Merc 7.4 330 to 502 Ignition change over Confusion.
 

I have been asking many questions, and done many searches, and am still a little lost. Hoping to get all the info and have it in this thread so other people can find it all in one place without googleing other sites and forums. I keep getting answers that dont match and dont want to have a gear wearing problem in a new motor. I know i need a Melonized gear, but do i have one already??

My problem is that my 454 was a gen VI in a 1998 baja and im pretty sure the motor is a 1997, i know the motor has never been out. Engine ser. OK199057 casting 10237297
comes up as a 1996-1998 L29 Vortec 7.4 large oval gen VI. The motor may or maynot have had a rollor cam. Its hard to tell but the fieche and even then i know merc does weird thing with useing olf motors. When did they start running roller cams. Any way to cross the merc cam number to see what the old cam is in a GM number?

Now when doing a 502 crate marine motor, what do i need to do about the ignition. I have the Thunderbolt V ignition i believe, there isn't any info on the distrubitor, but i do have the Knock sensor module on the side. Does the Thunderbolt IV disttibutor have a knock senor? or just the V.

What needs to be swaped?
-rev limiter wrong for the new 502?

-ignition timing curves wrong?

-Distributor gear, need to be swap as it may not be a Melonized gear. WILL the GM melonized gear fit the merc shaft? gm number 10456413

-What is the distrubitor shaft size?

-does the knock sensor need to be disabled, and what ignition module should be run with a 502 415 stock with 800carb and emi exhaust.

-What should the base and overrall timing be set at?

Really want to keep the stock distributor, dont have anymore cash for MSD setup, but do want do do this right the first time.

The distributor will fit and work.I did the same thing but i'm using Thunderbolt IV module and dizzy.Base timing will depend on what module you use.Usual is a 24 degree so base timing would be 8 for a total of 32.
You should never check timing at base or idle anyway it should be done at maximum advance.Usually about 3000RPM.
Don't have an answer on whether the Thunderbolt 5 module will work.

just so you have an idea on what you are working with, Here is your engine info:coolcowboy:

ENG serial number: 0K199057 Model number 474B110KS 1997 MERCRUISER TB5, W/PS, TWOPCEX, WORO, GEN6 7.4L BRAVO
Engine Manufacture Date: 04/17/1997

Thanks, i'll keep info on the motor.

I think my stock distribitor will work, gear is harderned, but i have decied to just for cheap insurance do a GM melonized gear on the merc.distributor. Removed the old one and the shaft was .491 so i'm good there.

Now just fiquare out way around 4800 rev limiter with out going msd and crane.