High Altitude Prop

[lcgordon]

I was told some people on here may have some high altitude prop experience.

My boat 1994 American skier TBX, 350-260hp, max rpm 4400-4800.

Stock prop 13x13 OJ gets me 42mph @4300rpm

Bought a Acme 541 13X12 gets me 41-42 @4200rpm

 

Im considering the 1609 or the 913. I slalom 60% and barefoot 40%. I dont want to completely loose my slalom pull but am willing to sacrifice it a bit to get a couple more mph for footing.

 

I posted on here because I was told there may be more high altitude guys on here.

Oh Btw im in denver @5280'

[GregHind]

Keep the prop, install vortec heads, intake and roller rockers. Rejet carb and add 100hp

[Alberto Soares]

I have a 2010 Malibu LXI, it came with 13x11.5, I changed to a 13x10.5 and it raised about 350 RPM's for the same speed. I am at 4500'.

 

Visit www.deltaprop.com, on the top left click on I WANT EXPERT ADVICE, fill the table with all the info you have, they will send you an email with the best propeller configuration for what you want.

[lcgordon]

Thanks for the advice. I will do that.

[shyskier]

Midskier on American Skier site can help also.

[TallSkinnyGuy]

My understanding is that to increase top-end speed you would normally increase pitch (e.g. going to a 13x13 Acme), but that will reduce your WOT RPMs and you are already below your recommended range. The props you mentioned changing to will likely increase your WOT RPMs into the proper range, but you will probably not get a top-end speed increase and more likely will lose some top-end speed.

 

If altitude is the issue and you want more top-end speed you are going to have to get more from your engine rather than from your prop, as GregHind suggested.

[lcgordon]

I just bought a OJ 304 13x11 to try out it came from a guy at high altitude. He said it helped his boat. Even if it does not give me more top speed it will be better on my engine.

[kingshredd]

I have a 1992 California Skier, we have a cabin on a lake at 5400ft and I run the same prop as I do down on Lake Oroville that sits at about 950ft. Really not much change getting my 210lbs out of the water and the top end is only down a couple mph. Really not worth for me to change things out for my regular skiing speeds.

[sunvalleylaw]

Bumping this to piggy back off someone else's thread rather than start anothr. My new to me boat has a 13x13 4 blade, what appears to be stainless steel prop. I don't know the brand. It is marked VP. The boat has been used at essentially sea level in Issaquah, WA, and now will be used at 5800 feet of elevation at Magic Res. in Idaho, and at 6547' at Redfish Lake, also in Idaho. Think it will work well enough? My boat has a BTS/SL Cruise speed control system that might need to be tweaked to work correctly at altitude I suppose. Though at Redfish, there is no course so I could just use the speedos.

[paco]

@sunvalleylaw I think your prop will be OK, but probably not the best choice. Try it out as is and if it doesn't suit you @lcgordon actually has a prop he's been trying to sell. Think he's tried several. Acme 13x10.5 three blade. That four blade is actually a good prop and provides a good pull on a 1:1 transmission, also adds about 100 rpm to slalom speeds. It will not do well for top end though.

[sunvalleylaw]

@paco Thanks for the reply. The former owner says that he could get 43 top end full out with just him in the boat and little gas. I will see how it does for me and how it pulls. I do not barefoot, so am not worried about huge top end speed. If it is close, I probably won't worry about it. And at the higher lake, there is no course, so just freeskiing and boarding. So maybe the prop will work. Will just ski it first before worrying too much about it.

[TallSkinnyGuy]

I don't remember the formula but I think it is something like 3 hp an engine loses for every 1000 feet up in elevation. So, your boat is definitely not going to be producing the same amount of power it did in Issiquah. As I understand it, the main issue is potentially lugging the engine -- like you can do in a manual transmission car if you are in a gear too high and trying to go up a hill (you push the gas down but the car still slows down as you go up the hill). Apparently this is bad for engines.

 

There will be a recommended wide-open-throttle ("WOT") RPM range for your engine, probably something like 4400-5200 or so (check your manual). If, for example, you can only reach 3800 RPM at WOT then you are under propped and should get a new prop. If you find you are under propped you should record RPM at a couple skiing speeds and at WOT and call Acme or OJ Props and have them help you figure out what prop would work best for you at your elevation and based on your performance desires.

[sunvalleylaw]

Thanks @TallSkinnyGuy

[lcgordon]

BTW the prop is sold. But yeah a buddy of mine had basically that prop on his 93 prostar and it did pretty well for him. It got dinged up so he switched to a different prop tho.

[DW]

@ 6000' the air density is 84% and pressure ratio is 80% of sea level value so you will see a similar (% of sea level) power level for a NA engine, so ~80%. Nice thing about a big V8, power curve is pretty flat so not as challenging to extract maximum performance but to optimize different props will work better at each elevation.

 

To recover the power loss, and as noted, you will need to stuff more air in to the combustion chamber, camshaft/cylinder heads are good options but take care to not hurt off idle performance as that is a key element to pulling up a skier/footer. SBC options include Vortec or even fast burn cylinder heads, and a ZZ4 cam is pretty good option although the marine cam is a very good cam, but ZZ4 does have more lift & duration. An easy mod to the marine cam would be 1.6 rockers (1.5 are standard). You also might take a look at your spark arrestor, it might just be an air flow limiter also.

[sunvalleylaw]

BTW, I was incorrect when I posted before. It is a 3 blade 13x13 marked vp. I misunderstood the prior owner over the phone. It is stainless. Will see how it works, then take the good advice here based on WOT and RPM's and go from there. Will try to keep it as simple as I can

[sunvalleylaw]

BTW, I was incorrect when I posted before. It is a 3 blade 13x13 marked vp. I misunderstood the prior owner over the phone. It is stainless. Will see how it works, then take the good advice here based on WOT and RPM's and go from there. Will try to keep it as simple as I can