No idea.
In ancient times, 2003 or so, this boat had 502s installed that had were rebuilt by Jo-Mar and had some mild modifications (cams and roller rockers), and was supposedly tuned by Tyler Crockett. The hour meters that are in the boat now, have date stickers on the back from around that time period. However, the motors were painted blue back then, whereas they are now black (but the blue paint is still visible where the black has been scraped away in spots). I have no knowledge of what was done to the motors between roughly 2004 and 2018.

https://cimg9.ibsrv.net/gimg/www.off...67764663b5.png
Looks like at >3000 rpm, timing gets pulled out. Drops from high 30s to 27-28 degrees from 3100-4800 rpm.

When a mefi3 tune is stock, at 3600 70 map it has 34 degrees, at 100 map it has 20 degrees, at 4800 at 70 map it has 35 degrees, at 100 map it has 26. at 5200 at 80 map it has 35, at 90 map it has 32 at 100 map it has 29. since most run at about 94, 95 map at wot, they blend between the 90 map and 100 map table.most likely those high numbers you saw in bottom were the 70, 80 map numbers that meant you were at part throttle, fwiw, Smitty

Correct, those numbers were at part throttle. Does the above info you provided also hold true for an MEFI 1 system?

For the most part yes. As you approach the 90-100 kPa arena at WOT and 4800-5200 rpm (top of the MEFI 1 rpm band) timing will roll back a little. I don't have the big block numbers off hand but it does it for the small block 350 of that era. You just want to be careful with timing getting back too far at WOT as it elevates exhaust gas temps by delaying the combustion event. Valves and exhaust seats don't like this. The motor will lay down on the big end as well. I've run some VP110 and played with timing in the 36-38 degree range and got no extra fun out of the motor. 32-34 seems to work optimally with appropriate fuel delivery and AFRs in the 12.5 ish zone.

Another data point today.
I swapped props. Prior props were Hydromotive Quad IV 4 blade 26P, port side had Lab markings on it, stbd looks fairly stock. Solid Hub. As a reminder, 72mph at 4500-4600rpm indicated (or 4700-4800 actual).
New props Bravo 1 24P, appear to be stock, Flo-Torq hubs.
Test run today 68mph @ 4700 rpm indicated on tachs (so probably 4800-4900 actual). So Dropping to 24s got me a little more rpm but less MPH.
Boat feels stuck to the water at top end. I know the pad bottom Dominators don't like a lot of trim but it just feels plow-y. Cruise is great.
Tempted to try a pair of Mirage Plus as I've liked them on other boats I've had.

Another bit of data that I've neglected to mention:
Some prior owner had the aft 2' or so of lifting strakes removed from the hull. Presumably this is when the boat had some big blower motors in it, as evidenced by the now blocked off thru-hull water pickups when some other kind of drive was also installed.

Any thoughts?

Follow-up:

In desperation/frustration, I studied the Merc parts catalogs a bit. From what I can see, no MEFI1 system with the old Keihin injectors ever was equipped with 43psi fuel pressure regulators, even if Cool-Fuel 2 Equipped. Up until now, I'd been going with the presumption that a Cool Fuel 2 system utilized a 43 psi fuel pressure regulator.

I decided to swap the 43 psi regulator for the 36 psi regulator, on the starboard engine only (because the port side is impossible to get to without pulling the header and other stuff). On a test run yesterday, I got about 200 rpm more out of the Stbd engine than I've seen before, AND, that sag in power past 3/4 throttle was gone on the Stbd engine if I advanced that throttle alone and left the Port engine at 3/4.

Seems to me that the sag in power past 3/4 throttle (which coincided with an injector pulsewidth of >9.0msec) was due to a rich condition, not lean as initially thought.


So, one of my winter projects will be installing a 36 psi regulator on the port engine.