Re: 262 Vortec V6 timing issues, need some smart folks to help. sorry a bit long and technical.
Cameron, you will want to educate yourself on Gasoline Marine Engine Ignition Timing, and what and how timing affects performance, and the risks of too much TA (total advance)!
As Mark said, "the marine engine won't tolerate blind tuning adjustments"..... and I'll add "Particularly incorrect ignition timing adjustments"..... and even more particularly, excessive TA.
You mentioned "Detonation"! Good for you, because that 4.3L uses the full dished piston. Not a great combo for marine use.... and especially if you are considering TA numbers in the range of 32/34 degrees!
If gone un-checked, detonation is one the worst enemies of a gasoline marine engine!
Also, it is not always audible enough for us to detect by ear alone!
Again....."the marine engine won't tolerate blind tuning adjustments".
I would agree that the Thunderbolt IV module is a bit on the conservative side with regard to TA.
A mechanical system may be a better choice, but ONLY if you can find an ignition curve chart for this exact engine in this exact jet pump scenario. Then you could plot a new curve, and not worry.
Question: is the Thunderbolt IV ignition one that must be put into BASE mode in order to set BASE advance?
I'm not a M/C guy, so don't know the answer to this (see the appropriate M/C OEM manual for this procedure).
Cameron, you mention 22* total, and then you mention 32* and 34* total, but make no mention of RPM.
When we start playing with ignition advance numbers, there must always be an RPM associated with spark lead in degrees BTDC......... IOW, at which crankshaft degrees BTDC this advance comes on.
It is critical to know the RPM at which the TA will occur!
Furthermore, the greater TA #'s that we can toss at a car SBC engine, will not work with a Marine engine. You'll burn some nice holes in the piston tops if you do.
So I'd suggest NOT using any ignition advance curves, or any ignition TA numbers, etc, that pertain to automotive..... they simply will NOT work!
If this were mine, I'd try to get my hands on an ignition curve chart/timing specs that work well for this engine/jet pump application. It may be considerably different for this engine being used with the jet pump -vs- an I/O application.
Rick ... aka Ricardo
28' SDN F/B w/ twin Volvo Penta 5.7L DP's