Super Jet Stroker Cranks

[McDog]

Aren't they lighter too? Know how much lighter?

 

[Bobert540]

PHP 4mm and 10mm LW cranks are about 2lbs lighter.

 

[NVJAY775]

Boarder line sticky here. Excellent info and read fellas. Thanks to all for posting up and schooling me.

 

[VinnieMaxx]

Any engine is just an air pump, air/fuel in, compress, power stroke, and exhaust gas out.

Displacement (cc or ci) is a function of how much air the engine can displace in one revolution.
To figure displacement you take the bore diameter and stroke length to figure the volume of air the engine can move in one rotation x’s the number of cylinders. This is simplified and there are other factors to consider however bore and stroke are the key factors.
The more air you move through any engine the higher the power potential the engine has.

The volume of air that moves through an engine can be modified many ways I.E. turbo charging, super charging or in stand up PWC’s as weight is always a factor the bore and/or the stroke can be modified the increase the displacement of the engine. The simplest way to gain displacement is to bore the cylinders and install larger diameter pistons. However there limitations to cylinder boring so the next way to increase displacement is to increase the stroke of the piston in the cylinder to move more air (more cc’s). When you move to a stroker motor there is more complexity due to added machining required to accommodate the longer stroke in the engine cases. We all know more complexity = more $$$ but can yield more power when properly executed.
So in summary a longer stroke crankshaft will increase the displacement of the engine by allowing the engine to move a larger volume of air per engine revolution thus increasing the engine power potential. A stroker crank along with a larger piston bore diameter will yield maximum engine displacement for maximum engine power.

 

[spenaroo]

Great summary

 

[kevbo]

Considering that the flywheel is the balancer that helps maintain bearing life, doesn't all lighter flywheel of any kind increase engine vibration and therefor decrease crank life? Total loss being the lightest and therefor most harmful?

Its called mass balancing, Seadoo puts them on both ends of the crank. The bearings arent loaded so much on watercraft since the case is mounted in rubber. Light flywheels and exhaust allow the engine to move more but is not an issue except for more carb and bendix wear.

 

[waxhead]

Any engine is just an air pump, air/fuel in, compress, power stroke, and exhaust gas out.

Displacement (cc or ci) is a function of how much air the engine can displace in one revolution.
To figure displacement you take the bore diameter and stroke length to figure the volume of air the engine can move in one rotation x’s the number of cylinders. This is simplified and there are other factors to consider however bore and stroke are the key factors.
The more air you move through any engine the higher the power potential the engine has.

The volume of air that moves through an engine can be modified many ways I.E. turbo charging, super charging or in stand up PWC’s as weight is always a factor the bore and/or the stroke can be modified the increase the displacement of the engine. The simplest way to gain displacement is to bore the cylinders and install larger diameter pistons. However there limitations to cylinder boring so the next way to increase displacement is to increase the stroke of the piston in the cylinder to move more air (more cc’s). When you move to a stroker motor there is more complexity due to added machining required to accommodate the longer stroke in the engine cases. We all know more complexity = more $$$ but can yield more power when properly executed.
So in summary a longer stroke crankshaft will increase the displacement of the engine by allowing the engine to move a larger volume of air per engine revolution thus increasing the engine power potential. A stroker crank along with a larger piston bore diameter will yield maximum engine displacement for maximum engine power.

The issue with that is with the yamaha engine is that it already has to little transfer port flow for the size of the engine. if you big bore it you are moving into the transfer flow even more with a big bore sleeve. This is just one of the reasons that the stroke is a better option on yamaha based engine than a big bore. So in theory more capacity is more power in reality its not quite right with the yamaha based engine if you do it incorrectly.
Im not saying what you wrote is right its just a cut and paste from a txt book and is really just a generic statement

 

[masterblaster]

The issue with that is with the yamaha engine is that it already has to little transfer port flow for the size of the engine. if you big bore it you are moving into the transfer flow even more with a big bore sleeve. This is just one of the reasons that the stroke is a better option on yamaha based engine than a big bore. So in theory more capacity is more power in reality its not quite right with the yamaha based engine if you do it incorrectly.

this is a much bigger deal than most realize,its so easy to do it just the slightest bit incorrectly and lose a ton of power potential. The more motors I personally experience the more I favor strokers and big flow. Ive been doing some experimenting to that point. The motor scotti was referring to above is a perfect example,8 mill lamey with tiny pistons,sub 800cc motor.Hit hard, pulled great all the way to top end,made way more top end power than any of us would ever need for non racing purpose.For freeride/rec ski we have so much simpler setup to configure,We dont have to worry about sustained top end,mph gains.Just has to hit hard and pull good on midrange. huge advantage in designing and tuning the setup. Its all about flow....not CC

 

[Dustin]

For my 5mm stroker, what looks to be the best port timing, with different base gaskets/spacers? Looking for freestyle.