its a modification I dont mind altering some driving mannerisms in order to figure out how to be efficient with it.

[mrk1]

Is there a service manual for this car yet? I need to get ahold of the torque specs and what not for installing a new final drive.

[OrbitalEllipses]

Originally Posted by mrk1

Is there a service manual for this car yet? I need to get ahold of the torque specs and what not for installing a new final drive.

There was a service manual many moons ago, grasshopper. It might have even posted on this website. Maybe.