I have noticed on my timing light that when I have all my timing in at 2800 RPMs plus it reads 32*, but in the main spark table the value I have at 2800 RPM plus is 30.23*. The main spark table is the only table I use for spark and I have the base timing set at 8* BTDC in the constants. I have that matched to the distributor. So I was wondering why it's off by two degrees but I might have found out. I was looking at the engine build sheet and see the cam was installed 2* advanced. So if you guys agree this is the discrepancy would I correct it by going to 10* base timing in the constants and leaving the distributor at 8* or the other option, leaving the 8* in the tunes base timing constants and moving the distributor to 6* BTDC??
I was just looking at the cam info on Comps site.
http://www.compcams.com/Company/CC/c...?csid=176&sb=2
I think its saying I should have 6* base timing? If thats correct should I set the constants base timing to 6* and the distributor to 4* BTDC being the cam has been installed 2* advanced?? Thanks

 

Spark timing (SA) and cam timing have nothing in common.

As for the SA being off see this thread:

http://www.thirdgen.org/techboard/di...ncy-table.html

Explains more then you may want to know.

Although, there can be other modifiers to the commanded SA. Check what the ALDL link has to offer for SA.

RBob.

 

Its not due to the cam timing position.
The reading with the light at idle (8*) puts the firing of the spark reletive to the rotation of the crank irregardless of where the cam is.
My guess is that there is a bit of vertical play in the distributor shaft.
The gear may be pushing upwards harder at high RPM than at idle adding the 2 degrees. (at least I think that is the direction it will go)
I was just pondering the excess movement looking at my severely worn bronze gear on my sloppy distributor.
The SA table can only command what is wanted, there is no way of verifying that it is what you physically got in relation to the crank without the timing light. Not without crank/cam sensors to indicate the position to the ECM.
IIRC the SA can only calculate from the last firing position and that is only reletive to the pickup coil in the distributor itself, not the crank.

 

thanks guys, i'll just verify timing with the timing light as the true timing not the SA table.