IO540 Lycoming Thunderbolt vs Reg Lycoming

[paul330]

Sounds like they are doing what Aerosport Power have been doing to their engines for years ...............

[leok]

I paid the extra for the Thunderbolt for all of the reasons mentioned above, plus one more. I was able to go to the Lycoming factory and watch the engine build. I was told that was a bit unusual, but everyone was very nice and supportive. I made a real effort to not be a pain to anyone. The result was a good schooling on the engine build and a very smooth running engine. I view it as one of the highlights of my build experience.

I was not allowed to pick up any tools (union shop) but ask any questions I had along the way. I was able to get a full tour of the factory as well. Jeff told me that the porting, polishing and balancing adds about 1 HP per cylinder, give or take.

[DanH]

A stock Lyc has set limits for rotating and recip balance. The T-bolt limits are a bit smaller. The difference is not huge, but like so much in aviation manufacturing these days, the exact numbers seem to be a state secret. See Henry VI, Part 2, Act IV, Scene 2.

The "port and polish" is balancing of a different kind. The ports are not enlarged or changed significantly. The idea is to put a set of cylinders on the flow bench, find the best flowing one, and then tweak the others so they flow the same. The end result is similar volumetric efficiency for all. If every cylinder gets the same air charge and the same fuel delivery (adjusting GAMI spread is your task), they make similar power.

Regarding smoothness, it's my opinion that the cylinder flow balance is more valuable than the rotating/recip tweak, in particular for a 540 with its long crank.