Jetting at altitude...

[Tahoe CAL]

Hi all,

Just joined the jet boat community with the purchase of a '16 242 Limited S E-Series this month. This forum has been super helpful as I was doing some research on which boat to go with / what to look (out) for, etc. So, thank you to all who contribute!

I've seen a couple of threads on here regarding performance related issues at altitude. I spent my first weekend on the water up in Tahoe (6200' MSL) and I'm experiencing lower than expected WOT RPMs (6200-6300) and speed (35mph). Engines have 80 hours, no cavitation, and seem to run very clean otherwise. Based on what I've read here I'm planning on:

• changing out spark plugs
• checking (perhaps removing?) air filter (unlikely to find anything)
• run higher octane (93) with ethanol trt (not sure how long the current tank has been in the boat - or what was in it)

Any other suggestions? I know I need to research a high elevation impeller. Anything I should be alarmed at beyond that? I haven't had a compression test done and I don't have a baseline WOT at or near sea level. Won't have that until October-ish.

Thanks much!

 

[djetok]

Hi all,

Just joined the jet boat community with the purchase of a '16 242 Limited S E-Series this month. This forum has been super helpful as I was doing some research on which boat to go with / what to look (out) for, etc. So, thank you to all who contribute!

I've seen a couple of threads on here regarding performance related issues at altitude. I spent my first weekend on the water up in Tahoe (6200' MSL) and I'm experiencing lower than expected WOT RPMs (6200-6300) and speed (35mph). Engines have 80 hours, no cavitation, and seem to run very clean otherwise. Based on what I've read here I'm planning on:

• changing out spark plugs
• checking (perhaps removing?) air filter (unlikely to find anything)
• run higher octane (93) with ethanol trt (not sure how long the current tank has been in the boat - or what was in it)

Any other suggestions? I know I need to research a high elevation impeller. Anything I should be alarmed at beyond that? I haven't had a compression test done and I don't have a baseline WOT at or near sea level. Won't have that until October-ish.

Thanks much!

If the impellers are stock, you might need to look at another set of impellers or repitch the ones you have.

https://jetboaters.net/threads/550-set-of-3500-altitude-pitched-impellers.11261/

https://jetboaters.net/threads/2015-ar240-upgrades.8056/#post-390231

@J-RAD @Williamsone46 i are in Utah and may be able to help

@swatski also the man the tinkers with everything

 

[Recoveringfiberglassaddic]

Just out of curiosity as the new guy that lurks around here....

For higher elevation impellers is the pitch just changed as diameter is what it is?? Do you go to a flatter pitch?? I'm assuming theres some performance difference between stainless and aluminum as well??
For guys wanting to surf and carry additional ballast/lead would they benefit from a bigh altitude impeller??

To the OP, sorry in advance for the thread jack. Figured the answer to some of those questions may help you make an informed decision as well.

 

[Julian]

run higher octane (93)

Everything I've read says that altitude actually prevents detonation, so you can actually use a lower octane fuel and avoid detonation. Running 93 in a boat that calls for 87 is a waste of money - but some people think that high octane fuels have more cleaning additives (although all fuels are required to have cleaning additives). I'll be curious to see if your experiments prove all these articles to be wrong.....

 

[rrmidden]

Everything I've read says that altitude actually prevents detonation, so you can actually use a lower octane fuel and avoid detonation. Running 93 in a boat that calls for 87 is a waste of money - but some people think that high octane fuels have more cleaning additives (although all fuels are required to have cleaning additives). I'll be curious to see if your experiments prove all these articles to be wrong.....

Around here, if you want to avoid Ethanol, you have to go with higher octane fuels. Most places outside of the Milwaukee Metro Area will have 93 Octane without Ethanol. Up north there are a few more places that have 89 without Ethanol. I try to avoid Ethanol as much as possible, my truck (Tundra Crewmax) gets roughly 15% better fuel economy with Ethanol Free Gas. So typically, the cost of the higher octane fuel is offset by the better mileage.

 

[Gym]

I have discussed density altitude on this forum many times. Basically density altitude is actual MLS (altitude above Mean Sea Level) corrected for temperature, air pressure and humidity. For example @Tahoe CAL you're operating at 6200 feet MLS. Your boat will perform as if it is at 6200 feet ONLY if the temp is 38F, 29.92 hg air pressure and a dew point of -30F. Now let's look at more realistic conditions for your location. Let's say it's an 80 degree day with nominal air pressure and humidity. This will give you a density altitude of 11465 MLS. Meaning your car, boat or your body is going to think your at that altitude. Your car and boat have a computer to lean out the fuel mixture to accommodate the thinner air but the cost of doing so is performance. The only way to resolve this issue is to force more into the engine so you can burn more fuel to get more performance.

You can prove this in October-ish when you go to lower elevations to run your boat.

