X-18 Speeds

[The Hedgehog]

Just got a 383MPI/Bravo Package for the X-18. 350 hp with 325 at the prop.

What kind of speeds do you think I should see. Should I keep the standard X dim or raise it up a little. Don't want to get too agressive as we will use this as a runabout that the wife can drive.

[maddad]

Big Green ZX, another member here, gnupy420,(Gary) just put that combo in a later 18 and said 70 at will, a bit more with the right load and chop.

[The Hedgehog]

Big Green ZX, another member here, gnupy420,(Gary) just put that combo in a later 18 and said 70 at will, a bit more with the right load and chop.
That is sort of what I figured. Pretty solid for a turn key operation. I guess that I could try a shorty if i wanted to pick up a few mph

[maddad]

And solid looking too. Everything attached to the motor really cleans it up.

[Lenny]

I'd leave the drive in stock location, then opt for and spend a pile of money on a 2" shorter IMCO lower and play from there. These boats LOVE 3" of raised "X". Ask Doug Lovin and a couple of others. And perform well. 2" will be safer as a first shot.

Propped right, half tank, no load, tons of trim, I suspect 71-72GPS without the SHORTY.

Brad Verd had the same set-up in his immaculate '78 X-18 I believe. I am not sure how it all turned out.

[Last Real Texan]

Looks like good news

[BigGrizzly]

Leave the X in the stock position, especially with the stock BravoI. It will handle better(especially at low speeds) and get on plane faster. Do not kid yourself the shorty will be faster than any bravoI at the same X dimension. We have done this one several times. I will admit the 18 we did was a python viper, but as close to a real Donzi as you can get. We even put the shorty with a spacer to get the prop shaft at the same hight and found the IMCO faster. I have tons of hours on the water with 16, 18 and 22 classic hulls with various drives and for all around boating the stock location seems best. Stock being the ventilation plate is 3/4 inch above the lowest part of the hull except on the barrel back than 1 3/4 works better. When you get higher trim becomes less effective and more sensitive. In other words your always working it, which is just what my wife doesn't want! We ski off our 18 and a high X sucks for that. Remember if the QUEEN of the Castle isn't happy nobody is happy. Forget the "you can take the bounce out with the tabs" discussion that just doesn't work with the wife. The excuse is "this project is for you honey" and it better be darn close, so do it for her(sort of). BTW there is more to the IMCO shorty than just the higher X dimension, in case you haven't figured that out yet.

[The Hedgehog]

Leave the X in the stock position, especially with the stock BravoI. It will handle better(especially at low speeds) and get on plane faster. Do not kid yourself the shorty will be faster than any bravoI at the same X dimension. We have done this one several times. I will admit the 18 we did was a python viper, but as close to a real Donzi as you can get. We even put the shorty with a spacer to get the prop shaft at the same hight and found the IMCO faster. I have tons of hours on the water with 16, 18 and 22 classic hulls with various drives and for all around boating the stock location seems best. Stock being the ventilation plate is 3/4 inch above the lowest part of the hull except on the barrel back than 1 3/4 works better. When you get higher trim becomes less effective and more sensitive. In other words your always working it, which is just what my wife doesn't want! We ski off our 18 and a high X sucks for that. Remember if the QUEEN of the Castle isn't happy nobody is happy. Forget the "you can take the bounce out with the tabs" discussion that just doesn't work with the wife. The excuse is "this project is for you honey" and it better be darn close, so do it for her(sort of). BTW there is more to the IMCO shorty than just the higher X dimension, in case you haven't figured that out yet.


That is good info. I have looked at the Shorty and Merc side by side. The IMCO had much better hydrodynamics. Will stay conservative for now

[Woodsy]

Steve marr's X-18 runs a GPS 77-78 MPH all day long.... stock 350Mag MPI/Blackhawk setup!

Woodsy

[Mr X]

Steve marr's X-18 runs a GPS 77-78 MPH all day long.... stock 350Mag MPI/Blackhawk setup!
Woodsy
And of course, a much higher X dimension. :wink:

[boxy]

And of course, a much higher X dimension. :wink:

That, and a one way throttle.... :D

Stevie's boat is the only boat I have ever ridden in that you can physically feel accelerate as it re-enters the water after a launch...

[Mr X]

That, and a one way throttle.... :D
Stevie's boat is the only boat I have ever ridden in that you can physically feel accelerate as it re-enters the water after a launch...

Is there any other kind? :)

[Forrest]

Bill,

Even if you wanted to, you would have difficulty raising the X-dimension on a X-18 since the hatch is lower than on an 18 2+3. As it is, you'll have difficulty keeping the stock risers from hitting the underside of an unmodified X-18 hatch. It only gets worse with if you go with an aftermarket exhaust system such a Stainless Marine or Gil. After much searching, I finally found a stainless riser to fit a pair of Gil manifolds that would fit under my stock X-18 hatch with only minimal contact. The X-18 is tight on hatch height, so be careful what you do.

Also, if you want that X-18 to go fast, check the last four or five feet of the hull for hooks, bumps, and rocker. Many, if not most 18 Donzis out of the mid '70s have some hull straightness problems. My '77 X-18 has some rocker on one side that needs to go. That will happen during it's next restoration, which with a little luck, should be soon.

[The Hedgehog]

Bill,
Even if you wanted to, you would have difficulty raising the X-dimension on a X-18 since the hatch is lower than on an 18 2+3. As it is, you'll have difficulty keeping the stock risers from hitting the underside of an unmodified X-18 hatch. It only gets worse with if you go with an aftermarket exhaust system such a Stainless Marine or Gil. After much searching, I finally found a stainless riser to fit a pair of Gil manifolds that would fit under my stock X-18 hatch with only minimal contact. The X-18 is tight on hatch height, so be careful what you do.
Also, if you want that X-18 to go fast, check the last four or five feet of the hull for hooks, bumps, and rocker. Many, if not most 18 Donzis out of the mid '70s have some hull straightness problems. My '77 X-18 has some rocker on one side that needs to go. That will happen during it's next restoration, which with a little luck, should be soon.


That is a good heads up on the hatch. I did not know that. Plan to keep it stock until the warranty expires. Then who knows. Want it to stay user friendly but have never been successful in keeping anything stock.

The hull looks pretty true but will make sure that it totally the case.