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Engine size Pros and Cons

Based on Van's latest prices, The O360 is the same price as the O320.

So...... at least get the O360.
 
Mission?

I guess if we knew more about your "primary" mission it would help. Racing? Aero? Cross Country flying? Assuming you want a "normal" RV-8, get the exact engine/prop Van's recommends and your build and test time will be faster and easier.

Otherwise, anything from an 0-320 to an IO-540 will work, with tradeoffs.
 
I just went through this exercise.

Spent hours online and with the calculator, looking at everything from fuel burn, to expected KTAS, to range profiles, to the price of replacement cylinders, to perceived difficulty of each installation. Carefully reviewed each response to my VAF thread where I asked for opinions.

I finally just said heck with it and bought the Thunderbolt IO390.

Probably can't justify it for my mission, But it's ultimately what I wanted.

Where I'm going with this is that you can ask for internet advice and crunch numbers all day long, but ultimately you have to make a decision you can live with and it may not be the most practical one. Only you can decide.
 
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Desert Rat is exactly right. Unless you have a specific operating purpose, Van's recommended engine is usually the best option. More hp will give you more take-off and climb performance (As if the RV needed this), usually at the cost of money & weight, but very little, if any, cruise speed advantage.

Also, as Desert Rat points out, It's your airplane and it's experimental. If you want something in particular, do it!
 
Just me

But I chose the injected version of the Lycoming for two reasons: easier lean of peak operation, and no carb icing issues.
It seems the price difference is small. Also, it is amazing how many builders initially fly with a carb engine and than upgrade to fuel injection.
 
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Engine size?

Easy answer. Big as you can afford that the airframe can handle. You can never have enough horses under the hood. Fuel economy is only a small factor. I love the bigger horses and fuel injection is necessary for good life in the air.
I would buy the I0-360 because it will fly and sell faster when the time comes.
Enjoy spending the money cause it is gonna be quite a bit. Art
 
Just my opinion, of course, but best HP/$ is O360. Injected, if you want. The only reason to go angle valve is to go O390. There is no reason to go O320 unless you find a great deal. Simple formula, direct result :)

Tim
 
Desert Rat nailed it! I too originally planned an O-360 for my RV-8. Then after Van’s approved the IO-390 for use I was torn. After mulling over pros and cons for about a month, I bounced it off a good friend and his advice was “if you’re going to be a bear, be a grizzly”. That did it, along with the upcoming price increase. Now in the process of swapping out lower cowls with Van’s. Not looking back, full speed ahead. After all, what are friends for?
 
So my mission would be some light aerobatics but mostly cruising. Just wondering what true speeds are seen between an IO360 to a IO390. Thanks for everyone's input.
 
I consider the IO-360-M1B and Hartzell CS BA prop to be the perfect combination for the RV-8, both for power and weight.

The last cross country I did was 13.5K’, 175kts TAS at 7.5gph (LOP). The airplane was built for high efficiency cross country and I’m happy with the result.

One non-trivial point. The parallel valve IO-360 can burn 94UL or non-ethanol 93 octane pump gas. The IO-390 cannot.

Carl
 
Engine Size

Most people with “smaller engines” will tell you that’s the way to go. But, I’ve never heard anyone with a an angle valve and constant speed prop complain that they wished they installed a smaller/lighter combination instead. I’m very happy with my IO-360 angle valve and Hartzell BA prop!

Skylor
 
Engine Size.

The one thing you can be sure of is that Leaded Avgas will be outlawed either soon or next year. The hand writing is on the wall. We've been living on borrowed time.
 
Until G100UL is available, which is way overdue to the market thanks to some obstruction within the FAA, and now sorted.


As for engines, the parallel valve IO360 or IO375 are a good fit. I have no idea how you get a true real and verified TAS of 175 at 13.5k' while LOP, but hey, you will do 164 +/- for sure with the BA Hartzell.
 
Until G100UL is available, which is way overdue to the market thanks to some obstruction within the FAA, and now sorted.


As for engines, the parallel valve IO360 or IO375 are a good fit. I have no idea how you get a true real and verified TAS of 175 at 13.5k' while LOP, but hey, you will do 164 +/- for sure with the BA Hartzell.
Don’t know about 175 KTAS at 13.5k, but here’s 171 KTAS at 11.5k running LOP. Note FF is 6.3 GPH! That’s an IO360 with BA Hartzell. Sometimes you just find the sweet spot, but 170 KTAS at 7 GPH is very repeatable. Or if I’m in a hurry I can get an extra 10 KTAS (180 KTAS) at a little over 8 GPH.
 

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I consider the IO-360-M1B and Hartzell CS BA prop to be the perfect combination for the RV-8, both for power and weight.

The last cross country I did was 13.5K’, 175kts TAS at 7.5gph (LOP). The airplane was built for high efficiency cross country and I’m happy with the result.

One non-trivial point. The parallel valve IO-360 can burn 94UL or non-ethanol 93 octane pump gas. The IO-390 cannot.

Carl

Curious as to why IO-390 cannot burn the above? Is it purely the detonation margins?

thanks
 
Guys, I trying to decide what engine size for my 8.

I chose for weight consideration the (I) O-360. Due to the 9-1 pistons, ventury cut seats, performance camshaft, flow matched cylinders, DUAL "P" MAGS, AND LIGHTENED FLYWHEEL, and the HARTZELL 74" "TRAIL BLAZER" PROP, I elected to go with a parallel valve engine with a "counterweighted" crankshaft. This is really a misnomer, all crankshafts are counterweighted, however, due to vibrational analysis, the "harmonic balanced" IO-360 crank made sense, a penalty of 8 pounds, but a lot of piece of mind! My unit is still light compared to equal horsepower, dyno at 213 HP, that is as high as I am comfortable as going with reliability.

Runs great, no issues! Talk to LyCon!

Regards,

Gary
 
As said earlier, in Europe all angle valve engines will be useless in a couple of years if it continues like this with 100LL gettin more rare at airports.
 
Guys, I trying to decide what engine size for my 8.

Depends on prop choice. Can’t pick engine without consider your prop. With fixed pitch you could justify bigger engine from cost, weight, and takeoff performance. With constant speed prop you can get away with less hp plus the cost and weight trade works out better.
 
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Curious as to why IO-390 cannot burn the above? Is it purely the detonation margins?

Slightly higher CR won't allow enough detonation margin at the temperatures specified by certification standards. Given moderate CHT/oil/intake temperatures, standard ignition timing, and a cognizant meat servo on the knobs, it should do fine. Certification doesn't allow those caveats.

https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_33_47-1.pdf

To the OP's question...For an all-around performer flown mostly solo, and for which acro is an interest, I'd suggest the M1B with a Hartzell composite. The 390's 30 extra HP increases climb rate significantly (like 500 FPM), but the extra mass on the nose makes stick force per G quite high. Given limited interest in acro, and a desire for a CG envelope and climb rate which embraces a passenger/baggage mission, the 390 is marvelous.
 
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Basically Power vs weight and cost

Angle Valve Pro: More power
Angle Valve Con: More weight, more cost, future fuel availability?

Parallel Valve Pro: less cost, less weight, greater variety of options
Parallel Valve Pro: mods needed for more than 180hp, and still likely not quite as much power as a fancy -390
 
Angle Valve Pro: More power
Angle Valve Con: More weight, more cost, future fuel availability?
Parallel Valve Pro: less cost, less weight, greater variety of options
Parallel Valve Pro: mods needed for more than 180hp, and still likely not quite as much power as a fancy -390

The "weight" Con means much more than just payload penalty. Those who have not flown a truly light RV have no idea what they are missing.
 
Indirect evidence

The "weight" Con means much more than just payload penalty. Those who have not flown a truly light RV have no idea what they are missing.

If you want indirect proof, there are a number of Rocket builders/owners that have swapped or opted for a modified 4 cylinder. If you add economics to the equation, it starts to make even more sense for some. All said, many responders will try and valid their own choices in the responses. To the OP, build the plane you want.
 
With the price increases from lyc, at least entertain an engine from Titan. I have a quote from Them for less than $32K for a 195 HP O-370. I have not pulled that trigger yet so I am still geeking out on engine choices and have lots of time to decide.

That being said my RV6 had a 320 with Catto 3 blade and was fine. But when I was renting my buddy’s 8 with O-360 and fixed pitch prop it was substantially better performance wise and with PMAGs it had way better performance up high. I would be perfectly happy with his rig. So for now I will just stay out of CS airplanes or I’ll want one.. :D
 
I was reading this and thought it sounded familiar! And.....ummm, surely you mean "borrowing" vice "renting" Jordan ;)

With the price increases from lyc, at least entertain an engine from Titan. I have a quote from Them for less than $32K for a 195 HP O-370. I have not pulled that trigger yet so I am still geeking out on engine choices and have lots of time to decide.

That being said my RV6 had a 320 with Catto 3 blade and was fine. But when I was renting my buddy’s 8 with O-360 and fixed pitch prop it was substantially better performance wise and with PMAGs it had way better performance up high. I would be perfectly happy with his rig. So for now I will just stay out of CS airplanes or I’ll want one.. :D
 
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“If power is good extreme power is extremely good”
“If you want to add performance add liteness”

Pick your quote than find the engine option that matches, I went with the first this time. Might go with the second next time however extreme power sure is fun!
 
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