Has anybody ever seen an inboard (I/O) straight 6 pontoon?

[ronb]

Just curious.. I have a collection of Ford and Chevy six cylinders and my damned craigslist keeps taunting me
1975 17 ft Larson/Inboard - Fix up or parts - $400 (Lake Park,MN)
MERC INLINE 6 I/O 250 CHEV FOR PARTS - $250 (Henning mn.)

I like working on car motors, and just opening the cover on the Optimax makes me uneasy about working on it (other than bolt on and tune up items), I am sure as time goes on I will get more familiar with it and this will all seem like silly nonsense, but for now.. I like some heavy car motors... With it being inline there should be more room to work on either side of the motor.

I figure finding a suitable 3rd pontoon would be the biggest hurdle, the sixes are 2 cylinders longer than the v8 counterparts. But so much better low end torque, which I would assume would relate to being able to run a more agressive pitch prop at lower RPMs. And no V8 vibration from left to right..

thoughts? Ravings of a mad man with too much thinking time on his hands or a 'doable' project?

[badmoonrising]

Not on a pontoon, but when I was searching for 60s and 70s era Starcrafts to rebuild, alot of them came with inline 6's. They were excellent motors.

[ronb]

The Mercuiser 188hp (ford 302 v8) aren't really rated much higher then the 165hp (chev 250 i6). But they are wider, heavier and have that sweet v8 rumble.

I already warned my wife that I would be looking out for a good cheap project. And I am thinking an older I/O in an older 20ft pontoon (converted to triple) could be tons of redneck fun.

-ron

[Bamaman]

The Mercruiser 165 was the Chevy 6 cylinder, and it was much smoother and more powerful than the old tried and true Mercruiser 140 4 cylinder. I liked it.

The 165 hp was replaced by Mercruiser's 470 (170 hp), which was a huge 4 cylinder. It didn't work out so well, and was eventually replaced by the 4.3 Chevy 6 cylinder motor--a great boat motor.

[GregF]

My buddy had one of those Mercruisers with the I-6 Cheby

It turns out that is the 6 cylinder TRUCK motor, not the one they used in a car. We found that out the hard way.

[ronb]

The 250 chev in the barn is out of a 77 chev 1/2 ton truck.

[GregF]

The 250 chev in the barn is out of a 77 chev 1/2 ton truck.

That's the one you use on an old Mercruiser.
The one we butchered out of a Nova (cutting torch, bolt cutters and tow truck) didn't work.

[rancherlee]

I know my old 300-6 would have been a blast. The thought crossed my mind to find an old 302 out drive since the 300-6 has the same bell housing pattern and uses the same crank pattern too. Mine with 330tq @ 2000rpm and 240hp @ 4700rpm would have been a great toon engine.

[GregF]

We had a F-150 with that 300 ci 6 cyl.
It pulled my boat like a V-8.
It was also going on 210,000 miles when Obama gave me $4500 to crush it.

[ronb]

We had a F-150 with that 300 ci 6 cyl.
It pulled my boat like a V-8.
It was also going on 210,000 miles when Obama gave me $4500 to crush it.

Greg, you make me sad, those 300s were bulletproof low end torque monsters. While I do respect that the cash for clunkers program over paid for LOTS of junk cars, it destroyed a huge used car part inventory for those of us who enjoy scrounging. (I pulled a ZF 5speed from a 3/4t Ford after it was cashed for clunk.. $100, still looking for a project to put it in)

Well since nobody is telling me that its the craziest idea since the shake weight... how about ideas on what I could use for a suitable transom? Do you think a standard V8 transom (3rd tube) would be long enough? Or is that too generic and I need to do some measuring? Find a suitable boat donor and measure the inside dimensions and then compare them to 'standard' I/O transom (3rd tubes)

thanks for entertaining the crazy guy..
-ron

[ToonGuy]

Here ya go...OR I have a complete tri-toon chassis that used to be a 5.7L I/O

[GregF]

Ron, it is the I/O part that I think is crazy but if you are going for it, a fresh 300 is a pretty good choice. I am not sure what you could build that up to but 300HP is not a bad guess without doing anything too exotic. I would want EFI.
For longevity you are probably better off staying in the 250-275 HP range but you can get that with nothing but a decent manifold and exhaust system.

[Flanker]

I have a 1971 Sea Ray with the 165 6 cylinder...still runs strong today

[ronb]

300hp from a 300cu in Ford is not going to happen without forcing air through it, their heads (with all 12 ports on the same side) don't breath very well, you can't turn them too fast for too long unless you get a forged steel (industrial) crankshaft.

I'm not "trying to do anything', I like fun projects that are cheap (the funner and cheaper the better), I have no reason to change the HP ratings of the motor. Not saying I won't, but I don't need to. I would need to spend some time learning about regulations regarding spark arrestors and inboard motor requirements before dinking around with anything (intake/carburation/exhaust) related..

ToonGuy, your pictures are a bad influence on all of us. If you ever run across a center toon that will fit a 2007 South Bay 922CR with outboard let me know... My wife likes the sounds of a v8 inboard..but I pay the pontoon fuel bill..

But for a project like this, your pictured center tube structure would put it right out of any cheap budget...

-ron

[GregF]

The fuel bill is one thing that keeps me in a mid range. The other is a bay wide 25 MPH speed limit, where it isn't "slow speed only".