high altitude gearing

[rlamp4040]

I bought a boat from lakre Tahoe. It is geared for high altitude at 1.60. with a 20 pitch prop. I live in simi valley and will be boating down here and nevada, Can I have some ideals about what prop to get here. I have a reinell 240 br 5.7 gxi sx penta volvo.. Thanks It was boat tested and red lines at 39mph (thats what I was told by the shop) they suggested a 23 pitch.

 

[jimmbo]

Re: high altitude gearing

Something doesn't add up here. My Volvo SX has a 1.51 ratio, I run a 20 inch prop and at 4800 rpm I'm getting right around 60mph

 

[steelespike]

Re: high altitude gearing

Again another age secret.Also while speed is important speed,by gps, and at wot rpm is what we need.With a 1.60 ratio,20" prop with 9% slip at 39 mph I get 3600 rpm,certainly not redlined.Guessing 5000 rpm I get 53 mph. All these figures disregard the size of you boat that might increase slip a little.If tach was right at 5000 and 39 mph slip would be 34% pretty much unheard of.So it appears either the tach is high or the speedometer is low.
It occured to me you were calling your max rpm "redline" so perhap[s it was 3600?? but that would mean your 1400 rpm short.
Help me out.

 

[rlamp4040]

Re: high altitude gearing

I have not actually tested it yet. The shop did and I am not happy with what they did. They said it was red lining at 39 mph. Then they said there ideal of wot was 3800 to 4200 but the manual says 4600 to 5000 so they are off there. I tried to take it out friday but the shop left my battery switch on and drained both the batteries( and now my radio doesnt work). I originally took it in because I was told I needed to have the gears changed from high altitude to lower and it had died on me a couple times. I ended up getting a 23 pitch prop but like I said have not tried it yet. I am no einstein on boats this is my first and I am trying hard to understand but I would stay away from the place I went to. I was told by the the original dealer of boat it should go 65 mph. Of course I dont need that..Thanks

 

[QC]

Re: high altitude gearing

Something doesn't add up here. My Volvo SX has a 1.51 ratio, I run a 20 inch prop and at 4800 rpm I'm getting right around 60mph

I actually don't think so. That's 0% slip. GPS speed and an accurate tach is required for these calcs to be reasonable.

To the OP. A small block is not pushing a 240 anything to 65 MPH. 39 sounds light too though. This shop does sound a little on the shady side of things. Where are you? Altitude now? Who confirmed the 1.60 ratio? Any paperwork? Year model?

Edit: I see now that you are in the Castaic area. Where do you plan to boat and test?

 

[steelespike]

Re: high altitude gearing

While a gear change might be ideal it sure isn't necessary. and I'm pretty sure the max wot rpm is 5000. If the boat had a 20 inch prop you wouldn't increase the pitch when going to a higher altitude.At 6000 ft you lose about 18% power and a simple propchange should work fine.
While props can be confusing read the helps on the prop store page. It may help you understand better.We can sure answer any questions and are looking forward to hearing your results.I'm sure we can get you on track.

 

[rlamp4040]

Re: high altitude gearing

I have a 5.7 GXi 320 hp. I was just told it should go 65-lol- I have been told alot of things...bought it at lake tahoe, original purchase order says ordered with high altitude gears. stamp on outdrive says 1.60 I plan on boating san antonio, pyrmide and lake mojave in laughlin

 

[QC]

Re: high altitude gearing

OK, that 320 is a strong runner. I have some experience with one in a Chap 236. Decent 50 MPH combo although that was a Duo-prop. Still I think the 39 is waaaaay low as is the RPM, and and SX may even be faster than the DP. 20 seems short with the 1.60 gears which makes me confident that the shop numbers are a mess. You need to start from scratch I think.

When can you run her yourself? Do you have a GPS? Any way you can confirm the tach? There is usually a switch on the back of the tach for different engines. Make sure it is set to V8 and get us the numbers. She'll have a built in rev limiter so I wouldn't worry too much about "redline". If the dealer is calling it redline, he's a fool. If you are, we understand

 

[rlamp4040]

Re: high altitude gearing

The guy running the shop said "redline at 39 mph" I have not heard good things about this place but be it as it may....
I will look as soon as I can. Thank you

 

[QC]

Re: high altitude gearing

The guy running the shop said "redline"

Automatically says car guy to me . . .

Edit: Almost nothing of what they said makes sense.

 

[rlamp4040]

Re: high altitude gearing

actually when I mentioned his name to a couple other shops they laughed and said" good ol' Ed" I looked and saw 4,6,8 cyl with corresponding 1, 2, 3 and a switch but I am half blind and cant read it. I will have to wait for someone with eyes. I don't want to take it out my hands are to bog and to little of a space I am afraid I will Uck something up....

 

[QC]

Re: high altitude gearing

So I take it your in the SF Valley?

 

[rlamp4040]

Re: high altitude gearing

I am in simi valley but I took the boat up near castaic...