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thescooter
08-02-2011, 06:47 PM
Just checked my outdrive gear ratio on my twin volvo 250 drives on my 28' bertram baron.
Ratio is 1.35 is this 1.35 a good or bad thing?
thescooter

maddad
08-02-2011, 09:46 PM
It's not a bad thing. I've been trying to hunt down an early 250 with the "A" ratio for a few months to see if it will spin my solas prop faster without spinning the motor faster. If you think about swapping for another ratio I'd be interested in the set you have.
An A ratio spinning a 21" prop would be close to a B ratio spinning a 23" prop in real world usage.

mattyboy
08-02-2011, 11:04 PM
Mike

i might have a 250 A for sale in a week or so I'll keep you posted

thescooter
08-03-2011, 08:15 AM
thanks guys
my situation in short is.
had a new set 302s motors built.
the new motors turn 5800 to 6000 with old 15x17 props.
my old motors turned 4800 at best.
now what?
go for more prop say 15x23 (ex)?
is going to a 1.6 drive is a mistake?
also very interested in your 1.35 drive.
all suggestions in greatly accepted.
nick the scooter
here is a link

http://atlaswoodproducts.wordpress.com/2008/03/24/this-is-my1970-bertram-baron-28-twin-holman-moody-fords-302s-with-351-heads-one-of-aprx-10-left-of-only-50-built-click-on-pics-to-enlarge-them/

MOP
08-03-2011, 09:30 PM
Are 100% sure your tachs are set correctly? Set on 6 instead of 8 would produce readings in that range. If so going to 1:6 is the wrong direction, you may have trouble finding wheels with enough pitch.

thescooter
08-04-2011, 04:23 PM
ok will check.

mattyboy
08-05-2011, 06:49 AM
Scooter as it was explained to me changing the gear ratio is like changing an inch of pitch like in maddad's example ( 1.6 to 1.3 would be about 2 inches of pitch). i would not go to 1.6 drives that will bring up your rpms and force you too find bigger props 25 pitch or higher which are hard to find .

down in gear ratio or up in pitch = -approx 200 rpms
up in gear ratio or down in pitch = + approx 200 rpms

i would not make the jump to 23's either i would see if you can find some volvo ultras in 22 pitch in LH and RH then fiddle with the spinning out or spinning in. 22 pitch should drop you down from 5800-6000 rpm to 4800-5000 if your tachs are right but as phil said check your tachs first before making any changes.

thescooter
08-05-2011, 08:01 PM
thanks we are tuning things in this weekend!