Carrera 3.2 DME adjustment question
11-30-2001, 03:21 PM
#1
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Carrera 3.2 DME adjustment question
The following thoughts began swirling around in my brain after reading an earlier string that ventured into the area of 3.2 Carrera DME adjustments.
Here's what I understand from the post: there is a rotary switch on the DME with a number of detent positions corresponding to various fuel delivery increases (+6%) or ignition advance (-3 degrees). Any change in the fuel setting would really only effect full throttle performance, because at lower throttle positions (<75%) the O2 sensor would be correcting the fuel mixture anyway. But at some point over 75% throttle, data from the O2 sensor is overridden and the chip then looks to its preset maps. My car is an '84 California model, which ought to have some pretty conservative maps.
Here's my question. Along with a top end job (shot valve guides) my car was recently modified with C2 cams, ported heads, lightened clutch, dual outlet muffler and a tad more compression. But I haven't chipped the car yet and I'm not going to chip it for a few months while I spend money on other people for a change (holidays). So, for the time being wouldn't my full throttle performance benefit from tweaking the DME switch? Based on my mods, I'm thinking both 6% more fuel and 3 degrees advance. Can anyone with some knowledge on this make a suggestion?
Thanks in advance!
Here's what I understand from the post: there is a rotary switch on the DME with a number of detent positions corresponding to various fuel delivery increases (+6%) or ignition advance (-3 degrees). Any change in the fuel setting would really only effect full throttle performance, because at lower throttle positions (<75%) the O2 sensor would be correcting the fuel mixture anyway. But at some point over 75% throttle, data from the O2 sensor is overridden and the chip then looks to its preset maps. My car is an '84 California model, which ought to have some pretty conservative maps.
Here's my question. Along with a top end job (shot valve guides) my car was recently modified with C2 cams, ported heads, lightened clutch, dual outlet muffler and a tad more compression. But I haven't chipped the car yet and I'm not going to chip it for a few months while I spend money on other people for a change (holidays). So, for the time being wouldn't my full throttle performance benefit from tweaking the DME switch? Based on my mods, I'm thinking both 6% more fuel and 3 degrees advance. Can anyone with some knowledge on this make a suggestion?
Thanks in advance!
11-30-2001, 03:39 PM
#2
Hugh,
I would suggest you take the adjustments in stages. First, try 3% fuel increase and see how that feels. Then move up to +6% fuel, etc.
I have my '84 911 set at +3% fuel and that's fine for me because the car runs great, YMMV.
Bruce
I would suggest you take the adjustments in stages. First, try 3% fuel increase and see how that feels. Then move up to +6% fuel, etc.
I have my '84 911 set at +3% fuel and that's fine for me because the car runs great, YMMV.
Bruce
11-30-2001, 05:49 PM
#3
And I would add try to get some sort of objective quantitative measurement of the performance at each setting. I have heard stories of people adjusting/tuning/upgrading their cars, and then swearing they were faster/stronger. In the end they found out that they had, for instance, hurt low rpm power and left high rpm power the same so the car felt faster by the seat-o-da-pants-o-meter. So this can be a tricky thing without some sort of measurement.
Just one other thought. Doesn't ignition advance lead to *potential* detonation? So even with your mods if you advance the timing with the CA gas quality and Octane going down in a car that's not knock sensor equipped it could lead to problems. I'm not sure of this, but throwing it out there in case some of the wizards are around to corroborate or dispel.
Just one other thought. Doesn't ignition advance lead to *potential* detonation? So even with your mods if you advance the timing with the CA gas quality and Octane going down in a car that's not knock sensor equipped it could lead to problems. I'm not sure of this, but throwing it out there in case some of the wizards are around to corroborate or dispel.
