HPBCANADA.COM

A little bit faster, yes. The Yamaha 70 I last had on saw 62.1mph. It was all original, stock 1987 model, long shaft, except for the 1.85 gear small lower.. 62.1 At like 6600 or 6700rpm with the 19p prop I got from Jeremy.


This OMC 75hp has 30psi more compression than that Yamaha 70..

Excuses...the omc is faster and you haven't even hit the trim button!...been telling dok for years i'd give him an OMC

OMC is faster but Yamaha is still in business

I scoped the OMC pistons last night - piston wash is large.
Also, I need to set the timing properly with a test prop..
I might have a way to drop the motor by approx 3/8" without much work.
The other possible todo item is adding speed holes to the lower and airbox.

The piston tops have "75" stamped on them, with a triangle also stamped on the top - anyone seen that before, and know what they are?
Click here for the scope vid:

I can't seem to sell my 49ci so I might aswell keep it.
Maybe have 4-5 boats running 49s when racing returns!!??

The one you have for sale looks much nicer and is newer than my FrankenStinger. People should buy it if they want to do 65+ mph.
Or, yes, I'd be stoked for a subset of T850 for 49'r's and Yamaha 70's. A race within a race. Critches with 56'r's with beyond TORC T850 specs/power are certainly a level above.

That would be good to see on the course

Lowered the motor by approx 1/2". Today: Less wind and chop but saw only 63.0 @ 6330rpm, also 62.8, 62.5mph... Was able to trim up where I want it, the torque steer has increased significantly. When trimmed up I still get a lot of air in the tell tale. I stuck a pair of thermocouples on the cyl head and normal operating temps are in the 60's deg.C. When doing a speed run trimmed up high, with a lot of air in tell tale, temps get in to the low 70's deg.C. like 72, maybe 73 deg.C. So I think it is *maybe*? safe in terms getting cooling based on the temps, but why so much air in the tell tale? I did put the water pickup/outlet for the tell tale at the top of the exhaust when I had the exhaust open to redo the gaskets.

Also of note: I scoped the cyls - did see the exhaust chamfer - it is a real 75hp Stinger, Formula E, Sprint, etc.. Compression on all 3cyls was in the high 140's: something like 149, 145, 147... Jetting is still stock 56D. Timing - I'm not sure yet!! (I know - that was a risk I was worried about). I did make a TDC tool and marked TDC on the flywheel, but haven't put the test wheel on yet to do the adjustment.

I can't believe all the details that need addressing with this motor and setup. My setback plate is neg 5 degrees, and with the Yamaha Pro50 trim setup, still can't trim down enough to get on plane easily. I though lowering the motor would help. It needs a mod to the lower mount so that the lower mount doesn't hit the trim unit.

I'm stoked to try 54D jets, and timing it properly.

Was really hoping for mid 60's with this motor. Like I said in an earlier post, I thought this would be significantly faster than that older, original, stock 1987 Yamaha 70 that is at 118psi. It is only like 1 or 2 mph faster. That being said, 62/63mph is massively fun, and this thing pulls hard from like 5000 rpm up. Very much so worth the effort.

Very happy that the gearcase hasn't puked its guts. My confidence in OMC lowers is low.

Hey Matt, I used to race the 49.7 Stinger in both FE & SE classes. The OMC Stinger does not require high water pressure, but does require good water flow. The head temp of 143 degrees to 160 degrees F is fine. As for the timing, 19 degrees is good, but 54D jets are risky. We always ran 56D's and with higher compression we ran 57 & 8's. I believe the stock compression on a Stinger is 130-135 PSI. Your head might be cut down. Do some research on stock compression for the Stinger. If 130-135 PSI is correct, no way I would run 54D's. How do plugs read and what does piston wash look like?

We ran 65-67.5 mph on our Critchfield back in the late 1980's. Rpm was around 6500-6700 using a 12 5/8" diameter 21" prop. Also, Jake Elsey ran similar numbers with his 49.7 cid in T-850 class, early on. The centerline of the prop shaft should be about (1/2"-3/4") below the pad, on the Critchfield. I assume your running the OMC Nitro gear case.

we ran 70.2 https://www.youtube.com/watch?v=41b49FieyR8
with:
- OMC high compression head: 185 lbs
- 180 degree automotive thermostat
- 21 advanced timing
- .055 jets
12x23 Titus at 1" below pad
- 150 lb Voodoo