Fi21 Prop Upgrades

[sporte77 5]

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.

[lovetosurf 48]

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.

[h20king 794]

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

[wheels 151]

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. 

[h20king 794]

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 

[wheels 151]

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. 

[h20king 794]

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

[h20king 794]

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 September 13, 2018 by h20king

[wheels 151]

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. 

[sporte77 5]

I had the stock 1235. So I chose the 2277 15x15.75 prop  (Fi21 -409 - at sea level).  Ran it today.  It lowered my surf RPMs (mostly full ballast/11mph) from 4100 to 3600.  No noticeable loss of holeshot.  About 1 or 2 mph increase in top speed.  But I know if we go to altitude- I’m going to have to get a 16x13 to bring.  So I’ll probably just keep the  15x15.75 on, and get a 16x13 as my spare.

[EliteV 1]

2018 fi21 running the 16x13 as suggested by dealership. They pre warned me about the growl but it doesnt bother me. Surf RPMs are good about 3400. Only downside is how much fuel you burn when you try and go fast ha. I try and cruise about 22mph to help with economy 

[Zinger16 0]

On 9/12/2018 at 6:07 PM, 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 

I just tried a 16x15 on my 2018 409 fi23. Worked great for normal driving but couldnt get up to speed with fully ballast.  i just got a 3409  16x13 .150 prop which ill be trying todo in the Willamette (sea level).  @H20 KING have you done any more work or testing with your prop?  I was hoping to have a little more top end...  we go upto green peter which is about 1200 ft so i need to ensure it works for a little elevation.  

[InfinitySurf 302]

@Zinger16  The 16x13 will work with no issue at 1200ft, you really dont start getting any kind of elevation motor changes till you are 2500+ so between 0-1200 I honestly doubt you will notice any change at all.

[Zinger16 0]

Just tried it last night and it is a great surf prop for sure but barely any top end..  I dont need to fly down the lake but would like to be able to run 36 -37 wot and cruise  at 30.  I had a 2279 15x15.75 and it seemed to be just barely to much...  They have a 15.5 x15 that looks tempting :-)

[InfinitySurf 302]

You may be able to get a prop customized by having them redo the cup. As I understand it, the cup can effect the higher speeds so perhaps that is an option. I would suggest calling ACME as they keep a lot of prop data for all the different boats and would be able to recommend something that may work better for you without having to buy props without knowing. Believe ACME also offers a program where you can buy a prop and try it.... and if it doesnt work send it back to get something else from them.

Everything I have heard tho had the 16x13 working the best for the FI. Dont know if you will get a 30mph cruise out of it since PCM says not to run over 4000rpm for "extended periods", so I would assume to get the most engine life you would want your cruising speed at or below 4000rpm. My SV244 without ballast will run 25mph @ 3500rpm & 30mph @ 4000rpm but also does 39mph @ WOT. I am stuck using a 14" diameter prop tho.