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RV-7 and IO-390 perforance gains

jigeye

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I have seen a few with this engine. what do gain in performance vs. a IO-360? Would like some real world #s. thanks.
 
I have seen a few with this engine. what do gain in performance vs. a IO-360? Would like some real world #s. thanks.

After 1000 hours on my IO-390 I have only good things to say. Oil consumption is almost nil, climb performance is awesome, and fuel economy excellent... I flightplan for 165TAS with 74" Hartzell constant speed prop... Fuel flow around 8gph at altitude (wide open throttle)...

To be fair, however, I think RV's are optimized for 180 hp. In level flight cruise with other RV's... the -390 doesn't buy you much performance over a -360 due to airfoil design & drag.

The big payoff, in my opinion, is short field takeoff & climb performance.... making it ideal for high pressure altitude operations...
 
Simplified speed and ROC equations at the link. Baseline depends on which IO-360, 180 hp parallel valve, or 195 hp for an average angle valve. If comparing parallel valve to the 390, the ROC increase may be a little less than indicated, as the simple equation assumes equal weight.

www.danhorton.net/Articles/
then download "Speaking Truth To Power"
 
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Consider an IO 370

I replaced my 180hp O360 with a Titan IO-370. It's officially rated at 195 hp but un-official number is something in the 200-210 range. It weighs the same or a bit less than an IO-360 (I have the tapered cylinders).

I don't have exact numbers but I could tell immediately that is was a noticeable improvement. I gained at least 7kts in cruise and a big improvement in my climb. My rate of climb is limited by my nose up attitude and once I get to about 800 ft, I want to reduce my climb angle so I can watch for traffic in front of me.
 
Keep in mind that going to the IO-390 may reduce the ability to use mogas or other UL fuels, unless you get it custom built with a lower CR, in which case you will be giving up some of the performance benefits. Also keep in mind that the 390 will be heavier than a comparable 360, and every kg extra in engine is a kg lost in fuel or payload. You may be able to offset this my swinging a composite prop, so take this into account in your w&b and budgeting.
Not that any of this should concern me, as my next build is going to be all electric. Let’s just hope Lyten or some of their competitors with 500+ Wh/kg energy density can get to production sooner than later.
Tom.
RV-7, IO-360M1B
 
After 1000 hours on my IO-390 I have only good things to say. Oil consumption is almost nil, climb performance is awesome, and fuel economy excellent... I flightplan for 165TAS with 74" Hartzell constant speed prop... Fuel flow around 8gph at altitude (wide open throttle)...

To be fair, however, I think RV's are optimized for 180 hp. In level flight cruise with other RV's... the -390 doesn't buy you much performance over a -360 due to airfoil design & drag.

The big payoff, in my opinion, is short field takeoff & climb performance.... making it ideal for high pressure altitude operations...

I’m curious about your setup.. my fixed pitch Sensenich aluminum prop and O-360 with slick mags does 170 knots in cruise at 7gph. I would expect a little more speed with your setup over my -4. Granted, the -4 is a making a smaller hole being tandem.. what altitude are you flying? I guess these plane really just can’t push the airfoil much past the 170 mark, but I bet yours climbs like a homesick angel!
 
Speed

My 4 with an O 360, mags and a woody prop at 8000 ft DA and 2650+ RPM is pulling 208 mph with the new PR wheel pants. The original wheel pants I was only 201 mph.

I didn't think that there was that much of a difference between the different models.

Tim
 
My 4 with an O 360, mags and a woody prop at 8000 ft DA and 2650+ RPM is pulling 208 mph with the new PR wheel pants. The original wheel pants I was only 201 mph.

I didn't think that there was that much of a difference between the different models.

Tim

Wow, that’s 181 knots.. that’s smoking!
 
baseline --- which io-360? 180 HP or 200 HP?

I think your best 'real world' estimate is the factory performance specs at https://www.vansaircraft.com/rv-7/#aircraft-details-2

which shows going from 180 HP to 200 HP is worth 7 mph in cruise. Or +3.5%

So making an educated estimate - going from 200 HP to 210 is going to give you 3 mph or so added cruise speed.

To compare to your 3 mph estimate . . . . I used Kevin Hortons performance spreadsheets and methods to establish a performance profile for my stock M1B powered -7. Using the resulting drag-speed curve 200->210 hp would be ~3.5 kts around cruise. Pretty close to your "guess":D

I attempted to keep my drag low, but still have lots undone. I even did quite a bit of work for shrinking my exit, but it yielded no benefit, something I still don't understand. I must be as smart as a shovel based on my results.:eek: I don't think my -7 is anywhere the fastest 180 hp cruiser, but have repeatedly gotten 179KTAS at 8000DA plus/minus ~1.5 kts 2650RPM/best power mix. That is not what I use for cruise. 2450-2500 rpm, and best power mix gives 170KTAS -ish. 9.4 GPH, but typically get 165 ktas @2400RPM and 8.0 or less GPH, 8000DA.

I would love to have the IO390, though and sometimes drool over it now. The plan, though, is to stick with fixed power and sort out the understanding of drag first.
 
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I've said this before, but I wish Monty was still around to see how wildly popular the 390 has become.
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power vs weight

In my RV "super" 7, I used a parallel valve 0-360, Bendix fuel injection, 9:1 pistons; counterweighted crankshaft; flow matched cylinders, venturi cut valve seats; dual P mags; and performance camshaft. Dyno 213 HP. This is the most
I would go without sacrificing reliability. The light weight composite Hartzell makes up for the heavier crankshaft. 9500' - WOT - 2300 RPM leaned to peak = 164 Knots True at 8.2 GPH. I have flown other '7s with 390's in them, you feel the mass, not quite as "sporty".
DAR Gary
 
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