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Merc 2.5. Why are they better?

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Old 09-06-2010, 01:35 PM
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Who's building the 450 3.4L MERCS???
Id rather not say, he is well known in the drag circles.
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Old 09-06-2010, 09:07 PM
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I was talking to a guy today that said depending on the prop, it is better to take off with the drives out (+ trim) as opposed to in (- trim). He said this is good to throw the boat up on plane and to get the stern out of the water.

Any opinions on that?
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Old 09-07-2010, 11:13 AM
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I was talking to a guy today that said depending on the prop, it is better to take off with the drives out (+ trim) as opposed to in (- trim). He said this is good to throw the boat up on plane and to get the stern out of the water.

Any opinions on that?
In well over 40 years of boating, I have never found a boat that popped up on plane better with positive trim. If you want to get a boat up on plane, you need to get the bow back down as soon as possible. Whomever you talked to was wrong.
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Old 09-07-2010, 11:43 AM
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In well over 40 years of boating, I have never found a boat that popped up on plane better with positive trim. If you want to get a boat up on plane, you need to get the bow back down as soon as possible. Whomever you talked to was wrong.
It was a drag boat racer. I saw several others taking off this way with 2.5s, that is why I asked him about it. I thought it was odd as well.
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Old 09-07-2010, 02:20 PM
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I was talking to a guy today that said depending on the prop, it is better to take off with the drives out (+ trim) as opposed to in (- trim). He said this is good to throw the boat up on plane and to get the stern out of the water.

Any opinions on that?
I do that on my outboard boat actually, after lots of playing with it, we found that 0 works the best, not in, and not out, but the prop shafts straight in line with the bottom. It jumps way faster then when its trimmed in. 2 foot set back, engines mounted all the way up.
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Old 09-07-2010, 04:05 PM
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It was a drag boat racer. I saw several others taking off this way with 2.5s, that is why I asked him about it. I thought it was odd as well.
I am a Drag boat racer, I have a 530lb boat with 410hp and I trim it IN to launch, consider I am going 101-103 mph in 500 feet. If the boat leaves bow high and comes backdown again and kissis the water it kills your ET.
That being said I use 1/16 inch spacers to limit my trim in so that when I test I can figure out exactly every time where to start my trim out. I also use a delay computer activated by my foot throttle, then a duration programed so that my trim system runs the exact same time to set the boat. After that I fine tune the rest of the pass. I am also using a custom trim pump with a horizontal trim ram, and 24v on that trim pump to make all this happen FAST.

I can only see using positive trim if you need to aerate your prop(s), as a boat floping back into the water after it launches in all cases slows you down. could be that there trim isn't fast enough..... hard to say.
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Old 09-07-2010, 05:59 PM
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I am a Drag boat racer, I have a 530lb boat with 410hp and I trim it IN to launch, consider I am going 101-103 mph in 500 feet. If the boat leaves bow high and comes backdown again and kissis the water it kills your ET.
That being said I use 1/16 inch spacers to limit my trim in so that when I test I can figure out exactly every time where to start my trim out. I also use a delay computer activated by my foot throttle, then a duration programed so that my trim system runs the exact same time to set the boat. After that I fine tune the rest of the pass. I am also using a custom trim pump with a horizontal trim ram, and 24v on that trim pump to make all this happen FAST.

I can only see using positive trim if you need to aerate your prop(s), as a boat floping back into the water after it launches in all cases slows you down. could be that there trim isn't fast enough..... hard to say.
Now that explanation I can absolutely agree with. You want the bow down soon, but not slammed down. Too much negative trim could do that. Too much positive trim and all you get is a moon shot with the bow.

I might also add that drag boats are quite a bit different than offshore boats.
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Old 09-07-2010, 07:04 PM
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Now that explanation I can absolutely agree with. You want the bow down soon, but not slammed down. Too much negative trim could do that. Too much positive trim and all you get is a moon shot with the bow.

I might also add that drag boats are quite a bit different than offshore boats.
I completely agree.
Forgot to mention that, there is a sensation that the boat is coming on plane faster when it lurches up (in drags) as apposed to sliding out.
With all that said, I spend a lot of time in larger boats and I still can't think of one that gets on plane better with positive trim, unless the tabs are down and the props need to break free and trim is used as a patch.
Anyhow back to 2.5's..... still the coolest motor ever made.
CLAMP-ONS RULE, Car motors belong in CARS.
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Old 09-08-2010, 02:50 PM
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Why are they better.......................because with every 2.5L drag motor you get one of my fuel pumps, none better.
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Old 09-08-2010, 04:05 PM
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.
CLAMP-ONS RULE, Car motors belong in CARS.
Says the wanker with the "CAR MOTOR" in his Pachanga
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