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Got some questions about power, fuel burn, fuel type O320

GyroRon

Active Member
I just recently picked up a new toy, a RV-4 with a O-320 160hp engine. I have a few questions and would like some input.

First off, the plane has a 3 blade Catto prop on it. To me, the RPM seems low. I will try to fly it today and take notes of the RPM it achieves static, and during the take off run and climb out, then again at full power in level flight... But till then, I just think its a bit low, almost as if it is over propped.

In the panel there is a manifold pressure gauge. Prop is fixed pitch thou.

Also in the panel is a fuel computer that I can see my fuel burn.

So I am using the fuel burn rate, and rpm and manifold pressure all together to try to set the throttle for cruise flight. As it is, I am setting the power for about 2300 rpm, and seeing 22-23 inches of pressure and a fuel burn of around 9 gallons per hour. airspeed is only around 160 mph at this setting.

At those settings, I have ALOT more throttle lever to go forward, but then fuel burn goes up quite a bit too. I had always been told to expect 7-9 GPH out of a 320, so to go with more throttle, ( I need to experiment with it some to be sure ) I believe I will be in a GPH range of 10.5-11.5 easily.

If the plane didn't have that fuel flow gauge I would just throw the throttle further forward and go faster, but seeing 10+ GPH makes me think I am either giving it too much throttle or something???

Perhaps the fuel computer isn't accurate? IDK


So the other thing I wanted to discuss, is would it be SAFE to run car gas in this engine? It is a 160hp version, and the logs on this plane kind of suck... It appears to have gotten new cylinders back in 2012 or so, but doesn't say what brand or what compression ratio. All I could find was some paperwork from ECI authorizing some type of paint color application onto the cylinders, with a log book entry saying new cylinders were installed in 2012.

I have access to 90 octane non ethanol fuel, and access to 93 octane pump gas ( pumps all say it could have up to 10 percent ethanol in it )

I know some will say fuel costs should be the least of my worries, but it does add up! Av gas is currently 4.50 a gallon at my place, where as 90 octane non ethanol is 2.25$ a gallon currently. In a plane that may be burning 9,10 or even 12 GPH, That could be a savings of 20-27$ per hour.

I used the 90 octane for 5 years in my old Piper Tri Pacer with a 150HP 320. And have used it in my Jabiru 3300 powered Sonex for the last year and a half with no problems.

Your thoughts? And any factual info to consider?

And I guess, if the auto gas is not totally ok, but not totally bad, perhaps a mix of AV gas and autogas would be ok? I have a large 120 gallon fuel cell / trailer in my hangar, so I could fill it with a ratio of say 50/50 av gas and auto gas and fill the plane that way. Wouldn't save me as much money as going 100 percent auto gas, but could still save me 10-15$ per hour.
 
What are you doing with the mixture? That's a big component. What kind of magnetos do you have? How are they timed? Another thing that can help/hurt a lot. How are your CHTs? Do you have an engine logging device that could provide data for a service like savvyaviation.com?
 
IO-320 data

I have an IO-320 with a FP W-W GA200L prop on my RV-8. When I built my fuel system, I made sure it was going to tolerant of 93E10. I have run about 2000 thousand of gallons of 93E10 through it in 585 hrs with no ill effects. There is a big WARNING about using STRAIGHT auto fuel - it will vapor lock / boil in the fuel lines on a hot day / hot engine scenario. At low power / RPM, this can lead to the engine stumbling or it just quits. Running the boost pump helps, but I typically run 70 /30 100LL to auto fuel during the hot summer months and 50 / 50 in the winter.
As far as power settings, using the Dynon SV engine power percent as a gage, at 65% power, 158 ktas at 7.6 GPH, 70% power, 161 ktas at 8.0 GPH, 75% power, 165 ktas - 8.5 GPH, WFO 178 ktas at 11 to 13 GPF.

All of these numbers are at around 5000 to 8000 ft MSL and vary based upon density altitude.

I do not pay attention to MP and RPM, with a FP prop, you get what you get by running at percent power settings.

At WFO, my prop is turning 2750 RPM, which is right at its limit.

A three blade prop on an O-320 may not give you the best speed, but might give you better climb. I have found that the W-W 200GL is the best 2 blade prop for my configuration.
 
O-320

...And I guess, if the auto gas is not totally ok, but not totally bad, perhaps a mix of AV gas and autogas would be ok? I have a large 120 gallon fuel cell / trailer in my hangar, so I could fill it with a ratio of say 50/50 av gas and auto gas and fill the plane that way. Wouldn't save me as much money as going 100 percent auto gas, but could still save me 10-15$ per hour.

I live just south of you at SC76 (Unity Aerodrome) and have a fuel tank in the hangar. I have an IO-320,160hp, 8.5:1 compression ratio engine in my RV-9A. The engine needs 91 Octane and running straight 90 non eth is just not going to cut it. It is not worth the risk in our hot weather here where your CHTs are going to be up. I run 4 parts 90 non ethanol to 1 part 100LL and get good results. That mixture should give you 92 octane. Even in the hottest August days I never had any issues with either detonation or vapor lock. I have run 93 ethanol in my 9:1 CR Sonex and had issues with both vapor lock and with detonation so I cant recommend it. It also has substantial storage issues, both turning bad in a short time and in absorbing water from the environment.

