answers

Posted by marc b on March 30, 2000 at 01:56:40:

In Reply to: Forced Induction for E46 M3? posted by Marcus Frost on March 29, 2000 at 23:55:15:

with the compression ratio of the new M3 motor only being slightly greater than that of the E36, It is my educated opinion that you will be able to supercharge (w/o aftercooler) to approximately
450hp without much difficulty. The HP per liter measure of the new M3 is primarily due to its hig redline, rather than a drastic increase in torque (the increase in max hp from 6000 to almost 8000 allows the motor to generate significanly more hp). HOWEVER, since the redline is so high, it will make forced induction a more difficult proposal for several reasons.
1. for a centrifugal supercharger, where the boost is rougly a function of rpm^3, you will get much less of an advantage at, say 3000rpm then you will with an E36, however, at nearly all points in the torque curve the new motor outperforms the old by 17-20% (in torque) thus while the boost wont be as drastic, you will still get some, and it will go.
2. For turbo systems, most tend to drop off rapidly at high rpm (look at the S4 dyno curve) due to an inability of a small turbo (small to minimize lag) to accomodate such a high flow rate.
3. for a fixed displacement supercharger, like the mercs, #2 applies again

bearing this in mind, this is my guess (and a additional interesting bit of info for those that care)
the new M3 will accept centrifugal supercharging just like a E36, with peak HP in the 450 range w/o an aftercooler (~6psi) and 500 or so (9psi) with an aftercooler. However, if you look at the E36 supercharged torque curve (look at www.bmwmpower.com in tech data), imagine the torque curve higher (by about 20%) but stretched out all the way to 8k rpm. As for turbos, in order to accomodate the large flow rate w/ the 8k rpm redline and better intakes (to get the 343hp base level) the turbo will have to be significantly larger, and thus have slightly more lag. While a sequential turbo arrangement would help this ALOT, it is doubtful such a system would be devised

There is a different side though, I am working on a centrifugal supercharging arrangement that could allow the SC torque curve for this new motor to be tweaked to allow the SC to produce peak boost lower, w/o too much boost at the end (as I hope none of us want to lower that beautiful 8k rpm redline). if anyone wants more info on this, let me know

just my two cents,
again, no flames intended

as one more point, a supercharged M3 (E36) puts out ~90ft-lbs of torque per liter at redline, whereas the new M3 stock puts out ~70. if the new M3 put out 90ft-lbs of torque (an additional 28%) the peak hp would be approximately 450. If one looks at the dyno charts for SC E36 M3's, one notices that they produce the greatest torque gains near redline (where the supercharger is producing the most boost). In fact, for a stock 95 M3, a SC system (like RMS) is producing 285ft-lbs of torque at 6500, while the stock motor is producing 170, a whopping 67% increase! This is becuase the higher boost of the centrifugal SC at high rpm offsets the lower flow efficiency of the engine at high rpm.

So my final answer (thank you regis)
is 6psi SC will get you ~450+hp
a turbo setup will get you similar torque numbers (~350ft-lbs peak) but at lower values, and may drop off significantly unless larger (laggier) turbos or a sequential setup is used.

Thanks for the bandwidth,
Marc

: I've been discussing with a friend of mine about my probable future plans to supercharge my E46 M3. The thing is, when your getting so much hp per liter, forcing induction will probably not yield as much hp as say an E36 M3. I know there is always room for improvement on almost any engine, but how much more hp can you get out of 3.25L? Figure the E36's were 3.0 and got to 355 with a good supercharger setup is putting out 118hp per liter - it's a good 100+ hp increase setup. Now the E46 is putting out 105.5. If you get it up to like 120hp per liter, you get maybe 390. 390hp is only like 50 more hp. $5000+ for 50hp is a debateable upgrade IMO.

: I may be totally wrong in my calculations, so that's why I'm posting this message. What do you guys think? A Stage I forced induction system maybe get us up to 400hp? Is 50hp going to be worth the $5000+ most forced induction systems for BMWs? Is my engine logistics off?

: I can't wait to test drive one of these bad boys.

: -m