Can you explain Impeller pitch!

[rokcrln]

Just what it says. I have searched some but can not find a good explanation of just what the pitch numbers mean and what each one affects. So if you have a simple description for this that you can explain great!

Thanks,

Kevin
LFD Inc.

[Twinturbostang]

Re: Can you explain Impeller pitch!

The amount of pitch. So 16 is taller than a 15.5 and the 16 would need more power to turn.

Now a 9/17 is a variable pitch so you have half the blade bent at 9 for bottom end and then 17 on the top end.

[plagsage]

Re: Can you explain Impeller pitch!

From Skat Trak

"Pitch" Explained - "Pitch" Refers to the degree of angle of the impeller blades. Straight pitch impeller blade is angled the same from the front of the hub to the rear. Progressively pitched impellers change angle from the front to the rear. A lower number impeller produces more low end RPM, thrust and acceleration which will benefit a heavy rider and/or a low powered stock engine. A higher number pitch angle improves top speed. Check your current impeller and decide what you want to increase or decrease from there.

[RacerX2]

Re: Can you explain Impeller pitch!

MORE from Skat-Trak:

We take the responsibility of educating people about our impellers very seriously. There are many variables in impellers and watercraft that you need to be aware of and knowledgeable about before you decide to purchase one. We want you to make an educated decision on which impeller is best for you and your watercraft, and by choosing Skat-Trak, you have made a step in the right direction. The following are some critical factors that we feel our customers should know.

Weight:
Each watercraft is unique in hull design and horsepower. Some watercraft are designed to carry 1 person, and others up to 3 people. With a varying amount of riders, weight being carried on some craft can fluctuate up to 500 pounds. The more weight being carried, the more bottom end you will need to get up on plane quicker. Another example of low end thrust needed would be pulling a water skier or knee boarder. The desired performance is usually more bottom end, which will be achieved by choosing 1 pitch combination lower than our general recommendation listed. We do not suggest choosing a pitch combination higher than our chart suggests for light weight riders.

Desired Performance:
When we design an impeller, our goal is to reach the absolute best overall performance and efficiency possible. Our charts suggest the ideal impeller recommended for the many different models of watercraft in stock, limited, and modified form. We want to give you both bottom-end and top speed without having to compromise, but for those people who still prefer one or the other, they would need to choose a pitch one lower or higher than recommended. Some of the pitch recommendations are targeted at people seeking top speed or acceleration.

Horsepower:
With the many different manufacturers and models of craft available today, there are also different size motors. A common assumption in this industry is, the more horsepower you have, the higher pitch impeller needed. That is not necessarily the case, when we design a performance impeller, we start from scratch. There are many factors to consider within the design of an impeller that determine the overall load and RPM the watercraft will have. The pitch of an impeller can be deceiving. Because of the many geometric differences in impeller designs, including our own, there is no correlation in pitch between various impeller models. They do not represent your craft's potential performance at acceleration and top speed, but is simply the pitch progression of the outer blade angle. For instance, comparing the stock impeller pitch to our performance design to gauge the aggressiveness of the impeller would be an inaccurate reference. We base our recommended pitch off each specific design that we find most efficient on each craft, with various horsepower ratings in mind. The relationship between the impeller and pump exit nozzle diameter is also critical to the performance of the watercraft. All our recommendations are based on each craft's stock nozzle diameter. We test and develop impellers for each make and each model of watercraft, one craft at a time, so you can have the best possible recommendation available to you.

Altitude:
Altitude can play a major role in watercraft performance. Considerable changes in elevation require a lower pitch selection, the lack of oxygen to your engine will not allow it to run at it's peak performance. If you are higher than 4500 feet above sea-level, we recommend that you choose 1 pitch combination lower than what our general recommendation chart lists. This will allow your engine's RPM's to come up quicker and higher than that of your stock impeller, or the normal recommended impeller. All of our impeller recommendations listed are based on sea-level testing.

