Fast Fred's OMC Mod 50 secrets Thread #2

[Powerabout]

I rebuilt plenty of consumer engines that did big hours and either the noise from a cracked piston or the wrsit pin slogging out the pin bore gave the game up.
I do feel many of the boats were too heavy for the looper and we also had many twin rigs that should of had v4's.
The 2 cylinders ones on the other hand broke rods especially when over revved until both 2 and 3 had the upgraded rods and that fixed the problems.
I guess the piston was heavily built on the skirt to allow for the windows and the rod angle/side thrust which didnt help the weight with the small wrist pin....
That all history now...
So anyone checked their port timing after fitting long rods?

[Tim Kurcz]

Whoops boys.........

Guess I should have qualified my response: You're right, the factory cast pistons are known to crack, break, and blow chunks though the crankcase. This seldom does more than window the crankcase which quickly leads to engine stoppage.

What I'm talking about is race engines with forged Mod-50 or forged Wiseco pistons (service short rod style or McDaniels long rod style). None of these have ever broken. That said, typical lifespan for one of my race engines is 25hours (can be reduced to only minutes if run lean or over advanced).

Side note: We all know port timing is different between the short/long rod installations in the same bore. If nobody responds this week, I'll assemble and measure one (both ways) next week and publish the data.

[Powerabout]

Tim

I notice you run 2 pumps on your engines like a v6.
If a V4 can survive on one do you need 2 because the crank pulse is much lower on the 49/56?

and, OMC sold the SST 60 with an electric pump, which I would have thought unnecessary, was the above reason the issue?
I guess it all helps to prevent the China Syndrome

Thanks

[Tim Kurcz]

Indeed, I learned the expensive way that two pumps are needed when tall porting is used. Just a walk throught the pits tells me who is making power. If there's a single pump, most likely the motor is a pooch.

Taking a lesson from factory race teams, all my manual engines now use tandem pumps. My electric starts use an electric pump & regulator.

Beware to those who think jetting up is the solution. That will only drain your fuel bowls quicker, leading to a thermo-dynamic failure.

[Powerabout]

we also call it recycling...putting the aluminium on the sea bed from whence it came...a while back

[Roy Hodges]

I thought aluminum comes from Bauxite ore -the most common on earth, but expensive to
process (uses MUCH electrical power ) and magnesium is extracted from SALT water.

[Powerabout]

Correct it does and a place like OZ probably has a third of the worlds supply and OZ was under the sea for a few years while it was growing up.
Also explains all the other minerals and the salt problem we have in the middle.
Irrigate and we get salt.
http://en.wikipedia.org/wiki/Bauxite
Got the largest Diamond mine in the world as well...
and still high tax..so I moved

[David Mason]

I run one pump. I don't think mine is all that poochy.

[Powerabout]

What pressure do you get at WOT and what is WOT
thanks
Powerabout

[Tim Kurcz]

The OMC 49.9 triple is a known piston burner, so it's critical to confirm delivery pressure at rpm before hitting the race course. Having accumulated many offerings to the God of speed, I learned to feed the beast properly - the hard way.

All my manual triples now use tandem pumps and deliver >3.5 PSI @ 5000 RPM deadheaded through a 5/16" OMC primer bulb. My electrics are regulated to 3.5 PSI through a bypass return. These are the only two systems robust enough to keep these engines alive. The OMC service manual says these carbs are happy anywhere between 2.5 and 5 PSI. Fall below that for any reason and say hello to a new piston.

All that said, David Mason is indeed quite successful with one pump - probably on the ragged edge of delivery - and very lucky. But then again, port timing has everything to do with diaphram pump delivery. Perhaps he's running shorter porting than me.

Example: After burning down a piston, one of my customers tested his pump in a stock powerhead and again on his mod powerhead spun at 500 RPM on a test rig. The stocker delivered 17 oz/min, the same pump on the mod delivered only 11.5 oz/min. Adding a second pump to the mod, delivery increased to 18.5 oz/min. (All at zero pressure). This simple test proves the effect of port timing as it relates to diaphram pulse and pump performance.

Perhaps you've heard the saying: Too lean, too long, too bad! Tandem pumps or the electric system have eliminated piston burning due to fuel starvation. Now my efforts are concentrated on making more power.