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      01-25-2013, 01:20 AM   #62
bigjae1976
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Drives: 11 E90 M3 Individual
Join Date: Mar 2006
Location: Milwaukee, WI

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2004 BMW M3  [4.50]
2011 BMW E90 M3  [5.00]
2013 BMW 328i  [5.00]
A couple of things.

First, hardware. Supercharges add weight over and in front of the front axle. So the balance of the car changes. Not a big deal on the street but it does make a difference on the track.

My stock M3 will pull redline in 100 degree temps. I can't imagine how the engine is NOT pulling timing after about 10 minutes in the first session and not badly heatsoaked by the end of the day, intercooled or not. Case in point with my FI'd 330. My fastest lap in my 330 is consistently the first session of the day. I feel a HUGE difference in power when it starts mid 50's in the morning and gets to the mid 70's. I'm talking about probably a 10%-20% difference in some cases.

I think its a good guess that your DME is dumping fuel and pulling timing to save the engine because you have some detonation from heatsoak. Forget AFRs, they can be misleading. I'd log timing, fuel trims, and knock sensors. I've been doing a lot of research and learned quite a bit about FI and tuning with the recent maladies with my 330. Typically, what most companies do is add fuel and pull timing when the knock sensors detect detonation. Basically relying on the engine's DME to save your engine. When you add MORE fuel, you compound the issue. To a point, the unburnt fuel in the combustion chamber can be cooled by the "cool" spots (anything metal -cylinder walls, piston head, etc). So it gets expelled through the exhaust. You run into problems when the unburnt fuel is suspended in free air away from the cool spots. It heats up and detonates. Knock sensors go off. DME adds more fuel. More unburnt fuel is suspended in free air away from the cool spots. It heats up and detonates. Knock sensors go off. DME adds more fuel. More unburnt fuel is suspended in free air away from the cool spots. All the while, your AFRs will read rich and "safe".

In your case, the engine is still within a good spec for the piston to valve clearance which goes a long way to prevent detonation but its still not good to rely on knock sensors...if that's what is happening. In my case my engine builder sucked. There was too much clearance between the piston head and valves because they used a ghetto ass thicker head gasket. So my car was leaning on the knock sensors by the 3rd session, felt totally gutless by the 4th session. This increased the harmonics in the rotating assembly which vibrated my VAC oil pump shaft loose in 5 months.

I'm willing to bet that's what is going on inside of your engine at the track. If you did a post track dyno, I'd bet that you are below stock power levels.
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Last edited by bigjae1976; 01-25-2013 at 01:37 AM.
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