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View Full Version : donzi 18 classic stearn drive setup



nguber57
08-20-2003, 09:17 PM
I just restored a 1970 Barrel Back 18 Classic, with a new 350 chevy installed power trim, Volvo transom assembly, I have a 270 upper end, and a Speed Master style lower. Boat cavitates under acceleration, is there any certain prop that will help this, or do I need something else? Has anyone ever tried a standard lower unit or duol lower. PLEASE HELP!!! FAST!!

Stix Magill
08-20-2003, 09:37 PM
Does it plane off easily? At what speed does it cavitate?

nguber57
08-20-2003, 09:58 PM
Boat is hard to get on plane.With drive all the way down or in any position. The bow will lift slightly as soon as the bow starts to fall it will blow out.If you stay on the throttle hard it will plane after it shakes and you work the throttle until the prop bites

MOP
08-20-2003, 10:02 PM
There have been a few threads on the Volvo speedmaster some of the guys running them may have some input.
http://www.donzi.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=006350#000000
http://www.donzi.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=006053#000000
http://www.donzi.net/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=007684#000004

AVickers
08-21-2003, 07:31 AM
What prop are you running? I've seen a couple of speedmasters in person. Both were equipped with small-hub, high pitch 4-blade cleavers... Very radical-looking props.

Is the X-dimension of the drive shorter than w/ a standard 270 lower? If so, you might want to install an extension to get it a bit lower in the water...

GEOO
08-21-2003, 07:55 AM
The lower speedmaster unit can give you 8 to 10mph over the standard drive.
Most of the speedmasters were modified with longer cavitation plates. How long is your cavitation plate? I ran a Mazco outboard over the hub exhaust prop she hooked up nicely.

http://www.donzi.net/tech/Pulleng0002_sm.jpg

BRIAN73
08-21-2003, 08:50 AM
Hello,

My first thought is also the length of the cavitation plate. The the cav plate difference between a stock 270 lower and a E lower is huge.

I have heard of people welding an extension on and the problem was gone.

I'm using a three blade Merc chopper, hook's up like a bear.

I only have problems trying to spin a 14.25 by 28.
Very cranky planning off.


Brian

Ed Donnelly
08-21-2003, 06:03 PM
When I was running the twin turbos in my 16' I extended the cavitation plate 5" and widened it 2" on each side. I was running a 3 blade nybral prop...Ed