Jack Plate Installed w/ Pic, REV tested and need some advice

[therobzilla]

Team Colibri » Today, 00:05[/url]"]

Johny25 » Today, 08:11[/url]"]The sweet spot will be 6250 rpms or that is where you will get the 15 hp from.....anything above or below the motor won't be putting out 15hp although these motors can be run to 7k but I wouldn't do that to my motor personally. My guess is you may get another mph or so by going to an 11 pitch because with the numbers you posted you could turn it right in the sweet rpm area of the motor. Your slip numbers are not great but they are not terrible either for a small motor. It is hard to get under 13% or so with motors of this size. When you get over 20mph with a 15hp you are doing pretty good. Only other way to get more out of it would be to try and move the weight in the boat around or lose some weight entirely. Sounds like you have played with the trim and height of the motor and found how far is to far out of the water already. I would say you are getting just about everything you are going to get out of a 15hp

+1

OK, I will think through a 11 pitch prop, however I'm not so sure that the cost of a new prop would be worth the extra mph. I really appreciate you looking at the numbers, I was primarly after someone looking over what I had vs. what would be an ideal setup, and based on what you guys are saying, it looks like I've got the sweet spot setup.

My only other question is how does elevation affect this, when I get to 7500 ft elevation, without different jetting for elevation, won't I loose some power to elevation? I have heard that some guys are making changes in prop for elevation????

Thanks,
Rob

 

[Johny25]

Yes elevation will have an effect on your motor and you will lose HP the higher you go. My guess is you will see an RPM drop but being you are running 6400 plus already you shouldn't have a problem. I would be interested in seeing the different readings you may get when up that high. I have heard some guys running a lower pitch prop at high altitude to compensate and keep engine in the recommended RPM range.
I am no expert in high altitude operation but the way I understand it the air is less dense and has less oxygen so your motor should run rich. The motor is still pushing same amount of fuel with less oxygen....hence the rich mix. If you always run in high altitude I would suggest running smaller/leaner jets in the carb but be sure and change them back over when coming back to sea level as I believe you can run the risk of burning a cylinder.

 

[therobzilla]

Johny25 » Today, 11:00[/url]"]Yes elevation will have an effect on your motor and you will loose HP the higher you go. My guess is you will see an RPM drop but being you are running 6400 plus already you shouldn't have a problem. I would be interested in seeing the different readings you may get when up that high. I have heard some guys running a lower pitch prop at high altitude to compensate and keep engine in the recommended RPM range.
I am no expert in high altitude operation but the way I understand it the air is less dense and has less oxygen so your motor should run rich. The motor is still pushing same amount of fuel with less oxygen....hence the rich mix. If you always run in high altitude I would suggest running smaller/leaner jets in the carb but be sure and change them back over when coming back to sea level as I believe you can run the risk of burning a cylinder.

Heading to higher elevation tomorrow, as far as I can find, there is no information regarding high elevation jets for this motor, tried everything, even called BPR? They won't even talk to you if the motor is less than a 2000 years model.

Borrowed a 9 3/8" x 7pitch prop for up there, going to see how it works out with the elevation, going to be at 7500 and 9000 ft this weekend, will take some notes.

Thanks
Rob

 

[Johny25]

Be careful with that 7 pitch you could spin that motor to high. I would guess that you could turn that 10 pitch at around 6k even at those elevations. Yeah please post the info you get, will be useful info to those that run high altitude

 

[therobzilla]

Johny25 » 28 Aug 2013, 08:06[/url]"]Be careful with that 7 pitch you could spin that motor to high. I would guess that you could turn that 10 pitch at around 6k even at those elevations. Yeah please post the info you get, will be useful info to those that run high altitude

OK,

I'm up on the AZ high mountains, current elevation is 7600ft, and raining like mad I must say.

Stated the day with the 7 pitch, as stated above the motor even at this elevation will seriously overev with the 7 pitch, RPM's not even at WOT are in the high 6000, say 6700 and that's not even WOT with speeds holding steady at 17mph. Good thing I borrowed the prop!

Switched back to the 10 pitch, and the number are 6000 RPM's at WOT at 20 mph steady. Motor is running fine, no apparent decrease in motor operations, starts on second pull idles fine.

Johny25 you were right on the money!

Will check the plugs for sighs of performance when I'm done.

 

[BCOWANWHEELS]

hhigh altitude the air gets thin and you will definatly loose hp so if I was you I,d not run wot. on my semi tk. when I went over the rockys I was tought to pull them 2 gears less to protect the engine.
bob

 

[turbotodd]

BCOWANWHEELS » 22 Sep 2013, 22:23[/url]"]hhigh altitude the air gets thin and you will definatly loose hp so if I was you I,d not run wot. on my semi tk. when I went over the rockys I was tought to pull them 2 gears less to protect the engine.
bob

It will be low on power, no doubt! But the mixture will be richer, so no worry about burning it up by going lean. It'll just be a little fatter and lazier.

On the big diesel stuff, the turbocharger is forcing the air into the engine. Wastegated turbocharged engine is still going to make XX amount of intake pressure (boost). That being said if the turbo is already close to being out of it's peak efficiency based on shaft speed vs airflow, a little more turbo shaft speed might make it a little less efficient (heat) which can then affect power and EGT. Most modern engines will adjust just fine without fear of hurting it.

 

[BCOWANWHEELS]

on all my semi's they had no waste gates. and blowers was as big as I could by back then offered by cummins. they made a hi-altitude blower which I bought and when used at lower elavations really put the boost out but I had to watch it close as I could burn pistons really easy pulling hard. (dont ask me how I know lol)

on the jack plate, nice job pal,I,am building me one right now very similar to your design.
regards
bob