Prop Pitches are They Correct?

[2fast4u]

Are the impeller manufacturers at least consistent in their incorrect pitches? I don't really care if the 13/18 impeller I have is actually a 13/20 as long as when I order a 13/19 it is actually a 13/21.....

The quality of scat or solas impeller out of the box are extreamly bad at best. I have seen all three of the blades different from each other not to mention they don't even matched there advertised pitch at all. Dave at Impros ( www.impros.com) seems to be the most conscent on his pitches. I think he takes the time to correct these poor quality props befor he ships one out new even if it is a box stock prop ( not a race preped prop) you are buying from him. Tommy Jordan

[2fast4u]

bump back up for the new guys

[mikevv]

I have preached about getting the correct rpm's and prop pitches on your target rpm's. Now for my second sermon. When you are trying to get your rpm's correct you need to know just what prop pitch you actualy have. I have seen almost every brand and type of prop made and none of them are what the Mfg. said they were supose to be. The only way to know what you are dealing with is to put the prop in a pitch gauge and read all three blades both on the trailing and leading edges. There are a lot of good guys out there re pitching props. The tru prop pitch is the only way to start and go from there to get the end results you want. I see on the forum guy #1 has the same mods as guy #2 and has a ??/?? pitch prop and guy #2 try this same ??/?? prop and can't turn the rpm's guy #1 can. Well guess what even though both props have the same pitch numbers on them they are totaly different pitches. To make things worse some guys who re pitch props don't go up on the blade when re ptching as far others do and this also changes rpm's some too. So what is a guy to do? Try to get as close a pitch prop as you can to start with and try to get it repitched even one to three times till you get it correct for your rpm's, if you miss your target rpm's more than 450 rpm's or more you have got the wrong prop for your ski to start repitching on. Another problem for you guys to face is if you add more mods to your ski latter this prop prop is wrong also and usualy will require a different prop again. I just want to let you guys know why we see so many prop questions. Lets pray that everyone get the correct prop the first time! Amen, Tommy Jordan

Tommy
I completely agree with your point that you need to know what you have. If you look at the speeds and mods database on this site you can get pretty confused.
I have a related question that tries to take the prop angle out of the equation. If you look at the speeds and mods database you see very similar mods at a given speed but at very different RPMs. For example, if you pick 80 MPH as a reference and look at the RPMs people are posting to get those speeds it varies over 700 RPMs. I know there are a lot of variables that come into play but I thought the RPM to MPH relationship would be more linear.

1) The RPMs are not accurate? (See Motec/C5 at 8850 RPMs and 80.1 MPH or R2/B1 at 8180 RPMs and 82.4 MPH)
2) The speed was not done with a GPS?
3) Some other mod produced enough power (or less weight and reduced drag) that the setup allowed a higher speed with less RPMs?
4) There are just too many variables?

Your thoughts?


Mikevv

[Yellow93]

One way to answer that is this: Some people are trying to run 80 with a stock or C1 supercharger wheel, to do this they have to turn a higher rpm to in turn get more boost out of these lower psi wheels, and they do this by pitching the prop to get the rpm they need to run the number. On the other hand someone that is running an E1 or 15.5 ET wheel wouldn't need to spin the motor as high to get the same mph because their wheel is making boost a lower rpm.

[1_Fast_SHO]

One way to answer that is this: Some people are trying to run 80 with a stock or C1 supercharger wheel, to do this they have to turn a higher rpm to in turn get more boost out of these lower psi wheels, and they do this by pitching the prop to get the rpm they need to run the number. On the other hand someone that is running an E1 or 15.5 ET wheel wouldn't need to spin the motor as high to get the same mph because their wheel is making boost a lower rpm.

Agree, always believe in high boost with low RPMS, scare to spin the motor so HIGH

[mikevv]

One way to answer that is this: Some people are trying to run 80 with a stock or C1 supercharger wheel, to do this they have to turn a higher rpm to in turn get more boost out of these lower psi wheels, and they do this by pitching the prop to get the rpm they need to run the number. On the other hand someone that is running an E1 or 15.5 ET wheel wouldn't need to spin the motor as high to get the same mph because their wheel is making boost a lower rpm.

I am sure you are correct about higher boost wheels taking less RPMs for the same speed but the data doesn't support that by itself. Look at the Motec/C5 at 8850 RPMs and 80 MPH and compare that to the R2/C3 wheel which has the highest speed in the group at 83 MPH with only 8440 RPMs.

Mikevv

[Yellow93]

I am sure you are correct about higher boost wheels taking less RPMs for the same speed but the data doesn't support that by itself. Look at the Motec/C5 at 8850 RPMs and 80 MPH and compare that to the R2/C3 wheel which has the highest speed in the group at 83 MPH with only 8440 RPMs.

Mikevv

I can't answer that but I think there is something wrong with the numbers on that Motec/c5 ski if it only runs 80 at 8850 rpms! My R3/ET Low Boost ski will run 80+ at 8400 rpm so a Motec ski turning all of those rpms should run faster for sure.

[Diver]

I did this test on my freind ski,
I took the liner , prop and the reduction nozzle from my ski and install it on my freind ski and his ski hit the riv limiter @ 8900RPM like mine but his speed is 83.5 miles, but with the same set up mine hit 86 miles!

[enforcer]

I still think that RPM's have alot to do with these set-ups and spinning the motor up so high isn't necessarily right. No one has mentioned where the most torque/ horsepower is produced. I still believe that the engine RPM target is just as if not more important than prop pitch. If you spin a motor lets say 1k past the peak h.p./torque efficiency of a motor are you really producing more power? I know the more rpms we see the higher the boost, but that also means alot more heat and less power per lbs of boost.Bottom line is too many factors to toy with and alot of time is required to figure the best combo/set-up. I still believe not everyone will tell you all their tuning tricks because it takes alot of $$$$$$$$$$ and TIME!!!! Shit I'm still trying to figure out how to get past 82.5..... I saw a personal best of 82.1 at mudbug this year and I spun my best of 8560 R.P.M.s. This was done with a dynafly pitched by Jim but I'll still try my skat 13/25.....We'll see what's up.

[2fast4u]

I just got a 13/25 scat swirl prop and checking the pitch from Scat and it checked 13/22 on two blades and 13/22.5 on one blade. Remember this was suposed to be a 25 pitch from Scat. The more of these props I see the worse they get on being the correct advertised pitch. Everyone needs to check there prop in a pitch gauge to be sure what pitch they actually have! I am sure lots of guys are trying and buying different props and there results are all over the place.. Spend your time paying attention to what your prop is and where you want it to be and it will pay you big dividens in performance gains when done correctly! Tommy Jordan

[@JC]

I ordered my Skat 13/20 from Impros and emailed Dave before he sent it to see if they check the pitch before sending it out. He said they verify and correct the pitch to the true spec if needed and sure enough the blades were all very very close to being right on the ordered pitch.

[2fast4u]

I ordered my Skat 13/20 from Impros and emailed Dave before he sent it to see if they check the pitch before sending it out. He said they verify and correct the pitch to the true spec if needed and sure enough the blades were all very very close to being right on the ordered pitch.

Yep Dave at Impros does a good job of being sure these props that have such poor quality control on the pitch are pitched to what they are supose to be when he ships them out . Tommy Jordan

[2fast4u]

Bumping this back up for the new guys to read, Tommy Jordan