I have 502 with Thunderbolt IV ignition, and I have 2 ignition modules on my boat just in case 1 goes out.

Just for the hell of it I tried the other 1 and I lost 300 rpms at WOT. I couldn't understand why until I notice 1 advanced at 22 degrees and the other advance 20 degrees. The 1 that advanced at 22 gave me 5000 rpm at WOT the other just gave me 4700 rpm.

I would of never guess that 2 degrees of timing there would be so much difference. The total advance with the 1 module was 34 and the other was 32.

Could 2 degrees really change my WOT rpm that much? I just was amazed that what a difference 2 different modules can do. Not just better WOT rpms, but just the way the boat pulls from midrange to WOT. By the way this is on my new 502 crate.

You saw it with your own eyes If you use the other module just add 2* to the initial timing. Don't forget to remove the extra 2* when going back to the 22* module.
All adjustments being equal , on my twins , I've played with the timing of one engine or the other to get the tachs to match at WOT .

What base timing are you running?

vandeano, Would you care to trade your 20 degree module for a 24 degree module??

My base timing is at 12. The total advance is 34 with the 22 degree module. And obviously the 20 degree module total advance is 32. I was reading my Dennis Moore Performance book and there is a chart showing all the different ignition modules and the difference in degrees each one has at a given RPM. I always thought they where all pretty much the same other then the total advance. I just cant get over how much more power I feel from mid to WOT. The one that gives me the biggest bang has the # V8-HP 22R on the module. The other one I cant really see the # other then it has 20R on it.

TC the problem is the 20 degree module is mounted on the distributor. THe other module is the type that is mounted on it own plate. I happen to buy that one on E-Bay for $40 Look on E-Bay I see them all the time selling between $25 - $75.
If I happen to find one I'll let you know.

vandeano, I would appreciate you keeping an eye out for a 20 degree module. I have been watching on ebay for one but have not seen one lately. Thanks!!