How flat is the torque curve?

[1:1 Scale]

First, let me preface this by saying that I've never seen a dyno sheet for an O/IO-320 or 360, so forgive me if I'm way off base Lately I've been wondering what the shape of the tq. curve is on a "typical" RV engine. I sent Barrett an email several months back since they have a dyno, and didn't get a reply.

From what I've picked up here and there, the tq. curve doesn't seem to drop off within the normal operating range of these engines, is that correct? It seems a good way to tune these engines for best fuel economy would be to create an engine that produced peak tq. at low rpm (say~2000?), and would maintain it long enough to produce peak power at 2700. It seems (in my mind) that this would allow a pilot with a CS prop to run WOT and pitch the prop turn ~2000 rpm with minimal speed loss and minimal fuel burn. Am I off base?

Do you think this could this be done with the right cam and port work?

[Rivethead]

Well from what I remember when I had my engine dyno'd. At 800 rpm my engine was making about 3 H.P. It seems to me, as I remember it, there was a fairly steady rise, perhaps linear, up to 2000 rpm where it was making something just under 80 H.P. At 2700 rpm, however, it was making 193 H.P. From this I gather my engine has a fair gain in torque between 2000 and 2700 rpm. This info indicates, to me at least, that in the last 600 rpm the torque curve ain't flat at all.

[Rivethead]

I just went up and found my data sheet from Lycon so here are some numbers for you. The numbers are going to be listed as rpm;ft/lbs torque and samples of hp. (EDIT) This is a parallel valve IO-360 fuel injected with LASAR ignition and Vetterman exahaust.


800;22---------------hp=3
900;30
1000;38
1100;49
1300;68
1400;76-------------hp=20
1500;88
1600;102
1700;117
1800;136------------hp=47
1900;152
2000;166
2100;187
2200;212
2300;232------------hp=101
2400;263
2500;298
2600;329------------hp=163
2700;373------------hp=193

Do you think this could this be done with the right cam and port work?

Maybe if it were some REALLY good klingon cam and port work.

[Kevin Horton]

Originally Posted by 1:1 Scale

First, let me preface this by saying that I've never seen a dyno sheet for an O/IO-320 or 360, so forgive me if I'm way off base Lately I've been wondering what the shape of the tq. curve is on a "typical" RV engine. I sent Barrett an email several months back since they have a dyno, and didn't get a reply.

From what I've picked up here and there, the tq. curve doesn't seem to drop off within the normal operating range of these engines, is that correct?

Interestingly enough, the answer depends on which engine model you are considering. At lower rpm, the parallel-valve O-360-A engine produces more power for the same rpm and MP than the angle-valve IO-360-A series engines. The following data are from python scripts that I created that emulate the Lycoming power spreadsheets:

Power at sea level std day with 29 in HG MP:
rpm   O360A  IO360A
       pwr     pwr
       (hp)   (hp)
1800  136.3  119.7
1900  142.7  129.1
2000  149.1  138.9
2100  155.5  149.7
2200  164.1  157.3
2300  169.5  168.6
2400  174.8  177.9
2500  179.1  186.4
2600  183.4  196.0
2700  186.4  203.5


Torque at sea level std day with 29 in HG MP:
rpm   O360A  IO360A
       tq     tq
    (ft-lb) (ft-lb)
1800  397.6  349.3
1900  394.4  356.8
2000  391.6  364.7
2100  389.0  374.5
2200  391.8  375.4
2300  387.0  384.9
2400  382.5  389.4
2500  376.2  391.6
2600  370.4  395.9
2700  362.5  395.8

Note that on the O-360-A engine, the torque falls off as the rpm increases. On the angle-valve IO-360-A engine, with the tuned induction system, it makes less torque than the O-360 at 2400 rpm and below, but the torque really comes on at higher rpm, which allows it to make about 20 more hp than the O-360.

Originally Posted by 1:1 Scale

It seems a good way to tune these engines for best fuel economy would be to create an engine that produced peak tq. at low rpm (say~2000?), and would maintain it long enough to produce peak power at 2700. It seems (in my mind) that this would allow a pilot with a CS prop to run WOT and pitch the prop turn ~2000 rpm with minimal speed loss and minimal fuel burn. Am I off base?

Keep in mind that the speed you achieve is determined by the amount of power produced. If the torque is constant over the rpm range of interest for cruise (let us consider from 2000 to 2500), the amount of power produced will vary linearly with the rpm. The power at 2000 rpm will be 80% of the power at 2500 rpm. The speed varies as the cube root of the power (assuming no change in prop efficiency, and ignoring induced drag), so the speed at 2000 rpm and full throttle will be about 0.8^(1/3) = 93% of the speed at 2500 rpm and full throttle.

[Rockyjs]

Kevin,
Can I assume that the torque curve on my parallel valve IO360 will be similar to the O360A you give numbers for?

Thanks
Rocky

[Kevin Horton]

Originally Posted by Rockyjs

Kevin,
Can I assume that the torque curve on my parallel valve IO360 will be similar to the O360A you give numbers for?

I think that is a reasonable assumption. But I don't know how the induction system on that engine compares to the one on an O-360-A.

If you have a Lycoming operators manual, it will have power charts in it for the whole range of O-360s and IO-360s. Compare the power vs rpm and MP curves on the left side of the power chart for those two engines. Pick off a few power vs rpm and MP values. Torque = 5252 * hp / rpm.

[osxuser]

Originally Posted by Kevin Horton

I think that is a reasonable assumption. But I don't know how the induction system on that engine compares to the one on an O-360-A.

If you have a Lycoming operators manual, it will have power charts in it for the whole range of O-360s and IO-360s. Compare the power vs rpm and MP curves on the left side of the power chart for those two engines. Pick off a few power vs rpm and MP values. Torque = 5252 * hp / rpm.

If it's vertical, it's probably the same. O-360-A = IO-360-B series as far as induction goes.

[Rockyjs]

Thanks guys!
I've got a Superior horizontal using the VANs FAB located in the left inlet. I imagine that it is very close to the vertical induction as convoluted as the flow is through the FAB. The power charts I "borrowed" from Kevin are very close to what my Dynon is indicating. The manual I got with my engine is nearly worthless as it doesn't depict a Horizontal cold air inducted engine or give any power figures for that configuration.