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Dilbert
08-04-2002, 08:15 PM
I'm a new owner of a '97 classic 18 and have been reading this board with lot of interest. You guys are great! I've got the 5.7 w/260 hp, but got a 26 pitch quicksilver prop with it. Can only turn 3900 WOT. Debating on whether to get a 23 pitch or try to boost the engine output. Any easy retrofits to get me more power from this engine?

Rootsy
08-04-2002, 08:21 PM
i assume alpha w/ 1.5 ratio? 21 would be the pitch range for ya to start out at. you'd need the 350 mag to spin a 23 in that boat with the drive and gear ratio i am assuming you have.

MOP
08-04-2002, 08:22 PM
23 sounds like a step in the right direction, there are alot of good 18's up here. You can find answers to most anything.

Last Tango
08-04-2002, 09:10 PM
Try a Mirage 21P or Mirage 23P prop. Hopefully you can "borrow" them to test before having to purchase. Your engine should run in the 4400-4800 RPM range for wide open throttle. If you try the 23P first and still fall short of the RPM range move to the 21P. A 22P 4-bladed prop is also a possibility, but I tried it on my boat and really didn't like it - 2001 Classic 18 with MX6.2MPI and Bravo One outdrive with 1.50 ratio. I have 320 HP factory stock and run the Mirage 23P prop. I have tried the 21P and 22P and they were way too small. I have tried the 24p and 25P and they were way too big. (Remember that the 22 and 24 are four-bladded Bravo One props, and the 23 and 25 are three-bladed Mirage Plus props). Since I have 60 more horsepower than your boat, I would think the 21p might be the better choice for your first try if you can't just borrow one for free to try. Several people on this board have props available you could try at a Donzi event and then buy the one that works best from them.
The prop will make more difference for the least amount of money and hassel. It just seems to me that before you modify the engine, you should find the right prop, first. Then as time and money allow, make small progressive changes to the engine if you need more speed. Eventually, if you spend thousands of dollars modifying your engine, you may need to step up one size in prop.
I'm not certain if Palm Harbor is near Miami, but Madpoodle can probably provide a loaner prop to try at a SEADOG event.

Dilbert
08-04-2002, 09:18 PM
Thanks for the great info. I talked with the service guys at the factory and they said that this boat came with a 23 pitch vengeance prop. How is this different from the Mirage? Drive ratio on the Alpha is 1.47. They said that this boat should do just about 60 with that prop. Can feel the urge for more speed. Tired of getting blown off by waverunners...

Rootsy
08-04-2002, 09:38 PM
a vengence is not a whole lot more than an aluminum prop made outta stainless... basically an entry level stainless that doesn't have much in the way of performance geometry... the mirage and the turbo's and countless others tend to have more diameter, more rake and more cup along with a lotta other stuff... you might try a mirage it is the most popular generally... the turbos also work well... gonna find a lot of different camps and opinions here on the prop game i think... best thing to do is try as many as you can get your hands on... bring the seat of your pants and your gps too :D

Last Tango
08-04-2002, 09:40 PM
23 Vengeance is what is on my buddy's 2000 Z22 with the same engine and drive as you. His boat is a lot heavier than yours. He runs low 50's with that set-up, at 4500 RPM. Not a direct comparison to your boat, but the engine/drive/prop combo would be similar. You should be hitting high 50's to 60 with the right prop.
I'm not a prop expert on the engineering side so I can't explain the difference between a Vengeance prop and Mirage Plus prop. However, generally, the Mirage Plus is built for top speed and the Vengeance is built for family boating (torque in the middle speed ranges for towing skiers).

Ranman
08-04-2002, 09:54 PM
I used to own a 96 18 Classic with your engine combo. It came equipped with a 21 Vengeance and that is what DOnzi recommended to me also. If you are going to try a new prop, I'd definatly go with a Mirage Plus. Make sure you get the "Plus" designation as it is an improved version of the Std Mirage. Also, you might try a Turbo prop from Precision Propellers. You can find them at www.turbo-props.com. (http://www.turbo-props.com.) I currently run a Mirage Plus on my 97 350 MAG (300HP, 1.65:1 B1). Many other board members are using the Turbo props with great success on the CLassic hulls and I intend to try the same. BTW my 96 18 with the Vengeance and 260HP motor ran 4800 RPM at about 59MPH.

Stix Magill
08-04-2002, 11:20 PM
Dilbert,
Congrats on the new Donzi! I agree with the above posts. A Mirage 23 or 21 would be excellent props to experiment with. If you pull skiers etc. start with the 21 for a better holeshot. I have a 1997 5.7 Mag./Alpha and a 23 Mirage on My Minx and I see 60 on the GPS. I would think you would top that. Let us know what you find out.