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Prop Tune up for a old 240 Baja 468 with a samll blower.

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Old 07-12-2011, 06:34 PM
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Default Prop Tune up for a old 240 Baja 468 with a samll blower.

My boat is a 1988 240 sport baja 24 degree "v" with a 468 engine, un-identified merlin heads ,177 blower @4.5 psi. and a comp 280 cam, water cooled tube headers, currently a 4 blade Bravo 26p prop. It will run 40.0 mph at 3100 rpm and 65 at 4700 rpm running heavy with 75 gallons of fuel and 400 lbs of passangers. This is GPS and the only known facts so far. I have been drag racing for many years on land and can atest that the engine seems to running as intended from idle to wot. Cannot confirm drive ratio. As I slowly trim it out it will not react at all at first then finally gain 1-1.5 mph in a very narrow range of trim setting before blowing out with over triming.

Just for fun, Side by side with a friends newer 1993 Baja 240, shallower "v" lower profile boat, we can run the exact same 3100 rpm at 40 mph but he has a known 502 efi 1.5:1 and a 3 blade 25p, I think a mirage. can't figure this one out ??? I know he is lighter and the hull is easyier to go faster by a bit but wow !!!

#1..On my boat, What is your thoughts as to it's performance ???

#2..Where do you think we can go with mine to make it a better all around setup. I guess I am not real unhappy with it now but know it needs the prop cleaned up and it could be a little faster on top or just more efficiect maybe all around. Comes out well now. Prop is currently a tad ragged on the tips.




Last edited by Doug Doty; 07-12-2011 at 07:02 PM.
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Old 07-13-2011, 09:45 AM
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Doug,

Hey buddy. I have a similar setup. I just posed a question on the prop forum as well for advice on hole shot. I am running a labbed 26p hydro 4blade and am getting very similar speed/rpm #s as you are.
Have you tried any other props besides what you are currently running?
How long does it take to plane with your current setup?

I suppose it will be beneficial to follow each other's threads.

Todd
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Old 07-13-2011, 10:35 AM
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Doug,

Hey buddy. I have a similar setup. I just posed a question on the prop forum as well for advice on hole shot. I am running a labbed 26p hydro 4blade and am getting very similar speed/rpm #s as you are.
Have you tried any other props besides what you are currently running?
How long does it take to plane with your current setup?

I suppose it will be beneficial to follow each other's threads.

Todd
I saw your post too, I think my boat is a good bit heavier and the bottom is a deeper "v" but still interesting. your boat is the same hull as my buddy I referanced in the original post and his is certainly faster on top end although we have not had a gps in it. Is your speed stated gps.
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Old 07-13-2011, 03:58 PM
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Yes, it's gps speed.

Speaking of which, I would love to get my hands on one of those livorsi gps speedo's!
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Old 07-14-2011, 12:35 AM
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Your 240 hull is the same as 24 Outlaw. They also have the prop set up to be very deep in the water. You would see a lot more top end speed with a 3 blade Mirage Plus prop and the boat will respond much better to trim. It will get on plane a lot slower though.
From what you posted about the engine, I'm sure it would be happier spinning up another 500rpms or so at WOT also. I would try a stock 23 Mirage Plus and go from there. Use BBlades test program.
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Old 07-14-2011, 06:26 AM
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My budy has a mirage 3 blade 25 he is cycling out. I will try it for free first and then have more relevent data to report and then plan to follow your suggestion.
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Old 07-14-2011, 04:25 PM
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If this helps any.
I have a 89 Baja 23'5 Force
My engine (548CI) is suppose to be, at least when dynoed 629 HP. Im running a 24" 4 blade Hydromotive at just over 5600. for 74MPH GPS
I picked up either 6 or 8mph( I forgot) on my cruise speed going with a 4 blade. Im guessing I probably lose around 2MPH on top end going with the four blade though.
As said before go down in pitch to around a 23. Do you know what RPM your making your best power at? Im sure its in the 5-6 k Range.
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Old 07-14-2011, 09:20 PM
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If this helps any.
I have a 89 Baja 23'5 Force
My engine (548CI) is suppose to be, at least when dynoed 629 HP. Im running a 24" 4 blade Hydromotive at just over 5600. for 74MPH GPS
I picked up either 6 or 8mph( I forgot) on my cruise speed going with a 4 blade. Im guessing I probably lose around 2MPH on top end going with the four blade though.
As said before go down in pitch to around a 23. Do you know what RPM your making your best power at? Im sure its in the 5-6 k Range.
Do you know how deep of "v" is on your hull and or the weight of the boat ??

Thanks for the comparitive information, I would think my 468 at 7 psi and a little more reved up might be nearing that power level but not as flat of curve as is desired for a boat. I do not know enough about this engine to be sure other than the obvious and that stated on the reciepts that the PO give me. I just bought it recently to toy with when at the marina on weekends so it will get weekly tweaks and tests. I would guess the merlin heads are likely too big for the cubic inches but the blower might mask that some. The cam is a comp. 280 symetrical pattern design so that stands to be improved too. I am going to try my buddies 25" 3 blade mirage plus and stack that data on top of what I already have for now and then share this with someone like bblades to try and get them the info needed to help optimize my setup. I will pull the motor down this winter and end up making more power as a result. I am fairly certain it is a thrown together combination and not a well matched group of parts. I am curious if it is worth making a labbed prop now or if it will be completely wasted after making another 100 hp. or so next season.
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Old 07-14-2011, 10:05 PM
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Mine is 20 degree dead rise and dry weight 3,650
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Old 07-16-2011, 01:22 AM
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Quote:
Originally Posted by Doug Doty View Post
Do you know how deep of "v" is on your hull and or the weight of the boat ??

Thanks for the comparitive information, I would think my 468 at 7 psi and a little more reved up might be nearing that power level but not as flat of curve as is desired for a boat. I do not know enough about this engine to be sure other than the obvious and that stated on the reciepts that the PO give me. I just bought it recently to toy with when at the marina on weekends so it will get weekly tweaks and tests. I would guess the merlin heads are likely too big for the cubic inches but the blower might mask that some. The cam is a comp. 280 symetrical pattern design so that stands to be improved too. I am going to try my buddies 25" 3 blade mirage plus and stack that data on top of what I already have for now and then share this with someone like bblades to try and get them the info needed to help optimize my setup. I will pull the motor down this winter and end up making more power as a result. I am fairly certain it is a thrown together combination and not a well matched group of parts. I am curious if it is worth making a labbed prop now or if it will be completely wasted after making another 100 hp. or so next season.
I would bet you are in the 550hp range with what you have and most likely to make the power, it will need to spun at 5200-5400rpms.
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