ctadams21

Just checked the modules on my T-bolt IV ignition (on HP500 carb motors) and the are different from side to side. Port side has v8-22 and starboard has v8-22a which may explain why the two motors never ran in sync.
I guess the advance is coming in sooner on one than the other. Which would be the best to keep and which should I swap out?

CTA

excursion

I did not know that there were different Thunderbolt IV modules, I have three of them and going to test this weekend with props and rpm's. I looked at all of mine and they all say
V8-24, but the number in front of that is different, What does this mean?

Griff

HP 500's should have the V8-HP module.
20* of advance all in by 3000rpms.

ctadams21

Thanks for the info.
Are these available from Mercury. Thought I read that some Modules were no longer made.

Griff

All are still available, as far as I know, just some of the part #'s have changed.

I have 2 v8 22 modules in the book I have. Neither one has an "a" on it though, so I'm not sure which module is which.

One has all 22* in @3500rpms and the other has 22* all in @ 4500rpms.

excursion

What is a V8-24 module for? I am going to try these on my HP500's, to bypass the rev-limiter's.
Also I have been told that they come in on the advance earlier and idle smoother. Any truth??

Griff

V8-24's are used on most mag engines.

The won't change where the rev limiter comes in. The rev limiter is a separate component.
You will have to retard initial timing to compensate for the addl advance and may not idle as well. Also full advance does not come in till about 3700rpms.

custommarine

The Mercury service manual for V-8 GM engines has a graph with the advance and RPM for the different boxes.

excursion

I dont have a rev-limiter any more, it was taken out when I did away with the Thunderbolt V ignition box. All I have hooked up now is the TB IV module, which does not have a rev-limiter in it.

What is the diffference between the V8-22 & V8-24 modules?

Should I try and find the V8-22's , would they work better?

Dave_N

Don't have the graph for V822, but here are the V824 and V820R.