5.0 GL SX Volvo Prop selection at altitude

[5280glastron]

I've been all over the web and these forums trying to find some comparison points for my boat, engine and altitude for prop selection this winter. I wanted to share my results after a few test runs and 2 prop variations so other's could reference my experiences.

I also have a question that's been really bugging me, that I'm hoping for feedback on as well.

I bought a 2001 Glastron 195 this in January. I live in Denver, and purchased the boat from a guy in Pueblo who took the boat only to that lake. Pueblo is at a lower elevation 3000ish if I remember right. He had a bit chewed up 3 blade aluminum prop on it that was a 19" pitch. I knew from experience that this was probably more prop pitch than the boat needed even at that elevation, especially for my usage (slalom skiing).

Elevation at my local lakes is a mile high (5280 ft.) so if I wanted good acceleration for skiing here, I'd need to go down in prop pitch. I wanted to test out the existing prop on a local lake to get WOT range with the prop (despite the fact it was already a bit chewed up from hitting something in reverse, causing extreme cupping on the trailing edge). I got it on the lake in March (yes, somehow there was open water here in Denver in March, although only at the smaller local lake Cherry Creek).

My test day results were:
WOT 4000-4100 (trimming to the absolute max before cavitating then returning the trim just beneath the water) and I managed to get the boat to 41-42 MPH (GPS). (300lbs of gear on boat with full tank)

I knew the bad prop was having some impact, most likely on the max MPH was my impression. So I ended up buying a Solas HR Titan 4 blade 15" pitch.

I just got back from the lake test of the new prop and this is where my results have me wondering a few things. The lake test results got interesting.
WOT 4300-4400 (the minimum Max RPM for this engine) and I got up to 39-40 MPH (GPS). (500lbs of gear on boat with slightly less fuel 85-90% full).

So, I added some weight and increased my RPM by 300-400 but why so little?? The previous prop was 19" and a RPM change per one inch of pitch change should be 100-200 RPM so I really suspected that I might be over revving at 4800-5000 RPM.

I've done some prop slip calculations too, and these have me even more confused. For example:
Prop Slip Calculator | Propellers | Mercury Racing
Pitch: 15
Ratio: 1.6
RPM: 4400
Speed: 39
Slip: 0%

So somehow I'm achieving 0% slip? That's not possible. So with the cupping on the HR Titan, I adjusted pitch to 16 to account for this supposed impact of cupping and it still says my slip is 6% that seems impossibly low.

Am I crazy or does is my RPM gauge lying to me? If I was at 4800 RPM in reality, that would seem more likely as the slip goes to 8% and with cupping and possible 100-200 RPM range that put me at 10-15% slip that seems to be the more accurate range for a 4 blade.

Any thoughts? The boat only weights from 2250 - 2500 empty so it's lightweight but Is it even remotely possible I'm getting 0%-6% slip as the raw numbers indicate?

 

[Sea Rider]

Re: 5.0 GL SX Volvo Prop selection at altitude

Will that combo be living at 5280 ft of elevation ? You could maximize engine performance installing a high elevation carb kit. Usually comes in 1000 Mt increments. The higher the altitude, the less diam the jets. Check if there's a available kit for that engine assuming it's a carbed model. Can play with less jets along less pitch props to bump rpm higher. Combo will perform much better than if playing with prop alone.

Happy Boating

 

[dan02gt]

Re: 5.0 GL SX Volvo Prop selection at altitude

On a good day you would probably be getting around 9-10% slip with that setup. So I suspect you're correct that your tach is reading a little low.

 

[steelespike]

Re: 5.0 GL SX Volvo Prop selection at altitude

If we go backwards 40 mph,typical slip of 13%,15" pitch and 1.60 ratio we get about 5200 rpm.
Maybe not that high but you will have borrow a shop tach to know for sure what you have.
We know your speed is right,your ratio is right,prop is right 13% slip is pretty typical
Lower slip would calculate lower rpm but at 10% we are still off it's just a matter of degree.

