7100 RPM/41MPH Max

[Banditgrrr]

Went to the river yesterday and had performance issues (or at least I feel like there were). At max throttle, I was at 7100 RPM and topping out at 41 MPH. Does this sound right? Here's the relevant data. Just looking to know if this speed/RPM sounds right or if there's something I should look for.

1. Water was pretty flat
2. Air temp was 107, water temp was 71
3. In the bow: 1 adult (150 pounds), 1 kid (60 pounds). In the rear: 1 kid (50 pounds)
4. I upgraded to an SVHO and added a 2nd pisser for water flow
5. Impeller and wear ring seem to be good with no obstruction
6. Replaced the seal on the clean out plug 6 months ago and seems to be seated fine
7. Noticed there's about 8" of water in the ski locker but no idea how it's getting there. Relevant just because this would be extra weight.
8. Made sure that nut is adjusted on the throttle cable so there's maximum throttle
9. Bimini top is open for shade
10. I was headed down river so the current was with me, not against me

Could there be anything I'm missing? I would think I should be at about 7700 RPMs which would give me a few more MPH but also I'm assuming I could be wrong and 7100 rpm's and 41 mph would be normal in this situation.

 

[REM835]

As far as speed goes I don’t think you that far off. Weight in the bow always seems to scrub a few mph. That in addition to the Bimini being open. I would be concerned with the amount of water in the ski locker.

Your RPM does seem low but might be result of heat soak with the 107deg temps. The SVHO cooler helps but in my experience does not get rid of it completely.

For reference, I upgraded to the SVHO cooler but do not have dedicated pisser. I did do a high flow strainer though. I get just shy of 7500rpm and after running hard for awhile drop to 7200rpm. Prior to upgrade I would drop to 6800.

How has it performed in the past? Do you wet slip? There seems to be a lot of little things these are sensitive to. Any cavitation? Maybe check your air filter. Not sure, just throwing some stuff out there.

 

[Banditgrrr]

Appreciate the response. It doesn't seem like there's cavitation but I'm not getting that "get up and go" type of response out of the hole like some people with the Lucky 13 describe. I want to say I used to be up at the 7700-7800 and about 46-47 under the same conditions. I do not wet slip. My I live 30 min from the river so I take it out at the end of each day. Perhaps I'm just not remembering correctly. I'm going to try and track down why there's water in the ski locker. Going to try and look at the online diagrams and see where it may be coming from. I don't recall ever seeing water in the anchor locker. I'll check the air filter again but I thought last time I checked it, it seemed pretty clean.

 

[WildBillF1]

Sounds about right, it was a hot weekend. I was on Lake Mohave this weekend and saw similar performance.

 

[2kwik4u]

I'm on a mobile device so I can't see the year/model, but that seems pretty close to on target for a 155mm pump to me.

I was running 42mph at 7400 rpm yesterday in my '17 AR190. Two kids in the bow, 3adults and a toddler in the cockpit.

 

[Banditgrrr]

It's a 2015 AR192. I guess maybe I was wrong and perhaps 40-42 is the norm. I was thinking it should be closer to 47-48 under these conditions.

 

[WildBillF1]

It's a 2015 AR192. I guess maybe I was wrong and perhaps 40-42 is the norm. I was thinking it should be closer to 47-48 under these conditions.

Best I've seen on the GPS is 48.6 mph.

 

[Matts18]

You mention the Lucky 13 cone.....have you recently installed this? I understand that it can impact top rpm and speed depending upon how it is set up.

 

[Banditgrrr]

I have not purchased the Lucky 13. I've read a little information on here about them reducing cavitation but wasn't aware they can help with RPM and top speed. I'll do some more reading and if that's something that may help, maybe I'll purchase one. Just looks a little confusing on how it's supposed to be set up.

 

[2kwik4u]

I have not purchased the Lucky 13. I've read a little information on here about them reducing cavitation but wasn't aware they can help with RPM and top speed. I'll do some more reading and if that's something that may help, maybe I'll purchase one. Just looks a little confusing on how it's supposed to be set up.

@swatski did a SIGNIFICANT amount of R&D on the L13 setup with a 155mm pump. He has an excellent thread with testing and results around here somewhere. I keep saying I'm going to bookmark it, but never do.

Basically the L13 will allow you to load the pump to the point it will pull the revs down, or "stuff the pump" as some call it. You want to adjust the L13 with the included spacers until you don't have any cavitation, then adjust venturi nozzle diameter (by grinding), or impeller pitch until you get your revs back. The end result of this test/check process is no cavitation, and higher top speed from increased pump efficiency. It's a lot of testing/trial/error though.

