prop advise for baja 275
03-17-2013, 02:11 AM
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prop advise for baja 275
we have a baja 275 wwith ilmor 625 v10 bravo XR
we try to pick up some speed .
propellor bravo 1 ,25 lab finish, 5900 rpm,74 Mls
what propellor should I try to pick up a litle more speed?
we try to pick up some speed .
propellor bravo 1 ,25 lab finish, 5900 rpm,74 Mls
what propellor should I try to pick up a litle more speed?
03-17-2013, 09:58 AM
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Location: LAKE LIVINGSTON TEXAS
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Do you know your drive ratio? I know I maxed my pitch out with 2 people in our boat, but have to change props when 4 or more go out with us, when we ski/tube....a 25 seems slow at 72...a friend of ours has a 502 mpi on a 24 footer turning a 26 bravo 4 blade getting 78 gps'd. I would use a prop calculator after obtaining your drive ratio, however they are only theoretical values. When I went from a 19 to a 23 mirage.....talk about a maaaaajor change. Although we were close to the values, it totally changes bottom end and handling. I would also consider how many people you plan on entertaining as well.
03-17-2013, 11:42 AM
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i run a 26 3 blade on my 27 but only has a 454. tops out at 55, see if a friend or someone around ya had a 26 u can try for the day. thats what i would do.
03-17-2013, 04:35 PM
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16 is a little high, 12-14 seems to be normal, single digits would be perfect setup. Try a 26p bravo 1 4 blade "
I will be sursprised if he can get a 275 hull to run fast with slip numbers in single digits as the hull is about identical to the 272 and most of the fast ones includiing mine have always ran the best numbers with slip in the range you are seeing (15-20%). Now is your boat going as fast as it can, most likely not. I do see that the hp peak is at 5800 and you are past that, does it hit 6000 instantly or does it build up to it there? In comparison my 272 runs 74-76 under PERFECT conditions turning a labbed 26 pitch around 5400-5600 when running with my blower belt off (motor made 655 gross hp at 5600 on dyno) and slows down to low 70's with full tank of gas, full load of passengers, etc, post what you end up with as this is great stuff, Smitty
I will be sursprised if he can get a 275 hull to run fast with slip numbers in single digits as the hull is about identical to the 272 and most of the fast ones includiing mine have always ran the best numbers with slip in the range you are seeing (15-20%). Now is your boat going as fast as it can, most likely not. I do see that the hp peak is at 5800 and you are past that, does it hit 6000 instantly or does it build up to it there? In comparison my 272 runs 74-76 under PERFECT conditions turning a labbed 26 pitch around 5400-5600 when running with my blower belt off (motor made 655 gross hp at 5600 on dyno) and slows down to low 70's with full tank of gas, full load of passengers, etc, post what you end up with as this is great stuff, Smitty
03-17-2013, 05:06 PM
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If you increase your pitch you are going to decrease your rpms...if you do this, will you be able to decrease slip to increase speed? Else, you are going to decrease top end...
03-17-2013, 06:50 PM
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[QUOTE=jctexas07;3887259]If you increase your pitch you are going to decrease your rpms...if you do this, will you be able to decrease slip to increase speed? Else, you are going to decrease top end...[/QUOTE
Increasing pitch alone isn't necessarily going to lower "slip" its only going to lower rpm and once you get motor away from the power band boat will most likely go SLOWER. Going to a prop with more surface area/blades or effiecient design will lower slip but again as slip lowers you will get away from the power band peak and again may slow boat down. It may be possible to lower slip with a ideal prop and then have to go down in pitch to keep motor near its power band. Lets say your boat "peaks" at 600hp at 6000 rpm's, lets say it takes 600 hp to move your hull thru the water at 75 mph, your current prop turns 6200 and boat is running 72, you go up slightly in pitch and at same time a prop expert does some work to your prop to make it more effiecient, now boat goes 75 mph at 6000 rpm's and your pretty happy.
Scenario 2 (which is more real world)same everything except instead of having a custom tuned prop built you go up from lets say a 24 to a 26 , if your boat could turn it at the same slip you would now go 78 mph, problem is the extra 100 hp you needed to go 78 isn't there so instead boat just lugs at same speed and goes 5700 rpm's or maybe goes a mph or 2 faster and is below hp peak.
The boat would also then be a pig accelerating because it would be working harder to get to its sweet spot. Propping boats can be alot of trial and error and certain hulls have a "normal" amount of slip that just goes with the hull.
My own boat, I chased after lower slip numbers before convinced that there was some speed I was leaving on the table somehow, tried a 5 blade , boat cruised at a incedible slipe rate under 10%, it also torque rolled and went SLOWER at wot, then it sheared off a prop shaft. There is gains to be had, they are just smaller than what most would think they are unless you have the totally wrong prop on your boat to start with, Smitty
Increasing pitch alone isn't necessarily going to lower "slip" its only going to lower rpm and once you get motor away from the power band boat will most likely go SLOWER. Going to a prop with more surface area/blades or effiecient design will lower slip but again as slip lowers you will get away from the power band peak and again may slow boat down. It may be possible to lower slip with a ideal prop and then have to go down in pitch to keep motor near its power band. Lets say your boat "peaks" at 600hp at 6000 rpm's, lets say it takes 600 hp to move your hull thru the water at 75 mph, your current prop turns 6200 and boat is running 72, you go up slightly in pitch and at same time a prop expert does some work to your prop to make it more effiecient, now boat goes 75 mph at 6000 rpm's and your pretty happy.
Scenario 2 (which is more real world)same everything except instead of having a custom tuned prop built you go up from lets say a 24 to a 26 , if your boat could turn it at the same slip you would now go 78 mph, problem is the extra 100 hp you needed to go 78 isn't there so instead boat just lugs at same speed and goes 5700 rpm's or maybe goes a mph or 2 faster and is below hp peak.
The boat would also then be a pig accelerating because it would be working harder to get to its sweet spot. Propping boats can be alot of trial and error and certain hulls have a "normal" amount of slip that just goes with the hull.
My own boat, I chased after lower slip numbers before convinced that there was some speed I was leaving on the table somehow, tried a 5 blade , boat cruised at a incedible slipe rate under 10%, it also torque rolled and went SLOWER at wot, then it sheared off a prop shaft. There is gains to be had, they are just smaller than what most would think they are unless you have the totally wrong prop on your boat to start with, Smitty
Last edited by articfriends; 03-17-2013 at 06:52 PM.
03-18-2013, 02:46 PM
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What is your prop centerline now? This is measurement of distance your propshaft centerline is below your hull. I gained 3 mph or so with a -2 shorty bringing me from 8" up to 6" below pad. I had some ride quality issues with the shorty but hopefully my new prop fixed it. Smitty played around with a ton of setups with drive height in the past so I would keep to what he recommends and dont go off results with other hulls alone. For what its worth anyway....once the go fast bug bites it seems the search never ends 
