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IO-390 vs IO-360

cjjohns79

I'm New Here
I’m new to the group and looking to buy an 8 in the near future. Can anyone give insight about whether there is a noticeable difference between these two engines in performance.
Thanks for the help!
 
I suspect you’ll notice a bit more speed but probably not a lot however the additional hp will really show in takeoff and climb.:)
 
Its a significant difference from my 8a I had with a 180, my 390 At 8500 ft. 68% power 175 kt. TAS 8.3 gph (22 m.p. 2400 RPM) your prop could change the numbers quite a bit.
 
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“I wish I had less horsepower!”…..said no pilot, ever! :)

But honestly, the difference in performance between the two (assuming you;re talking angle valve to angle valve) is going to be pretty small. And also honestly, I have heard a number of guys with LOTS of RV-8 time that built a plane with an angle valve engine muse that if they built another one, they’d just go with a parallel valve engine because it makes the nose lighter, which makes for lighter handling.

Van originally designed the -8 for an O-320, but very, very few build that way!

With my 180 horsepower O-360, dual P-Mags, I cruised to and from Oshkosh this year at 170 KTAS burning about 8.8 gph. that’s just a data point, not a recommendation - just to help quantify things.
 
Parallel valve:

Stroked to 370-ish CIs
better breathing sump
EI
etc.

The HP numbers are then very close to the 390 at less weight and cost.

Yes, you could do much of the same to the 390 but a more economical path to 205->210-ish HP. Just another option to inform and cloud the OP's mind.
 
As with all our choices during a build, there are trade offs (no free lunch).

I suggest you prioritize your mission goals. For example:
- If time to climb is the top objective then a fire breathing big engine and minimalistic everything else (as in interior, avionics, etc.) is the way to go.
- If nimble for aerobatics, the 180hp IO-360 is generally considered the best match.
- For me I build my planes for efficient IFR cross country cruise. This again leads me to the 180hp IO-360 and Hartzell BA CS prop. My standard LOP cruise is 174kts TAS at 8.2 gph, 8K’.

As previously noted, the cost differential between the two engines in not trivial.

The IO-390-exp119 is an engine made to meet the mission of the heavier RV-14 (and that plane needs the extra ponies). I suggest for a standard RV-8 it is overkill.

Carl
 
The only RV I’ve ever flown solo is mine with a 180hp and composite CS prop.
I can’t imagine wanting the CG further forward for solo fun flying. The other thing nobody tells you is the max climb rate isn’t practical most of the time. The nose is pitched up so high you can’t see where your going. My problem is remembering when to stop climbing.
 
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“I wish I had less horsepower!”…..said no pilot, ever! :)

But honestly, the difference in performance between the two (assuming you;re talking angle valve to angle valve) is going to be pretty small. And also honestly, I have heard a number of guys with LOTS of RV-8 time that built a plane with an angle valve engine muse that if they built another one, they’d just go with a parallel valve engine because it makes the nose lighter, which makes for lighter handling.

Van originally designed the -8 for an O-320, but very, very few build that way!

With my 180 horsepower O-360, dual P-Mags, I cruised to and from Oshkosh this year at 170 KTAS burning about 8.8 gph. that’s just a data point, not a recommendation - just to help quantify things.

Count me as one of those guys that built an 8 with an angle valve IO-360A1B6 that would re-build with a parallel valve, non-counterweighted crankshaft (but still with fuel injection) if I could do it over again. It was a plus when doing cross country with a person and full luggage. But I mostly flew solo and it was a negative for me when doing acro. Heavier stick forces than I like pulling through the bottom of maneuvers.
 
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The cost of ego & bragging rights.
360 angle valve (200hp) over 360 parallel valve (180hp) add $8300*
390 angle valve (215hp) over 360 angle valve (200hp) add $4100*
total additional cost 390 over the parallel 360 a whopping $12400*
real time results to upgrading - maybe 5 or so knots cruise, higher fuel burn rate, greater climb rate at ridiculous deck angle that you will use how many times?
real time x/c performance - after a 3 hr flight leg, you will have just finish filling your first tank before your buddy with the 360 parallel engine pulls up behind you in the fuel bay.

*based on Vans engine pricing (stripped of accessories to keep the comparison level) Imagine how much fuel $12400 can buy!
 
