I'll throw my humble opinions into this thread: I'd like to see what you have to say, Dan, as I know you were considering a supercharger a while back...

A while ago, I was also in the market for forced induction for my 325i, and I came up with:

1. Dinan, centrifugal supercharging
2. ERT, centrifugal superchargin
3. Mosselman, turbocharging
4. Active Autowerke, turbocharging

I started reading turbo magazine...(horribly written, horrible graphics, but fairly educational as far as foced induction goes)...I also subscribed to the honda performance mailing list, which caters mainly toward the drag race scene in so california (compared to them, our signal/noise ratio is great.)

My priorities, from most important to least important, were:

1. reliability
2. serviceabilty, and the related "cleanliness of the installation"
3. power increase and the associated driveability
4. cost

Here is what I found:

1. Dinan and ERT centrifugal supercharging ISN'T the same as roots supercharging, as is the case w/ the SLK, Grand PRix, T-bird. As such, these 2 supercharging kits don't really make an appreciable difference until 3500 rpm or so, and then boost starts to build quite linearly. Boost is a linear function of rpm
2. In turbocharging, boost is NOT a linear function of rpm. As long as you match the turbine housing (and some other turbocharger specs) correctly to the displacement of the engine, you'll get a turbo that spools up very quickly, and can make appreciable boost as low as 2000 rpm.
3. However, depending on the state of the motor at t - 1, planting the gas a time t

   will not always result in x amount of boost...I think this is turbo lag. This does not happen w/ centrifugal supercharging. You can always predict the amount of boost you will get w/ supercharging. Supercharging wins the driveability battle.

4. Centrifugal supercharging one of the most efficient forms of supercharging..the

   parasitic loads are minimized in c. supercharging, but of course, it will never be as efficient as a turbo

5. The turbo kits probably make more torque under a broader range of rpms (and hence power)

   than the sc kits. The turbocharger wins the sheer power battle

6. compressing air always heats the air up, but the turbo kits produce more underhood temps

   because the turbo is mounted to the exhaust manifold, and that gets hot hot hot.

7. More air to burn means you need more fuel to burn it with.....
   1. The Mosselman kits use a variable fuel pressure regulator to provide for more

      fuel...this doesn't seem like a very accurate way of providing for more fuel.. in fact its very INaccurate.. compared with changing the fuel injection curve, this is like comparing carbs to fuel injection. I want engineered accuracy, not ball park correct. Mosselman out.

   2. The Active Autowerke kit mounts two additional fuel injectors upstream of the

      original fuel injectors and controls these injectors with a combination of HKS/GReddy computer parts and revised motronic programming. How can I be sure than all six cylinders receive an equal amount of fuel from the additional two injectors if they are mounted upstream of the original injectors? I can't. I don't like this "adding 2 more injectors in the vicinity of the intake manifold" idea. I don't like using HKS/Greddy computer parts to control these injectors... IMHO its kinda like a band aid...Its kinda like cadillac, when they say, "Our front wheel drive cannot cope w/ the 300hp from our Northstar engine, so we will use traction control, ABS, computer adjustable shock valving, and the like to 'control" the chassis as much as possible" If the factory tubocharged the M3, I'm sure they wouldn't add two more injectors and use more computers to control them. Plus, I don't like the turbo heat probelms, and the fact that a turbo literally cooks your engine oil. That's why AA suggests you use a HKS turbo timer, to keep your engine idling for a few minutes AFTER you have left the car, to let the oil circulate thru the turbo...I don't like this either...more bandaids IMHO!!!! Note: intercooling standard.

   3. Dinan supercharging...The powerdyne sc uses a self contained lubricant...no cooking

      engine oil. The sc's had also been redesigned (by powerdyne) as of November 1996 to account for internal sc belt/bearing failure experienced under high stress track conditions. no more failures with the new units...quieter too! Now, Dinan replaces the stock fuel injectors with bigger ones (the factory would have done it this way) I like this... Now, under boost, the HFM air sensor reads an "out of range" reading (too much air being pushed thru!) so Dinan gets around this by incorporating another black box to intercept this signal and spit out a correct reading to the motronic computer so the reporgrammed motronic will shoot out the correct amount of fuel to the injectors. This is good. Very factory like, except Dinan is a little pricey... Note: Intercooling an option.

   4. ERT supercharging...same thing as Dinan, except instead of the black box affair, they

      replace the HFM completely with a bigger european HFM that can correctly read the amount of air passing thru under boost, and reprogram the motronic to control the bigger injectors correctly. EVEN CLEANER! EVEN BETTER! They are cheaper than Dinan too. Note Intercooling an option.

For the reasons listed above, my humble money went to ERT. These are just my humble opinions... I'm not trying to flame anyone else's foced induction car, I'm just saying for my reasons, and for my priorities, I chose ERT. Make your own decisions. I like my car, I like my engine, but the bottom line is, I'm having fun. That's all that matters, no?

Jason Leung 1992 325iK