To Advance or Lock?
 

Should a performance boat engine ignition timing use an advance or be locked at the total advance?

Dennis Moores books recommend using the advance on marine ignitions, but does not reference why many (or most) performance maring engines have the ignition "Locked" at total advance. All of the engine builders (marine performace builders, not automobile) recommend locking out the ignition advance.

I am running a 350 sbc, 9.8:1, thu-hull exhaust, 228-228/.320-.320 @.050 cam, performer RPM intake, 715 vacuum carb.

I have been running 34 degrees locked advance.

What are the pro's/con's of locking the ignition?

Are you running the stock Merc Thunderbolt distributor and ignition module?
If so, the advace curve is built into the module.
His book on the SBC has the curves and max advance listed for the various module part numbers.

By locking the distributor in at 34* you're limiting the maximum alowable avance.

At what rpm are you using to verify it's at full advance? It might be somewhere around 3000 RPM.

Remember, Dennis said not to use any more advance than is required to obtain maximum speed.

One reason is that the engine doesn't require that much advance at idle. By leading the combustion process that much you will probably have to richen the idle excessively to compensate.

Why not just do it right and have the timing optimized for idle and higher RPM running?

I am running MSD-6M box with an MSD billet distributer.

Presently I am locked at 34 BTDC (from idle to infinity).

I run locked at 30 so motor will not die when going into gear. I have tried different curves to start at higher rpm to solve going in gear problem but got tired of fighing the problem. Been locked for 2 years now & wish I had done before.

I like my motors locked mostly blower motors,,

PLEASE JUST BE SURE TO CHECK PAST WERE THE TOTAL IS ,MONTHLY

In my Drag race days ( Cars ) I used to run a crank trigger. I would keep the advance locked in at 40*. I also ran a triple step retard system to turn it back a touch as I went through the gears. It worked great. The only real problem was starting the motor while it was hot. I would have to get it cranking with the ignition off, then hit the ignition switch. But, this was a race only application. I think you would be better off using an advance system. My .02

No problem running locked. I have plenty of power. Just curioust if there are any drawbackes, like increased chance of detonation when accellerating from idle.

Seems to me if a locked timing advance was the right way to do it GM , Ford, Chrysler, etc., would have done it that way all along...

Because it works doesn't mean it can't work better if set up properly. I run 20 degrees of centrifugal advance all in by 3000 RPM.

I am hoping we can get someone that understands the physics to explain. Most marine race engines are set up locked. (especially blower engines.)


JohnJan,

That statement is correct if you do not increase compression, go to a more agressive cam, change the intake, exhaust, etc... The manufacturers are VERY conservative in their setups; in order to minimize any warranty contingencies.