<< Jerry Hey wrote:
 >
 > It is time for me to decide on the drive ratios for my chain psru.
 > Basically, if I want to avoid special orders (and considerable expense)I
 > have two choices. 2:1 or 2.21:1.  The 2:1 would have max cruise (prop at
 > 2750) at 5500 eng . rpm.  The 2.21:1 would achieve the same at 6077
 > rpm.   Of course, the engine would be making more power in the latter
 > case.  With the extra power, comes additional heat generation.  I think
 > the guys who want to run the 2.8 gear box at over 7000 rpm may face
 > formidable cooling issues.  A lot of radiator core and a lot of air
 > will be required and that adds up to a lot of drag.  May be sound and
 > fury signifying nothing as far as practical, high speed cruising is
 > concerned.  But that is beside the point of this note which is my drive.
 >
 > It seems to me the 2.21 ratio would be just about perfect.  But I have
 > never heard of any one claim that they could actually cruise at 6000
 > rpm.  Even the planes in the Everett Hatch RACE, ran less than 6000 rpm,
 > I believe.
 >
 > I would like to think it would be possible to set the throttle at 6077
 > rpm and just leave it there.
 >
 > The Star Mazdas operate in this RPM range ( 6000 to 6800) and seem to
 > survive very well.
 >
 > I will appreciate anyone's commentary.    Jerry

I have my idle set just over 2,000 RPM just to keep the engine from shaking
the gearbox to pieces. The people with 13Bs are turning them over 9,000 RPM
with only an occasional rotor bearing failure. Oil temp is the culprit in
rotor bearing failures. A good synthetic and a big cooler is required. The
Mazda series cars can go three seasons or more between overhauls. There is
way less stress on the bearings below 7,000 RPM and that leaves temp as the
killer. The Mazda's have adequate cooling so there is no problem.
Lynn E. Hanover.

 
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