4.8is VS 4.4 sport comparison
 

This is more of an observation than a comparison. But i was bored and comparing stats on the 4.4 and 4.8 and noticed that the 4.4 and 4.8 have the same transmission and gear ratios for all 6 gears. But the final drive ratio on the 4.4 is 4.10to1 versus the 4.8 having a 3.91to1 final drive. Now i assume BMW did this to help the gas mileage on the 4.8 since they both achieve the same gas mileage stats. I see no other reason for giving the 4.8 that 3.91 vs the 4.10. So know i am wondering. If someone modded a 4.4 to the same hp and torque specs that the 4.8is has then technically the 4.4 will out accelerate the 4.8. And seeing that the 4.8 only has 40 more hp and 45 more lbs of torque it wouldnt be too difficult to hit those numbers. Plus i noticed that the 4.4 is 90 lbs lighter than the 4.8 giving it also another slight advantage if power were equal. As most of you know every 10lbs in weight reduction is equal to a 1 hp increase as far as acceleration goes. Meaning dropping the weight by 90lbs will have the same effect as increasing hp by 9hp.

Just one more point about the difference between a 3.91 rear diff and a 4.10 rear diff for those of you that dont think it will make a difference. Although it is not a huge difference it will definately be a noticable just from my past experience. I used to have A 540I without sport package. it came with a 2.83 rear diff gearing. Now BMW pit a 3.10 rear end in the sport package 540. So i bought a 3.10 rear diff and installed it in my 540 and 0to60 times dropped from 6.1 sec to 5.8sec. With just the diff change no other mod. It cost me 1500 dollars with labor. that is a huge difference. and i think the most bang for buck you can get on a bimmer. So know i am wondering for all you 4.8 owners out there that if you can swap the 4.4 diff into your 4.8 and it should definately help your acceleration. I wonder if it would be as easy as the swap i did in the 540. I know if i had a 4.8 i would def look into this mod.

Like i said i was bored but i think i bring up a valid point and was wondering if anyone else has thought about this and also any comments or opinions you guys have about this. Or maybe one of you has already tried this. And if not i think someone with a 4.8 should try. Like i said my 540 was a direct swap and only took 3 hours labor.

Wouldn't a gear swap require changing both front and rear differentials? Would it affect the operability of xDrive in any way?

That was one of my questions. Ive always had sometype of rear drive sports car so i dont know much about how the AWD works and how a diff swap would work. Would you have to change front and rear and maybe even the transfer case or just the rear diff. If this is possible to change just the rear i think it would be a worthwhile mod.

I helped a buddy do a differential swap on his Jeep years ago - I remember we installed Detroit Lockers on both the front and rear with 4.10 ratio gears in both. However, that was on a manual transfer case vehicle with none of the sophisticated systems on an X5.

The guy who can answer your question is Brett Anderson of Koala Motorsports (www.http://www.koalamotorsport.com). Brett is a technical advisor for the BMWCCA Roundel magazine. Koala Motorsports sells Quaife racing differentials for different BMW models, so it's likely that Brett would have the definitive answer. If you find out, post the answer. It would be good information to have.

Regards, Mike

Thanks for the info i will contact him next week and see what he says.

IMO, changing gears is one of the best mods to do to a car. In one of my old cars I changed the rear gear from 3.42 to 4.10 and it felt like it gained about 30-35 lb-ft and hp. Definitely makes the car a lot quicker and funner to drive.

That being said, I like the responsiveness of my 4.4 and don't think it'd be worth it (labor, recalibrate speedometer, 1st one to do this mod, etc.) to me to change gears. However, in something like an M3 it would be one of the first things I'd mod.

So let me get this straight...if the 4.4's hp is increase 40hp and 45 lb-ft torque through mods, which can be done through a Superchip [18hp], exhaust system [8-10] and CAI [10-13] (don't know about the torque, but the hp is almost certain), then the 4.4 should be able to accelerate faster than the 4.8 because of the final gear ratio? I'm curious because even though the 4.8 has only 40hp more than the 4.4, it's 0-60 time is almost a full second faster (.9 sec), which seems like a lot of time to make up for only 40hp. :dunno: Don't know much about gear ratios and the like, but if that's the case, I'm all about getting those 40 ponies to get my X that fast.