As for your power settings and fuel burn, there is not enough information to give any useful advice. The 9 gph consumption is about right for 75% power if you run rich. I never run rich, always lean of peak. In the 9A I get about 150 mph indicated, 155 TAS at 3000 ft at 6.7 gph. The 9 loves altitude and at 12000 ft full throttle (fixed pitch prop), 50% power lean of peak fuel burn is less than 6 gph with TAS of about 155-160 mph. LOP will always reduce the power (and speed) available of course, but does wonders for your fuel burn and the engine is happier with lower CHT, lower EGT, lower BMEP, what's not to like?. Power = fuel burned just no way around it. Best power is fast, but fuel burn is the cost. Fly down and see us sometime at Unity. We have another guy here from Fort Mill with a Just Highlander.
Ed
 
As mentioned, you don't describe how you are leaning. If you are running mixture full rich at cruise altitude, your results are not overly surprising. My 6 with a 320 does 185 MPH TAS at 8K' on 8.1 GPH while LOP. Expect a 4 to better that by at least 5-7 MPH. I do have EI that nets about a .5 GPH fuel efficiency over mags and a balanced injection system that also drives efficiency.

You need to do some searching on how to lean your engine at cruise. I also would not trust your fuel reading. Suggest you get the manual and run the calibration to ensure it is accurate.

Larry
 
Call Catto

with serial number off prop hub and they can likely tell who when and what the prop was built to do. Cruise, climb, or in the middle, or customers custom length/ pitch.

I run 93 octane non alcohol fuel in my 0320 D1A without issue. Lots of others do too, especially outside USA.

Good luck
 
93 non ethanol

with serial number off prop hub and they can likely tell who when and what the prop was built to do. Cruise, climb, or in the middle, or customers custom length/ pitch.

I run 93 octane non alcohol fuel in my 0320 D1A without issue. Lots of others do too, especially outside USA.

Good luck

Wow, I wish we could get 93 non ethanol in South Carolina. We can only get 90 with no ethanol.
Ed
 
What are you doing with the mixture? That's a big component. What kind of magnetos do you have? How are they timed? Another thing that can help/hurt a lot. How are your CHTs? Do you have an engine logging device that could provide data for a service like savvyaviation.com?

I have leaned it, but probably not far enough. I need to play with it some and watch the EGT while leaning to see where it a good spot mixture wise

The plane has a slick mag and a Pmag. The slick is supposedly set at 25 degrees.

Haven't paid a ton of attention to the CHT's. What would be good target numbers?

The plane has a ilevel device on it, I need to check and see if it data logs
 
I live just south of you at SC76 (Unity Aerodrome) and have a fuel tank in the hangar. I have an IO-320,160hp, 8.5:1 compression ratio engine in my RV-9A. The engine needs 91 Octane and running straight 90 non eth is just not going to cut it. It is not worth the risk in our hot weather here where your CHTs are going to be up. I run 4 parts 90 non ethanol to 1 part 100LL and get good results. That mixture should give you 92 octane. Even in the hottest August days I never had any issues with either detonation or vapor lock. I have run 93 ethanol in my 9:1 CR Sonex and had issues with both vapor lock and with detonation so I cant recommend it. It also has substantial storage issues, both turning bad in a short time and in absorbing water from the environment.

As for your power settings and fuel burn, there is not enough information to give any useful advice. The 9 gph consumption is about right for 75% power if you run rich. I never run rich, always lean of peak. In the 9A I get about 150 mph indicated, 155 TAS at 3000 ft at 6.7 gph. The 9 loves altitude and at 12000 ft full throttle (fixed pitch prop), 50% power lean of peak fuel burn is less than 6 gph with TAS of about 155-160 mph. LOP will always reduce the power (and speed) available of course, but does wonders for your fuel burn and the engine is happier with lower CHT, lower EGT, lower BMEP, what's not to like?. Power = fuel burned just no way around it. Best power is fast, but fuel burn is the cost. Fly down and see us sometime at Unity. We have another guy here from Fort Mill with a Just Highlander.
Ed
I am not far from you. Maybe Ill fly over sometime and we can chat in person.

Sounds like based on what your saying, I could likely be ok with mixing 50/50 av gas and 90 octane car gas. I need to run the math to make sure the savings are worth the hassle, but I love to save money when I can!
 
Leaning A Carb

Leaning
Watch tach and lean till you see a 10-20 drop in rpm. From there slowly lean till you see feel hear the engine stumble, twist red knob clockwise to smooth out.


TAS
Subtract MSL at home field, say 700, ’ from the 4500’ cruise, you get about 4000’. Take 2% add to indicated airspeed for every thousand feet, you get 8. 160mph x 1.08 = 172.8 mph TAS. Temp not in this equation , but likely not a huge impact.

