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IO390 FUEL CONSUPTION

henriquerv9

henriquerv9

Active Member
HI ALL,

JUST WONDERING IF ANYBODY IS USING A IO390 (210HP ENGINE). I WOULD LIKE TO KNOW HOW THIS ENGINE IS PERFORMING FUEL CONSUPTION LET'S SAY, AT 8000' AND 75% AND 55% POWER. IS THE CONSUPTION CONSIDERABLY HIGHER THAN A TRADICIONAL IO360 180HP ENGINE?


THANKS ALL


HENRIQUE CASTRO
 
Scott Farner is in Phase one at Chino with his IO-390x-- I'll check with him. Or if any of the Chino guys read this they see him regularly.
 
Horses Eat

henriquerv9 said:
HI ALL,

JUST WONDERING IF ANYBODY IS USING A IO390 (210HP ENGINE). I WOULD LIKE TO KNOW HOW THIS ENGINE IS PERFORMING FUEL CONSUPTION LET'S SAY, AT 8000' AND 75% AND 55% POWER. IS THE CONSUPTION CONSIDERABLY HIGHER THAN A TRADICIONAL IO360 180HP ENGINE?

THANKS ALL HENRIQUE CASTRO
Click to expand...
For a guess you can ratio the HP 210/180=1.16 to get an approximate fuel burn. Horse power: Horses eat. The more ponies the more fuel. It is basically a function of HP.

You could throttle back and burn the same fuel as a 180 HP, e.g. same airspeed, but apples to apple 100%, 75% and 55% power you will make 16% more power and burn 16% more fuel. Yes?

Compression ratio is higher with the IO390 and should be more efficient. So the HP ratio may be off a little in favor of the IO390. Also since the IO390 is really closer to a IO360 angle valve it would be better to compare those two engines.

Dan has a IO360 angle valve and flys w/ LOP operations often and gets great reported fuel econ. However if you are putting a XIO390 you probably can afford the fuel. Its only money you can't take it with you, why make the kids rich when you die. :D
 
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I don't have any good numbers yet as I have been pretty conservative with the mixture. I haven't ventured down to 55% yet; still breaking in the engine, but at 75% and 8000 DA, I'm around 12gph.

Scott
 
IO-390 compression ratio

The compression ratio I was quoted by Barrett for an IO390 was 8.7:1. This is a LOWER compression ratio than most IO360s I've seen in RVs.
 
The IO-390 compression ratio is 8.9:1 Don't know what the actual fuel consumption really is, but at 75% leaned to BSFC of .52-.53, you should see right around 13 GPH, 10 @ 55%.

Allen
 
Picking a Nit

If you take two engines, identical except for displacement (same CR, prop, etc) and run them at the same HP, the larger one will have greater pumping losses and therefore, all other things being equal, will be less efficient. This is pretty much the same as the observation that the same RPM and MAP will give more HP at a higher density altitude, assuming the same RPM and MAP can be reached at the higher altitude. The reason is the resistance offered by the throttle plate. I don't know if this is a big deal, but it's fun to think about these things.
 
Fuel burn

I have about 96 hours on my RV-7 with an IO-390 and a 72" whirlwind prop (new 74" Hartzel arrived today). I usually cruise at 11k-12k ft (airport here is at 5,800 ft) and burn 7.4 GPH at 53% power, 50deg LOP.

At sea level takeoff (everything forward) it burns about 20GPH, and at lower altitudes it's something around 10-13GPH depending on the power. I haven't flown much at lower altittudes so it's not documented.

Hope that helps.
 
MCA said:
I have about 96 hours on my RV-7 with an IO-390 and a 72" whirlwind prop (new 74" Hartzel arrived today). I usually cruise at 11k-12k ft (airport here is at 5,800 ft) and burn 7.4 GPH at 53% power, 50deg LOP.
Click to expand...

And how fast is your RV-7 under those conditions?

