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View Full Version : Need some help! PLEASE



Ramman
07-23-2004, 10:17 PM
I just bought a 1987 Z-21 with the 454 mag and the alpha 1 drive. I bought it about a month ago, and have been having some problems. When I bought the boat it had a 21 pitch mirage prop on it, I put it in the water for the first a few weeks ago, and the boat would not push the prop, no take off, the RPM's were under 4000, the secondaries weren't even opening! So anways I went and bought a 19 pitch x 13.5 aluminum merc prop and what a difference! Im right at 4800 RPM's at WOT and Im topping out at around 56 to 57 mph. But I ended up finding out that the previous owner had put a new outdrive on it, Im concerned that the ratio in the drive is wrong, Because from what I've been told the boat should be able to push a 21 pitch no problem???? Does anyone have any suggestions? Please Help!!!

Donzigo
07-23-2004, 11:11 PM
Before Mercury came out with the Bravo, they made the Alpha drive with the 1:30 to 1 attached to the 454 engine. The original pairing of 454 to Alpha drives in 1987 had the 1:30 to 1 ratio. Your 454 should have a top RPM of 4,400 RPM and the correct ratio should be 1:50 to 1. The 21" to 23" Mirage should be the correct pitch for the propeller. If your Alpha has the 1:30 to 1, it will give you problems. I had the 454 with Alpha in my 1987 Z-25 and it gave me fits.

The boat should go about 55 to 60MPH, when set up properly.
Fishboy & I are always shocked when people say these boats go 70 / 80 MPH. (Maybe if an ex-wife pushs your truck/trailer/boat rig off the side of a mountain........oooooohhhhh bad thought.)

Good luck on your new boat.

Fish boy
07-24-2004, 07:27 AM
the 21 new from the factory with stock power I beleive had a top speed just slightly under 60 mph with tank half full of fuel. SOunds like you are getting pretty close to the correct speed with the correct rpms. Donzigo is correct about it coming with an alpha.

Fish

Ramman
07-24-2004, 01:25 PM
Alright well my next question is, how can I get more top end out of this boat? If I changethe gear ration in the drive, will that make any difference? I was even thinking about upgrading and putting a bravo drive on it, but Im not sure how big of a project that is, or if it's worth doing??? Thanks for the help guys!!!!

Sam
07-24-2004, 04:11 PM
So does this mean that your a fleet captian now ?

Sam :yes:

Ramman
07-24-2004, 04:20 PM
huh?

Ed Donnelly
07-24-2004, 05:45 PM
Welcome to the board RAMMAN, There will be a little confusion for a while,as, another member has a name very CLOSE to yours. He is RANMAN. I am sure the 2 of you will get along splendedly...Ed

Sam
07-25-2004, 11:18 AM
Poodle, who told on me. Actually I've been on the water trying to catch up with my Donzi buds. I guess a 150 Yamaha is no match for a Donzi.

Sam :eek:

TuxedoPk
07-26-2004, 12:47 AM
Poodle, who told on me. Actually I've been on the water trying to catch up with my Donzi buds. I guess a 150 Yamaha is no match for a Donzi.

Sam :eek:

:cistineb: Sam, how'd you miss us 3 days in a row? You and Jamie must have looked for us as hard as OJ's been searching the golf courses for the real killer.

Seriously we had a great time and we wished you had joined us.

GKricheldorf
07-27-2004, 09:49 AM
Ramman,

I was running a 19 degree 3 blade cleaver for some time on my 87 Z25 w/454. My drive ratio was 1.32:1 and i was hitting 56 on average. I had a ding in the prop that was giving me slippage. I'm fairly sure i could have squeezed a few more mph's out had i replaced it.

Be gentle with your drive. They are not very strong mated with the 454.

Ramman
07-27-2004, 11:06 PM
Yea Im guessing thats why the previous owner has already replaced the drive. Im really thinking about upgrading to a bravo drive, anyone have any input on this? Is it worth doing, and how big of a job is it to do?