If you are buying there is probably no choice. Is the airplane in front of you acceptable, whatever motor it has? If looking for a 390 only it will be a long search. There are probably plenty of other criteria to consider before the engine. Quality of build, non-factory changes, time-in-service, history, then consider the engine, what is in the panel and the paint job.
 
Ridiculous Deck Angle??

Climbing at 2,500 FPM I can see exactly where I'm going...

UP

UP

UP

What's ridiculous about that?
 
Just another data point or two on the matter

Climbing at 2,500 FPM I can see exactly where I'm going...

UP

UP

UP

What's ridiculous about that?

And if you don't want to climb that fast, lower the nose and go

FAR, FAR, FAR

FAST, FAST, FAST.

Worked with my friend to get his RV8 squared away to make the trip to Airventure this year ( He received and "Outstanding Workmanship Award".).

For reasons mentioned earlier here, we had replaced a 200HP IO-360 with the 215HP IO-390.

I did some of the test flying with BOTH engines.

And because I had a lot more RV time and he had never flown into OSH, he asked me to fly it up there (with him as passenger).

Now, previously, "Widget" had given me the keys to his 200HP RV8 during the time I had been flying my 160 HP RV6. WOW!!! Smooth! Power to use but not abuse.

Well, this RV8 was like that with the 200HP but when the change was made to the IO-390, WOW! WOW!

You don't NEED the extra horsepower of course, but I must say that when we were fully loaded and taking off with the OAT approaching 100* F, having it made ME feel a lot safer.

As I recall, we flew there and back with another friend who has a 180 HP RV6, and I think we were burning about he same amount of fuel.
 
Marc Cook did a very good comparison in the September, 2009 issue of Kitplanes magazine in which the IO-360 parallel-valve and IO-390 angle valve engines flown back to back in the Glasair Sportsman. In that airframe the conclusion was the biggest differences were cost and climb rate and maybe a little top end speed. In cruise, at matching airspeeds the IO-390 may have been slightly more fuel efficient.
 
Parallel Valve VS Angle Valve

Another Data Point:
When I was searching for my RV8, the chaps at RV specialists Hotel Whiskey Aviation (Chuck Wilson and Jeff Hansen) strongly advised that I stick with a parallel valve engine with a constant speed prop for all around best performance. After flying 2600 hours on my parallel valve IO 360 powered RV8, and having done the acrobatic maneuvers fly-off for two RV8 aircraft with angle valve engines I am absolutely convinced of the correctness of their advice. The angle valve powered aircraft, because of the additional nose weight, are very heavy and slow reacting in pitch. On one aircraft we added 16 pounds of lead at the tail to get the aircraft within CG. however, it did not help with the heavy pitch stick forces required. It would be interesting to get Steve Smith's input here, as I expected the stick forces to be less. A possible cause might be the increase in polar moment of inertia with the weight at both ends of the aircraft.
 
Probably offsetting phenomena. (Intent of) Adding the weight would be to improve concentricity of the CG and pitch axis; would certainly lower the stick force in pitch. The integral contribution of the added weight to the polar moment of Inertia is proportional to the the square of the distance from said axis, thus increasing it. I believe these are probably off-setting each other for the most part. Would be interesting to plot the results of both lines and see where they intersect. Hopefully some smart people will weigh-in.
 
To steal Paul's quote with a slight modification:

"I wish I had more weight on the nose!" ...said no RV-8 pilot, ever!
 
Plus, when people say they have a 360 you can put your nose slightly up in the air and say "Oh <pause for effect> I have a 390" in a way that sounds like they made a terrible decision and should feel bad about their purchase.
 
I’m new to the group and looking to buy an 8 in the near future. Can anyone give insight about whether there is a noticeable difference between these two engines in performance.

I built a 390 powered -8 back when 390s were rare, kit only packages, mostly because my friend Monty was very proud of his creation and I had some spare money. No regrets. Yes, it has high stick forces, but in fairness, it also has a heavy metal Hartzell. I could make it better with $19,000 worth of carbon.

It's a fastback, so it has a larger rear baggage compartment. Ms. Patti does not travel light, but here the rule is simple...if it fits, it goes. CG is the best and the worst reason to install an angle valve.

