Cranckshaft degrees

[hupiveneilija]

Hello everybody!
Im just wondering that why nobody is ever talking how many degrees they have ex. or transfer duration etc. And how little or big you can go for port timing changes if you are aiming the motor to some specific use or if you want to raise the powerband higher than stock is.
Hopefully You get the idea what im trying to say.
Feel free to speak and say Your opinions here outloud. Word is Yours!

Jani

Ps. Ive done something to my omc 3cyl, hope it works😂.

[filthy phill]

why would they need to talk degrees ? this two stroke not 4 stroke.
its simple enough to work out with a degree wheel what the duration is, and you cant change it other than the heights.
the exhaust can only go so far before you go through the metal of the block.

you dont go smaller on the ports or you will gain nothing, just lose lots of power,
to raise the ports on this block the maximum sizes are measured from the top of the block down.
for example
minimum distance from top of block to the top of boost port is 1.860 inches .
minimum distance from top of the block to top of the transfer port is 1.825 inches..
minimum distance from top of the block to top of the exhaust port is 1.450... and then put a chamfer to make it 1.393.

this is what has been done with this block to get SST60 performance. for lightweight tunnel hulls .


degree wheel is not needed as port heights are there for all to see. its not like your using a different crank or longer/shorter rods and changing crank throw.
or making totally different type of sleeve , So why would anyone talk degree's ?

now regards the head being so much smaller in the combustion area, can you tell us what fuel you plan to run this motor on ?
petrol from auto garage in finland ?. or pure race fuel with octane of 120 ?
from what I read your normal car fuel is about 95 ( usa 91) octane,

have you cranked this over to find out how much compression yet ? I think about 210 psi cold..

[hupiveneilija]

Hi,
I know that you can measure distances from topdeck but for me its kind of easyer to understand in degrees generally. For examble stock ex165* and mod175*.

[zul8tr]

Easy to convert piston depth to degrees if you know the various depths of ports and the piston pin offset (if any). If interested I have a detailed MS Excel spreadsheet that calculates in 1 degree increments piston: position, velocity, acceleration and G load with input of: piston pin offset, rod length and stroke. It includes graphical output of position, velocity, acceleration and G load. You can modify it for your needs for 2S (also 4S) with input dimensions, notes, etc as desired. It is metric but conversion to inches is easy. And it is gratis.