"Balls to the Wall" 231 speed

[231LV]

Although I have owned my 231 for nearly 20 years, I almost always ran it LOP except during takeoff and climb where it was full forward on everything. Recently, I decided to start experimenting with the performance envelope. What I have discovered is the 231 is a pretty fast airplane even down low. On a flight earlier today in no wind conditions, I decided to see how fast I could push the plane. At 8500 ft and full tanks ( I had just fueled) with myself as the only passenger, I recorded the following; prop set at 2500 RPM, 95% power, full rich and cowl flaps closed, a 21.6 GPH burn yielded 177 knots in level flight. My TIT stabilized around 1390 and my hottest cylinder was 341. I'm wondering how this compares with other 231's? Oh, it has a Merlyn and an intercooler

[Tom 4536]

1 hour ago, 231LV said:

Although I have owned my 231 for nearly 20 years, I almost always ran it LOP except during takeoff and climb where it was full forward on everything. Recently, I decided to start experimenting with the performance envelope. What I have discovered is the 231 is a pretty fast airplane even down low. On a flight earlier today in no wind conditions, I decided to see how fast I could push the plane. At 8500 ft and full tanks ( I had just fueled) with myself as the only passenger, I recorded the following; prop set at 2500 RPM, 95% power, full rich and cowl flaps closed, a 21.6 GPH burn yielded 177 knots in level flight. My TIT stabilized around 1390 and my hottest cylinder was 341. I'm wondering how this compares with other 231's? Oh, it has a Merlyn and an intercooler

You actually run full throttle with an intercooler??? What is your MP?

[231LV]

27 minutes ago, Tom 4536 said:

You actually run full throttle with an intercooler??? What is your MP?

wasn't quite full throttle...95%....MP was 32.7 inches

[carusoam]

Got any JPI data to share with that?

-a-

[Guest]

2 hours ago, 231LV said:

Although I have owned my 231 for nearly 20 years, I almost always ran it LOP except during takeoff and climb where it was full forward on everything. Recently, I decided to start experimenting with the performance envelope. What I have discovered is the 231 is a pretty fast airplane even down low. On a flight earlier today in no wind conditions, I decided to see how fast I could push the plane. At 8500 ft and full tanks ( I had just fueled) with myself as the only passenger, I recorded the following; prop set at 2500 RPM, 95% power, full rich and cowl flaps closed, a 21.6 GPH burn yielded 177 knots in level flight. My TIT stabilized around 1390 and my hottest cylinder was 341. I'm wondering how this compares with other 231's? Oh, it has a Merlyn and an intercooler

21.6 GPH, I’m blushing!

Clarence

[Phil EF]

I get 160k at 75%, about 12.5gph tit around 1450. (GB engine) around 8000’. 
Never tried 100% in cruise. 

[DanM20C]

4 hours ago, 231LV said:

At 8500 ft and full tanks ( I had just fueled) with myself as the only passenger, I recorded the following; prop set at 2500 RPM, 95% power, full rich and cowl flaps closed, a 21.6 GPH burn yielded 177 knots in level flight.

I did a similar speed run at 18K and was right around 196ktas, same power settings LB with intercooler and Merlyn.  Being nearly 10K higher would give me about 20kts so we are very close to the same.  
 

cheers,

Dan

[RJBrown]

This is why I converted my 231 to a Rocket.

73% 20gph 200 knots @ 12,000’ faster higher. Up to 238 kts @ 24,000

slowed down to normal 231 speeds it costs about 1 gph to be able to go much faster.

your 12.5 @165 becomes 13.5 @165 

pushing a 231 that hard will limit its life. Original sales literature said 231 mph @ 24,000’

flown according to the book most 231 got their first overhaul around 1200 hours. mine got a TSIO520NB at 1200 hours.
When I bought it stock I trusted the 1800 hour TBO. The high oil consumption within 100 hours of purchase was a surprise.

after needing an engine I looked at the planes for sale. It was early enough that most of the fleet either were under 1200 hours or had had their first engine around that number. With intercoolers wastegates and knowledge 1800 in now a real number. 
But: if I were in the market I would still figure a 1200 TBO 
 

[aviatoreb]

That's interesting 231LV and consistent with what I see.  So same airframe here I would expect roughly the same speed on same horsepower at same altitude.  Fuel flow aside because at 95% you needed excess fuel for cooling and detonation margins. 

95% of 210 is about 200hp.

on my rocket, 200hp is about 65% of 305 which is a standard cruise setting and book says 18gph at that setting rop.

I would say yeah 177TAS is in line with what I would see at 8500 ft, maybe 180TAS, but pretty close.

[231LV]

11 hours ago, RJBrown said:

This is why I converted my 231 to a Rocket.

73% 20gph 200 knots @ 12,000’ faster higher. Up to 238 kts @ 24,000

slowed down to normal 231 speeds it costs about 1 gph to be able to go much faster.

your 12.5 @165 becomes 13.5 @165 

pushing a 231 that hard will limit its life. Original sales literature said 231 mph @ 24,000’

flown according to the book most 231 got their first overhaul around 1200 hours. mine got a TSIO520NB at 1200 hours.
When I bought it stock I trusted the 1800 hour TBO. The high oil consumption within 100 hours of purchase was a surprise.

after needing an engine I looked at the planes for sale. It was early enough that most of the fleet either were under 1200 hours or had had their first engine around that number. With intercoolers wastegates and knowledge 1800 in now a real number. 
But: if I were in the market I would still figure a 1200 TBO 
 

I have a JPI and monitored all temps...hottest was 340 and TIT was 1390....engine won't be harmed with those temps...just burned lots of gas

[Mike A]

On 5/14/2021 at 7:06 AM, RJBrown said:

73% 20gph 200 knots @ 12,000’

Nearly double the fuel burn to get 25 additional ktas while demolishing your useful load with a bigger engine? Hard pass.
 

This is from last weekend in my stock 231. 

[RJBrown]

19 hours ago, Mike A said:

Nearly double the fuel burn to get 25 additional ktas while demolishing your useful load with a bigger engine? Hard pass.
 

This is from last weekend in my stock 231. 

 

Climb to 26,000@ 1500 fpm. 20gph 238 knots @ 24,000 

pull power back to 231 levels and get almost same mileage. Still climbed higher, then slowed down and went further. Or ? Take your pick.
it’s called flexibility. At 11420 you are still below the MEA 15 miles west of my old house. 
The usefull goes up with Rocket conversion. It can carry more, higher, further and faster. 
What do you buy a airplane for? To go slower?
But a M20K is the best plane ever, Rocket is just its peak.