Supercharge? or Naturally Aspirated (Mods)?

[JohnnyGraphic]

Yes, MAYBE top end. You'll really have to drive fast and far to reach the limitations of a shorter rear end in terms of top speed. You do have to shift earlier in each gear. So, it ruined by 0-60 runs because my 2-3 shift happens around 52 MPH(?) or so. But, I never really time myself so it doesn't really matter. It does make corners and squirting in and out of traffic much easier, not to mention a lot more fun!

Gas mileage went down about 2 MPG. Not a huge difference in my book. But to each his own.

I can't remember what I spent for it. But, if you find a wrecked auto 330i, they carry that diff. A LSD would be even better, but more pricey.

Johnny

[danewilson77]

Top end and gas mileage..

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unbearably?

[Johnmadd]

I have a 4.10 led in my e30 and it revs real high on the interstate, 3200 rpm's at 75-80. It still gets like 24 mpg's, and very reponsive at that rpm.

[ZHP-FTW]

Great idea with the brakes. That I will do! And about turbo why that over s/c?

http://www.superchargersonline.com/content.asp?ID=19

[ZHP-FTW]

An alternative to turbo/supercharging your car is a shorter rear differential. It's called a poor-mans supercharger!!! I went from a stock 3.07 to a 3.46 and it made a great and fairly inexpensive upgrade. More shifting to do, but you keep your engine totally stock! Johnny

I wouldn't exactly say it's the same as a S/C/ Turbo, I went from a 3.07 to 3.38 and did notice a nice difference, but not anything like a 150 hp gain.

Do you lose top end that way? What are the other disadvantages?

I can still reach 160mph with my new 3.38. Might have lost a few mph at the very top, but how often do you max out you speedo? The only slight disadvantage is a little more shifting and slightly higher rpms at cruising speed. But I don't mind either.

[az3579]

unbearably?

Dude, 2mpg is a huuuuuuuuuuuuuuuuuuge decrease. It really does add up when you look at how many miles you get out of a tank. For someone like you and I, that would be completely unacceptable considering we drive the tires off our cars (30k miles a year). As a toy, it's something I would do, because I wouldn't care about gas mileage and it wouldn't get driven enough for it to matter. But as a daily driver, I don't see how one can live with it...

Sure does have a nice kick to it though.

I have a 4.10 led in my e30 and it revs real high on the interstate, 3200 rpm's at 75-80. It still gets like 24 mpg's, and very reponsive at that rpm.

Those rpms seem way too low for that speed. I would imagine something a lot closer to 3500-3800rpms for that speed with a 4.10... that's insanely short.

[Nivo]

An alternative to turbo/supercharging your car is a shorter rear differential. It's called a poor-mans supercharger!!! I went from a stock 3.07 to a 3.46 and it made a great and fairly inexpensive upgrade. More shifting to do, but you keep your engine totally stock!

Johnny

I would love to hear your reasoning behind this.

We all know a lower geared rear end (higher number final ratio) doesn't make the engine put out more horsepower as the rear end is after the engine. What it does is allows the engine to spin the tires faster. I have seen on many occasions that a lower rear end final ratio lowers your torque output thus reducing you power output. OMG no way, why , how the? well changing the rear ends final ratio will change your 1:1 of the 4th gear, on most cases you will need to dyno in the next higher gear to get that 1:1 back.

what happens is that you are shifting quicker through the gears, reducing your top end (unless redline is raised). giving the impression of more power.

A supercharger and turbocharger does indeed increase the power at the engine. A rear end doesn't.

There is no replacement for engine modifications to increase the actual power which translates to more WHP. You can shift the power around with gearing but you will not make more power, especially anything close to superchargers and turbochargers.

and with a turbocharger you want to keep the longer gearing as turbos work off engine loading, no load no boost. lower the gearing and you may not reach peak boost.

[mimalmo]

Keep in mind, he's talking about minor changes in final drive ratio. Nobody here is going from their 3.07 to 4.55 gears or anything that drastic. If someone has to go to the next gear for a dyno run, I don't see why that would be a problem but I'm not big into dyno runs so maybe you could elaborate why this would be bad?

If it spins the tires faster, doesn't the car respond better to throttle input changes?

Here's a good resource for those interested in driveline changes.
http://www.bokchoys.com/differential...calculator.htm

[Nivo]

Keep in mind, he's talking about minor changes in final drive ratio. Nobody here is going from their 3.07 to 4.55 gears or anything that drastic. If someone has to go to the next gear for a dyno run, I don't see why that would be a problem but I'm not big into dyno runs so maybe you could elaborate why this would be bad?

If it spins the tires faster, doesn't the car respond better to throttle input changes?

Here's a good resource for those interested in driveline changes.
http://www.bokchoys.com/differential...calculator.htm

The point is, it is not a "poor mans" supercharger. The response is better by the way of the lower final drive but doesn't get more power. which was what the statement was comparing, the final drive vs a supercharger.

I am not saying it is not a good investment to get quicker acceleration on a stock car-modified.

Well to the OP of the thread if you are not mechanically inclined then maybe the Supercharger is quicker/easier to install.

Personally I love turbocharging, All our cars are turbo but the BMW which i am going to turbocharge myself.

[JohnnyGraphic]

O.K. Let me clarify for you. When I mentioned that an 'alternative' to supercharging/turbocharging was a shorter rear-end, I was just mentioning that it was something to consider. Maybe the OP or others reading the forum don't quite have the money to alter their cars the way a supercharger would. It was just something else to consider. I didn't mean that it increased horsepower or torque. It just made 'different' use of what you had. Made the car more responsive than stock. It wasn't as expensive either. So, not the same...just different.

Don't get your panties in a bunch over this ok?

Also, fuel economy-In my opinion, 2 MPG isn't much for what I do. I highly doubt that it will make a HUGE difference in one's pocket book. Maybe someone here can run the calcs, but I'm looking at a difference of about $15/month at 15k/year @3.50/gallon.

I can't make a decision for you modders out there, I can only tell you what I did and why I like/don't like what I did. FWIW, I wish I could afford a supercharger. I would have gone with an ESS Tuning Stage 2 supercharger. But, that would be about $6,500(?) plus installation. And, it isn't legal in California, so I would have to unbolt it every 2 years. I don't want to deal with that. Also, I would have to spend extra cash for upgrades to my braking system and possibly strengthen my rear subframe. Maybe. Not sure.

Cheers!

Johnny