Merc V6 History

[John Schubert]

Wow, John was that based on the v6 production block or was it a custom job?
I think Mr Nerstrom did the looper, he wrote about it on here once before?

Yep. Nerstrom is the guy. Not totally sure what block, but my recollection is that it was the production block, but my recollection tells me (sometimes false) that all that work was pre-production so as to get a competitive race engine on the water.

[Da Bull]

This is getting all mucked up, it needs to stay on topic.

Yes, I agree.

[194268]

I apologize for going of topic about OMC. Question, did DOC Morgan, Les Cahoun, Lyle Forsgrine (sp) or Bob Menleskie (sp) have any input in the Mercury V-6 program ??

[rckid74]

What the Back-Drag does is lean out the motor at higher speeds, for economy. The suction on the float chamber lowers atmospheric pressure inside, and this restricts fuel flow. The vent jet provides a controlled opening, i.e. a smaller jet would restrict air rushing in the float chamber and result in a leaner mix; a larger jet would restrict less air and do the opposite. Merc found out this wasn't such a good idea, leaning out an I-6 makes it prone to detonation and burnt pistons/rings. Especially with the alcohol-laden fuels we have today.

[rckid74]

What the Back-Drag does is lean out the motor at higher speeds, for economy. The suction on the float chamber lowers atmospheric pressure inside, and this restricts fuel flow. The vent jet provides a controlled opening, i.e. a smaller jet would restrict air rushing in the float chamber and result in a leaner mix; a larger jet would restrict less air and do the opposite. Merc found out this wasn't such a good idea, leaning out an I-6 makes it prone to detonation and burnt pistons/rings. Especially with the alcohol-laden fuels we have today.

The above is something I found on the internet.

[powerabout]

Was there any design requirement to suit any overseas markets?
( fuel maybe?)

[rckid74]

I apologize for going of topic about OMC. Question, did DOC Morgan, Les Cahoun, Lyle Forsgrine (sp) or Bob Menleskie (sp) have any input in the Mercury V-6 program ??

None of those had anything to do with the production V6, at least before it went into production. In the following years, as we got into fuel injection, Dr. Morgan and Les Cahoun may have had some input but I don't really know because by mid 1976 I was taken off the V6 project to start the V4 design. At that point another engineer by the name of Mark Curtis took over the V6 and followed it in production for many years after. He deserves a lot of credit for making it what it is today.

[rckid74]

Was there any design requirement to suit any overseas markets?
( fuel maybe?)

Just the use of metric fasteners. Otherwise I don't recall any.

[Merc Fanatic]

Slightly derailed or not, this is still the best thread I've read on here. I appreciate all the effort that has gone into putting it all together and am looking forward what is coming next.

[dale robertson]

The T-3 development must have started pretty early, as the factory race team had them at the 1974 Nationals in Eufaula. They kept them covered up even when working on them.

[kcrochet]

Interesting and appreciated read!! Thanks!

[rckid74]

After OMC announced their V6 in the summer of ‘75 the s##t did hit the fan at Mercury. Everyone from the CEO right down to me got together and tried to decide how to get at least 200 HP out of our V6. True, we had pulled 200 out of the 2 liter by raising the RPM to 6000 but we hadn’t done any endurance testing at that speed and that would take time and who knows what problems would have cropped up. Also, bottom end power had been sacrificed to get the 200 HP.


No, everyone agreed that we needed more cubes. We were spotting them 28 and that was just too much. I had allowed for boring out another 1/8 inch to a 3 ¼ bore which would give 131.9 cubes but that still would not be adequate. It looked like the only way was to get rid of the iron liner and chrome plate the bore. This allowed for a bore of 3 3/8 giving us 142.2 cubes which seemed like it would be enough.


However, getting rid of the liner presents a real problem in diecasting the block. Salt cores were the only possibility at that time and they were still very experimental. So we started a crash program to learn how to make and use salt cores to form the transfer passages. These are strong enough to withstand the very high pressures, loads, and temperatures when the metal is rammed home in the die. They are then dissolved out by soaking the blocks in hot water for awhile.


The 142 inch displacement proved adequate and that engine was in production for many years. Fuel injection and then direct injection were added later and eventually they found a way to bore it out even further to 3.5 inches for 153 cubes which is where it stands today.


I’m very proud of that engine and the roll I played in getting it started way back when. I occasionally see one when on trips here and there and get a thrill seeing it run.

[transomstand]

I’m very proud of that engine and the roll I played in getting it started way back when.

As you should be, still an excellent engine 40+ years later.

[powerabout]

sure its definitely a hall of fame engine

[maynard]

Great thread! We had a 79' 1750 when I was young, there's nothing that sounds as great. I just picked up an '81 225 and don't even have a boat to put it on yet lol! Keep it coming!