Impellers other than factory but factory pitch, Which to buy?

[OperationROL]

The results for the 6WC impellers on my AR240 are in... and I'm liking them!

Conditions were pretty great so I ramped it straight up to WOT.
View attachment 101831

View attachment 101830
- 45.2 MPH GPS @~7500 RPM (highest top speed and RPM I recall witnessing)
- 4500ft Elevation
- Calm conditions
- 95% fuel
- Crew: 2 adults and 2 young children
- Bimini up

View attachment 101829
30 MPH at 5900 RPM (I can't recall prior)

It also seemed to improve mid-range acceleration, based purely off feel.

I did make a couple surf runs with full Transom Bag and 1/3 under seat and 2/3 ski locker. I wasn't on board to experience the loaded performance, but my wife said it seemed to pull fibe all the way up to 12 MPH.

Overall, I'm pleased with the results. Nothing lost and positive gains. I recommend them for anyone boating at elevation.
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Your RPMs are pretty close. Have they always been that close? Or.....is this a result of the new impellers? My RPMs are usually 7600 port and 7000 starboard. I would like to get that more synced if possible but have been living with it as a factor of having the same impellers with different loads on each side of the boat, since Yamaha did not pitch them differently to accommodate for the difference in load.

 

[J-RAD]

Your RPMs are pretty close. Have they always been that close? Or.....is this a result of the new impellers? My RPMs are usually 7600 port and 7000 starboard. I would like to get that more synced if possible but have been living with it as a factor of having the same impellers with different loads on each side of the boat, since Yamaha did not pitch them differently to accommodate for the difference in load.

It's actually the results of the Ridesteady system which syncs them digitally. I love it! However, the new impellers were pitched specific for port and starboard which may be helping the efficiency. I didn't attempt running with the sync off to see how they were playing together.

 

[OperationROL]

It's actually the results of the Ridesteady system which syncs them digitally. I love it! However, the new impellers were pitched specific for port and starboard which may be helping the efficiency. I didn't attempt running with the sync off to see how they were playing together.

Go ya. Very nice!

 

[swatski]

Your RPMs are pretty close. Have they always been that close? Or.....is this a result of the new impellers? My RPMs are usually 7600 port and 7000 starboard. I would like to get that more synced if possible but have been living with it as a factor of having the same impellers with different loads on each side of the boat, since Yamaha did not pitch them differently to accommodate for the difference in load.

That's a big difference... 7,000 RPM at low altitude, if consistent, is very low. Factory pitch being off is a possibility. With the AK hulls (and same pitch impellers) the strdb may spin slower but not by that much, I would say 200 RPM max (delta).

I find the L13 to be just about perfect tool for the job of equalizing side to side differences in those new hulls (by varying spacers). Maybe @Ridesteady can comment, I do not think the RS system would synch at WOT but I could be wrong. Good question, actually!

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[Ridesteady]

Maybe @Ridesteady can comment, I do not think the RS system would synch at WOT but I could be wrong. Good question, actually!

If you have sync FULL / AUTO set, then yes, Ridesteady will try to sync anytime the boat speed is above 8 MPH (even when OFF).

At WOT, it's hard to know whether sync will be achieved or not because there is sometimes "throttle saturation". In other words, the throttle valve continues to open, but no more output / RPM is achieved from an engine. So, Ridesteady may be lowering an engine's throttle in order to achieve sync (up to its limits), but may not be able to achieve it because the engine stays the same speed (i.e. still in saturation). I suspect this may happen more at lower elevations, as perhaps air intake no longer is the limiting factor.

If you're just looking to get max top speed, you might want to turn ENG SYNC to ON or OFF (i.e. not AUTO), and turn Ridesteady to OFF. Ridesteady will not try to sync the engines this way, so you'll get max output out of each engine.

 

[2kwik4u]

I suspect this may happen more at lower elevations, as perhaps air intake no longer is the limiting factor.

I think this is very much the case at WOT. The intake can flow more air than the engine can produce useful power from. At WOT, load from the impeller is the limiting factor, not airflow. This is evidenced by people "under pitching" the impeller and running all the way up to the electronic limiter. Lessening the load increases the revs.

At what point the limiting factor transfers from throttle to the applied load is hard to say, and most likely a VERY case dependent point.

Excellent post BTW!

 

[swatski]

Swatski now you need to try them and see how they do at a lower elevation.

Got the 6CW impellers today. Except... one is a 6Cw, the other is... not.




Called Babbitt's and as always they were very responsive, rushed the second 6CW for me, shoudl be in tomorrow.

I like them, they do screw up a fair amount but always work with you at the end. Like when I was buying a center panel windshield to replace mine that broke - they had to resend a new part... 3 times. Whoever was packaging it in a warehouse was just not very good at it, lol, the first three shipments had corner lip completely smashed. Babbitt's had just been sending and resending until they got it right. Oh, well.

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[J-RAD]

I've still not had the chance to drive fully ballasted with my wife surfing but tonight I think the new impellers surprised my wife. Filled the ski locker @ 3/4 full and topped off the transom bag as usual. However, due to a miscommunication my wife accidentally over filled the under-seat bag to 100%. Despite that, it got up to surf speed and the wake was BIG. I wish I'd gotten a different perspective. She sid she knew something was different because if the amount of list and handling. We ended up draining it a bit.

