Thunderbolt IV Ignition - can a V6 version be used on the V8?

[troynjen]

Fast forwarding three years in the saga of first used boat ownership, I am on my third engine. I did it all on a shoe string and craigslist. Bottom line, now I have a V8 OMC (core) 5.0 Chevy on a Merc. 1.5 ratio outdrive with a 14x19 prop. Compression is > 180 on all cylinders. I took the implements off the original Mercruiser V6 and built off this block, intake, etc. I bought new parts for the items that could not be used from the V6. It has been forever in the making and I had a little help from and old mechanic that knew what he was doing several thousand beers ago so I cannot trust that it was all done 100% correctly. One of the reused items was the
the thunderbolt ignition. It has V6 stamped into it but I cannot find if this is an issue or not since it is just an amplifier. Let me know if you guys have any ideas on this one.

I put in new plugs, wires, etc., but I cannot get it to run well. It was running fine on the water 2 years ago but never over 3500 RPM and could not get the power the V8 should have had (35 MPH top speed with just me). Now that it is out and getting ready for the first summer of real use, it will start with 50% of throttle only. It runs poorly at this fuel level and below this it dies immediately. Before I had this issue I suspected an ignition problem but hung it up for the last 2 years. Let me know if you have any ideas.

Thanks,
Troy

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

can a V6 version be used on the V8?

No, you need the correct one for a V8.

 

[troynjen]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Hoping to not repeat your tag line Don

i have found two different TB IV ignitions. There is a 22R and a 20 both are for V8 but I cannot tell which. I have read that the wrong one will blow immediately so ... I want to do the job right the first time and not "blow" 200 bucks. Any suggestions? I assume one is for a 5.7 and one for 5.0 but cannot find the answer.

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Maybe you should throw some years into the equation. I know the standard 5.0 and 5.7's are using the 22, and on some MIEs and Mags they use the 24. Not sure what a 20 is. V6 is 14.

 

[troynjen]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

The core from the OMC is a 1990 (I think). I am not sure how to tell the year on the engine. The only cast characters I found we're GM 5.0L G. Took out the plugs and 1 and 6 were not nearly as black. Number 2 was really black and was wet with fuel. I expected 2 plugs to be brand new.

Will I need a new wiring harness too?

 

[Bondo]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

I took the implements off the original Mercruiser V6 and built off this block, intake, etc. I bought new parts for the items that could not be used from the V6. It has been forever in the making and I had a little help from and old mechanic that knew what he was doing several thousand beers ago so I cannot trust that it was all done 100% correctly. One of the reused items was the
the thunderbolt ignition. It has V6 stamped into it but I cannot find if this is an issue or not since it is just an amplifier.

The core from the OMC is a 1990 (I think). I am not sure how to tell the year on the engine. The only cast characters I found we're GM 5.0L G. Took out the plugs and 1 and 6 were not nearly as black. Number 2 was really black and was wet with fuel. I expected 2 plugs to be brand new.

Will I need a new wiring harness too?

Ayuh,.... How are you firing a V8, with a V6 distributer,..??

Has the guts been changed to an 8 cylinder firing reluctor,..??

The V6 module is sometimes used on forced induction motors, but Never on a naturally aspired motors,...
Not enough advance in 'em...

 

[achris]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Ayuh,.... How are you firing a V8, with a V6 distributer,..??...

My thoughts exactly....

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

I can't imagine it even running with a 6 cylinder distributor installed, and kind of assumed the distributor was one of the new items he had to put on it, while hoping he would be able to use the ignition module from the 6.

 

[achris]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

I can't imagine it even running with a 6 cylinder distributor installed, and kind of assumed the distributor was one of the new items he had to put on it, while hoping he would be able to use the ignition module from the 6.

I've seen those SBC engine running with holes in them!! If he does still have the V6 rotor wheel in it would explain why it doesn't have much power :facepalm: and he's getting funny reads on the plug firing ends.... I don't know, I've seen and heard sillier things.. This site's a great place to read about people doing daft stuff to engines.... (you more than most, should know that! )

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Yes, and I also know that you aren't going to get 3500 rpm out of a V8 with a V6 distributor in it. You would only have 1 cylinder that timed correctly the rest would be way off, and 2 of them missing completely.

I put the wrong (V6) rotor on a V8 Thunderbolt IV distributor in a V8 and it wouldn't start at all. Just backfired a time or two, almost stop the engine and all sorts of carrying on. Let alone 3500 rpm under load.

 

[troynjen]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

You are right - it would not crank. I used the distributor from the omc, new cap, new wires, v6 amplifier. I did not know at the time the amplifier needed to be changed. It ran 30 at top end and idled well so not too bad but certainly not what a 5.0 should do. It only gave isues after getting it out to finish the remodel this year.

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

You are right - it would not crank. I used the distributor from the omc, new cap, new wires, v6 amplifier. I did not know at the time the amplifier needed to be changed.

You can't hook a Thunderbolt amplifier to an OMC distributor. Post some pictures of your distributor and amplifier hookup.

 

[Glastron_V210]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

If your ignition system is stand alone (IE: not tied into a engine control module), then why not replace the entire ignition system with something like this:

http://www.ebay.ca/itm/Mallory-YLM6...r_Truck_Parts_Accessories&hash=item4d01a97746



Get a regular coil, wire it in and be done with it!



Chay

 

[troynjen]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Thanks for the lead Chay. I am not certain but I think that would bypass the momentary kill switch that enables the neutral engagement from forward or reverse. It certainly is cheaper than the amplifiers I have found.

Don, I will post some pics when I can get them in daylight - this Tuesday at the earliest. In the mean time, thanks to you guys I know for sure I need a new amplifier. Now the challenge is to find the right one. I found a list of engines and the recommended part for the amplifier. Based on other forum topics my 14093627 is a 87 - 91 305. The list has three different part numbers for the amplifier. They are: 15248A 1, 15899A 1, 805361T 3. Any idea which one I need? The difference on the list seems to be TB IV, IV (2) or IV (1), respectively.

Also, I believe I have determined the proper gear ratio on the Alpha one should have been 1.65 and I put in a 1.5. The 1.5 was only used on the LX version - I cannot tell if this is an LX or not. Any suggestions on proper identification. For a newbie, that OD install was incredibly difficult and I would really rather not change it out. Any suggstions?

 

[Don S]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

In the mean time, thanks to you guys I know for sure I need a new amplifier. Now the challenge is to find the right one. I found a list of engines and the recommended part for the amplifier. Based on other forum topics my 14093627 is a 87 - 91 305. The list has three different part numbers for the amplifier. They are: 15248A 1, 15899A 1, 805361T 3. Any idea which one I need? The difference on the list seems to be TB IV, IV (2) or IV (1), respectively.

If you have an OMC distributor and not a Thunderbolt distributor, then you don't need an ignition amplifier. Omc distributors all had internal modules and advance. You are trying to put two systems together that can't be put together.

Also, I believe I have determined the proper gear ratio on the Alpha one should have been 1.65 and I put in a 1.5.

I.5 is what is supposed to be on a V8

 

[starwriter]

Re: Thunderbolt IV Ignition - can a V6 version be used on the V8?

Answer is "NO".V 6 is a V6 a V8 is a V8.