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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Tracking, Autocrossing, Dragstrip, Driving Techniques > JB4 Map 6 users - check in here



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      09-18-2013, 09:51 AM   #1
ashmostro
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JB4 Map 6 users - check in here

I recently started playing with Map 6 with the desire to achieve a balance between power and controllability as one transitions into throttle as you're winding out of an apex. At my last track day, Maps 2 and 5 which I had been running on the street were way too touchy as the car dips into boost from vacuum very agressively. It's entertaining on the street but not very delicate at the track.

So I started playing with map 6 by doing a pure linear map maxing out at 5000 rpm, starting at 9 psi at 1500. In all cases I have taper down to 12 psi at redline starting at 5500.

Well, since I have a 335is, the DEM boost targets are higher than 9 so that was meaningless that is until Terry came out with ISO 26.5 which allows me to tell the JB4 to ignore DME boost targets or not! So cool. BUT, then I found out that there's a risk of pulling a boost leak code as the DME will could see boost levels below target and freak out. As a result, I raised my starting boost level to 11 psi at 1500 to prevent that from occurring. I could do a back end flash but I haven't gotten around to that yet.

Anyhoot, I loved the low RPM control and mid to high RPM power (reminds me of the feel of the S65 albeit with 2k less revs, but still...) But then I felt that the way the power came on was too peaky and sudden, kind of like a huge ST Supra. I don't like that.

I thought about that some more and realized that what might be happening is the effect of rising RPM contributing to an accelerating power curve rather than a linear one. To offset this, I adjusted the boost curve by thickening it up at low-mid RPMs and tapering it back to the linear curve before 5000.

Tested the map the last two days at it feels GREAT in spirited canyon carving. Can't wait to try it out on the track.

Open to thoughts, comments, suggestions, etc.
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Last edited by ashmostro; 09-19-2013 at 04:54 AM.
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      09-18-2013, 11:09 AM   #2
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Most of us who circuit race with this car use flash tunes.
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      09-18-2013, 11:25 AM   #3
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Thanks for the input.
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