Real HP Numbers

When I replaced my O-290D2 with an ECi O-360 kit engine, I didn't do anything special with the engine, other than put it together. My compression ratio is 8.5:1, no special cylinder porting, etc.

I do have a custom FAB that I had to create to fit my Sam James cowl and I have dual P-mags which I have tuned to CHT, not power. (I reduced the Offset and the Max Advance by -1.4 degrees, nothing special.)

The other day when I performed the time to climb tests that I posted in this thread, I did a couple of speed runs down at 8000' DA to see how my new timing configuration was working to keep the engine cool.

This evening I finally pulled the data from the SkyView and found I was going a 175.7 Knots TAS at 8,264' DA while turning 2805 RPM with 22.9" MAP and drinking 10.7 GPH (Leaned 100* ROP) with an OAT of 7*C/44.6*F.

I plugged those numbers into a %power calculator I found on line and it indicated I was putting out 201 HP, more at sea level.

Is that even possible?

Hmmmmm...

Rule of Thumb for ROP OPS: 1gph = 10hp. So, 10.7gph = 107hp.

This formula works in every aircraft engine (piston) that I have operated from an A-65 thru R-2600.

Have another look.

Carry on!
Mark

N941WR said:

I plugged those numbers into a %power calculator I found on line and it indicated I was putting out 201 HP, more at sea level.

Is that even possible?

Click to expand...

I'd question the HP calculator. Where did you find it online?

I would question whether you were ROP...10.7 gph at over 2800 RPM? If LOP, you multiply fuel flow by 14.9, so 10.7 * 14.9 = 159 HP.

Mark Dickens said:

I would question whether you were ROP...10.7 gph at over 2800 RPM? If LOP, you multiply fuel flow by 14.9, so 10.7 * 14.9 = 159 HP.

Click to expand...

I couldn't run LOP at that power setting if I wanted to. 16 GPH is what I saw when breaking the engine in.

I was looking for that formula but couldn't find it, thanks.

Bill,

I have the same ECI motor, and while snooping around some company propaganda I seem to recall them reporting the mill to create 188 HP to begin with!

So, if you believe that number...

BTW, I do agree that it seems to have plenty of power and based upon how much fuel it can drink if you don't throttle it back... that could be true!

Sooooo... For whatever that is worth, certainly not even the standard two cents!

CJ

Short answer - no.

No it is not correct. Some assumption is wrong, and the only way to get real hp is torque. Kevin Hortons engine power spreadsheet indicates 170hp. That is a best possible based on factory data. But even that is still extrapolating for 2800, and correcting for temps. No allowance for timing adjustment to MBT. Pretty good speed though! If you only knew drag, and prop efficiency.

Probably be best way to objectively determine hp is knowing airframe drag and doing several different climbs. Climb is definitely indicating real work, ft-lb/min, if you know your real weight. More assumptions.

0.5 lbs / fuel per hour per HP

Was taught to use 0.5 pounds of fuel per hour per horsepower produced.

(10.7 GPH X 6) / 0.5 = 126 HP.

RV6_flyer said:

Was taught to use 0.5 pounds of fuel per hour per horsepower produced.

(10.7 GPH X 6) / 0.5 = 126 HP.

Click to expand...

If it was 170hp then the BSFC calculates as .378 lb/hp-hr - pretty good. The advanced timing probably helps with getting to MBT, max-best-torque, but I don't think Kevins spreadsheet accounts for that. It is pretty low for any rich condition. But, I knew of one Continental that ran .333 in cruise. It was LOP. I don't remember the conditions, but just the SFC. Assuming SFC yields HP, so we could just guess at HP, but SFC is a little more constant.

Bill,

If you were at 8k', you couldn't be making more than roughly 75% power. Maybe a couple of points higher due to the 2800 rpm number, but not much. The Pmags will likely get you one or two percentage points improvement in fuel use for the same cruise HP, over the .45gph figure I used below.

Unboosted, any internal combustion engine will make around 75% of rated output when operated up at 7500-8000 feet, wide open throttle, and at the rpm for full power rating at sea level.

It's difficult to see how a random 'online' HP calculator could give any kind of realistic estimate, unless it's tailored for a specific airframe. If the one you used was written for a typical GA aircraft, it would probably assume that it took much more HP to go that fast (it would assume much higher drag).

At that altitude, it would be very difficult to hurt the engine at *any* mixture setting; the output power (and chamber pressure) is down so much that the exhaust valves and piston tops just aren't stressed.

Lyc's power charts for 180 hp 360s typically show almost exactly 10 gph at 75% power. This works out to roughly 0.45 lbs per HP per hour. The old Lyc charts often showed the engine leaned *to best power* (which was sometimes PEAK, or just rich of peak, egt) for fuel flow at 75% & lower HP numbers. If you were running 100 rich of peak, and 100 rpm faster than rated rpm, you'd flow a bit more fuel.

{Aside to Mark, F1 Boss: I feel a bit weird questioning someone who's designed and brought to market an aircraft, but that 1gph=10 hp number (which comes to 0.6 lbs per hp per hr) sounds like a full power number, using fuel to cool the engine; not a properly leaned, <=75% power number. Am I wrong?}

Assuming you have a basically stock airframe, and it's straight, another way to approach it is to look at Van's 75% (of 160 HP) number for the airframe, and 'back into' the power it would take to get from that number to your number. Power goes up with the cube of the speed ratio. Fuel flow for 75% of 160 HP, properly leaned, is ~9 gph. (160hp*.75=120hp 120*.45lbs=54lbs/hr 54/6 lbs per gal=9gph) As I mentioned in the 1st paragraph, the Pmags might buy you a couple of tenths of a gallon, when flying at altitude.

Charlie

Exactly!

{Aside to Mark, F1 Boss: I feel a bit weird questioning someone who's designed and brought to market an aircraft, but that 1gph+10 hp number (which comes to 0.6 lbs per hp per hr) sounds like a full power number, using fuel to cool the engine; not a properly leaned, <=75% power number. Am I wrong?}

You have it exactly correct.

BTW all questions welcome.

Carry on!
Mark