Hello all,

I have a 1983 Gen IV 454 mag engine in my boat now, the book calls for 10* initial timing, is that still a valid setting with today's gas with ethanol? I run 89 in it with the 10% ethanol. When I can get it, I run 100%, gas sometimes its 87 others its 89. I was thinking about bumping the timing to 12*, it definitely idles better there, I have not brought it up on plane at 12* however.

Also would any one know what the total advance is on the thunderbolt 4 amplifier Merc part # 15248T02 (current number) 390-7804A3 original number? The sticker on mine had been painted over so I don’t know if its 20 or 24* total advance. I'm assuming its 24, but we all know what happens there...


Thank you for any input

--clawless

From another OSO member, can't remember who.
Assuming you have the aluminum module (big square aluminum box bolted to the exhaust manifold)
390-9607A3=22 DEG @3500
390-7804A3=24 DEG@3750
390-957A1-20 DEG @3000
Hope this helps.

Exactly what I was looking for, thank you!


Any thoughts on upping the timing 2*? I have the 24* box, giving me 36* all in, provided no one changed it over the years, no reason to think anyone did. I feel I slight surge at around 3700rpm so I'm assuming that's because it goes all in there.

thanks!

--clawless

No reason to increase it and no gains to be had running 36* on a stock 454Mag.
The module you listed has 24* of advance. Leave it at 10* base timing for a total of 34*
That surge is probably the secondaries on your carb opening. The timing advance increases in small increments every 100rpms from 1000rpms to 3700rpms.

I'd do as stated above, but run ethanol free fuel if you have it available.

They didnt have a 454 mag in 1983.

OK ill stick with the 10*.

Unfortunately the three marinas around me only have E10, closest one with 100% is kinda far but on the way when I take long weekend trip, they are starting to get to know me

I swapped a bad 330 for the 370 of the same year range, was the 370 not considered the mag?


--clawless

370 Cyclone was made 1978-1987. Others in it's family were the 400-420-440-460 Cyclones. Does the guy got any more he wants to trade for junk 330's!!!

Ok Cyclone it is!

Sorry, by swapped I mean replaced a shot 330 with a fresh rebuilt 370. Everything transferred over except the intake. The power steering bracket had to have its holes made bigger. Also had to tweak the carb, I found the original internal setup on here I believe. This is the engine the boat should have had to begin with.

--clawless