Mercruiser Thunderbolt IV Ignition Module
 

I am looking for a pair of Mercruiser Thunderbolt IV Ignition Advance Modules. Specifically the V8-24 modules, the old part number was 15248A1 and the replacement number is 15248T01. They are embossed (heat stamped) with V8-24 near the connector end. If you have a lead on some, please PM me. Not needing new, would prefer used, I am running some test and was wanting to try before buy.

Send a PM to Sick Stinger. I would bet he has some.

The V6 module has 2 degrees more advance. You can use those, but just make sure you account for the diff.

Huh????

A V8-24 has 24* of timing advance and is at full advance around 3500rpms.
A V6-14 has 14* of timing advance on a V6 engine and only about 10* of advance on a V8 engine and is at full advance around 1800rpms on a V8 engine.

This may help.
https://cimg4.ibsrv.net/gimg/www.off...63a8e4d7bc.jpg

Alternative facts Gary. I know you’re trying to peddle your stash of diesel ignition modules. Busted!

LOL, That's the chart I posted on OSO about 15 years ago. Its from Dennis Moore's BBC Marine book.
And the first V8-22 column is actually a V8-22A that came on the 525SC's.

Yea but mine are wireless.

Sorry Griff. I have no excuse for it, and have never substituted a V6 module but worked with a guy who swore they were the hot ticket and I never paused to do the math in my head to see how backwards his idea was. I vomited out bad info. Thanks for calling me on it.
Every Tbolt 4 motor I've played with I just set them at 36 degrees at whatever rpm they stop climbing and forget about them. I do like to use a piston stop and timing tape to make sure the TDC mark is accurate, especially on motors over 10 yrs old and anything that has been backfiring.

No need to be sorry:lolhit: I know you give out a lot of really good detailed info on a lot of topics.

The V6 modules do work well in some cases, especially on big cam engines with idle issues and on some blower engines.
They are pretty much one step away from running the timing locked.
IMO, the V8-HP modules have the best timing curve for most performance apps, but they are getting hard to find.

[QUOTE=Griff;4717862
IMO, the V8-HP modules have the best timing curve for most performance apps, but they are getting hard to find.[/QUOTE]
So would the V8-24 be choice #2?

I like this module, ran it on a couple carbed 502's..........set base timing @ 8* all in @ 32*

The V8-22(second column) would be my second choice and then V8-24 closely behind it.
Its nice to be able to run a little more initial timing to smooth out idle.
The V8-24 will still work fine in most cases though and was probably used the most by Merc.

Absolutely surprising what just an extra 2*-4* of idle can make on some motors with a little extra cam and/or aluminum heads have, especially for cold start. Typically makes non choked carbs start easy too.

PM sent to OP. I'm using the V6 modules on a pair of bored out 454's with 250's on them. I'm getting a total of 8* advance and all in at around 2500rpm

I'm thinking of V8-24 for my 502 w/731 cam and air gap intake 800 holly stainless Gen III exhaust (all else stock). Any thoughts?

I have a v8 hp module...if ur intrested

I would use a V8-HP. You're building an engine very similar to an HP500 and they used the V8-HP

Sorry, I have not been keeping up with my own post. Been busy fixing house issues, hot water tanks and humidifier. Hot water tanks done for now and parts on order for the Humidifier. Here are my thought on the timing for my particular set up. Engines are bone stock 502Mags with QJ Carbs. I am running 34 degree total timing with the stock 20 degree modules. Issue I see is that these are not full in until 5000RPM. Original thinking by Mercruiser back in the day was these engines have to run everywhere and good gas was sparce and engine life could be reduced with crappy gas and tooo much timing. I am not concerned with the gas issue. I run clean gas with no alcohol and usually higher than 87 octane. Never had issues with fuel, so that is out of the equation. I have so much initial advance, that engines crank hard and slow when warmed up. I also am wanting to see how engines will work with all in advance at a lower RPM.

What is your normal cruise RPM now? Would be curious to see what your EGT's are currently at normal cruise speed. Since you are bone stock the 24's should work out well for you with taking some initial timing back out.

The V8-24 module is full advanced @ 3750

March timeframe I will have one (V8-24 Gen 1) for sale if you do not get one before. I will be taking off of my boat then.

In that case, I'd use the V8-24's as you are thinking. Not sure why Merc used that 20R module on 502mag carb engines. Having 14* of base timing really should not make it crank slow though.

I'm finding looking up the part number (BAM) that the module was used for only the 502 inboard between 93-96

https://www.mercruiserparts.com/1524...-mcm-s-b-09-14

502 Mag, 8.2L, 600SC & 800SC V8 20R 817509T 817509T 817509A10
as per PPT site.

3000-3500RPM. If the water is has a slight chop and the cruisers are docked, which usually means during the week, I will bump it up to about 4000RPM.

Thanks to everyone's input. I have modules coming in the mail and should be able to do some testing in Mid-March. Big thanks to Ramos45 for the parts.

Questions regarding a Thunderbolt IV model# 3L04A V6-22 installed my V8 engine?
 

Questions regarding a Thunderbolt IV model# 3L04A V6-22 installed my V8 engine?
I have a 1994 Chaparral Sunest 220 boat with a GM 305 5.0L V8 engine.
I recently changed out the spark plugs, wires, distributor, and cap and noticed I have a Thunderbolt IV model# 3L04A V6-22 ignition module in my boat. I never knew.
Note: I checked my timing last year (before I noticed this) and it was at 8 degrees BTDC.

• Should changed this out the ignition module for a V8 model or will this model# 3L04A V6-22 work?
• Should I adjust the advance? to what?

Any recommendations to get the most power out this boat are welcome?

Thank you,
Captain Cory