 

[Julian]

Around here, if you want to avoid Ethanol, you have to go with higher octane fuels. Most places outside of the Milwaukee Metro Area will have 93 Octane without Ethanol. Up north there are a few more places that have 89 without Ethanol. I try to avoid Ethanol as much as possible, my truck (Tundra Crewmax) gets roughly 15% better fuel economy with Ethanol Free Gas. So typically, the cost of the higher octane fuel is offset by the better mileage.

Premium here in NC is 70 cents more per gallon which by my quick math equates to just a little over 25% more costly, so you are paying 10% more for not using ethanol....and the yamahas engines and tanks are designed to handle ethanol. That said....I get much of my gas on the lake...which is even more expensive....BUT no ethanol!!! So I just bend over!

 

[Gym]

Changing your spark plugs to iridiums and changing your fuel to higher octane will lighten your wallet, which will lighten your boat but it won't change physics.

 

[swatski]

• changing out spark plugs
• checking (perhaps removing?) air filter (unlikely to find anything)
• run higher octane (93) with ethanol trt (not sure how long the current tank has been in the boat - or what was in it)

None of those, really. Maybe air filter if it's clogged.

As far as things that would actually make a difference I would consider ribbon delete and impeller repitch.
The first is a DIY, the second - I would call Impros and talk to Glenn.

Using premium at high altitude in a Yamaha 1.8 engine with no ECU reflash you will run slower rather than faster, if anything. You do want lower octane, more combustible, so 87 or less.

My 0.02

--

 

[Matt Phillips]

I am in Tahoe all summer, and this is my third summer on this boat and had 5 summers on the 09. It's common to lose about 1,000rpm off the top end due to elevation.

Here's some stats I notice: I only get 6200-6300 out of the engines at the lake. 35MPH seems a bit slow, but as I can get up to the low-mis 40s. One thing to pay attention to is the weight you have in the boat as well as the wind and waves as all three will affect your top speed dramatically. For example, I had 5 people in the boat on Saturday and she was doing about 25MPH at about 5800rpm. on July 4th with 12 people in the boat, it took 6000rpm and about 2-3 minutes before she climbed up on a plane and she would only do about 13mph.

Compare that when I had the boat down at Nacimiento at the beginning of the season (or even up at Shasta) and she will turn 7000+ and top out close to 50 mph.

These normally aspirated engines will struggle a bit to breathe up at the lake.

For those who rep itch for altitude, how does it affect lower elevation performance?

 

[Tahoe CAL]

None of those, really. Maybe air filter if it's clogged.

As far as things that would actually make a difference I would consider ribbon delete and impeller repitch.
The first is a DIY, the second - I would call Impros and talk to Glenn.

Using premium at high altitude in a Yamaha 1.8 engine with no ECU reflash you will run slower rather than faster, if anything. You do want lower octane, more combustible, so 87 or less.

My 0.02

--

Very helpful. Thanks for the reply and the suggestions

 

[Tahoe CAL]

I am in Tahoe all summer, and this is my third summer on this boat and had 5 summers on the 09. It's common to lose about 1,000rpm off the top end due to elevation.

Here's some stats I notice: I only get 6200-6300 out of the engines at the lake. 35MPH seems a bit slow, but as I can get up to the low-mis 40s. One thing to pay attention to is the weight you have in the boat as well as the wind and waves as all three will affect your top speed dramatically. For example, I had 5 people in the boat on Saturday and she was doing about 25MPH at about 5800rpm. on July 4th with 12 people in the boat, it took 6000rpm and about 2-3 minutes before she climbed up on a plane and she would only do about 13mph.

Compare that when I had the boat down at Nacimiento at the beginning of the season (or even up at Shasta) and she will turn 7000+ and top out close to 50 mph.

These normally aspirated engines will struggle a bit to breathe up at the lake.

For those who rep itch for altitude, how does it affect lower elevation performance?

This is really helpful, Matt. Thanks for the reply. Out of curiosity - have you done any of the other modifications mentioned on this thread (ribbon delete / impeller re-pitch)? Thanks again!

 

[Tahoe CAL]

I have discussed density altitude on this forum many times. Basically density altitude is actual MLS (altitude above Mean Sea Level) corrected for temperature, air pressure and humidity. For example @Tahoe CAL you're operating at 6200 feet MLS. Your boat will perform as if it is at 6200 feet ONLY if the temp is 38F, 29.92 hg air pressure and a dew point of -30F. Now let's look at more realistic conditions for your location. Let's say it's an 80 degree day with nominal air pressure and humidity. This will give you a density altitude of 11465 MLS. Meaning your car, boat or your body is going to think your at that altitude. Your car and boat have a computer to lean out the fuel mixture to accommodate the thinner air but the cost of doing so is performance. The only way to resolve this issue is to force more into the engine so you can burn more fuel to get more performance.

You can prove this in October-ish when you go to lower elevations to run your boat.

