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As some of you know, I have a 1991 502 with a procharger i have a thunderbolt IV ignition. The thunderbolt on there is a v-6 14. It is off of a v6 and is supposed to be used for better low end on the 502(this has been confirmed by 3 diff. marina's) My problem is that I am running really flat on top, any more than 3/4 throttle (4200-4400 rpm) the power and rpm's drop off. If I back the throttle off it starts to run strong again. I am already into my secondary (I think). After looking over some fuel issues, I checked my timing. I have 16 deg at 1200 rpm, which is what I am supposed to have with this v-6 unit on my 502. The unit is supposed to advance 14 deg. well at 3500 rpm I am only at like 20 or 21 deg. I even rev the motor higher for a sec and it still showed me no gains in advance. The way I am checking my timing is with a timing light with a retard dial. I turn it to 16 deg. At 1200 rpms and the timing light shows the balancer mark hitting right on the 0 deg mark on the timing chain cover timing marks. But when I move the retard dial on the timing light to 30 and run the motor at 3-4k I never see the timing mark on the balancer. As I start to turn the knob down in deg, I start to see the balancer mark again. and when I get to 20 or 21 it is lined up with the o deg timing chain cover marks again. If I am doing all of this right, and I think I am. I am only getting like 20-21 deg of total advance, or am I the only thing retarded here? I assume if I am truly only getting 20-21 deg of total advance that this would make me very flat up top. Any advice would be great!
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Don't know much about the thunderbolt, but you should be around 28 to 32 degrees total, all in before 3000 RPM
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one thing to make sure of b4 you start changing a lot of things is to check your lite to make sure its dialed in correctly. i've seen those dial types be ok at 1 setting and way off at another.
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502, I think your problem is with the ignition system. I am not positive but pretty sure the thunderbolt has a built in rev limiter plus it will limit your total advance to about the numbers you are posting. I was told that was done by Merc to us from braking the motor. Much less stress on it if the RPM and total advance is limited. If you have access to a non-marine distributor with 24 degrees of advance built into. I would recommend changing it out and see if this helps. Do not connect any parts of the thunderbolt system. With the change you should be able to set your initial timing to about 10-12 degrees and the check the total at about 3500. It should be in the 34-36 degree range.
