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Thread: speed

  1. #1
    need a faster boat
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help..

  2. #2
    260 STINGER
    BOY THATS A TOUGH ONE! I THINK EVERY ONE WANTS A FASTER BOAT,I KNOW I DO TO. I REPOWERED MINE LAST SEASON, IT HAD TWIN 260 HP 350'S,I CHANGED THEM TO 325HP 350'S BECAUSE I WAS TOLD I COULD PICK UP 10 MPH.GUESS WHAT? I GOT HALF THAT.NOW I'M THINKING OF PUTTING ON 4" EXHAUST TO UP THE HP'S.IF I WAS SMART I'D LEAVE IT ALONE!BY THE TIME I'M DONE I PROBALLY COULD HAVE TRADED THE BOAT PLUS THE MONEY I'VE SPENT ON THIS ONE,I COULD HAVE BOUGHT A NEW ONE!!! GOOD LUCK!

  3. #3
    HP350SC
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Start with a stainless 21p High-five prop.Thru-hull exhaust and MSD or Crane ign. next.Then you are ready for the 144 Holley supercharger that I have brand new! I just sold my 20' Blue Water(same hull as yours).Did 58mph stock 350 mag.(1992)with above prop. Did ign.,exhaust,cam and blower which took it to 70mph.Changed to Dart heads to drop compression,upped boost to 7lbs. and ran the 25p high-five and was at 72mph. Your alpha will take it,just go easy out of the hole and service it regularly.Just shake hands with your checkbook and welcome to the boards!

  4. #4
    Dr. Eagle
    The Alpha drive won't handle (reliably) a whole lot more than is hooked up to it now. Merc uses the bravo for the 350 Mag at 300 ponies.
    I remember reading that it generally takes between 13-15 HP per mph as a rule of thumb. You are not going to get much more out of that engine drive combo.
    You could modify the existing 350 or put a crate engine in the boat with up to 400 hp on as long as you switch over to a bravo. Otherwise take along a spare alpha.
    As for the exhaust, I am afraid you will probably be disappointed in the results. I put on IMCO Powerflow exhaust manifolds and 4" through hull tips on my old Day Cruiser with the 350 HO King Cobra combo and the results were one mile more on top. Helped in acceleration, but top end was like nada for over $2K.
    [ October 01, 2003, 05:54 PM: Message edited by: Dr. Eagle ]

  5. #5
    Dr. Eagle
    HP350SC:
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Start with a stainless 21p High-five prop.Thru-hull exhaust and MSD or Crane ign. next.Then you are ready for the 144 Holley supercharger that I have brand new! I just sold my 20' Blue Water(same hull as yours).Did 58mph stock 350 mag.(1992)with above prop. Did ign.,exhaust,cam and blower which took it to 70mph.Changed to Dart heads to drop compression,upped boost to 7lbs. and ran the 25p high-five and was at 72mph. Your alpha will take it,just go easy out of the hole and service it regularly.Just shake hands with your checkbook and welcome to the boards! I'd say you were pretty lucky. I know of a lot of people with stock power that have their Alpha blow up after just a few years. If you want to turn the key and have it go, personally I would not make these kind of mods. If you do make these kind of mods, while they might work for a while ....be sure to carry a tow rope.
    [ October 01, 2003, 05:22 PM: Message edited by: Dr. Eagle ]

  6. #6
    HP350SC
    Dr. Eagle:
    HP350SC:
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Start with a stainless 21p High-five prop.Thru-hull exhaust and MSD or Crane ign. next.Then you are ready for the 144 Holley supercharger that I have brand new! I just sold my 20' Blue Water(same hull as yours).Did 58mph stock 350 mag.(1992)with above prop. Did ign.,exhaust,cam and blower which took it to 70mph.Changed to Dart heads to drop compression,upped boost to 7lbs. and ran the 25p high-five and was at 72mph. Your alpha will take it,just go easy out of the hole and service it regularly.Just shake hands with your checkbook and welcome to the boards! I'd say you were pretty lucky. I know of a lot of people with stock power that have their Alpha blow up after just a few years. If you want to turn the key and have it go, personally I would not make these kind of mods. If you do make these kind of mods, while they might work for a while ....be sure to carry a tow rope. I actually had upgraded to a bravo when I did the blower...however,my friend ran a 20' Bayliner with similar power on the alpha with no probs.Actually placed well in the 2002 Portland poker run. Of course it's better to have the bravo, but if you drive it with common sense and don't hammer it it will last awhile.It also depends how heavy the boat is.His boat is only around 2500 lbs.Incidentally,I did thru-hull exhaust in preparation for the blower,and only bought stainless tips,elbows and hose.Couldn't justify stainless marine manifolds for $1300.

