What Im wondering is when you (if you) start with an unknown untimed engine combo where do you start

I have read here someone recommended unplugging the timing set connector. Measuring manifold vacuum while adjusting for the most vacuum. Then dialing in the timing light to see where the timing is at that vacuum. Then after resetting base timing, data log to see what cell to plug the measured deg of timing into.

How correct is this info?

If the idle cell is the starting point, how much do *you* adjust the surrounding cells, and why.

I guess what Im asking is, is there any specific strategy or pattern I should be looking for to start my table

Would some of you share *your* process for adjusting the timing cells line by line and row by row.

Thanks in advance....

Pun intended

Jason

 

As far as idle I looked at the VE cell it idles in and then made the surrounding cells the same should it wander into that cell(s). Not sure if your tune uses a special idle cell. then I set the "constant" for idle that I believe is determined by <RPM to that same SA. When I started I think my SA for idle was 24? I experimented changing all the above at 2 deg increments(reduced) and determined idle quality without regard to VAC although the VAC-MAP did change. I ened up with 24 as being the final choice.

As far as cruise SA I was told the max MPH possible for steady RPM/load is the way to look at SA. I used a stock L03 SA table and only adjusted the WOT areas. I am at 36 deg SA for WOT. I believe I did get knock counts at a specific RPM/MAP around 3600 rpms with 92 octane and took out 2 deg there and surrounding cells smoothened that SA table and that was it. I ran 89 octanne and no reoccuance of KC.

 

Y'know, I've never really got a clear awnser on the preffered method of spark tuning without a dyno. Without a direct method of seeing your results it's really a crapshoot, even with a good tune the afr can wander a good bit. Grumpy used a combination of egt's, oil temps and mph to get a working estimate of where timing should be. In his words- you really need to do the zen thing and look at what the motor wants.

Where is it 'happiest'? You need to make sure you've got fueling damn close before you can go after spark. Then you can tell with relative ease if the engine's happy with the spark it's got. Does it feel sluggish or rough? Probably not enough timing. Does it feel like you're running up against a load or 'laying down'? Probably too much. I 'feel out' where it wants to be first, then look at other things to dial in where it's running best.

 

BL you make a great point. too much timing and the heat of combustion is absorbed by the piston and the engine and oil. Too little and it appears in the headers as increased EGT. One need to do a dance between max power and melting parts. Years absck I ran EGT on my 2 cycle but never advanced timing from stock even though other racers did so. 2 deg as I recall. My EGT just allowed me to fiddle with A/F. They always saw max power is just B4 you burn it down.