Omc 140hp cross flow

[Jimmybar]

make the rods and pistons weigh the same

with the rods I balance the little ends first on a pivot , then adjust the big ends, to 1gr... the pistons,,,will check squish zone with plastsine ,then going to cut the skirt to allow for max intake to the crown at TDC and wide enough to allow for the four ports to take a breath . bit different to a scallop on the 9 pages..then take them to within a 1gr as well , somewhere near the mark ???

[powerabout]

I was thinking to get the slide rule out and see the area of the scallop versus slotted piston?

[Jimmybar]

I was thinking to get the slide rule out and see the area of the scallop versus slotted piston?

yes , that's one part . then add induction port timing . then crankcase compression timing. add a bit of assumption on pulse timing . sprinkle with anticipation. and" whoa lah". see you on race day !!!.PS reality is . we have a passion for these old bangers . and love it .cheers

[71V153]

My Baja 15ss ran 62.9 with a stock, carbon encrusted '83 140. Bolted on the transom.

Run 66.7 with a fresh "7 1/2 paged" '77 140 on a 4" jackplate.

In retrospect. Next time I'm just gonna buy a bigger motor ...

[Jimmybar]

NOW THAT'S JUST TO EASY ..Ha Ha hahaha

[olboatman]

My Baja 15ss ran 62.9 with a stock, carbon encrusted '83 140. Bolted on the transom.

Run 66.7 with a fresh "7 1/2 paged" '77 140 on a 4" jackplate.

In retrospect. Next time I'm just gonna buy a bigger motor ...

Did you have a low water pickup on that 77 140?
Gary

[olboatman]

I should have asked where the prop shaft hight was in relation to the hull bottom?
Gary

[Jimmybar]

Did you extend the slots right to the bottom open to the crank case or only fed through piston slots?

ok , after much airflow testing , and with consideration to the dilemma of 1 3/8 with no performance benefits . and constant piston burns . this is what I,ve found ,
refer to 1 3/8 ' carbs post

[powerabout]

did you machine the block to match the piston?

[Jimmybar]

No . here's a pic of the 90hp block ported to 140+ hp . going into service with" mod 3 "pistons .. I did test the matching slots ,in pic 2. but found air flow much higher. but crankcase compression lower !!better suited to higher revs ,,not required.

[powerabout]

you said airflow much higher, how are you measuring that?

[Jimmybar]

Sit down, grab a beer. and get your head around this , I set up a compressed air jet into the intake duct then set a db meter at different spots . piston chamber. intake transfer. crankcase area . and measure the db sound level at different crank angle tdc to bdc . this gave me a measurable difference at different points. put that info on a graph. tried factory . 9 pages .and mod 3 . the higher the pitch and sound the faster the air , and lower db's more volume , bit out there . but so is science , its the pulse wave . that's the one . want more ???

[powerabout]

ok, I can understand that.
you said you kept burning pistons, what mod caused that?

[FMP]

Hey Jimmy,
Good stuff , too bad about the burn! Where's the burn, on deflector, all pistons. Just picking up this read again , this burn is recent?

[powerabout]

I wonder with a stock engine or even a scalloped block, can you use a bypass cover that has a floor in it to help turn the flow to 90 degrees and into the cylinder?
Now we are trying to get flow into a sharp edged port