140 looper at 6000rpm

[reeldutch]

the motor is a 87 smallbore rebored to accept 88 big bore std pistons.
timing set at 18* give or take 1*

compresion is 130 on all 4

prop size 13 3/4 X 17 sst

wot rpm 6000 (teleflex tach)
speed 40 mph teleflew speedometer
humingbird fishfinder with wheel 41mph

prop slip is:

40X1056
---------- X100 = 83
3000 X 17

so my prop slip would be 17 %

is this correct?

 

[72SideWinderSS]

Re: 140 looper at 6000rpm

Try,
(Pitch X RPM) / (Gear Ratio X 1056) = Theo Speed

(Theo Speed - Actual Speed) / (Theo Speed) = Slip

Don't forget to add an inch to the pitch for the cupping.

 

[Seasport]

Re: 140 looper at 6000rpm

Or try this:
http://continuouswave.com/cgi-bin/propcalc.pl/

 

[reeldutch]

Re: 140 looper at 6000rpm

so if all the imputs are acurate the prop slip is 17% wich is a little sloppy.
the motor is mounted on a bracket with a 4" ofset and the antiventilation plate about 1.5" above the keel.

i just think that it could be the hull or prop causing this slippage.

just want to get it running as fast as posible

i realize for better economy i should run a 4stroke or dfi engine.

reeldutch

 

[reeldutch]

Re: 140 looper at 6000rpm

oh yeah its on a 1973 20' mako center console

 

[ezeke]

Re: 140 looper at 6000rpm

Did you try it with the a/v plate any closer to the keel?

 

[reeldutch]

Re: 140 looper at 6000rpm

ezeke you mean dropping the motor?

i believe it would drop the rpms a little.

i'm just curious in how efficient a older hull can perform. should i just be happy with about 17% slippage.
i did some calculations and if i get it to 8% i would only gain 4 mph.

i just might try different props see how it does.