 

[5280glastron]

Re: 5.0 GL SX Volvo Prop selection at altitude

Will that combo be living at 5280 ft of elevation ? You could maximize engine performance installing a high elevation carb kit. Usually comes in 1000 ft increments. The higher the altitude, the less diam the jets. Check if there's a available kit for that engine assuming it's a carbed model. Can play with less jets along less pitch props to bump rpm higher. Combo will perform much better than if playing with prop alone.

Happy Boating

I can't seem to find anything on carb kits or rejetting (i'm too young to know hardly anything about carbs). Any chance you can point me in the right direction?

I thought about going out and getting a 4 barrel carb but I'm down on the high cost at this point. If rejetting will give me 5-10% back what altitude took away it'll probably be worth it. Esp. if my tach is reasonably accurate.

 

[5280glastron]

Re: 5.0 GL SX Volvo Prop selection at altitude

If we go backwards 40 mph,typical slip of 13%,15" pitch and 1.60 ratio we get about 5200 rpm.
Maybe not that high but you will have borrow a shop tach to know for sure what you have.
We know your speed is right,your ratio is right,prop is right 13% slip is pretty typical
Lower slip would calculate lower rpm but at 10% we are still off it's just a matter of degree.

So you're siding with the tach being off ~500 rpm? I actually have a shop that'll be able to investigate, but I'm trying to see if that's really what's going on here. Is there something about the HR Titan's cupping that could be giving us some false readings for a 15" to say our pitch calculations are inaccurate?

 

[steelespike]

Re: 5.0 GL SX Volvo Prop selection at altitude

The Titan could lower slip being a 4 bld. cupped prop. Perhaps to single digits but unlikely.
It is some times suggested to calculate cupped props at an inch higher than the listed pitch.
But it seems this would aggravate our numbers.
Your tach is fairly young But still could be off 500.
Right here recently we have had two tachs at about 1500 rpm high.

 

[jimmbo]

Re: 5.0 GL SX Volvo Prop selection at altitude

The Holley 2 bbl is almost the Perfect size for that engine up to 5000 rpm at sea level. Going to a 4 bbl, unless very small is not going to help you at all. On a Holley, changing the jets will mainly affect the main circuit metering, when the power valve opens that circuit will still richen the mix up the same avount as before, as it has its own metering orfices. Overall the mixture will still be richer than optimiun at WOT, and not easy to change on the power circuit. Also with higher elevations a change in the power valve opening point is also needed.

 

[Sea Rider]

Re: 5.0 GL SX Volvo Prop selection at altitude

If it's a carbed model engine, could check with Volvo if they happen to have high altitude carb kits, if probably do, get the 5 K Ft kit. According to my elevation experience (Andes thing) the combination of jets and props produces a much better engine performance, that's with outboards. Inboards probably have their own tech issue.

If injected should have a kind of automatic high elevation compensator as found in cars, but that we don't know for sure ?

Happy Boating

 

[5280glastron]

Re: 5.0 GL SX Volvo Prop selection at altitude

I can't seem to find anything on carb kits or rejetting (i'm too young to know hardly anything about carbs). Any chance you can point me in the right direction?

I thought about going out and getting a 4 barrel carb but I'm down on the high cost at this point. If rejetting will give me 5-10% back what altitude took away it'll probably be worth it. Esp. if my tach is reasonably accurate.

Wanted to cycle back to this. Any help on finding a high elevation carb kit? I don't even know if rejetting is a separate part or just configuration like timing or fuel. I'd be a big fan of anyone who could link to such a kit.

 

[Sea Rider]

Re: 5.0 GL SX Volvo Prop selection at altitude

Rejetting is taking carb appart and changing internal standard jets for less internal diam ones, as to pass less fuel and air into combustion chamber to compensate power loss at higher altitudes. The highest the altutude, the worst the engine will work. Check with Volvo, probably have them. A combination of jets + less pitch will make the day. On carbed 2-4 stroke outboards no need to play with timing.

Happy Boating

 

[bajaunderground]

Re: 5.0 GL SX Volvo Prop selection at altitude

5280G...

I'm actually at the same point in deciding what to do?