  7. #7
    Dr. Eagle
    HP350SC:
    Dr. Eagle:
    HP350SC:
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Start with a stainless 21p High-five prop.Thru-hull exhaust and MSD or Crane ign. next.Then you are ready for the 144 Holley supercharger that I have brand new! I just sold my 20' Blue Water(same hull as yours).Did 58mph stock 350 mag.(1992)with above prop. Did ign.,exhaust,cam and blower which took it to 70mph.Changed to Dart heads to drop compression,upped boost to 7lbs. and ran the 25p high-five and was at 72mph. Your alpha will take it,just go easy out of the hole and service it regularly.Just shake hands with your checkbook and welcome to the boards! I'd say you were pretty lucky. I know of a lot of people with stock power that have their Alpha blow up after just a few years. If you want to turn the key and have it go, personally I would not make these kind of mods. If you do make these kind of mods, while they might work for a while ....be sure to carry a tow rope. I actually had upgraded to a bravo when I did the blower...however,my friend ran a 20' Bayliner with similar power on the alpha with no probs.Actually placed well in the 2002 Portland poker run. Of course it's better to have the bravo, but if you drive it with common sense and don't hammer it it will last awhile.It also depends how heavy the boat is.His boat is only around 2500 lbs.Incidentally,I did thru-hull exhaust in preparation for the blower,and only bought stainless tips,elbows and hose.Couldn't justify stainless marine manifolds for $1300. That makes sense...I could not imagine all of that blower induced torque being absorbed by the alpha.
    You are right about driving it easy, when you have a bunch of ponies and torque it would be common sense to be easy out of the hole where most of the stress on the drive would occur.
    I would definitely think twice about the IMCO powerflow or similar exhaust again. When I get my next daycruiser I will probably do what you did, tips and elbows to open it up. Best bang for the buck!

  8. #8
    Thunderbutt
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Buy mine 20 foot Spectra v-drive

  9. #9
    eliminatedsprinter
    need a faster boat:
    i have a 1998 20 foot reinell with a 5.7 lx 250 hp with a alpha 1 merc on her. my question is how much can the out drive take as in hp and what can i do to get more speed out of her with out putting a ton of cash in her..?im running a 18 inch prop 21 pich..can i put a different prop and will it hert the out drive, or over rev the moter?i can do about 50 mph now at 5000 rpms....i would like to see 60...or more..i know buy a jet but i like a all round boat...lol...thanks for the help.. Some have said go ahead and pile on the power and just drive it easy. If you were to do that what would be the point? If you get much better hole shot sooner or later you will use it. Also remember if you are zooming along at a much higher rate of speed and you catch too much air that prop may very well spin more RPM's than your alpha can handel. If I were you I would either bump up the power a little and put on a good stainless prop to get it up to around 60 mph and leave that way. Or I would keep it as is (or just add a better prop) and as economical as possible and save for a faster boat. As I said before, I'm kind of conservative about stuff like this. For reasons of safety, because my family rides in my boat with me. And for reasons of economics, because I'm not made of money.
    [ October 07, 2003, 02:24 PM: Message edited by: eliminatedsprinter ]

  10. #10
    Dr. Eagle
    Having sold my Eliminator offshore boat with the twin big blocks this summer, I decided I was going to downshift back to that 21' openbow daycruiser like I had before buying the Eliminator.
    So I bought an Ultra 21 footer yesterday and it has the same engine/drive you have been discussing here. I am not going to get crazy with the boat in modifying it, my take is to get a good prop, do the exhaust if you want to pump up the holeshot and midrange, perhaps have the heads worked over, you may be able to get a cam and install it too, but I would not build more than 300 HP if you want reliability. Giving the rule of thumb I have heard many places, that would give you between 3 and 4 mph.
    As far as the high five prop is concerned, my understanding is that it is really a low end prop for holeshot. If you want top end a three or four blade stainless prop may actually be a better choice.
    You might want to contact a reputable shop, like Teague Custom Marine or someone that deals with these boat/drive/prop combinations. I have grown wary of the local boat dealer. You may want to look at the advertisers in Hot Boat and contact one of them for recommendations.

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