High Altitude Impellers

[FSH 210 Sport]

This is for anyone running a Yamaha jet boat that is looking to gain some performance due to horse power loss because of altitude and high elevation. The rule of thumb is 3% horsepower loss per 1000‘ of elevation gain. Typically the hp loss is greater due to heat and or high humidity. For me, at 5000’ on a 90* day, the horse power loss will be 22-25% due to that much less air. The hp loss applies to any normally aspirated engine.

You can see from the density altitude calculator below that the altitude my engines think it is on a 90 day is 8240’, and on this day the hp loss is just a hair shy of 22%.



I talked with Glen at Impros this afternoon, short story, they have a lot of experience with setting up impellers for high altitude. This looks like the safest way to increase performance on my 210 FSH.

PWC and Jet Boat Impellers

www.impros.com impellers

impros.com

 

[Calphor]

Impros is one of several companies (probably the best known) that repitch impellers to allow you to recover top end rpms. It is a relatively common way in the Intermountain West to get most of the performance that the folks closer to sea level get out of their boats.

 

[FSH 210 Sport]

Impros is one of several companies (probably the best known) that repitch impellers to allow you to recover top end rpms. It is a relatively common way in the Intermountain West to get most of the performance that the folks closer to sea level get out of their boats.

Thanks for your comment Calphor! I know that outdrives can either use a different pitch prop and or lower gears the out drive but did not know until today that different pitch blades were a thing for jet boats..

Glen also said that they vary the pitch slightly between port and starboard so your engines turn the same rpms at WOT..

As with different props, there are different options with the impellers, you can get a low end one for towing skiers, towables etc. in addition to just getting a set of “ lower gears”

 

[FSH 210 Sport]

Update:

I got to test my Impros tuned Solas high altitude impellers over the last few weeks. They are about as perfect as can be for 5000’. At 5000’ I get 7950 rpms on both engines now, whereas before the best I could get was around 7100 rpms, and the port engine always turned faster than the starboard with the OEM impellers, with Glen tuning each impeller for its intended installation, now the port and starboard engines reach the same peak rpms.

At one of the lakes around here that is lower at 3200’, I’m at the full 8000 rpms. When I go to east river with an elevation of 1600’ I’ll probably be under propped so to speak, but I think Glen helped me to get a great compromise.

The weather now is cool to cold, air temps in the 30’s-50’s with the water temps at 44*. Those peak rpms will drop off some when the weather gets up to 95* and the density altitude goes up to 8250’ from 5000’.

Best cruise of 27mph has now increased 500 rpm from 6000 to 6500. Fuel consumption increased from 7.9-8 gph to roughly 8.3-8.4gph. If I drop the speed to 25.-26 on the water wheel, I get 7.9-8gph.

Boat:
Dry weight: 3003
Fuel: 52 gallons= 312
Full live well: 215
Gear: fishing, tools etc… 200
Three persons on board: 530
Trolling motor batteries & charger: 103
Trolling motor: 40
___________________________________
Test weight 4403

Conditions:
Solas impellers
5000’ elevation
Temp 45*
Dew point 35*
Altimeter 30.01
Density altitude 5252’
Relative density 85.52%

OEM impellers
5000’ elevation
Temp 90
Dew point 50
Altimeter 29.9
Density altitude 8240’
Relative density 78.03%

Best Fuel economy:
OEM impellers: 27mph, 8gph @ 6000 rpm = 3.37 mpg.
Solas high altitude: 27mph, 8.4gph @ 6500 rpm = 3.21 mpg.
Loss of .16 mpg. and 8 miles of range.

Top Speed:
OEM 33 mph @6900-7000 rpm
Solas high altitude 41 mph @ 7950 rpm

Summary:
With the solas impellers the boat does not have that hard punch off idle to full throttle, and you notice less bite when maneuvering using split or dual throttles. However, what the impellers lack in hole shot, they quickly make up for in full power thrust as the boat gets moving. There is a bit of cavitation from standstill to full throttle with the Solas impellers, however, after helping @Zeusmotorworks with his cavitation issues and realizing that my clean out plug seals are shot as well, I cannot assertively say whether or not the Solas impellers cavitate or not. Once I get my new seals and re test I will post the results. There is no cavitation any other time that I know of, even when making such tight turns the boat winds down to nothing.

I do not have a time to 30mph for the solas, but the OEM’s were about 6 seconds, but, it seems to move right along. When moving along at full throttle and making tight turns the speed does not fall off like it did with the OEM impellers.

Last summer I had 6 people on the boat and was towing Big Mable HD with two people on it, the only way I could get on plane was to head downwind, and I could barely get on plane 6400 rpms. Everyone still had a great time but I was not happy with that level of performance. I am confident that with the tuned Solas impellers the towing performance will be greatly improved, as well as the fuel mileage being improved under heavy load as well.

