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View Full Version : How fast should a z21 go?



jamieZ
08-05-2011, 08:44 AM
I have a 1988 Z21 Donzi with a 350 Mag and side exhaust. Runs great, starts well,sounds very strong. I run a 19 inch quicksilver S/S prop (WOT 4600 RPM). The boat is in excellent condition and I am very proud of it. It will do close to 50MPH, is this right or should it go a little faster? The reason I ask is looking at the used boat section, boats with the same power/size owners are claiming speeds closer to 60MPH. Is this wishfull thinking or am I running a little slow. I don't know. Any input or comments would be helpfull. Thanks, Jamie

joseph m. hahnl
08-05-2011, 05:06 PM
I have a 1988 Z21 Donzi with a 350 Mag and side exhaust. Runs great, starts well,sounds very strong. I run a 19 inch quicksilver S/S prop (WOT 4600 RPM). The boat is in excellent condition and I am very proud of it. It will do close to 50MPH, is this right or should it go a little faster? The reason I ask is looking at the used boat section, boats with the same power/size owners are claiming speeds closer to 60MPH. Is this wishfull thinking or am I running a little slow. I don't know. Any input or comments would be helpfull. Thanks, Jamie


Rpm is low for a 19 pitch. 350 Mag should be 1:1.5 gear ratio. I run a 21 pitch @ 4800 RPM full trim . Granted a Z21 is just slightly heavier than my Minx. You could try more trim to get the RPM up, but I doubt a 19P will reach 60MPH.

younger
08-07-2011, 09:21 PM
snowboater runs a sweeeet 502 bravo in his flawless z21 and runs around 70. I believe the 502 is a 502 hp create motor.

The Hedgehog
08-07-2011, 10:52 PM
80 with a blown sbc

EricG
08-07-2011, 11:09 PM
My old Z with the same power/drive would do about the same. I could get 51 GPS with a 21 cleaver...but that was about it. I think mine was a bit tired, but I don't think you are too far out of the ballpark.

Back when those boats were new, that was fast. Also remember that a speedo will often read very optimistic...so that may be where the 60Mph claims are coming from...

Donzi_Dude
08-08-2011, 05:33 PM
i seem to remember claims of mid-high 50's with that set-up.


sounded high at the time.

:confused: