Alpha N vs. speed density

sc91183 · Post by **sc91183** » Sun May 14, 2006 3:56 am

My 1983 Porsche 911SC with MS II version 3.0 running software version 2.25 runs much better in Alpha N mode then speed density what would the reason for this be? The car has stock pistons,cams and ignition but aftermarket TWM independant throttle bodies ( 46mm ) and 30lb. per hour injectors. Just curious if others have had similiar results?

muythaibxr · Post by **muythaibxr** » Sun May 14, 2006 5:56 am

ITB's are hard to tune on Speed Density. You have to create a table that has most of the MAP bins from 80-100 kPA (on my car half the MAP bins are there). Alpha-n allows you finer control since it's based on the amt of throttle movement and not vacuum (ITB's don't hold vacuum well once open).

I actually wrote some code to test an idea I had about tuning ITB's. I noticed that it was hard to control the AFR with nothing telling the MS engine load at low throttle positions, and I noticed that above about 20-25% throttle position, It was hard to keep the AFRs consistant.... meaning I'd be at 98 kPa, and move the throttle, and while the MAP stayed the same, the AFR would change.

To help fix the problem I saw, I added some code that lets me run a SD table at low throttle positions, and an AN table above that. I have yet to tune it yet though, so I don't know if my idea is good or not.

To answer your question though, most people think it's easier to tune ITB's with alpha-n.

sc91183 · Post by **sc91183** » Sun May 14, 2006 10:33 am

I appreciate the reply. I am a newbie to MS and really don't know the workings very well but I'm learning. The guy I purchased my kit from runs his Porsche with ITB's with a speed density setup but his map/baseline setup would not make my car run very well. I tuned it and basically gave up and on a whim I did a MAP with Alpha N and she liked that so I basically stumbled on a setup she liked.