I love jet skis

i just got this 750 small pin and it has been ported.My question is what can I expect from this porting, it looks like they stepped the roof height up about 1 mm.But why the step and not just raise the whole port?

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mcn6

Good question... From the pics it looks more like the step is 6 or 8mm higher than the rest of the port and anybodies guess how much higher the rest of the port is??? The transfers and 5th ports look like they were worked over pretty good too.
Anyway, by stepping the top of the port, duration is increased. At the same time, by making the step instead of raising the whole thing, port time area is significantly reduced over that of a more conventional exhaust port geometry. In my way of thinking the step defeats the purpose of raising the port to begin with??? Not sure why someone would shape an exhaust port like that, but my guess is that the power band for that cylinder is going to come on in the upper rpm's like a light switch, all on or all off... But thats just my "guess". I would be interested to know how that motor really runs when you get it going though.
BTW, are the pistons at BDC in the pics?

I love jet skis

Thank for the reply.Yes the piston was at bdc in the pics and I should have it in the water in about a month so ill be sure to let every one know how it runs.Its in my friends rec ski so I hope its not a light switch

mcn6

Really!! It is impossible to tell from just looking at the pics, but it appears the pistons at BDC are blocking quite a bit of the transfer and exhaust port area. That being the case, then the cylinder has been lowered quite a bit. Weird, lower the cylinder and raise the ports??? I am taking my lightswitch "guess" back and saying I don't have a clue what it will do... Be carefull swapping heads or domes around with that cylinder if it has been decked that much. You have any way of getting an accurate measurement for overall cylinder height?

I love jet skis

I can measure it.Do I need to remove the cylinder to do that? what other measurements should I take? ive got some 6" digital calipers and a 2inch drop indicator

s10parts4u

hey this is indirectly related to porting, but does anyone drill boost holes in the sides pistons like other mnfr does??? supposed to make a ripper mid range?? any one seen it done yet??

mcn6

Yes, cylinder needs to come off. Use your calipers upside down for the ports... Just need the overall cylinder height (should be 5.292"+/- from gasket mating surface to gasket mating surface. also need dimension from top of deck to top of exh port step, same thing to bottom of step. also top of deck to top of main transfer port, top of 5th port and top of bust port.

mcn6

I think what you are referring to are "piston intake port windows" which are normally seen on "cylinder reed" design intake tracts. As far as I know they would be no benefit on a "case reed" set-up like a Kaw 750.

octane114

from what i can see, the ports have been widen. just have to watch how close the ring pens are, you get them too wide and it hangs up and tears $hit up,6800-7200 things come apart quick, fast and in a hurry. it more mid range. and you dont change any of the port timing cause you didnt raise anything. i have bulit a few motors with a very simular port job, been very pleased with it and have had no trouble with anything.

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octane114

yes you can but it's to know what you are doing. its called finger ports. lets more spent fuel/exhaust out faster. engine runs cleaner and stronger, it helps out whole setup

__________________
it is what it is . it's all good