Mercruiser Thunderbolt IV Ignition Module

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12-12-2019 | 10:21 AM

#21

F-2 Speedy

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From: Midwest & T-Rock

The V8-24 module is full advanced @ 3750

12-12-2019 | 10:33 AM

#22

GLENAMY 242SS

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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.

12-12-2019 | 01:23 PM

#23

Griff

Charter Member # 55

Joined: Oct 2000

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From: Omaha/LOTO

Quote:

Originally Posted by Helmwurst

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.

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.

12-12-2019 | 02:11 PM

#24

AllDodge

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From: KY

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

12-12-2019 | 02:29 PM

#25

GLENAMY 242SS

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

12-13-2019 | 08:17 AM

#26

Helmwurst

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From: Lake Ozark, MO USA

Quote:

Originally Posted by Knot 4 Me

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.

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.

12-18-2019 | 03:23 PM

#27

Helmwurst

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From: Lake Ozark, MO USA

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.

Last edited by Helmwurst; 12-18-2019 at 03:23 PM. Reason: Spelling

08-04-2024 | 10:54 AM

#28

Captain Cory

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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.