While it was a long road to get to this point, I’d say the juice is definitely worth the squeeze. My boat will, relatively speaking, now rip along and is super fun to throw around after a long day of fishing, and there was a minuscule impact to best cruise fuel economy, I’d call that a win. I’ll be doing some long cruises this summer and will be watching the long run fuel economy.

 

[FSH 210 Sport]

Update:

So now that summer is really here and daytime temps are in the 90’s at the lake which is at 5000’ above MSL. With yesterday’s atmospheric conditions this produced a density altitude of 8382’.




With fuel load of 88%, just me and gear the engines topped out around 7500 rpm’s and 36-37 mph on the water wheel and gps. So it is clear the 50° increase in ambient temperature resulted in a loss of 400 rpm from my last update in May.

Just for the heck of it I pulled the air cleaners and made another speed run in each direction, I picked up another 200-250 rpm’s so I ordered a set of Riva racings K&N drop in replacement air filters, while mine are yellowed somewhat, they do not seem to be oil fouled. Hoping that these filters will get me those 200 rpm’s I’m losing with the paper filters.

RIVA Yamaha EX/EXR/VX (TR-1 engine) Replacement Performance Air Filter

Our RIVA Yamaha EX/VX (TR-1 engine) Replacement Performance Air Filter directly replaces the stock paper element delivering performance through greatly improved air flow without sacrificing filtration or reliability.

rivaracing.com

Fuel economy is holding pretty steady at 3-3.1 mpg, the range is pretty broad, it holds these economy numbers between 7.7 and 9 gph albeit with slower and higher cruise speeds / rpm’s respectively.

Last week I was at another lake who’s altitude is 3200’, it was hot and I had three other people onboard. I don’t have the info to run an accurate density altitude, but if input yesterdays dope but reduce the above MSL to 3200’ it shows a density altitude of 6193’, roughly 2200’ of elevation drop. At that lake I was getting almost 8000’.



I‘m pretty happy with how the impellers are working out for my area and appear to be a great all around compromise in performance and fuel economy for altitudes from 1600’ to 5000’. I have yet to get over to east river and it’s 1621’ above MSL altitude, once I do I’ll report back.

Im hoping this next week with ambient temps forecast to be near 100° we will break out the tubes for the first time this year and see how the boat performs compared to last year.

 

[FSH 210 Sport]

Update:

Was at a lake that is 3200’ with an air temp of 95°. Had two of my friends with me, full fuel and their gear. Hit 8000 rpm and 41 mph on the water wheel and 38 mph on the gps.

I’m super happy with these impellers, perfect compromise for my needs.

 

[FSH 210 Sport]

Update:

Finally made it over to lake Oahe …
Elevation1620’,
95° air temp in the afternoon, and high 60’s in the morning,
water temp 78°
80% fuel,
Aux tank (22 gallons) 100% fuel

Density Altitude 4247’


In the cooler part of the day rpm’s are what appears to be 8150 / 8200 rpm at wot so I’m assuming the engines are up against the rev limiters, 42 on the water wheel 39.5 mph gps, about 7.5 seconds to 30 mph. There is a notable difference in power, and you can see it in the density altitude of 2390’.



In the afternoon I’m getting 8000 rpm, 41 mph on the water wheel, 38 gps. Those stats are with just me on board, with my friends son who is 205# the speed was a bit lower, maybe 36 mph, and mpg was 2.6-2.7 with 100% fuel on both tanks, I’ll get some more mpg stats today as I’m cruising up to at least Cow Creek Marina and then on up to the “Combine” land mark, probably a 40 mile round trip. I wanted to make a run up to Mobridge and back, at least 250 mile round trip but that trip doesn’t look like it’s in the cards this time, it’s supposed to get windy tomorrow with 20 mph winds and gusts to 32 mph gusts out of the south east which would make for some good size waves on the way back.

Again pretty happy with the overall compromise on these impellers, they work good at my local lake on a hot day, 7500 rpm, and here on a hot day 8000 rpm. Maybe a little more pitch down here would net a tiny improvement in speed, and perhaps an increase in mpg, but then they’d be dogs up high.

 

[FSH 210 Sport]

On the last day at Oahe I put in around 0500 hrs to fish for a few hours before I had to go, right before I left around 0900 I decided to do a little rip around the water it was a little breezy and a 2’ ground swell. Upwind and head sea was 39 on the water wheel with both engines revving over 8000. Down wind and following seas was 42 maybe 43 on the water wheel and 40.3 on the gps, the fastest I’ve seen it go since the day I test drove it on the Mississippi River. It was around 68°, and I had a 46% fuel load. I suspect that with the OEM impellers there might be a bit more speed to take advantage of the lower density altitude.

Again great all around impellers.