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DonziJon
01-06-2007, 06:33 PM
Recent thread about "Small Mods" devolved into a discussion about a 78mph 18 Classic.

RedDog said he had an 1990 18 Classic with a 454, 420 HP motor that would only do 71mph. I have a real problem with that. How can that be?

Just a point: My Minx will do 60 on the GPS with 260 HP at the flywheel. 63 mph on the pitot tube speedo that came with the boat. I think Mercruiser changed the HP rating around 1992..to.. HP AT The Prop. The outdrive uses up about 30 HP. So my Minx is about 230 HP at the prop. Probably all Irrelivent.

OK: How is it possable that RedDogs 18 ONLY does 71?? 420hp..less 30 hp loss at the OD (it's a Pre 1992) comes in at 390 HP at the prop. I think that boat should be a LOT faster. Does the weight of the 454 in the back of an 18 make a difference? Does the boat become "squirely" with the extra weight aft, and HP?

Geeos boat is in the back of my mind which confuses me. That boat does around a 100mph, does it not??? I understand that boat has an "Arnesen" drive. Just wondering. John

BigGrizzly
01-07-2007, 09:53 AM
First off, GEOO's boat was a rocket bock with 474+ cid and over 750 HP and an Arneson drive with NO trans and a special Tfin on the bottom of the drive to make it handle. That boat thinks its a 30 foot ZR and GEOO is not a novice driver. Red Dog bough Genuine Risk. Rick had installed a 454 in the 18 classic . It will take every bit of 400 hp to do 70 mph in a 18 classic hull. I have 400 in my Corsican and can do 67mph on GPS on a good day. Red Dog's numbers are real and he is a good driver. This is just the way it is. Poodle's X18 will do about 78mph but he has a worked 383 small block. This is a horsepower and torque game. Do you really want to know how many 80mph Bass boats that I pass in my 18 Corsican?

DonziJon
01-07-2007, 03:41 PM
Thanks Grizz for the response. It seems to me that I've heard a lot of 22 Classic owners of relitively new boats talk about doing over 70 any day of the week. It seems to me, if you put the same HP and torque in a smaller.. lighter boat it should be faster, ..assuming the boat is managable to drive. I'm guessing an 18 is probably 2300 pounds. The Minx is 2700.

You mentioned Poodle has an 18 with a "reworked" 383 that will do 78. How does that work? Is the weight of a Big Block a disadvantage in the 18?? John

Ranman
01-07-2007, 04:01 PM
Yes. An 18 with a BBC is VERY stern heavy. The added weight in the rear slows you down so you now need more HP to get the hull up out of the water in order to go faster. 71 in RedDog's old boat sounds conservative to me. I thought he did 72-73MPH with that setup. Also, 420HP at the crank would be 380-390PSHP.

For reference, my 18 with a 300 PSHP runs 68-69MPH. An 18 Scorpion (350 PSHP) will run 71-73'ish.

BUIZILLA
01-07-2007, 04:07 PM
474+ cid Im a thinkin' it was a bit smaller than that...

:wink:

Rootsy
01-08-2007, 06:36 AM
all the HP and torque in the world won't do yoiu a bit of good if the other boat is "more slippery" going through the water... fluid dynamics probably plays just as great if not a greater roll than power...

i believe i read in previous posts that "might mouse's" powerplant was around 436 CID and into the 4 figure power number realm with the "small pulley"

My neighbor and fellow board member DougL has an 87 18 with a "warmed up" 350 and and alpha SS and he has nearly 83 on GPS...