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Date: Mon, 28 Mar 2005 20:19:40 -0600
From: Barry Gardner <barrygardner@mindspring.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] under drive pulleys
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Kevin,

Sign me up. I'm fitting them to '86 - '88 13B blocks but am not sure 
whether that's a 17mm or 19mm hole.

As for double pulleys, I have no idea whether that's good idea or not 
and am interested in other opinions.

Check my math: The ratio of the pulleys' diameters would determine the 
reduction. Assuming a 5" and 3.5" combo, the water pump would be going 
70% of the speed of the engine, right? So at 8000 rpm, the water pump 
would be 5600 rpm, well below anyone's fears of cavitation.

Barry Gardner
Wheaton, IL

kevin lane wrote:

> I spoke with a machine shop friend today about making pulleys.  He 
> shows me his Mazda race car with a 400hp PP 13B, which I didn't know 
> he had.  He believes that a single pulley with a deep groove should 
> work fine, and that yes, often one belt will take out the redundant 
> belt.  He runs his engine up to 9800rpm without belt problems.  His 
> pulleys are 5 1/8 on the water pump, 3 1/2 drive, which just about 
> touch.  He can make us sets for $110, a bit more for double pulleys.  
> He has an automatic tool changing mill with something like 27 tools 
> available on this giant chain.  It is way cool to watch run.  Pulleys 
> get made on the lathe however.  AL comes in 5 and 5 1/2" sizes, so a 
> 5" pulley may be a better buy than 5 1/8".  He would make the pulleys 
> to order, not as batches, so a 17 or 19mm center hole is no problem.  
> I wondered how many people were interested in getting some made.  I 
> have not seen any for sale at these prices, although I may have missed 
> some.  I saw some sets as high as $350.
> Kevin Lane  Portland, OR
> e-mail-> n3773@comcast.net <mailto:n3773@comcast.net>