Really appreciate the reply, Gym. I've read your comments on density altitude over the past few weeks - they're helpful. I'm a private pilot -- and have studied (and experienced) DA in Cessnas. We have specific tools to calculate the loss of performance for flight characteristics. I haven't found similar performance charts for boating (yet). I was fully expecting performance loss -- just wasn't expecting to lose ~1000 RPMs and +15mphs. That said, in reading the responses sounds like I'm in the ballpark. Which is great news because my original concern was - is there anything else going on with the engines that I need to worry about (compression/timing, etc)? Again - appreciate the help!

 

[Tahoe CAL]

Everything I've read says that altitude actually prevents detonation, so you can actually use a lower octane fuel and avoid detonation. Running 93 in a boat that calls for 87 is a waste of money - but some people think that high octane fuels have more cleaning additives (although all fuels are required to have cleaning additives). I'll be curious to see if your experiments prove all these articles to be wrong.....

Thanks! And, you hit the nail on the head -- I was thinking (perhaps erroneously) that running a tank of higher octane might "run a little hotter" and clean out the injectors. Low probability "fix", but thought it was worth a shot once. Feeling more confident that the only thing awry is the effects of altitude.

 

[swatski]

running a tank of higher octane might "run a little hotter" and clean out the injectors

That may work in several modern vehicles however the 1.8 N/A Yamaha engines do not have knock sensors to pull/adjust timing, either way.

You could talk to Riva guys about getting an ECU reflash, it will help with fuel economy (albeit requiring premium) and give you some power gain in mid range but there is really nothing they can do at the top end at WOT, so your top speed will not increase.

--

 

[Gym]

Really appreciate the reply, Gym. I've read your comments on density altitude over the past few weeks - they're helpful. I'm a private pilot -- and have studied (and experienced) DA in Cessnas. We have specific tools to calculate the loss of performance for flight characteristics. I haven't found similar performance charts for boating (yet). I was fully expecting performance loss -- just wasn't expecting to lose ~1000 RPMs and +15mphs. That said, in reading the responses sounds like I'm in the ballpark. Which is great news because my original concern was - is there anything else going on with the engines that I need to worry about (compression/timing, etc)? Again - appreciate the help!

Being familiar with DA is a good thing. You can use your E6B or DA calculator for the boat just as you do for the plane. Obviously you're not using it to calculate take off distance or climb performance over a 50 foot obsticle but it will calculate the DA your boat is operating at. The only way to change the calculation is to ram more air in and/or cool the air going into the engine. Both of those solutions will cause the ECUs to deliver more fuel to the denser/cooler air giving you more power. Keep the blue side up in the plane and down in the boat.

 

[W3bexec]

I boat at 5776 with the lake at 90% full, need to get them re-pitched for sure. Even re-pitched I top out at 7100 RPM and 46 MPH on a good day.

 

[dzeppos]

Your issue is very normal. I was boating at Shaver Lake with my 16 242- just a few hours south of you in June - at an altitude of 5500-5600 Feet. My top speed was 39 to 41 depending upon fuel/and passenger load. Couldn't get above 6700 rpms (where at Lake Nacimiento - I can do 48-49 all day). I usually boat in low altitudes, so i'm not bothering with changing my impellers. However, on the fence about the Ribbon Delete. They say it makes a more significant performance difference for high altitudes, but concerned about additional noise (and possible wife complaints). Don't mess with the gas -87 Oct is the way to go at all times.

PS - I've always wanted to try Tahoe - and I'm sure it was beautiful.

 

[Tahoe CAL]

None of those, really. Maybe air filter if it's clogged.

As far as things that would actually make a difference I would consider ribbon delete and impeller repitch.
The first is a DIY, the second - I would call Impros and talk to Glenn.

Using premium at high altitude in a Yamaha 1.8 engine with no ECU reflash you will run slower rather than faster, if anything. You do want lower octane, more combustible, so 87 or less.

My 0.02

--

@swatski (or others) can you confirm that this (RIVA Yamaha 08-12 1.8 NA Intake Manifold Upgrade Kit) is the correct part for the ribbon delete. I called RIVA and they could not confirm that the 2016 is the same manifold. Their part is "certified" for years '08-'12. Based on all of the threads I've read I'm pretty sure this will work but I know you've done this so I thought I'd ask. Thanks in advance!

 

[swatski]

@swatski (or others) can you confirm that this (RIVA Yamaha 08-12 1.8 NA Intake Manifold Upgrade Kit) is the correct part for the ribbon delete. I called RIVA and they could not confirm that the 2016 is the same manifold. Their part is "certified" for years '08-'12. Based on all of the threads I've read I'm pretty sure this will work but I know you've done this so I thought I'd ask. Thanks in advance!

I can check later for you but the only way to know for sure is to look up the parts fiche and cross reference intake part number, they (Yamaha) switched it around from plastic (smaller diameter) to metal a couple of times in various models with no particular pattern.
Need to know if CARB (four star) model but this is one parts side easy to check part numbers in fiches:

2016 Yamaha 242 LIMITED S (SAT1800C-R) OEM Parts, Babbitts Online

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