Q1. Does the pitch of one brand impeller compare in performance to a different brand impeller with the same pitch?
A. No, unfortunately it is not as easy to compare impellers on watercraft as other types of drivetrain like typical gearing on most vehicles. Each of the impeller manufacturers today (including the original impellers on current PWC) measure the blade sweep in a different way. Which means the percentages of blade length per angle of progression vary from model to model. There are also many geometric differences between the different brands and models of impellers, for example- blade length, hub size, root angle, and position of the impeller in the pump. These and many other factors are at least as critical as outer blade angle, and all have a large effect on the load and efficiency within the pump.

Q2. Does the number that my impeller is labeled mean that is literally the pitch of my impeller?
A. Not exactly. The numbers refer to the outer blade angle of each impeller blade. Although commonly used in this industry, the word pitch does not apply to a PWC impeller the way it does a boat propeller. Where the pitch on a boat prop refers to the distance the unit moves forward per revolution, PWC impellers use numbers that reflect the outer blade angle, which identify how aggressive the impeller is, and also as stated in the question is a ãlabelä to distinct between other labeled impellers for ease of applying each impeller to a particular watercraft. The number of that angle cannot always be taken literally, because all of the impeller manufactureâs today have been known to slightly change an angle or length of the blade to optimize performance, and not change the ID of the impeller because the label of that impeller is already known to perform with certain characteristics on certain watercraft.

Q3. Does making a few modifications to my PWC like changing the pipe or raising the compression mean that I have to change the impeller to a different one?
A. Not usually. People commonly feel that they should or need to change the impeller with every modification made to the motor. This is usually not the case, typically the same impeller that works well in a stock application, works well on a boat that is classified as a limited. Our impeller recommendation charts will give you a very good idea of the type and pitch impeller that works best on each watercraft. Owners of watercraft modified to limited or more need to remember that a higher pitch does not always mean more speed, motors have a range that peak horsepower is produced, and the impeller can limit or allow the rpm's to reach a certain level.

Q4. Does the combined weight of me and my passenger(s) make a difference on which impeller pitch I should buy?
A. Sometimes. The recommended impeller is determined to be an improvement when directly compared to the performance of the stock impeller. If the watercraft was carrying the same load previous to the impeller change, the increase will still apply. Sometimes people will drop down a step to maximize the acceleration of the watercraft when normally carrying heavy loads. Read more about this subject in the Impellers 101 section.

Q5. If I buy an aftermarket performance impeller, will my watercraft gain top speed?
A. Not always. Some impellers are designed to increase top speed of the watercraft, some are designed to increase the acceleration, and sometimes we can squeeze both out of an impeller design. It is always best to specify the type of performance increase that you are looking for when purchasing an impeller, or refer to our Impeller application charts located in the impeller section of this web site.

Q6. If I install an aftermarket impeller on my watercraft, how much performance gain should I expect?
A. The increases an impeller will provide whether it is top speed or bottom end, vary with each application. Sometimes we can get a specific design impeller to produce 2-3 mph top speed with no other modifications, and sometimes we can only promise 1-mph gain. Some impellers are designed specifically to reduce E.T., which are very popular for closed course racing, and recreational riders interested in more acceleration or towing power. Also, when we develop an impeller design that is more efficient than the original impeller, we offer a variety of choice's to accommodate the many different variables that are usually present like, rider weight, altitude, motor modifications, and the riders performance desires.

Q8. If I purchase a Skat-Trak impeller, am I getting the same type of impeller that the professional racers use out on the racecourse?
A. Almost always. Every one of our impellers go through the same type of production process and quality control phases. There are a few exceptions to this question, and that is because the watercraft owner may have modified the pump in a way that an impeller off the shelf would not fit correctly, or the individual request's a special type of impeller and/or pitch.

Q10. Will a Swirl type impeller make my watercraft go slower?
A. Not always. Like all other impeller designs, there is a specific pitch recommended for each watercraft, and by installing the wrong pitch on your PWC in an attempt to maximize performance gains, you can actually lose performance. In most cases, the Swirl design maximizes low to mid range acceleration, while retaining top speed compared to the original impeller. This style is very desirable in closed course racing, or conditions where the water is usually rough. In some applications, we find top speed gains as well.

Q11. Are Skat-Trak impellers made in the USA?
A. Yes, Skat-Trak is currently the only major aftermarket PWC impeller manufacturer in the USA. We pride ourselves in the quality of our products, and our guarantee of our customers total satisfaction.