Looking for good performance chart for 150HP O-320

YellowJacket RV9 · #1 01-14-2017, 02:49 PM

I have been looking at some of my data, and I think that the % power numbers my GRT EFIS is returning are a bit off. I believe this is due to not being able to read my O-320 performance charts very well, as they are from a poorly scanned document. I am looking for either a cleaner copy of the performance charts, or even better, an engine performance chart of the type the GRT units use - they have one online for the 160HP (http://www.grtavionics.com/documents...ing%20O320.pdf), but not the 150.

If anybody has anything like this for the 150, I would really appreciate a link or a copy. Thanks!

Chris

Scott Hersha · #2 01-15-2017, 07:35 AM

Link below for a power chart - there are many references like this online. Just look for the chart for your engine (150 hp). I have a similar issue with my GRT Sport, but in the other direction. My O-320 puts out about 180hp. I've used charts and well known formulas to come up with my own power chart for my airplane and I think it's pretty close. Once you figure out the power settings from the lycoming charts for your engine, I think you can go in to the set up menu and change the numbers on that graph. Then your % of power indication should be more accurate. Using SFC to determine hp works pretty well too, and there is an SFC curve on one of the lycoming charts that should be pretty accurate.

http://www.grummanpilotsassociation....ors-Manual.pdf

YellowJacket RV9 · #3 01-15-2017, 07:44 AM

That is perfect, thanks Scott! Surprised I hadn't found that yet.

Chris

humptybump · #4 01-15-2017, 06:58 PM

Scott etal,

One thing confuses me from that document. It states "O-320-E2A
150 hp at 2700 rpm, or 140 hp at 2450 rpm"

I don't understand how the same engine can have such different numbers. According to the document, the 150hp E2A produces 110hp at 2450rpm.

How can the samecengine produce both 140hp and 110hp at the same RPM? I would seem to require a significant change in manifold pressure?

Scott Hersha · #5 01-16-2017, 08:12 AM

Glen,
I don't think the difference is that great. It looks to me like it's either 110hp/2450rpm, or 120hp/2450rpm. The difference between these two is compression ratio - 7.0:1 for the 150hp motor (@2700rpm), and 8.5:1 for the 160hp motor.

humptybump · #6 01-16-2017, 11:55 AM

Yes, the two different O-320's (150hp vs 160hp) do result in about 110hp vs 120hp at the corresponding RPM.

What I was confused about was specific to the O-320 E2A which is only 7:1 compression and 150HP. I have read this engine has a derated power designation for 140HP. It just doesn't seem to make sense that documentation implies the derated version generates 140HP at 2450rpm and the non-derated generates 110HP at 2450rpm. I'm guessing there is a mistake somewhere in these various documents (but can't be sure).

YellowJacket RV9 · #7 01-16-2017, 03:26 PM

Okay so I have pulled some better data from the more readable charts and will update my EFIS tomorrow, but have some confusion about the "Delta HP" chart that is also needed.

Per GRT, at a number of different altitudes, you calculate the BHP at a given MAP and RPM and then compare it to the same RPM and MAP at sea level, calculating the difference (Delta HP). My question is, do I use the same MAP and RPM at each altitude level?

The manual says to use a common cruise setting, and their example is 2300 RPM and 17" MAP, which produces 88BHP at 14000' and 65BHP at sea level, for a Delta HP of 23. So far so good, matches my chart. But at other altitudes, I get different BHPs for those settings that do not match GRT's chart, so I am assuming that at each altitude, they are using different settings and recalculating the altitude and sea level BHPs. That would also explain why their Delta HP chart peaks at 12000' rather than being linear.

I know the above sounds convoluted, but hopefully somebody has done this by hand before and can understand my struggle. I know my numbers won't be too different for my 150HP, but my OCD demands all be perfect. Thanks!

Chris

Scott Hersha · #8 01-16-2017, 05:10 PM

Chris,
I understand the OCD necessity of getting this right (actually, I think it should be CDO so that the letters are in their logical, alphabetical sequence). I think you should take that power graph with a grain of salt, and the Delta HP scale is confusing to me too. I haven't tried, but I'm wondering if you can change the numbers on the graph in the set up menu. That would be the only way to get a reliable % power indication. As it is, I just decided to not show the %power indication and use my power chart instead. I'll see if I can make changes on my GRT graph and let you know if that works.