I have the below Chris Craft with the Ford 5.0FL with 1.66 gears. Currently running 39-40mph (GPS) 4,000-4,100rpms with 3 blade aluminum 19P prop. My WOT sweet spot is 4,200-4,600rpms. I just ordered the 17P Solas HR titan 4 blade stainless steel. I have not adjusted for altitude (boat was sold at Rocky Mountain Boat Company in Pueblo and lived it days in the reservoir -~4,300'~ and around Colorado) I think the 19 is too much prop for this boat/set-up (2,650 dry weight). I'll report back what I find once I get her run.

Your correct in assuming the you will be around 10% slippage with that set-up. I, personally, wouldn't mess with re-jetting the carb as if it's a Colorado boat originally, then it was possibly set-up for this elevation from dealer/factory? I'm betting your tachometer is off? What's the HP rating on that 305? 220hp?

I run at Horsetooth Res. in Ft. Collins (~6,300') and run about 5 mph slower with my Baja and the 21P prop (compared to Pueblo).

~Brett

 

[jestor68]

Re: 5.0 GL SX Volvo Prop selection at altitude

A "mile high" is not considered "HIGH" altitude and does not normally require changing jets.

It usually just requires adjusting prop pitch, which you've done.

Your mistake in playing with the slip calculator is that you failed to add the inch of pitch(to 16) to account for the cupping on the HR Titan prop

If you do that and use a normal 9% slip, it comes out to about 4752 rpm.

With a range of 4400-4800, you're good and your tach appears to be wrong. Sometimes cleaning the pins on the back of the tach(where the harness plugs in) returns things to normal.

FYI; changing jet sizes does not really produce more power at altitude; it just saves a little gas as the motor is not running a little rich.

Consult a Volvo dealer in your area concerning any jet changes. Be advised that if you change jet sizes(smaller), you cannot operate at lower altitudes any more without risking blowing up your motor by running lean.

Reading the plugs will tell you if a jet change might be needed.

 

[Sea Rider]

Re: 5.0 GL SX Volvo Prop selection at altitude

Yep, will need to determine which is considered a "altitude", usually above 2 K meters will need a pitch change and a carb rejet and pitch change above 3 K meter. That's if available jet kits are found. At high altitudes, less diam jets will help the engine to start better specially on first starts.

Both will compensate power loss as to feel the engine more responsiveness, not as to sea level though, but much better than if nothing is done. When I drive my car to above 3K meter elevations, the sluggish feeling is as if riding a donkey.

Happy Boating

 

[5280glastron]

Re: 5.0 GL SX Volvo Prop selection at altitude

The Titan could lower slip being a 4 bld. cupped prop. Perhaps to single digits but unlikely.
It is some times suggested to calculate cupped props at an inch higher than the listed pitch.
But it seems this would aggravate our numbers.
Your tach is fairly young But still could be off 500.
Right here recently we have had two tachs at about 1500 rpm high.

A "mile high" is not considered "HIGH" altitude and does not normally require changing jets.

It usually just requires adjusting prop pitch, which you've done.

Your mistake in playing with the slip calculator is that you failed to add the inch of pitch(to 16) to account for the cupping on the HR Titan prop

If you do that and use a normal 9% slip, it comes out to about 4752 rpm.

With a range of 4400-4800, you're good and your tach appears to be wrong. Sometimes cleaning the pins on the back of the tach(where the harness plugs in) returns things to normal.

FYI; changing jet sizes does not really produce more power at altitude; it just saves a little gas as the motor is not running a little rich.

Consult a Volvo dealer in your area concerning any jet changes. Be advised that if you change jet sizes(smaller), you cannot operate at lower altitudes any more without risking blowing up your motor by running lean.

Reading the plugs will tell you if a jet change might be needed.

Thanks, I'll report back a tach test in the next week or so. Also, thanks for the info on the jetting. It seemed like a lot of work, I do sometimes go to Grand Lake up around 8,000 ft but I'm not planning on skiing much in <60deg water. The most important performance will be on a powell trip this year, and it's lower than denver (3500). So long as I'm not over revving with my normal load of 5-6 people in denver I'll be happy.