Simple Question From an Ex Pro Jet Skiier

by Riff
(Southern California)

I'm a former pro standup jet ski racer. I've recently been a casualty of the switch to 4 strokes by the 'powers that be', so I take great interest in your writings here. And it also means I comprehended 98% of everything you wrote which leads me to ask:

Why haven't you built one of your motors?

What would it cost to do such? (A 1000cc twin). Billet cases and cylinders would save $ as sand casting would be more expensive I would assume. By my guestimations, it could produce about 300hp.

But in jet-skiing, as most motorsports, HP isn't as important as torque is. Especially since our archaic jet-pumps are so in-efficient that very little of the hp actually makes it to the water. Jet-pumps as they are today, do not perform past 8400 RPM, and in my case with standup jet skis, the vibrations and pull from high revving motors are impossible to hold onto at race pace for an entire moto, no matter the athlete.

The best ski's I've ever ridden rev'd in the low 6000s. The power was smooth and a rider could ride full throttle forever without suffering fatigue no matter how fast the actual mph were. They produced about 155 HP and only did 63-65 mph but my lap times were my best ever.

Current jet skis off the showroom floor have about 80 HP and go about 50 mph. I last raced on the world circuit, and at the time the pro class went by Grand Prix rules. The GP class had no homologation requirements so it allowed for privateers to compete on the same playing field as the factory's. We were allowed to explore the limits without useless rules (that the factory's never abided by anyways). My GP class ski went 67 mph and had roughly 170 HP. As you can see that even though the horsepower tripled, the top speed only went up 30% from stock. This exponential in-efficiency (for lack of a better term) is due to the poor pump technology (it is said that even the most efficient jet pumps are only 25-35% efficient) and in reality, that is where our sports technological focus should be. Simply making a jet-pump 50% efficient would double the top speed of a stock ski (and not affect engine life), while tripling the horsepower only has a marginal effect and all the while becomes less rideable. But I digress, sorry...

... my point is, in our sport, the issue is very much the same as dirt bikes. We don't need more horsepower, we need better pumps. But horsepower/torque isn't a bad thing either, I'd love to ride a 300hp twin at 6000 rpm, I'm guessing about 75-80 mph. We also need 'clean' technology for obvious reasons. There's nothing more valuable than our planets water supplies.

The reason I'm against 4 strokes, aside from the problems you so properly articulated in your article, is that in my application, the extra moving mass of the cams creates a gyro effect that affects the handling very much in the same fashion that a 4 stroke dirt bike is affected. 4 stroke engines are heavier and because of that gyro effect, are harder to lean and maneuver... they ride you much more than you ride them. They are not nimble and not nearly as fun to ride as a result. And in racing, the lack of nimbleness severely hampers a racers choice of lines available when entering a corner. The 4 strokes cannot turn nearly as sharp. Thus tracks have been adjusted to favor the 4 strokes, leaving the 2 strokes with no advantage other than reliability (the obvious problems that arise with water ingestion speak for themselves so I won't go into detail).

I would love to explore what it would cost to build a prototype of one of your motors, or at least explore the possibility of converting the SKI DOO E-TEC twin for a stand up jet ski. Current GP class rules allow for unlimited cylinders (but 2 or 3 are best) up to 1100cc. At 600cc and producing 120 hp the E-TEC would already out perform every showroom production standup (of which there are 4 models currently in production) on the market.

How hard would it be to bore the motor & stroke the crank and add 150-200cc to the E-TEC? In stock form 120 HP would be an industry first while at 750-800cc / 150+ HP@6-6500RPM the E-TEC would be a competitive engine package at the highest level. And the 'clean technology' aspect of it call is a HUGE bonus factor.

Thank you for your time, I eagerly await your response.

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Feb 28, 2010
by: Chris Brantley

I've noticed that jet-ski's these days have huge engines putting out huge hp. 1500cc supercharged 4 strokes delivering 260hp! I think the whole "personal" in Personal Water Craft has left the equation. It's a pretty expensive and heavy way of overcoming the efficiency problem!

Dec 28, 2009
From Theory to Practice.
by: Tim Hickox

I'm going to get into this, in detail, soon. I am currently working on the construction of a FAST engine for the 300-mpg vehicle. It is a 200-cc single.

I found someone who remanufactures engines - all sorts, lots of big diesels. He is interested in the FAST concept (he has an engineering degree from Germany). He has all the tools to make everything, so we just do it. You need to find someone like this.

For your needs, I would have you consider a triple, based on the SkiDoo 600. That would give you 900-cc. A V-3 is the best layout - two cylinders up, with the third in-between, lying down 90-degrees from the others. Use the standard cylinders, heads, pistons, rods, etc., with the E-TEC. The main construction would be a new crankcase.

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