Two different modules
 

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

Re: Two different modules
 

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?

Re: Two different modules
 

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

Re: Two different modules
 

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

Re: Two different modules
 

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.

Re: Two different modules
 

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??

Re: Two different modules
 

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.

Re: Two different modules
 

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

Re: Two different modules
 

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?

Re: Two different modules
 

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

Re: Two different modules
 

Best I can tell I would be better off to have timing all in by 3500 as oppossed to 4500. Now it's just a matter of finding another module to match my the one I have (v8-22). Guess I'll end up putting the v8-22a on ebay......

Re: Two different modules
 

To confuse matters even more, Mercury has a V6 module for big blocks as well. The module can be bad and the engine will still run. You may lose top end. If you have twins it will be obvious over 4000 rpm, not below.

Re: Two different modules
 

They won't idle smoother. You will have to retard initial timing and they may idle worse.

Re: Two different modules
 

Here is a chart with the advance curves for most modules. There are two V8-22 listed. The 22a has the advance curve that doesn't go into full advance until 4500rpms.

Re: Two different modules
 

On my 502 mag carb. engine I ran the v-6 module which only has 14 degrees of advance. This lets you run more initial timing without to much total advance. This made my engine idle better and have alot more bottom end responce. You could tell a big differance in how responsive the engine was.

Re: Two different modules
 

A V6 module has 14* advance on a V6, but only about 10* advance on a V8 engine.

Re: Two different modules
 

Thanks Griff, I think I'll try to find a 20* or 22*. Not much out there though. My next thought is to try to sell the T-bolt stuff and drop in some DUI distributors.

CTA