Updated porting temp plate
- Thread starter waxhead
- Start date
Open/non-tuned exhausts are not the best application for any jetski since max torque is always around 5000rpm. Our pumps don't make much load at that rpm. A tuned pipe will boost peak torque and you can set that boost at whatever rpm the pump wants to run , which is usually over 7000 rpm. I was thinking more of general two-srtoke tuning rather than jetski specific tuning. I have some small 25-50cc engines that are loaded to turn 7000rpm and are at their best with a 150 degree exhaust port.
waxhead
wannabe backflipper
- Location
- gold coast
Absolutely you can make power at high RPM with a lower exhaust port as you are talking about. However, the power is not coming from the exhaust port height — it’s coming from the blowdown port time-area. The exhaust needs to dump enough pressure so that when the transfers open they don’t stall and reverse the flow in the transfers. Now, if you have really good flowing transfers, then you can run a lower exhaust as the time the transfers are open allows enough to scavenge and fill the cylinder enough to make power. Unfortunately, we don’t have transfers that flow that well so we have to open them sooner. Of course this directly affects blowdown port time-area due to the exhaust opening and the transfer opening getting closer together. If we had a better flowing exhaust port then we could, of course, drop the pressure in the cylinder sooner and so the transfers would not stall, however the transfers in the Yamaha are crap. If we were to run triple exhaust ports as in most modern two-strokes then we would not have to run an exhaust port as high to drop the pressure. Even if we had the Kawasaki exhaust port duct which is not massively oversized like the Yamaha we could lower the exhaust port height — but Yamaha didn’t give us that.
In short: on these Yamaha cylinders, you raise the exhaust port not to chase timing, but to create the blowdown time-area needed because the transfers and duct aren’t good enough to support higher horsepower otherwise.
In short: on these Yamaha cylinders, you raise the exhaust port not to chase timing, but to create the blowdown time-area needed because the transfers and duct aren’t good enough to support higher horsepower otherwise.
Wax I apologize if I've asked this before but I don't' recall, what sort of impeller/pump setup are you running with these 195 degree exhaust port cylinders.
Seems like it's going to want a pretty low pump load to really shine, everybody with their 10/16 hooker that they run on a 179 degree stock 61x cylinder with a B pipe and 35cc ADA head might need to make some adjustments.
Seems like it's going to want a pretty low pump load to really shine, everybody with their 10/16 hooker that they run on a 179 degree stock 61x cylinder with a B pipe and 35cc ADA head might need to make some adjustments.
A 62t motor done with the yamanube templates and all of the rest of the stuff you have listed there really is a pretty nice motor if you don't want to go all the way to to the "all of it" approach of the wax templates.
My next yamaha motor will probably be an 85mm bore with the wax template porting to try it out. I expect it will be a lot of power but a little trickier to tune than a typical much lower port motor.
waxhead
wannabe backflipper
- Location
- gold coast
I’m running a 12/18 with a solas 12 vane pump. I did have a 11/17 in it and it was a rocket but was giving away a lot of top end. I had run this same engine with a 10/16 hooker and it rips off the bottom and throttle response.
Pulling that impeller in a mag pump would be awesome. What hull were you racing that in? Assuming that was with the rest of your mini weapon setup 84mm, .8 squish, 200 compression, dual 46s, zeel, your sxr chamber, and a few other secrets?
Fast.Jimmy
Came here cause I keep sinking snowmobiles
- Location
- Nelson B.C. Canada
A wicked idea, and another clean print! Hats off to you Wax. Thank you for sharing these, and for giving the community access to FX1 chambers
Im curious if your willing to pass along any other pieces of the recipe. Particularly on a 61X cyl. I've read some guys like to stick close to 81mm becuase the transfers struggle to flow the bigger the bore, but it seems your increased blow down should help address this, do you typically go to 84mm on a 61X? Also curious what compression and static timing you run
Im curious if your willing to pass along any other pieces of the recipe. Particularly on a 61X cyl. I've read some guys like to stick close to 81mm becuase the transfers struggle to flow the bigger the bore, but it seems your increased blow down should help address this, do you typically go to 84mm on a 61X? Also curious what compression and static timing you run
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waxhead
wannabe backflipper
- Location
- gold coast
Thanks Jimmy. Im a small bore guy for sure, can explain it soon but im about to head off to the gym. Please remind me in a few days and i will put something together
waxhead
wannabe backflipper
- Location
- gold coast
Its in a 2008 plus hull. I was using a tbm ride plate an an r&d grate, it was with one of our pump cones and a protec mach two pipe. I have since gone to a prowatercraft plate, our sxr chamber. I went back to 46mm carbs from 48s to take some hit off it as it was beating me up, I also went for a solas stator as they hook up better than a cone but they are twice the price and heavy. Its a well rounded race boat now