87TurboIroc
New Member
- Joined
- Jan 30, 2012
Ok now I'm a bit baffled. Decided that I needed some fun tonight and threw the exhaust back on the car at 10pm.. and the rocker arm that I had off to check the cam lift and timing. For my fun, I decided I would 'assume' that the timing in the MS was higher than what was actually happening at the distributor.
My butt dyno says the car would need about 12 degrees of additional timing to make the power it should be (this assuming that everything else about the engine was right but the timing was wrong). In the interest of preserving the engine I cut that in half and added 5-6 degrees of timing above 180 KPA between 3700 and 5400 rpm. Drove the car around, no detonation at all. Felt slightly better but I've been fooled before. Next I pulled over and added another 2 degrees of timing. This time I smoothed in the additional timing below 3700 and also between 100 and 180 KPA as well. The car seems to be coming alive now. It's not amazing yet but I actually felt a little impressed at the performance. This was with about 14.5 psi on the gate.
This puts me at "28.2 degrees" of timing at 4600 rpm and 15 psi. To me this seems excessive on 93 octane and 8.6:1 compression. Now the more interesting part... I looked at my data log expecting to see it a bit lean because of the additional timing. Instead I now show rich, very rich in fact. As rich as 10.2 and averaging about 10.6 in during boost. It seems some strange things are at work here.
Possibly it's been misfiring/not burning all of the fuel due to extremely retarded timing, which manifests itself as a lean condition and was addressed by adding more fuel... and now the correct amount of timing is burning all of the fuel, but the excess fuel is now creating a rich condition. With an AFR of 10.2-10.6, this could also be padding the timing a bit and preventing detonation. I'll have to be careful as I lean the tune.
The next thing is... if the above is the case, how could it be that 23-25 degrees is no where near enough timing at 15 psi? I mean to the extent that it would generate a misfire or unburnt fuel situation.
The only clue I have is in the setup of my megasquirt. Instructions for connecting it to HEI state to set the ignition trigger to 'rising edge'. My car will not run correctly at that setting, so it is at falling edge. In theory, this should be ok as long as your idle timing table matches a timing light, but perhaps triggering off the falling edge exponentially generates a late timing error as RPM increases? Not really sure how to verify my high rpm timing other then standing over it on the dyno! Not really what I like the thought of doing.
So the bottom line is it is responding 'ok' to additional timing. Once I get the fuel back to 10.9, it should make some more power. Will it be enough is the question.
My butt dyno says the car would need about 12 degrees of additional timing to make the power it should be (this assuming that everything else about the engine was right but the timing was wrong). In the interest of preserving the engine I cut that in half and added 5-6 degrees of timing above 180 KPA between 3700 and 5400 rpm. Drove the car around, no detonation at all. Felt slightly better but I've been fooled before. Next I pulled over and added another 2 degrees of timing. This time I smoothed in the additional timing below 3700 and also between 100 and 180 KPA as well. The car seems to be coming alive now. It's not amazing yet but I actually felt a little impressed at the performance. This was with about 14.5 psi on the gate.
This puts me at "28.2 degrees" of timing at 4600 rpm and 15 psi. To me this seems excessive on 93 octane and 8.6:1 compression. Now the more interesting part... I looked at my data log expecting to see it a bit lean because of the additional timing. Instead I now show rich, very rich in fact. As rich as 10.2 and averaging about 10.6 in during boost. It seems some strange things are at work here.
Possibly it's been misfiring/not burning all of the fuel due to extremely retarded timing, which manifests itself as a lean condition and was addressed by adding more fuel... and now the correct amount of timing is burning all of the fuel, but the excess fuel is now creating a rich condition. With an AFR of 10.2-10.6, this could also be padding the timing a bit and preventing detonation. I'll have to be careful as I lean the tune.
The next thing is... if the above is the case, how could it be that 23-25 degrees is no where near enough timing at 15 psi? I mean to the extent that it would generate a misfire or unburnt fuel situation.
The only clue I have is in the setup of my megasquirt. Instructions for connecting it to HEI state to set the ignition trigger to 'rising edge'. My car will not run correctly at that setting, so it is at falling edge. In theory, this should be ok as long as your idle timing table matches a timing light, but perhaps triggering off the falling edge exponentially generates a late timing error as RPM increases? Not really sure how to verify my high rpm timing other then standing over it on the dyno! Not really what I like the thought of doing.
So the bottom line is it is responding 'ok' to additional timing. Once I get the fuel back to 10.9, it should make some more power. Will it be enough is the question.