 

[J-RAD]

I've still not had the chance to drive fully ballasted with my wife surfing but tonight I think the new impellers surprised my wife. Filled the ski locker @ 3/4 full and topped off the transom bag as usual. However, due to a miscommunication my wife accidentally over filled the under-seat bag to 100%. Despite that, it got up to surf speed and the wake was BIG. I wish I'd gotten a different perspective. She sid she knew something was different because if the amount of list and handling. We ended up draining it a bit.
View attachment 102441

I obviously tried to post this last night while I was falling asleep... fixed it.

 

[swatski]

That’s very good news, Im itching to swap mine.

The 6CWs are so much taller! I mean, you can just see it, no need to measure. I can not believe I never noticed it in the past but most of my impeller work was in a single engine and with various brands so it all gets mixed up.

I tell you though, everything is completely empirical there, just trial and error. There is no telling what will happen until you are doing it, I don’t care who you are. The guys at Impros doing it fittheir entire lives are still having you test and find surprises more often than not. With progressive pitch and blade/root size/shape difference the possibilities are endless and the sweet spot is tiny!! Especially with the n/a drives, with a supercharger I think the guys have a much bigger target they can hit.
And no supercharger and altitude - that’s where one needs to get creative!

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[swatski]

FYI - got my second 6CW from Babbitt's, one day later. I think they are great. I didn;t ask for anything, they just rushed the order.

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[swatski]

Finally. Done.
Now if it only stops raining.

I swapped both of my OEM/factory 6AP10 impellers with the "single" OEM 6CWs. Very curious about the results. Since my 6APs are basically new /looking still pristine it should be a fair comparison.
I left the L13 setup the same, 3 spacers on the PORT and none on the STRBD side.

The 6CWs (on the sides) are about 1/2 inch taller and look massive next to the 6AP (in the middle):
View attachment 104739

View attachment 104744

Even though the trailing edge pitch appears the exact same:
View attachment 104743

I had to set up my impeller swapping station again:
View attachment 104740

And find my "breaker bar"! (it makes quick work of it)
View attachment 104741

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[J-RAD]

Finally. Done.
Now if it only stops raining.

Raining here too...

 

[swatski]

Wow, the combination of 6CW plus L13 = a killer combination. I knew it from testing in 190, no idea what the heck took me so long to switch to those in the 240!!

The hole shot is amazing, the boat jumps out of the water, pulls like a mo-fo, lol.
The top is still solid 45mph, top RPM about 7,500.
Cruise is also a bit faster for given RPM, for us typically around 5,800-5,900 and around 30mph, so that's nice, too.

These are hands down the best results I've had in a while, I'm so happy.

Of note, the OEM 6CWs are a bit louder (as compared to the OEM factory 6AP) with a different tone, they are much taller and stick into the intake tunnel.

Awesome mod.

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[J-RAD]

Wow, the combination of 6CW plus L13 = a killer combination. I knew it from testing in 190, no idea what the heck took me so long to switch to those in the 240!!

The hole shot is amazing, the boat jumps out of the water, pulls like a mo-fo, lol.
The top is still solid 45mph, top RPM about 7,500.
Cruise is also a bit faster for given RPM, for us typically around 5,800-5,900 and around 30mph, so that's nice, too.

These are hands down the best results I've had in a while, I'm so happy.

Of note, the 6CWs are a bit louder with a different tone, they are much taller and stick into the intake tunnel.

Awesome mod.

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I'm not going back... lol! Huge improvement for me across the entire range. It's a different boat. I think we're confirming the results with each boat that makes the trade.

 

[jacoviii]

Well that is it. I'm getting me some. But you top speed is 5-6mph slower then my '18 242x. Is it a small trade off for the better low/ mid range?

 

[Neutron]

I would like to see a real world side by side holeshot and midrange punch race to see the comparison
Same fuel/ weight load etc..

 

[swatski]

Well that is it. I'm getting me some. But you top speed is 5-6mph slower then my '18 242x. Is it a small trade off for the better low/ mid range?

So hard to tell with top speed, but with high temps and humidity I have not seen much more than 45mph before the switch from 6APs to 6CWs, I can;t tell how much I lost on top, maybe nothing.

EDIT: My before and after was different days, lake, weather, etc.

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[swatski]

I would like to see a real world side by side holeshot and midrange punch race to see the comparison
Same fuel/ weight load etc..

That would be nice albeit there is always some variation difficult to account for. But that would be ideal - having a "reference" boat to test against.

If I have a bit of time in the Fall I would consider doing the swap again, just for kicks. With something like L13 spacers it is relatively quick and easy and can be done on the ramp, with the impellers it is slightly more involved.

The change is real, no doubt bout it, both performance and sound.

These things impeller always baffle me, lol - in this case I expected a big drop in top RPM as the size difference is NOT negligible, the 6CW is visibly taller, the trailing edge pitch seems the same as far as the edge but it must "progress" more mildly (?) and the blades must be a tad longer as the leading and trailing edges line up at the same rotational spot. IDK...

I would venture to say anyone interested in better hole shot would be happy with this swap.

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[swatski]

Here is the 6CW (right) matching the trailing edge of the blade - exactly - with the 6AP (left):


Here are two brand new 6CWs - with the trailing edges matching up:


Impeller with different trailing edge pitch will no match, the edge of the blade will be higher or lower when sitting on the flat surface like in those pics.

I always check that all blades line up, and that has been the case with cross-matching these impellers. I had seen them out of wack before out fo the box, but these were perfect.

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