CHT
Keep below 400 degrees F and you’re fine. If/when over 400 keep the time brief.
 
So went up in the plane this afternoon to try to get a handle on what its doing.... So here are some observations...

1. With the mixture full rich, engine warmed up to 115 degrees oil temp, brakes locked, full throttle only produced 2010 RPM.

2. After checking static RPM, went and took off. Had a passenger in the back that was observing the digital Tach... The RPM went up to 2090 RPM during the takeoff run and initial climbout. After airspeed got up and a little over 100 mph, the RPM came up to the very low 2100 range and stayed there as we climbed out at a indicated 1200-1500 FPM climb to 4000 feet MSL.

Then leaving the mixture in full rich and throttle wide open, slowly but surely the plane accelerated all the way up to 180 MPH indicated, and RPM peaked at right at 2600 RPM. Manifold pressure was showing around 25 inches as I recall, fuel burn computer was showing 16 GPH.

I could back the power back, and begin leaning and could get 160-165 MPH indicated, with a fuel burn rate of 9.1 GPH and manifold pressure reading of 22 inches. Admittedly, I probably could have leaned more... I never heard the RPM drop and wasn't monitoring the EGT or CHT temps. Not that it counts for much, but I had pulled the red mixture knob back about a third of its travel in the quadrant, but no further.



I agree with one of the people that replied that the fuel computer might not be accurate. I am not sure how to check that, other than possibly flying for a set period of time, landing and refilling and see what the plane took to refill. Seems like that method could still leave a lot of error.

My gut tells me the plane is over propped. It performs decently, but only turning a little under 2100 rpms till the plane is well above 100 mph seems to be leaving a lot of performance untapped. I hate the idea of having to send off the prop for a repitch on my new toy... It might be over a month id be without a plane!
 
Leaning
Watch tach and lean till you see a 10-20 drop in rpm. From there slowly lean till you see feel hear the engine stumble, twist red knob clockwise to smooth out.


TAS
Subtract MSL at home field, say 700, ’ from the 4500’ cruise, you get about 4000’. Take 2% add to indicated airspeed for every thousand feet, you get 8. 160mph x 1.08 = 172.8 mph TAS. Temp not in this equation , but likely not a huge impact.

CHT
Keep below 400 degrees F and you’re fine. If/when over 400 keep the time brief.

The mixture in this plane is a knob on a lever. Pull back to lean.

Comparing my GPS ground speed to the indicated airspeed, the airspeed indicator might be a tick off, I think it shows a slightly faster speed than it really is going. I know GPS speeds will be affected by wind, but just in general flying in various directions it seems like it might read slow. For example, today I practiced a few stalls, and with two people on board, flaps up it was stalling at around 72 mph. With full flaps it was stalling around 65 or so. Seems like it should fly a little slower than that before stalling?


CHT's, I did look at them from time to time while flying back from Florida, and I am not sure they were even out of the high 200's. I will have to check again next time I fly. They for sure weren't anywhere close to 400 degrees. And the oil next got much hotter than about 165...
 
Until you verify the accuracy of your airspeed (converted to TAS), fuel flow, OAT (so we know DA), and tach we are just chopping with a dull hoe......

Congratulations on your new ride but until you have accurate instrumentation and fly precisely there is no way to get a handle on whether or not your -4 is performing as it should.

But my first impulse is that it is pretty close to where it should be. A fixed-pitch prop on these slick aircraft will have a lot of pitch unless all you want is a climb prop. It's like taking off in 4th gear..... ;)
 
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So went up in the plane this afternoon to try to get a handle on what its doing.... So here are some observations...

1. With the mixture full rich, engine warmed up to 115 degrees oil temp, brakes locked, full throttle only produced 2010 RPM.

2. After checking static RPM, went and took off. Had a passenger in the back that was observing the digital Tach... The RPM went up to 2090 RPM during the takeoff run and initial climbout. After airspeed got up and a little over 100 mph, the RPM came up to the very low 2100 range and stayed there as we climbed out at a indicated 1200-1500 FPM climb to 4000 feet MSL.

Yeah, I would say you're over-proped! The standard way I check a prop is to climb to 8000-8500' MSL. At that altitude the engine can only develop 75% power max and Lycoming says you cannot hurt an engine leaning to any degree at 75%. So I get to that altitude and set wide open throttle and lean to peak power (max speed). Compare speed to what others are getting with the same airplane and engine or borrow a prop and try the same test. Generally you should be able to max-out the engine RPM at peak power--2700 RPM usually. I don't usually cruise at peak power (Cozy IV)--I am usually a lot leaner than that--but it will give you a pretty good indication of what sort of prop you have. You could sacrifice cruise speed for more of a climb prop but 2090 rpm is only taking off at maybe 55% power. The engine must turn fast to develop 100% power. It's a tradeoff but you are giving up too much takeoff power with the prop you have [IMO]. :)
 
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