BANG FOR THE BUCK.... GO 49 OMC...CHOOSE WISELY

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

sheuninck wrote:

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

Well there's my problem! I have none of that, haha.
I think my boat is closer to 325lbs, and the pad is worn and hooked.

150 is light, holy crap!

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

hec2buck wrote:

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.

Thom, thanks for the details - this helps a lot. Nice to hear what others have seen with this motor.

Hounddog · **Joined:** April 3rd, 2012, 1:52 pm **Posts:** 3168

Matt, there is more information on this thread.
viewtopic.php?f=19&t=3461&hilit=Jake

Matt, over the years here is what I have learned about the 49 V hull on the race course.
- most racers in Canada over propped their motor....they ran 23 pitch....top end was better....took too long to get there
- 66 to 68 mph was best for a legal 49........6500 to 6800 rpm
- it was faster than a STOCK 70 hp 56'r
- an early 75-76 motor will turn 7100 to 7200 rpm on a very light 150 to 200 lb hull
- the later motors on the heavier hulls run the same ......63 to 66 mph
- running 160 lb compression on a stock 49...slows it down....145 to 150 is best

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

What kind of piston to bore clearances have you folks experimented with? I'm asking because I found some lightweight pistons but they are measuring approx 2.9915 to 2.9925in.
Service manual says 0.0045 to 0.0065 clearance..

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

I have a fresh block and rings, but all the pistons I have are oval - 7, 8 thou clearance on one axis, about 3, 4 thou on the other. Any suggestions or recommendations? There are some NOS pistons on ebay but pics show corrosion, etc.. Was hoping not to have to bore hone since the block is NOS.

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

The added clearance is ok, but you will have to warm engine up longer and run it a little hotter ( water temp ). The oval condition of .007-.008" is too much. There is no fix. New piston is the answer. The other is very borderline. I have never tried to put a piston in a press, to get rid of ovality. Was always afraid I would crack the skirt, because the OMC pistons are cast.

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

Thanks Thom,
I wasn't sure what the limit would be for risking it. This is old stuff except for the rings and block. I'll hold out for better pistons. I've taken apart many old blocks now and all pistons clearances are seemingly huge. Maybe that's the reason they were "junk" blocks.

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

Can't you bore oversize and hone those old blocks?

mattmak · **Joined:** June 5th, 2015, 8:56 am **Posts:** 533

hec2buck wrote:

Can't you bore oversize and hone those old blocks?

I have new old stock crank, block, rings all in standard size, and a bunch of donor "junk" blocks to salvage pistons, rods, etc from. But it seems like none of the pistons measure up as useful. This is for a hobby/nostalgia project, not for racing. If I have to I'll grab some piston/ring kits I will, but was hoping to not spend too much on this one. How close are aftermarket pistons to being within spec relative to a new standard bore block? If the bores are exactly 3.000 inches, are new off the shelf pistons going to have correct clearances?

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

Try Wiseco Piston, they are very close.

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BANG FOR THE BUCK.... GO 49 OMC...CHOOSE WISELY

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