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east tx skier
05-10-2006, 09:00 PM
I'm posting this for a new user.

I'm a new owner of a Mastercraft Boat, i just bought a prostar 205 1993, and i'm going to use the boat at 9.000 Feet. What can I do to improve the performance ? And What can you recomend me to do, because I'm going o use for slalom ski.

Thanks.

Freddy Arguello

Quito-Ecuador
Sud-America

88 PS190
05-10-2006, 09:19 PM
a local mechanic should be able to rejet and tune your carb for your altitude.

I'm not sure how much change in power you'll be talking about vs. lower altitude, but should still be capable of good performance for slalom skiing.

Might make barefooting a bit on the slow side.

east tx skier
05-10-2006, 09:20 PM
What about reproping?

Hoosier Bob
05-10-2006, 10:10 PM
I would have the Carb serviced at a local speed shop that is experienced with the elevation. Rejetting is probably all it will take. I would not reprop because at that altitude you will still have a very rich setting. Don't forget to get rid of your gas! Gas sold at higher altitudes is manufactured for the altitude I believe. Here is some info to give you a basis to begin.

JET CHANGES AND ALTITUDE AND TEMPERATURE
Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees Fahrenheit. Once you know the correct stock jetting for your particular Holley carb, you can determine whether you live or race at an altitude above sea level. For every 2000 foot increase in altitude, you can reduce the jet size by one size. If you had a carb which has a stock jet size of 80 and you live or race at 2000 feet above sea level, then you would use a #79 Holley jet in the carb. Similarly, a change in the carb's inlet air temperature may require a change in the jet size from the stock calibration. Many racers go a step further by combining all of the weather varibles, temperature, barometric pressure, dewpoint and humidity with the altitude of the track they are racing at to determine the "density altitude". This is a "corrected" altitude above sea level. From there they can determine whether a jet change is necessary to maintain performance or whether to change their "dial in" (if they are bracket drag racers).

You can look at MorTec's HOLLEY CARB INFORMATION page to find the stock, standard, sea level, calibration jets for your particular Holley four barrel carb

Good luck and take care! :D

fly4food
05-12-2006, 12:49 PM
If you don't want to redo the carb, a simpler approach is to just readjust (lean) the mixture. This can be done by adjusting the mixture screws on the carb until you get peak performance. With the engine idling you back the screws out until the engine starts to run rough, then advance them a half turn or so. Just remember, the boat might not run at all at sea level without adjusting the screws again.

WakePowell
05-12-2006, 01:30 PM
I ran my boat at 9,400 feet last summer and it was a challenge. It is a 2005 fuel injected L-18 (8.1 liter) and at first it did not have enough power to get on plane. Once the EMC adjusted we were okay but there was a noticeable power loss from 5,800 feet. If you are going to pull skiers at that altitude frequently I would invest in a small B&M supercharger.

pilot02
05-12-2006, 01:57 PM
If you don't want to redo the carb, a simpler approach is to just readjust (lean) the mixture. This can be done by adjusting the mixture screws on the carb until you get peak performance. With the engine idling you back the screws out until the engine starts to run rough, then advance them a half turn or so. Just remember, the boat might not run at all at sea level without adjusting the screws again.

Leaning the mixture in this manner will only effect performance in the idle range. It will not improve power.

bigmac
05-12-2006, 02:03 PM
I ran my boat at 9,400 feet last summer and it was a challenge. It is a 2005 fuel injected L-18 (8.1 liter) and at first it did not have enough power to get on plane. Once the EMC adjusted we were okay but there was a noticeable power loss from 5,800 feet. If you are going to pull skiers at that altitude frequently I would invest in a small B&M supercharger.

B&M is a nice unit, but centrifugal superchargers are RPM-dependant and tend to work distinctly better at high RPM. I'm not sure that a positive displacement supercharger like a Whipple twin-screw wouldn't be a better choice for a ski boat that's looking for better low-end torque. I guess my first approach would be a consult with an experienced high altitude service tech with an eye toward rejetting/re-tuning/re-propping, and considering a supercharger if that high altitude performance was just unacceptable for the boat's intended purpose.

http://www.pacificp.com/cat/images/items/Carb%20BiBl%20-%20large.jpg

CoFooter
05-12-2006, 02:09 PM
When I had a carb engine and ran at 6,000 ft, I re-jetted and re-propped. Leaning the air /fuel mixture at idle won't help you at all except at idle. About all you can do unless you want to install a higher CFM carb. Holley has a table of jet size vs altitude. Prop guys (ACME/OJ) can help you with the prop size. At 6,000 ft I went down 1.5" in pitch from stock on a 3 blade, but that varies with your prop. Speed improvement with a new prop is only marginal, though your RPM's will come into range. Bottom line is performance (RPM) with a stock set-up is supposed to degrade 3% for every 1000 ft of elevation. Do the math at 9,000 ft and its pretty sad. Ever notice how all the barefooters at high altitude have outboards?

bigmac
05-12-2006, 02:10 PM
Leaning the mixture in this manner will only effect performance in the idle range. It will not improve power.It's been many years since I worked on a Holly carburetor, but, yeh, I thought the mixture screws on a Holly carburetor were for idle only. High-flow states (WOT) should put the carb into the high speed jets, and the only solution is to re-jet.

Leroy
05-12-2006, 03:19 PM
Good story Doug, so you are moving to Denver? Would the new users boat be red?:uglyhamme

east tx skier
05-12-2006, 03:21 PM
Nope. I promise it's not me. :)

rodltg2
05-12-2006, 03:47 PM
im no help, but remember this guy is in ecuador. going to the local speed shop, buying superchargers etc... may not be an option...

Thrall
05-18-2006, 08:04 PM
Rejetting, timing advance, and repropping for the altitude are IMO what needs to be done. I'm no Holley carb tech, so don't know what to do there (threw one in the garbage once, that's about all I 've done w/ 'em).
Roughly, on a normally aspirated 2 or 4 stroke engine, you'll lose about 3% power for every 1000' in altitude.
Starting w/ a 285 hp HO (at sea level, probably where it's rated at) puts you at about 217hp at 9kft.
Lean out the carb, timing can advance a bit as you're not burning as big a charge, and the prop.
PM Storm861triple. He knows Ford motors and runs in UT.