BAD-HABIT

Have a 89 SBC. Running 9.3 Compression,Roller Cam with 112 dg lobe center. 218/224 duration and .503/.510 Lift. Using Edelbrock performer Intake and 600cfm carb. with L31 Vortec heads. The late model Mercruisers with the Vortec's run 8 degrees. Should I use this as a base line (Late Model Mercruiser with Vortec Heads) or should I be more aggressive..I am running the stock Thunderbolt IV ignition. My box is the early design and has NO numbers on it so I have no idea how much advance I have and what the curve is......Any help appreciated....
"Bad-Habit"

Tinkerer

The initial degrees of advance is not as important as the total advance. It should be 34 to 36 total degrees. If you have too much initial advance it may be hard to start because the starter will be fighting the early ignition. What I did was hold down the kill button untill the motor got turning over than release the button.

bobl

The Vortec heads do not require as much advance as other SBC heads. I just built a similar engine and it liked 32 degrees total advance. Power actually fell off when I tried 34 degrees. This was on 87 octane. You might be able to run a little more timing with premium though. Don't even worry about timing it at idle since you don't know your curve. Set it at 32 at about 3500 RPM and whatever the initial is, so be it.

Bob

TomZ

There should be a part number for the module somewhere on spark module. The part numbers are listed in Dennis Moore's Marine Performance books. If you can find the number on it I can look it up for you and tell you what the curve is, etc.

My module advances to 24 degrees by 3750. I set my vortec motor at 32* so I leave it at 8* at idle speed. The modules may be a tad bit different depending on whether you had a Magnum or plain-jane 260 so this may or may not apply to your setup. Generally, they get to peak advance around about that point.

Let me know what the P/N is (if the module is painted over like mine was, you can peel the decal off and you'll find the numbers stamped on the backside of the decal.

Tom

FlyFast

8 works good on my 96 vortec 350 with a edelbrock air gap and a 600cfm carb, stock merc cam and stock merc ignitiion.

BAD-HABIT

Yep....Found the numbers...Its a 24R. All in by 3750. I will run 8degrees at idle to start.....I think the factory SBC's with the Vortec heads run 9.5-1 Compression ratio. Im only running 9.3-1 so hopefully this will be a good place to start.....

"Bad-Habit"