Can you have more power and reliability?

QUESTION: It seems that most automotive engines can be boosted in power to approximately one horsepower per cubic inch (obviously at the expense of reliability). Would it be possible to boost a Lycoming 720 engine to, say, 500 or 600 hp and be reliable enough to compete in a race such as the ones at Reno?

John Crow
via email

ANSWER: John, you raise an interesting question and I’ll attempt to answer it without getting myself in trouble.

I don’t think I’ve ever heard about boosting an engine to approximately one horsepower per cubic inch, but it sounds logical in certain circumstances.

Going back a number of years you may recall that Piper produced a prototype aircraft called the “”Pocono.”” It was to be the prime aircraft used by commuter airlines to feed major airport hubs, before the turbine engine really had a foothold in that market.

After much study, Piper elected to go with a pair of turbocharged Lycoming IO-720 engines. This aircraft was actually to be a piston powered “”wide body”” and therefore was quite large. If my memory serves me correctly, the turbocharged 720s were rated at 525 hp each. The program at Piper was dropped and Lycoming did not continue with its program at that time.

Could it be done? I believe so and probably somewhat easier nowadays with advancements in technology. Would it be a viable program for Lycoming to enter at this time? I seriously doubt it, unless one of its OEM accounts could convince the company that the market was there for such an engine.

When it comes to “”wild things”” for special applications like Reno, then most anything is possible as long as the most important component is there and lots of it. That component is, of course, money! I believe you could boost a 720 to the horsepower range you mentioned and still maintain a certain amount of reliability for a Reno shot.

John, if you decide to do something along these lines, I’d really appreciate being kept informed of the progress.


Boy, did I ever tramp on my tie in my Dec. 24, 2004, article “”What engines should I avoid?”” I mentioned how Lycoming identified the O-320-H2AD with the latest configuration by modifying the engine serial number. I stated they added the letter “”A”” (which is used to identify a wide deck engine) following the serial number, but that is incorrect. The company modified the engine serial number by adding the letter “”T,”” not an “”A.””

So, let’s set the record straight. If you have a Lycoming O-320-H2AD with the engine serial number ending with a “”T””, i.e., L-XXXX-76T, then you’ve got all the goodies of the latest configuration, consisting of the wide lobe camshaft, large diameter tappets, and the new series of crankcase that is used with the large diameter tappets.

I apologize for any hypertension, rapid heart beats or any other results of my misstatement.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to:

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