mrhartge
demonic entity
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this is interesting.Can I make my 325is outrun a M3? [ Alan Rich :: 27 Oct 2000 ] As an owner of both an extremely-modified E30 M3 and a project E30 325is, I will answer that.For this answer, I will reference the February 1988 issue of Road and Track magazine, in which there was an excellent road test comparing the M3 with the 325is.Let's start with the road test. In acceleration, the 325is is only SLIGHTLY slower than the M3. (Zero to 60 in 7.5 seconds compared to 7.1 for the M3. Quarter mile in 15.7 seconds at 88.5 MPH compared to 15.4 seconds at 91 MPH for the M3). AND THIS IS WITH A GEARING DISADVANTAGE !!! Yes, the 325is has a 3.73:1 ring-and-pinion ratio whereas the M3 has a 4.10:1.Doing nothing other than putting a 4.10:1 differential in a 325is will instantly make it faster than a stock M3 except for top speed.How is this possible, you may think, because the M3 has 192 horsepower compared to 168 for the 325is?This is where people's thinking goes wrong about what makes a car fast:It's not how much horsepower the engine makes; It's better explained by the power-to-weight ratio (the car's weight divided by the engine's horsepower). But since the M3 and the 325is weight about the same, that STILL doesn't explain how the 325is with 24 less horsepower can outrun the M3.The answer is in the area under the power curve of the engines. You can't accelerate all the way from zero to whatever with the engine always at the peak power RPM... so the shape of that Horsepower vs. RPM graph determines how much power goes to the wheels in real-world acceleration runs. The six-banger power curve is fat while the M3 is more like a spike, typical of a peaky twin-cam four. The area under the power curve of the six-cylinder is greater than the area under the power curve of the four cylinder, for the total RPM range used in accelerating. That's why the 325is is faster when you give it the same gearing.See my other tech article "Pros and cons of changing ring-and-pinion ratio (differential) for performance" for more detail on this differential gearing bizness.Now, with a good chip, properly done cone airfilter conversion, and a good premium free-flow exhaust system, your 325is engine will roughly match the stock M3 in PEAK horsepower, if that's what you like, IN ADDITION to having the fat power curve coming from the two extra cylinders. Upgrade to a 2.7 liter conversion with a Schrick cam and Mass Air Flow meter and you will outrun all but the very most radical E30 M3's... and you can start looking for E36 M3's to rumble with.Does all this make the 325is a superior performance car to the M3? No. For the race track, I would still take the M3 any day over the 325is. The light-weight four-cylinder engine gives it better handling and braking dynamics. The numerous other high performance factory upgrades (which CAN be fitted to the 325is) make it a better track car. On the track, you can keep he RPM's up where the M3 motor puts out its power, so the fat power curve of the 325is loses its advantage.But for the street, I would pick the 325is any day. It FEELS faster than the M3 on the street even when it's not. And engine upgrades are achievable within my budget. I can build a 250 horsepower 325is six-cylinder for a few thousand dollars... have you looked at the prices for the BMW Motorsports / Evolution engine parts required to get the same level of power out of the M3 engine? Alan Rich
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