I personally slapped the L13 in with all the spacers two seasons ago, and haven't touched it since. That was the setup I was running this weekend to get 41mph@7,400rpm. I have zero, and I mean freaking ZERO cavitation at this point. Even with some significant loading I can't get the impeller to slip. This tells me I can probably remove a few spacers (or repitch the impeller, or bore the nozzle) to get some of my revs back, as I'm currently only turning 7,400 rpm. If I could spin up to 7,600rpm pretty reliably I think I could pick up a few mph maybe. I don't want to sacrifice the holeshot "traction" though, and honestly I cruise around 30mph pretty much all the time anyway, so it might be waste effort for me.

If I remember right, the 192's have the same 155mm pump as the 190's. The 195's gt the upgraded 160mm pump right? If that's the case then it shouldn't matter what's spinning the impeller (supercharger or not), the output rpm and resulting speed should track pretty much the same between the engines.

 

[swatski]

That was the setup I was running this weekend to get 41mph@7,400rpm. I have zero, and I mean freaking ZERO cavitation at this point. Even with some significant loading I can't get the impeller to slip.

That is fantastic!
I wouldn’t change a thing!

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[2kwik4u]

That is fantastic!
I wouldn’t change a thing!

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I've been pretty happy with it. Really on the fence about adjusting it honestly. I've mostly left it alone because I haven't had the time to goof with it, however as the little one becomes more self sufficient my time is coming back to me.

I went back and watched my "launch" videos from the day I installed the L13 just now. There is a clear "bounce" in the tach on the first one. I don't think it was cavitating audibly, but you can watch the tach spike to ~7800 and then come back down a shade. In the second video it rises slightly more gradually, and there is no "bounce" or "spike" at the top.

Here's before (Launch is around 0:20 mark):

Here's after (Launch is around 0:05 mark):

edit:....also just noticed the speedo isn't telling too big of a lie at 40mph either. GPS was reading around 38mph, that's only a 5% error. so my 41@7400 this weekend might have been more like 39@7400. Either way I'm pretty happy with it as an normally aspirated boat at near sea level. Still accelerates faster and has the same top speed as my old 3.0L I/O that was a foot shorter.

 

[swatski]

I've been pretty happy with it. Really on the fence about adjusting it honestly. I've mostly left it alone because I haven't had the time to goof with it, however as the little one becomes more self sufficient my time is coming back to me.

I went back and watched my "launch" videos from the day I installed the L13 just now. There is a clear "bounce" in the tach on the first one. I don't think it was cavitating audibly, but you can watch the tach spike to ~7800 and then come back down a shade. In the second video it rises slightly more gradually, and there is no "bounce" or "spike" at the top.

Here's before (Launch is around 0:20 mark):

Here's after (Launch is around 0:05 mark):

Personally, I have always found hole shot and pulling power way more satisfying in these boats than chasing top speed (and taking minutes to reach it! Lol)

Conversely, nothing is less satisfying and more frustrating to me than not being able to get out of the hole when pulling, or loaded heavy.

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[haknslash]

Any time we had someone in the bow even just wife and kid it would drop the top speed 3-4 mph. I don’t recall my RPM’s dropping that low. Check your intercooler and supercharger charge pipe fittings as well for any boost leaks. I had a boost leak once and it dropped my performance to around your numbers.

 

[chrisinslc]

Personally, I have always found hole shot and pulling power way more satisfying in these boats than chasing top speed (and taking minutes to reach it! Lol)

Conversely, nothing is less satisfying and more frustrating to me than not being able to get out of the hole when pulling, or loaded heavy.

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Considering hole shot, I just tested my impeller which was adjusted a 3rd time by Impros. My performance is the best I have encountered thus far, but now when I hit it, RPM's shoot to 7800 RPM for a second or 2 and then come down to 7300-7400 and it starts to grab. I assume that is cavitation. Is there anything I can do about that or not really worry about it?

 

[swatski]

Considering hole shot, I just tested my impeller which was adjusted a 3rd time by Impros. My performance is the best I have encountered thus far, but now when I hit it, RPM's shoot to 7800 RPM for a second or 2 and then come down to 7300-7400 and it starts to grab. I assume that is cavitation. Is there anything I can do about that or not really worry about it?

The L13.

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[chrisinslc]

The L13.

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Since I am already struggling to get my RPM's up at my elevation, you still think the L13 cone will help?

 

[swatski]

Since I am already struggling to get my RPM's up at my elevation, you still think the L13 cone will help?

It will help with the hole shot, essentially eliminates impeller slippage. But it may shave 100-300 RPM on top which may be harder to regain.

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[sleepybear723]

107 outside, likely intake temp of 140+. I’d say you’re down about 50+ hp due to altitude density.

 

[Liveto99]

I don’t know if weight in the front of the boat changes the intake amount or the line of water flow through the pump but in my boat a couple people up front will knock a few miles per hour off the top speed.