Request - M20J Cruise Perf Numbers for Benchmark!

[testwest]

That 15.13 factor is based on compression ratio, and is correct for an 8.7:1 CR engine like we have in the IO-360-A*. Interestingly, if you happened to have the Firewall Forward STC for the IO-360, it would be a 10:1 CR, and that gives a factor of 16.6. So at 9gph LOP in a standard IO-360, you get 135 hp (67.5% power, a very good place to cruise) and in the Firewall Forward STC, that same LOP fuel flow gives you 148 hp (74% power).

For this reason, I have always been surprised that STC has not been more popular. It is also the reason I avoided all of the low compression ratio options on the Aerostar...they are terrible as far as efficiency goes.

[jetdriven]

I wonder about the long term durability of the Firewall Forward 10:1 CR/ STC.  I remember reading somewhere that the rings and pistons take a regular beating from detonation and the top end requires frequent work.  i definately see how it can be more efficient.

[testwest]

TAS calculation from Byron's sheet #2

KIAS: 141

KIAS (IC): 141 since we don't have an instrument correction card. Byron! Homework for your next pitot-static check!

KCAS: 139 (from the Mooney POH Airspeed Calibration Chart)

Ind Alt: 4500'

Altimeter Setting: 30.23

OAT: 48 de F:

From the "MyE6B" app on the iPad:

TAS: 148 (you calculated 152)

Density Altitude: 4479 feet

Pressure Altitude: 4215 feet.

If your TAS is verified correct by some other method like a low altitude speed course or GPS speed course, I still think you have an issue with that airspeed indicator, and it is reading about 3 or 4 knots low.

[KSMooniac]

I've read/heard of more than enough problems over the years with that FF STC in terms of mechanical reliability and company performance to keep me from considering the mod.  We're already working the IO-360 fairly hard at 8.7:1 IMO, and a smarter (albeit more expensive) mod is forced induction so that we could run 80-85% LOP all day long at any altitude.  

[testwest]

Yes, indeed! What you said.

[carusoam]

Compression ratio, timing, and high octane fuel will get you efficiency.  The margin for error begins to erode.

Well instrumented engine, quality 100LL, attentive operator can avoid detonation.

Norman, with 10:1 CR, was the maximum HP rated above the original 200?

Best regards,

-a-

[testwest]

I think it was 210hp or so. And you are right, it is possible to reduce margins if you pile up a few mods....

[KSMooniac]

The Turbo Bullet mod back in the 80s added a turbocharger (not turbonormalizer!) to the J and it included lower compression pistons (I think 7:1) and ran the MP up to 36 or 38".  I've read comments that it apparently made something noticeably more than 200 hp based on takeoff and climb performance, and of course the engine was stressed accordingly.  There was a fatal accident in 1993 with one of these planes and it was essentially due to a power loss for undetermined reasons on takeoff.  Afterwards, the FAA took another look at the mod and released an AD to limit the MP to 33" which I believe returned it to a 200 hp max rating with the lower compression pistons.

I don't know how to calculate the HP increase between 33" and 36" or 38" but I am curious.  With today's instrumentation I wonder if an IO-360 could be run safely at greater than 200 HP...