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sporte77    4

I wanted to start a thread for Fi21 owners who have upgraded their stock prop.  I've got a 2018 Fi21 with the PCM L96 (409) engine.

My stock prop is the ACME 1235 (14.5x14.25).  At sea level, I'm seeing about 4100-4300 RPM surfing w/ full ballast & about 10.5-11mph.  Top speed is about 33-34 at 4900 RPM.  Also, the holeshot is just fine.

Anyone gone with a bigger prop to get the RPMs down?  Please share your actual experience.

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lovetosurf    46

Yes & yes, we run the 16x13 prop on our Fi23 409, same shaft with 500lbs extra lead at 5500ft elevation. Surf Rpms are between 3500-3800 depending on speed and crew, top speed is 32mph wot.

I personally think if you’re at low elevation you could run the 16x15, acme just recently came out with one for that shaft size, think it’s a 3337 if I recall correctly.

For what it’s worth I personally know 2 other FI owners locally running the same setup all with close to 100 hrs this season and no complaints. Keep in mind that up to a year or 2 ago even the supercharged motors were on 1 1/8th diameter shaft.

hope that helps.

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h20king    772

We run the 16 X 13 and are at sea level. Tried other props but the 16X13 works best.

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wheels    143
5 hours ago, h20king said:

We run the 16 X 13 and are at sea level. Tried other props but the 16X13 works best.

H, did you go back to running your 16x13, read you were getting prop growl from it and not on the 15.5”? I just put a 16x13 on my 17 Ri237 with the h6 and I got prop growl from it. The prop was a little too aggressive also so after spending lots of time talking to Jim from acme, he has no idea why it’s growling, I am going to try the 16x15 this weekend. 

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h20king    772

Yep back to the 16X 13 yes I do get some growl but it is what works. I went with the 15.5 X 15.5 for a while and it worked great at sea level but we went to one of our lakes at 2000ft and could not get to speed so we went back to the 16X 13. I am having some more cup taken out to try to get rid of the growl 

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wheels    143
2 minutes ago, h20king said:

Yep back to the 16X 13 yes I do get some growl but it is what works. I went with the 15.5 X 15.5 for a while and it worked great at sea level but we went to one of our lakes at 2000ft and could not get to speed so we went back to the 16X 13. I am having some more cup taken out to try to get rid of the growl 

More cup taken out? That will make it even more aggressive and raise rpm do you need more torque? I must have spent an hour talking to Jim at acme about this and he was amazing. He said we would add 45000 of cup to the 16x13 for my instance which would bring that prop to around a 14” pitch. The 16x13 was more power than I needed and I feel I have room to drop rpm and still have plenty of power. He said the 16x15 with its lower cup than the 16x13 will really be like a 16x14.5. I am eager to see what happens with the 16x15. I have all the stats on rpm and speeds both loaded and unloaded from my 15x15.75, and 16x13 to compare to. 

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h20king    772

Acme recomend I have. Thirty thousands removed from the cup when I called about the prop growl  so going with there advice 

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h20king    772

Just read your post again and believe acme is just guessing and really has no idea. I spent a hour on the phone with Jim over a month ago guess I better call him again before  I have the prop reworked LOL 

Edited by h20king

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wheels    143
31 minutes ago, h20king said:

Just read your post again and believe acme is just guessing and really has no idea. I spent a hour on the phone with Jim over a month ago guess I better call him again before  I have the prop reworked LOL 

Yeah in hear ya, I talked to my dealer today who has been out in lots of the 18 ri237’s with the 16x13 and he said no growl. The only difference is the prop shaft size, well I guess the hill is a little different at the back corners too but can’t see either of those making a difference. Will post up my  findings when I try the 16x15 this weekend. 

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