See full version: 4 stroke vs 2 stroke
I have the older style hull (08, so non-s3) and it takes the waves a lot better and drier than my 97 gtx yet is still very playful. The new S3 hulls feel way heavier. The RXT-X has 93 hours on it now and has given me zero problems except a hood strut going bad. I just put gas in it and check the fluids. (outside of flushing, etc that you will be doing to any ski) here
If you are looking to get a cheap ski, your best bet is an older 2-stroke. You can get a $1k-$3k ski and have a ton of fun with it. You may have to do a top-end rebuild on the 2-stroke every few years, which is roughly a $500 DIY job or $1k at a shop. Just depends on how much you ride it, how well you maintain it, and the particular motor. The lower HP engines tend to have a longer life than the higher HP engines. [links]
If you want something that's heavy, big, boat-like, something you have to take to the dealer for service, but doesn't use much gas, get a 4-tek.
I'm biased because I'm a 2-stroke guy. If you want something fun to ride, something you can maintain yourself, something that requires little maintenance, and something economical to buy, and uses lots of gas, get a 2-stroke. here
With the 4-stroke comes added weight and complexity of course there's no getting around that. Your 4-stroke PWC is going to weigh more (but likely have far more horsepower) than it's 2-stroke counterpart. there are some advantages to that though: they punch thru rough water with a much smoother ride as any heavier watercraft would be expected to. The supercharged models can attain some amazingly high speeds and the accelleration is just wicked. Superchargers are a wear item though and require periodic rebuilding. speed costs, how fast can you afford to go? Non-supercharged models are alot of fun too though their speeds are more similar to the 2-stroke predecessors as a result. They aren't really meant for jumping wakes and such, but I've seen Youtube videos of some guys in Australia jumping 12 foot ocean swells on RXT SeaDoo's (supercharged) and a 4-stroke Kawasaki (also supercharged). they were getting tonnes of air time, looked terrifying to me but different strokes for different folks! LOL! here
Personal water craft, or PWCs as they have become known, after making a rapid entry into the market, have established themselves as a very popular boating medium internationally. Although I confess they are not my idea of a good time, I can see the attraction and the reasons for their success. But what do you get when you combine waterjet engineering and PWC styling with RIB technology and a deep V hull. The answer is the SeaDoo Explorer.I had occasion to try my hand at one of these stylish little numbers earlier this month and I have to say it was a most interesting experience for two reasons. Firstly it was blowing a northerly force 7 and secondly, only a week earlier I had been testing a jet boat right at the other end of the evolutionary scale - a high spec. 7.5m diesel powered offshore commercial RIB with a Castoldi waterjet, built by Valiant in Portuagal. It made for an interesting comparison for the Explorer is a mere 3.96m in length and powered by a single 85hp Rotax marine power plant. here
Engine 85hp Bombardier Rotax twin Cyl. 2-Stroke [links]
LOA 3.96m BOA 2.06m Draft 25.4m Deadrise 20 degrees Dry Weight 322kg Capacity 5 Passengers/474kg Fuel 48.4 litres (12.8 Gal) Engine 85hp Bombardier Rotax twin Cyl. 2-Strokeread review from powerandrib magazine:
Engine 85hp Bombardier Rotax twin Cyl. 2-Strokeread review from powerandrib magazine: here
Capacity 5 Passengers/474kg here
Well I actually did pull the head yesterday .. (monday) and there were some tears/or rough spots on the o-ring. I know this wasnt the best thing to do but I robbed one from my parts ski. [links]
Your wondering, "well how can the water get past 150# of pressure?" Easy, . when the piston is on the down stroke. During the down stroke, fuel is being sucked into the cylinder, there is no pressure at that point. Every time the cylinder drops, if you got a breach in your water jacket, then, it will suck the water in with it.
Congrats on your new title here
Will that be in the top end gasket kit or seperate?
Sorry to get back to you so late. just busy as hell. Here, at work, at home. Oh, and on the water. here
Combustion of the fuel/air mixture does not happen all at once like an explosion does. It happens as a progressive burning of the fuel, starting from around the spark to the outermost combustion area. When the spark happens in relation to crank degrees before top dead center (°BTDC) of the piston is something that needs to vary according to engine rpm so that maximum combustion pressure of the burning fuel/air mixture happens between 15 and 20 degrees after top dead center (ATDC). That is necessary for the most power to be transmitted to the gears/sprockets/tire. As engine rpm's increase, the amount of time from the piston being at a set amount of °BTDC to being at top center decreases. But the amount of time that the fuel/air mixture needs to burn remains the same (with the exception above 7000rpm when the extra turbulence caused by the squish band shortens the time needed to burn). Going only by this aspect of combustion it would be ideal for the CDI to increase the °BTDC of the timing as the rpms increase, in a linear fashion. This is more or less true for a 4 stroke engine, but for a 2 stroke there are other factors to consider:
1. Since a 2 stroke has combustion once every crank cycle (whereas the 4 stroke combusts once every 2 cycles) then the pistons top temperature can get high enough to melt it at high engine revolutions with the timing advance equal to that of a 4 stroke engine.
2. At high rpms the delivery ratio of fuel/air becomes less and the pumping loss of engine power becomes more with increased timing avance so that it is accumulative enough to weaken engine power at high revs. "Pumping loss" refers to the power detracted from the engine because of the force needed to push the piston up to top center against the pressures of the compressed gases and the pressure caused by gas expansion due to combustion.
3. Making the ignition and combustion happen later at high rpms increases the powerband of the engine equipped with an expansion chamber because the exhaust exiting the exhaust port is still burning and is therefore hotter than it is at lower rpms. That increased exhaust temperature allows the pressure/sound wave to travel faster. A pressure wave that returns to the cylinder sooner than normal better matches when the piston upstroke happens to prevent loss of fuel/air charge out the port. That in effect it allows a wider powerband of engine power.
AFFECTS OF THE IGNITION TIMING here
Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.
The following is from Eric Gorr's paper "Basic 2 Stroke Tuning" where he talks about advancing or retarding the whole ignition curve of an advancing/retarding CDI on a dirt bike by changing the stator position CW or CCW: [links]
Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak [power] of the pipe. [links]