Typical cruise is 180+ KTAS with burn in the low 9's. Climb rate is proportional to excess power, so if you have 20% more excess, you get 20% more rate. Density altitude should never be ignored, but it's mostly a non-issue for an -8 with a 390. Here's 800 ft or so of roll at Johnson Creek on a warm June afternoon: https://youtu.be/yJeYto8dHYc

Yeah, 12 years now and I still like it.
 
I’ve owned both, the 360 flies lighter to the touch and has better glide, but it’s hard to argue these #’s in cruise.
 

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One consideration not mentioned, fuel options.

The 180hp IO-360 allows use of 93 octane auto fuel or when available Swift 94. The angle head options require 100LL or the new (and at an unknown price) 100UL.

This is the driving reason I declined Thunderbolt’s free option to put 9 to 1 pistons in my new Cold Air Sump IO-540. The extra 10-15 ponies would have been nice, but not enough to accept this pending fuel cost risk. Perhaps as we gain some visibly on 100UL cost this can be revisited.

Carl
 
One consideration not mentioned, fuel options.

The 180hp IO-360 allows use of 93 octane auto fuel or when available Swift 94. The angle head options require 100LL or the new (and at an unknown price) 100UL.

Let's remember Lycoming's current non-approval of mogas for the 390 is based on certification criteria. We're not limited to a particular configuration (ignition timing and exhaust pressure being two examples), nor is there any good reason to run near limit temperatures.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_33_47-1.pdf
 
I definitely said it!

To steal Paul's quote with a slight modification:

"I wish I had more weight on the nose!" ...said no RV-8 pilot, ever!

I have an RV8 which I originally built with a Lycoming 0-360 with a Catto 3 blade fixed pitch prop. The CG was so far aft if I put say a 230 LB passenger in back I would add 30 LBS to the fwd baggage compartment. If going x-country heavily loaded I couldn't put much at all in the aft baggage compartment.

I replaced the Lycoming and Catto prop with a BPE IO-360 200HP angle valve engine along with a Hartzell constant speed composite prop. This resulted in a very forward CG which is great for fully loaded X-C putting the CG right in the middle of the envelope. I can cruise 190 knots rich of peak but burning more fuel obviously than lean of peak (I'm usually in a hurry). I do add 25 LBS to aft baggage solo.

It's all about the mission! I don't do a lot of ACRO so I'm not concerned about heavy stick forces. Pro's: I can be heavily loaded in both baggage compartments and go really fast with incredible take off performance.
Con's: I have to add weight aft for solo flights and with heavier stick forces. I probably burn more fuel than most but even that I'm ok with to go fast.

One size doesn't fit all it is mission dependent in my opinion. I would 100% go with the angle valve if I were to build again because it fits my mission. If I were really into ACRO I would probably go parallel valve.
 
Whats cruise like at a more average power like 65/75% ?

Standard “I want to get there but not blow too much gas” cruise.

IO-360-M1B with AFP FM-150C, standard 74” Hartzell BA prop.
Carl
8-A5179-D8-F90-D-45-DC-8169-F63886571831.png
 
Standard “I want to get there but not blow too much gas” cruise.

IO-360-M1B with AFP FM-150C, standard 74” Hartzell BA prop.
Carl
8-A5179-D8-F90-D-45-DC-8169-F63886571831.png

Carl, perfect! Provides a very close cruise comparison with an early 210 HP 390; same prop, both 66% power and ~0.4 BSFC (0.404 vs 0.398).

The math to predict speed based on the 390's extra HP is...

180 x .66 = 118.8
210 x .66 = 138.6
176 knots x ( 138.6 / 118.8 )^1/3 = 185 knots

...and here I'm showing 187 with Ms Patti on board and a bit more gas. The addition is in the scatter, or reflects less drag due to the fastback and a closed cooling outlet, depending on viewpoint.
 

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Manifold Pressure

Carl,

What air inlet system are you running to get 22.3" at 9000'? Ram air of some sort, or the cowl inlet intake with a snorkle? I'm curious.

I know Dan has a pretty well documented filtered ram air system (nicely designed and tested), and you seem to be matching (or beating) his MP.

My poor O-360/carburetored RV-6 can't get anywhere neat that pressure that high.

Laird
 
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Carl,

What air inlet system are you running to get 22.3" at 9000'? Ram air of some sort, or the cowl inlet intake with a snorkle? I'm curious.

I know Dan has a pretty well documented filtered ram air system (nicely designed and tested), and you seem to be matching his MP.