Thanks,
Martin
 
**If you take two engines, identical except for displacement (same CR, prop, etc) and run them at the same HP, the larger one will have greater pumping losses and therefore, all other things being equal, will be less efficient. This is pretty much the same as the observation that the same RPM and MAP will give more HP at a higher density altitude, assuming the same RPM and MAP can be reached at the higher altitude. The reason is the resistance offered by the throttle plate. I don't know if this is a big deal, but it's fun to think about these things.**


Since we're picking nits... Uhh, no. The reason it makes more HP at the higher DA is that there is less exhaust back-pressure and the cylinders have a better volumetric efficiency.
 
mgomez said:
And how fast is your RV-7 under those conditions?

Thanks,
Martin
Click to expand...

160 kts TAS as displayed (and calibrated) on the GRT EFIS. I know that's slower than a 180-hp RV-7A. Don't know why though. :confused: Am working on trying to figure that out. Any thoughts are appreciated.
 
Question for Walter

Walter Atkinson said:
**If you take two engines, identical except for displacement (same CR, prop, etc) and run them at the same HP, the larger one will have greater pumping losses and therefore, all other things being equal, will be less efficient. This is pretty much the same as the observation that the same RPM and MAP will give more HP at a higher density altitude, assuming the same RPM and MAP can be reached at the higher altitude. The reason is the resistance offered by the throttle plate. I don't know if this is a big deal, but it's fun to think about these things.**


Since we're picking nits... Uhh, no. The reason it makes more HP at the higher DA is that there is less exhaust back-pressure and the cylinders have a better volumetric efficiency.
Click to expand...
Walter, I'll agree, now that you've pointed it out, that the lower back-pressure would give you more HP, but doesn't the lower pumping loss with WOT also give you HP? In other words, aren't they both having an effect? Thanks.
 
I think the exhaust back pressure reduction is a red herring. Yes, the exhaust pressure is lower, but so is the crankcase pressure. It's the differential pressure across the piston (combined with the swept volume) that represents the energy loss. I don't think it will change much with altitude.

The volumetric efficiency will improve slightly, due to the lower mass of trapped residuals, but this is small beer.

Without doing the calcs, I'd guess that the reduction in intake pumping losses will be the largest player.

As an experiment, you could try measuring the change in fuel flow at constant power with and without carb heat selected. At high power levels, you probably won't see much difference, but at lower airflow/power the carb heat will be more effective and the change in manifold pressure (due to heating) will be accentuated. The exhaust back pressure will be similar.

A
 
So how does the 390 perform???

MCA said:
I have about 96 hours on my RV-7 with an IO-390 and a 72" whirlwind prop (new 74" Hartzel arrived today). I usually cruise at 11k-12k ft (airport here is at 5,800 ft) and burn 7.4 GPH at 53% power, 50deg LOP.

At sea level takeoff (everything forward) it burns about 20GPH, and at lower altitudes it's something around 10-13GPH depending on the power. I haven't flown much at lower altittudes so it's not documented.

Hope that helps.
Click to expand...

OK, so what kind of performance have you been getting with that engine? Climb? Cruise speed? Is it worth the extra fuel burn?

I really can't make up my mind between a 150 hp and a 210 hp engine. Between CS and FP. Long cheap cruises vs fast climbs. I can't decide.

JCB
 
There's a bit more to it than that...

OldAndBold said:
OK, so what kind of performance have you been getting with that engine? Climb? Cruise speed? Is it worth the extra fuel burn?

I really can't make up my mind between a 150 hp and a 210 hp engine. Between CS and FP. Long cheap cruises vs fast climbs. I can't decide.

JCB
Click to expand...

He quoted 160 KTAS in response to my question on this subject.

It's worth remembering that the differences in fuel burn due to the engine is going to be tiny. At equal speeds in equal airplanes, they'll all burn roughly the same fuel (give or take a few percent.) Things like prop choice and rigging make a big difference too. Fuel economy (but not speed) will be strongly affected by weight, too. You can easily make a 100 lbs difference by your choice of engine and prop. That's a 5-6% difference in fuel flow at best endurance.

The other thing to bear in mind is that the effect of the engine is not just on performance. I've heard that 150 HP RV-7s with fixed pitch props can't carry much weight in the baggage compartment.
 
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