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Bob, the compression for the turbo rotors on some models of the 13B were as low as around 8.4:1. If that is also true of the 13B, then my opinion is you will see a considerable improvement in power over the low compression rotors. I went from the 9.4 to the 9.7:1 rotor on my two rotor and liked the results. I know that small a difference in compression should not translate into a terrific power increase, but it seemed make a noticeable difference. Now the challenge is getting the 9:7:1 - there are not many used ones out there and those that are can be very worn. Make certain you check the apex seal slot wear measurements before you stick any in your engine (actually all of its seal slots should be checked) if using used ones. If apex seal slot wears past the limit and if you are using the somewhat brittle stock apex seals, they will break - don't ask me how I know.
One thing make certain you are getting 9:7:1 rotors. If you place a straight edge across the compression dish and then measure vertically down until you hit the top of the rotor it should be around 3.8-4 mm. If it measure more than that it may be the lower compression 9.4:1. But, even the 9.4:1 should make a noticeable difference IF the stock turbo 20B is using the 8.4:1
Ed
----- Original Message ----- From: "bob.kaufmann" <bob.kaufmann@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, February 03, 2008 4:44 PM
Subject: [FlyRotary] Low compression rotors
Gang
I have a 20B that I have taken the turbos off and will be using it in an
aircraft, a RV-10. A friend of mine said that I should use the 9.7
compression rotors instead of the turbo rotors. What say you all?
I have pulled the engine off to powder coat the engine mount and if I'm
going to switch rotors, now is the time before I hang the engine again. I
have the flat plate on milling machine so I could make plates for the 20B if
people wanted. I think I would be competitive. I would like to do them in
groups of ten if people are interested.
Bob K
Finished except all the parts aren't together yet.
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