My poor O-360/carburetored RV-6 can't get anywhere neat that pressure that high.

Laird

This is the stock snorkel but using the AFP FM-150C. At some point I’ll modify the snorkel following the lead of what was done on the RV-14 with the shift over to the IO-390-EXP119. They got a nice bump in MP from this mod. I’m using the FM-150C and not the FM-200 like the EXP-119 uses so I suspect I’ll not get as much gain.

For vertical intake I enjoyed good MP on my old RV-10. I had a straight in shot from the engine air intake on the James Cowl, but modified the filtered air box to accept the taller K&N E-1000 filter. The mod was simply to flip the FAB top over to have the edge go over the sides of the fiberglass. This provided the extra height for the taller filter.

The new RV-10 project will have cold air sump horizontal injection and I’ll be using a new filter box that Jimmy at James Cowl is working on.

Carl
 
This is the stock snorkel but using the AFP FM-150C.

Carl, might want to check that MP indication.

Run the numbers. At 9000 ft, 176 KTAS, and 54 OAT, pressure is 21.39" Hg and available dynamic pressure (q) is 1.07 Hg.

Can't get 100% conversion of dynamic pressure in an open-ended system. The ballpark is more like 75%, thus q applied to increasing MP would be roughly 0.8" Hg, not the full 1.07".

Next consider manifold pressure loss due to flow through filter, fiberglass snorkel, the FM150, and the intake tract between the throttle and the cylinder head. How much is the loss? My airbox has a larger filter, no duct, and no entry bend. The smaller throat of the FM150 results in 6" H2O more loss than an FM200. The M1B and the 390 have the same horizontal intake sump. Having measured my total intake loss at three altitudes, I'd estimate your 9000 ft loss at about 15" H20, a bit more than 1" Hg.

So, 21.4 + 0.8, less 1 = 21.2", more or less. 22.3 is unlikely.
 
Awhile back Dan saw that my MAP was also reading high. I did the ground calibration (several times on different days) and adjusted it in the Dynon menu:

i-FtnmCTh-M.jpg

Ended up adjusting it down by 0.5" Hg:

i-XXfj8jD-M.jpg


Below is a screenshot from my RV-8 with the Lycoming YIO-360-M1B, Avstar FI, LSE Plasma III & Slick mag, and Hartzell 72" BA prop. Note that the IAS reads about 4 MPH high, so this is about 200 MPH TAS/173.8 KTAS. Similar conditions as Carl's above, and similar performance.

i-N6vvNVG-L.png
 
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To steal Paul's quote with a slight modification:

"I wish I had more weight on the nose!" ...said no RV-8 pilot, ever!

Count me as one of those guys that built an 8 with an angle valve IO-360A1B6 that would re-build with a parallel valve, non-counterweighted crankshaft (but still with fuel injection) if I could do it over again. It was a plus when doing cross country with a person and full luggage. But I mostly flew solo and it was a negative for me when doing acro. Heavier stick forces than I like pulling through the bottom of maneuvers.

Would seem that an 8 with one of the new Whirlwind 300 series would be a nice match; 3 blades but only ~35 lbs IIRC. The performance reports here have been impressive. 20 some odd pounds off of that station would be pretty dramatic per what's been stated here. Depending on mission of course, would seem a great match for IO390 powered 8. Anybody?
 
Would seem that an 8 with one of the new Whirlwind 300 series would be a nice match; 3 blades but only ~35 lbs IIRC. The performance reports here have been impressive. 20 some odd pounds off of that station would be pretty dramatic per what's been stated here. Depending on mission of course, would seem a great match for IO390 powered 8. Anybody?

Well that’s the prop I’ve settled on with the the parallel valve 360 on my -8, and its a great combination. But you’d have to check with WHirlwind to see if its an allowable prop for the 390 - not all combinations are supported.
 
Would seem that an 8 with one of the new Whirlwind 300 series would be a nice match; 3 blades but only ~35 lbs IIRC. The performance reports here have been impressive. 20 some odd pounds off of that station would be pretty dramatic per what's been stated here. Depending on mission of course, would seem a great match for IO390 powered 8. Anybody?

I went with the WW 300/72 to put on the front of an IO390 EXP 119 on my 8 fastback. Like Paul said, I wish I had less horsepower said no pilot ever!

I’ll let you know next summer how the combination turns out.
 
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