I have a Performance Engines IO-550 that started out with 10:1 pistons until they rubbed the cylinders due to improper piston-bore clearance.  It later failed in flight due to an ancient, out of tolerance rocker arm broke due to high cycle fatigue.  The crankcase and a lot of other stuff was found to be out of tolerance during the teardown and inspection, and this stuff had to be replaced. So be careful with your engine.  It could bite you.  There are at least half a dozen Performance Engines units in Lancairs that went in for premature teardown long before TBO and were found to have a lot of out of spec, non-conforming or old parts installed.  I believe the FAA investigation continues. 

 

Be careful.

 

Addressing your questions, dyno tests by Barrett Precision Engines with 10:1 pistons yielded about 325 HP, almost 5%  more power, and about what you would expect with the compression increase.  What this means is that the conversion of avgas to power has a conversion constant of about 15.7 HP per gallon per hour operating at 50F lean of peak. 

 

So to make 65% of originally rated horsepower of 310 HP which is 201.5 HP, divide by 15.7 and you get 12.8 gallons per hours which is where I used to fly.  With the stock 8.5:1 pistons, the conversion constant is 15.0 HP per gallon per hour, and it requires about 13.5 gallons per hour to run at 65% which is where I run today.  So the  extra compression gives you a savings of almost one gallon per hour at the same power setting and speed, certainly worthwhile over a period of 2000 hours. 

 

To bad that Performance Engines screwed up on my engine.   It cost me big time, and continues to do so.

 

Sadder but Wiser Fred

 

 

From: Dan Ballin

Date: 18/01/2012 4:21:54 AM

To: lml@lancaironline.net

Subject: HP