Wow Work's been crazy and I haven't gotten a chance to get on here. I have so much catching up to do. My 2 cents. If you have money and you've been wanting to do it for a while now, you have my support. YAY, I wanna see project pictures!
Yup! My 3.73 was dying a loud terrible death, I found a good deal on 4.10 viscous out of an ix, so I figured I'd give a shot. I actually liked it, the extra grunt in 1,2,3 were well worth the added highway RPM's. I did the same thing when I had my R6, went -1, +2 (front and rear respectively) although once that set was done I eventually went back to just +2 on the rear, it actually felt faster that was since it stayed in the power longer. I will eventually go back to a 3.73, but for now that's another $250-400 that I can keep out of the budget.
You won't need the 4.10 with the twincam for sure. They have scads of bottom end torque. You'll be much happier with the 3.73 when you find one. I have one, but it is non-LS, so you probably don't want it.
With the 4:10 what is your RPM at 60mph and 75mph? I am planning to buy my brothers ix with an auto and I am going to convert it to a manual, so of course it has TWO 4:10s in it.
The answer is: probably almost exactly what it is in your M3, since you have a 4:10 and the overdrive is the same gearing even though you have a 265 in the M3.
So in other words way the h**l up there!! It is about 4k at 80mph. The M3 is a buzz bomb and I love it. But I don't know if I want an M20 spinning that high all the time. I am planning to put miles on this car. I guess I will do the swap and see how bad it is, unless CJ Morgan buys that ix and I can get his diffs.
It is if you like fuel economy and longevity. However, tip in on the interstate is much improved with a 4:10.
I do care about longevity and economy, but economy and an ix don't go together very well. It won't see much highway use, that is what the E36 is for.
Are you seriously telling me that running 4k constantly is going to significantly reduce the life of the engine? Despite preventative maintenance and not redlining the thing constantly? I understand if they were to redline it constantly every day, but 4k is only the middle of the rev range and I personally don't see it as being all that strained if traveling on the interstate. For my car, maybe as mine has a 4.5k redline, but for an M20 good for over 6k rpm I just don't see the harm... Are we talking major reduction in life (50k +) or just a couple of thousand miles?
Well, there is basically no point in having the thing screaming around all the time if it makes low end torque. They put 4:10s in the auto ixs and the late auto convertibles due to the extra weight they have to lug around. THe 4 bangers got them because you have to rev the snot out of them off the line due to lack of torque. THe M3 got it for fun and because you have to rev the snot out of it to get the horsepower. To make a long story short, higer revs equal higher piston speeds and accelerations equals more wear. Are the BMWs up for it? Sure. Does that mean you won't pay for it in the long run? Depends on how long you run it. There is no telling how much life it takes out of the motor, but high revving engines require rebuilds more often than understressed engines of the same build quality/materials.
The typical life of an early M engine before a recommended rebuild is maybe half that of a non M engine (excl. the S50/52 US)
Why do you say except for the S50/52? What makes those engines different? I should be fine in that department though because this car is only going to see the track a couple of times a year and I don't kill the engine on a daily basis. I'm not knwn for redlining my engine, so hopefully with a bit of care, I should be fine.
THe S50/52 US are realatively understressed engines. They make more power than the M50/52 mostly through displacement and moderate cams. They are not redlined significantly above their normal counterparts, and are not given much shorter gearing. By comparison, the S54 is a highly streesed motor that puts out around 100hp/liter, has radical cams, an 8k redline, and does not last as long as an M54 (though the S motor has an iron block, so it is less susceptible to being nuked in an overheat.) The higher specific output engines also tend to twist and oval out the #5 and 6 cylinders over time. With your 2.93 gearing, you will be running around at fewer revs than the average S50, so it is not an issue. BTW, ask yourself why your 50hp/liter engine has 320k (I have seen over 400k on an eta) but you rarely see an i motor that has lived quite that long.
With a diff that spins the motor 27% faster, it is likely that there will be that much less life in the cam, bearings and rings. The cylinder walls seem to live forever, though, but I sure do see a lot of worn i cams. It also does not help that the i heads use stiffer valve springs so they can run at higher revs. Stiffer springs= more wear.
