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Conversion from Thunderbolt IV to Thunderbolt V

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kimberly_anne

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I have a 1991 Mercruiser 4.3L

I have a 1991 Mercruiser 4.3L 2bbl that I converted to a 4bbl by using an Edlebrock 3111 4bbl intake and Edlebrock 1409 carburetor and I was thinking of converting the ignition from Thunderbolt IV to V. To do this I think the only thing I need to do is to get a new Thunderbolt V ECM from eBay preferably. Has anyone tried this and are there any advantages to doing this? The advantages that I read about are some efficiency gains and a better idle.
 
"So, how much better did it ru

"So, how much better did it run with the 4 barrel? Come on, Chris, 'fess up!

Jeff"
 
Chris needs to go down to a co

Chris needs to go down to a county fair and get one of those spark enhancers.
 
"Hey Jeff,
You responded to m

"Hey Jeff,
You responded to my initial post on this website when I had major problems back in the late spring/early summer. I don't really know how much better it runs than a working 2bbl since I never really had a working 2bbl. I bought the boat used and had problems the first time I tried to open it up. It would only turn 4000 rpms and after 10 minutes the rpms dropped to 3000. Had water droplets on one side of the engine, #1 cylinder had zero compression. Exhaust valve was cupped. Engine started out in saltwater before I purchased it so it had quite a bit of corrosion. I replaced intake, exhaust manifolds and elbows, carb, heads, valve covers (one was rusted through), dipstick tube, circulating pump, exhaust shutters, and coil. Engine looks like a hot rod now with Edelbrock valve covers and a K&N flame arrester! I found out I could get the fancy stuff brand new and cheaper on eBay than from mercurypartsexpress.com. Engine really did not look that bad from the outside and it ran fine at the sellers house. I was told it had less than 200 hrs on it. Goes to show that you can't really tell the condition of an engine from the outside. I cleaned a bunch of scale out of the water jackets. I also installed a closed cooling system so that scale will never form again (I use boat for fishing in Lake Michigan so the closed cooling was not 100% needed but it makes it run better and then I don't have to worry about the block freezing). Besides I found a Mercruiser closed cooling kit brand new on eBay for $475. It's a $1200 kit from Mercury. It now runs at 4800 rpm and runs well. I have a slight hesitation on power up but I think I just need to adjust the linkage on the accelerator pump."
 
"Chris, are you running antifr

"Chris, are you running antifreeze now that you changed over the cooling system?"
 
"Hell of a good job, Chris! Y

"Hell of a good job, Chris! You're not the only one to discover Mercruiser parts are a ripoff. And they aren't necessarily any better than other brand parts, either.

Jeff"
 
"Hi Eddie,
Yes, I am running

"Hi Eddie,
Yes, I am running a 50/50 mix of the new Prestone formulation and distilled water. Should be good to 30 below. I also changed the thermostat to 160 degrees. Found out my temp gauge was bad so I ordered a new one. I installed an audio warning kit so I will know if the oil pressure or temperature goes out of spec. I use the boat for trolling and it has an autopilot so I am not at the helm all the time to keep an eye on the guages. The boat did not have an outdrive lube bottle and I wonder how hard it would be to add that? It looks like you need a way to get the lube through the transom and into the drive. It looks like there is a place for it on my Alpha One Gen II that may have a plug installed. It might be a simple job to remove the plug and then install a drive lube kit. I will have to take a look at that as well."
 
"With and encloesed system you

"With and encloesed system you can run up to 195 degrees. Raw water engines run in lakes and rivers should be no more than 160 degrees and raw water in ocean 140 degrees.
If you want it to run well, high performance spark plug wires are a good item. You won't get any noticeable power increase but it might give you quick cold starts, run a little smoother and add to safety."
 
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