How To - More Power & More Speed

First Things First, Be Reasonable, Fixing the Obvious, Baby Steps, Bolt-On Performance, Take the Plunge, Ultimate Performance, Summary

Topic:                           So you bought a bike and you want more Power and more Speed

Expertise Required:      From a newbie to a Jedi Master

Estimated Time:            Varies

Parts Neeed:               This also depends on your wishes

Tools Needed:             Ditto

First Things First:

There's POWER (torque) and there's SPEED. You can have one, the other, or both. But, you need to understand that having one doesn't always mean you have the other. The wetbike setup relies on THRUST generated by the pump for propulsion. So, if you increase thrust you increase power and speed . . . right? All things being equal - maybe. That is, one of the things not usually taked about is "drag" - the faster you try to go, the more influential it is.

Also, the dynamics of the pump setup need to be addressed in order to understand performance upgrades. The old 50-hp style setup (no intake fairing or scoop) has less ability to provide ultimate performance than the 60hp pump with a speed plug and nice intake scoop (Pro Scoop or Ultra Scoop).

Efficiency - this is one of the things that's often overlooked but has a HUGE effect on both POWER and SPEED. We'll talk about it more - but think of it this way . . . if the tranny in your car is slipping, you'll be down on POWER & SPEED. The same holds true on a wetbike - thus eliminating the "slip" (and increasing the efficiency) as much as possible will be very benefitial.

So, what now? 

Well - let's take a "phased" approach to getting more POWER & SPEED. We're gonna go step-by-step beginning with "Fixing the Obvious" and ending up with "Blueprinting for Performance".

Be Reasonable:

You need to be reasonable - and here are some things to consider:

  • Stock 50hp bike and 220lb or bigger rider - a couple of bolt-ons probably won't be satisfying
  • Tune your bike up first - have a good baseline to begin with
  • Chewed-up impellers and grooved wear-rings have a HUGE impact on performance
  • Check the obvious before beginning any perf. upgrades 
    • Does the throttle open all of the way?
    • Does the impeller and/or wear ring need to be replaced?
    • Is your pump sucking air? Does the ski need to be re-glued (using 5200)?
    • Is your nozzle bushing worn out - allowing the impeller to contact the wear ring?
    • Is your rear ski in good shape - not banana shaped and flexing?
    • Is your rear skeg ok? Are the front edges nice and straight and nick-free?
    • Is your bike tuned-up and able to hit the rev limiter at full throttle (5200-5500rpm)?
    • Does your motor have good compression?
    • Are the reeds in good shape - or is there excessive "spitting back" through the carbs?
    • Are your skis nice-and-smooth on the bottom - and are the edges smooth?
  • Do you have enough cash to do upgrades - seriously?

Fixing The Obvious:

OK - before you begin, you need to check the obvious. Remember - Wetbikes will make you look foolish - it's in their nature, so check everything. Let's begin a step-by-step approach towards better POWER and SPEED.

Inspection - you need to do it and you need to be thorough. We'll begin by looking at things that will have the most bang-for-the-buck first. Let's begin:

  • Inspect the front ski - look for damage to the flat surface - AND - the edges of the ski. If the edges are a bit ragged, make a note that you'll need to do a little TLC at a later date. Take the time to either WAX the bottom of the ski or WD-40 the bottom and top. This is good for 2 mph! Yes, WD-40 does make the ski very slippery - be careful
  • Inspect the rear ski. If you have a scoop, look to see if the leading edges are sitting flush on the ski  (note that not only is the scoop not flush - look at the "lip" of the pump sticking up and blocking water from entering the pump smoothly - ski needs to be removed and re-glued)
  • If your ski is really grooved and beat up, make a note that it'll need some TLC later.
  • Now swing around and look at the rear of the bike. Slide your hand up into the pump intake and see if you feel much play in the output shaft. You're looking to see if the bushing in the nozzle is showing much signs of wear. If you can wiggle the shaft much - time for a new bushing and seal.
  • Now - remove the nozzle (4 nuts) and let's look at the impeller and wear ring. Usually the impeller can be "cleaned-up" by dressing the blades with a file. If it's chewed-up too bad, time for a replacement. A "clipped-ear" impeller allows higher rpm but a stock "straight-blade" impeller does pretty good too. The Skat Trak 11-13 stainless impeller is a good alternate (make especially sure you have a good bushing too). If you have a pre '84 pump, you might need to use 2 or more thrust washers so that the Skat Trak blades won't contact the pump casting - be prepared and get a few just in case.
  • The wear ring shouldn't have any grooves in it. The impeller should not have too much gap - book lists it as 7.3" diameter.
  • Finally - look at the tail end of the shaft to make sure it doesn't have any grooves in it (which would allow water to get into end of nozzle)
  • Take notes on all that you found - you'll use this later.

Baby Steps:

Ok - you did the inspection; what's the next step? If your motor has good compression and is tuned up properly, it's time to get started. To begin with, you need to look at what will reduce drag first and then increase pump thrust second. Here's a list to start with:

  • Get that front ski cleaned up and the edges smoothed out - then wax/polish or WD-40 the hell out of it
  • If you weigh more than 220, drop 20lbs - you get 3 to 4 mph right there
  • Rear ski - if needed, drop the ski, change the gear oil, and re-glue ski (Ski Removal and Replacement). While you are there, smooth out any rough edges and wax/polish or WD-40 the hell out of it
  • Wear Ring, Impeller and Nozzle. Replace or dress-up the impeller, replace the wear ring (new nocks and o-rings too) and then cleanup and/or fix any nicked, bent or broken veins in the Stator - the idea is to make sure you are getting maximum thrust. Resist the temptation to smooth/polish the inside of the pump - it doesn't do much
  • Take a few minutes to dress-up the rear skeg while you have the pump/ski off of the bike. I like to take the skeg off and 5200 it back on - that way it'll still be on tight if the little screws loosen up
  • If you have a 50hp bike and a SUPER SCOOP - take a few minutes and clean up any dinged fins on the scoop. Then, lay down a heavy bead of 5200 and set it back down on the ski - then tighten it down and cleanup all of the excess. When you're done you can probably throw your shirt away too. Also, if you didn't do it when you did the ski removal and replacement - make sure the lip of the pump doesn't stick up above the edge of the ski - blocking water flow. If it does, use a 4-inch grinder or file and buzz it right down
  • Install a new engine plate-to-pump gasket, make sure you have both "knocks" in there and re-install the pump/ski

At this point you have a good baseline to begin with. You can now think about the next step in performance.


Bolt-On Performance:

Now you are ready to spend some money. If you really want to get away from the 28mph range you'll need buy a few goodies. A scoop is not mandatory, but if you ride in the choppy water, they really do a lot to keep the pump from cavitating. Here are the first bolt-on items most wetbikers go with:

  • Scoop - either a Super Scoop (2-blade style), a modified Super Scoop, an Ultra Scoop or a PRO SCOOP.
  • Intake Fairing - commonly referred to as a SPEED PLUG. Not needed if you have a Super Scoop - but works great with a modified Super Scoop, Ultra Scoop or Pro Scoop
  • Another nice bolt-on is the exhaust plate spacer. These have been made in various thicknesses over the years - and they do seem to add a little extra "punch". More torque right where you need it. Money well spent.

The addition of a speed plug and scoop is HUGE - both in the power arena and the speed arena. You'll see an increase in holeshot, mid-range power, and top speed. In fact if you add these to a 50hp bike you'll have the same top speed as a 60, but not the acceleration nor the ability to keep from "sinking in the corners". The 60hp motor just has a bit more torque.
Another nice bolt-on is the addition of velocity stacks - either aluminum or carbon fiber. I believe the benefits can be felt over the entire rpm range. Downside is that many bike will now leave a coating of fuel/oil on the fuel tank - from the "spitting back" through the carbs.

Take The Plunge

So . . . you did the above and you still want either more POWER or more SPEED. What now? Reach right back and pull out Hip-National-Bank and get ready.

The only way to increase POWER or SPEED now is to address the engine. If the compression is down a little, it's time for either a re-ring or full overhaul. What's the least expensive thing you can do to get more power out of the engine? There are 2 things:

  • Remove the head and get it milled at your local independant motorcycle shop - or machine shop. Mill the head to the point that the "counterbore" is eliminated - but no more
  • Use a dremel or hand-file and "match" the aluminum casting to the ports in the cylinders. It doesn't do a whole lot, but cleaning these up does make your motor run better

Not inexpensive, but worth the time and/or cost are the following:

  • Optional - if you are ambitious, have lots of time, and are careful you can "raise" the roof of the boost port on the bottom side. Have a look at the porting here - Porting by Watercross of Texas
  • If you are doing a rebuild - measure the height below the deck that the pistons are. Then have your machinist "deck" the block 95% of that measurement. This will help raise the compression - but not get you into the danger zone. If you take off 100%, be sure you have your head cut for proper squish

It goes without saying that nice, round bores will give the most power and deliver the longest ring-life. If there's a question about your cylinder's condition - BORE IT OUT and start fresh. The new pistons and pin combo is lighter than stock too. 

BIG BORE: It's worth it if you can afford it. If you decide to go up to 86mm or larger, now is the time. However, you might have to incur some additional expenses like decking the block, modifying all of your port timing, and custom head gaskets.

WPS Pipe - the add lots of "noise" but in my opinion really don't do a whole lot by themselves. If you can fine one in good shape run it - but don't expect to be blown away. They are best run in combination with higher compression and different carbs (like these below).

Ultimate Performance:

For the ultimate in performance, find the TMX carb package and/or setup Dual Mikuni SBN carbs with V-Reed cages. Back in the day, the TMX38 package was the setup to have. They will fell like they add 50% more power in the midrange, but it's probably closer to 30%. They will also burn 30% more fuel than stock - but it's a good tradeoff. All of the kits I've seen run Yamaha Banshee Reed Cages and spigot style carbs.

At this point the package you have put together is pretty good but is missing one thing - COMPRESSION. In order to take advantage of the Dual TMX's and/or the addition of a WPS pipe is to raise your compression up to 165psi or better. I recommend using a 60hp head (better cooling) and making sure you have the squish band setup properly. Get help from a 2-stroke performance expert to get you head setup correctly. Adding a little "pisser" on top of the head is extra insurance - to keep any bubbles from getting trapped and causing hot spots.

Note: If you plan to get to this stage, you need to have the ability to read spark plugs, jet carburetors properly, set ignition timing properly, and be able to figure out which "pitch" impeller is right for your combination. It is at this point that lessons learned become extremely costly.


So, what should the performance package really look like? Let's think about it in stages:

Stage I:

This should be your baseline with all of the obvious things addressed (engine tune, skis/pump, and scoop)

Stage II:

This is the addition of the bolt-ons (speed plug included).

Stage III:

This stage is where engine health and modification is done. Crank rebuilding with new bearings and center seal is mandatory - to insure that crank is true (and on 60hp cranks get the center plug welded in).

Stage IV and beyond:

This is the area that dives into custom ignitions (MSD), lightened flywheels, fuel injection, or turbo-charging. Something to address in the future. 




Copyright 2011 - Capt'n Obveeus

Joomla templates by a4joomla