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Deadlocked on engine selection.

FlynBrian

Member
I'd like to place an order soon for an rv8 fuselage and finishing kit but I just can't settle on which engine. I've been looking into the 200hp IO 360, IO 375 or the IO 390. I think I'm sold on a CS prop. I'm looking for an ideal power plant for my plane. None of these engines seem ideal when I look at cost, weight, well proven, RPM restrictions, each has its own downside.

1.) Are there insurance implications for using "Non-vans approved" engines (ie 390)

2.) Are there insurance implications at or above 200hp?

3.) Would any of these power plants work better for the RV8 airframe /CG?

4.) Is there a significant seat of the pants performance feel vs a 180 hp IO360 or is it just a waste of money given the added weight?

Advice needed from those with experience. Thanks!
 
...
1.) Are there insurance implications for using "Non-vans approved" engines (ie 390)
...
There wasn't for me. The insurance company never asked why kind of engine the plane had.

I went as far as asking one broker what they did for RV's with auto engines and was told that they lump the airframes together and don't look at the engine installed. YMMV
 
Like all things aviation, it is a compromise. Van says keep it light and simple. Others say you can never have too much HP. My RV-8 with a Superior IO360 and Catto prop comes in at 1062 pounds and meets or exceeds all Van's published performance numbers. More HP would add speed and climb but probably degrade the delightful handling a little. You need a "complex" sign off from an instructor for more than 200 HP. Insurance will depend on experience more than HP unless you go to a big six cylinder.
 
Thanks! That helps from an insurance standpoint. From an engine selection standpoint is it better to have a bit more weight on the engine for CG reasons? Would I be able to carry more passenger weight with a heavier engine up front?
 
Thanks! That helps from an insurance standpoint. From an engine selection standpoint is it better to have a bit more weight on the engine for CG reasons? Would I be able to carry more passenger weight with a heavier engine up front?

It is always best to build as light as you can because you can always add weight where you want it but it is very difficult to remover it.

Talk to the engine builders, they can pump a parallel valve 360 to over 200 HP without the added weight. The downside might be the TBO may suffer.

I'm not sure of the weight penalty of the other engines but typically all the extra HP does is help with climb, not speed. Van's list the climb rates for the -7 at between 1400 and 1900 FPM at gross (160 HP to 200 HP). How much more climb performance do you need?
 
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consider fuel requirements?

...since nobody has mentioned it; I like the option of my low compression engine to use auto fuel if needed. ( could be a plus if true 100 octane is phased out in the engines life cycle.)
If you don't care, then go ahead with one of the high comp. options; heck, it's kinda like free horsepower with very little negatives.
 
Do test-rides

I suggest you get two rides: one in a -8 with 200 HP and one in a 180 HP RV-8, and see for yourself.

Then you'll also have an opportunity to talk to the owners.

I have built two -7's and I guess it won't be entirely correct to compare those two models, but for me the added weight for the 200 HP was out of the question.

I've now flown 180 HP RV-7's with C/S props since 2008 and I'm very happy with 180 HP. I haven't missed those xtra 20 HP one bit....

But that's me....

BTW: another factor is the compression: I have now had my first -7 for sale for about nine months, and about 90% of the people who've contacted me for info, have been asking wether or not the engine can be run on Mogas...
High compression would've been a showstopper for those 90%...

So I'm certainly glad I went for 8.5 compression...
 
You'll get more opinions than facts here, so I'll throw some more confusion in ;)
  1. The basic 180HP engine (parallel valve) I think most would be considered a better start point than the 200HP angle valve (cost, complexity, heat, weight). I do not know the IO-375/390, but see where they start...
  2. The difference in weight between 180 and 200 core is easily allowed for / lost via choice and location of other components e.g. battery / prop
  3. "Max HP" sounds nice, but by definition you only have with 2700RPM and WOT. At low levels a 160HP RV-8 is "over-powered" by most measures. If high level cruising is a big factor, then more basic HP will give you a few more kts cruise.
  4. I doubt many are so wealthy that "max speed" is the top aim, rather than some compromise between speed and cost?
Would any of these power plants work better for the RV8 airframe /CG? ... Would I be able to carry more passenger weight with a heavier engine up front?
All subjective and subject to your aims. My aim is to get CG as far aft as possible for what I consider "more pleasant handling" i.e. fun / formation aerobatics / display flying. Move CG forward and the aircraft (relatively) becomes a "pig" to fly in that environment. Of course, the aft CG makes it a nightmare in IFR type flying / heavy pax, so if your "mission" is long cruising legs with an AP pilot in, then fwd CG may work for you...

There are many threads on here about the RV-8 and landing, and this thread, which basically end up with the RV-8 as a multi role aircraft, and large CG range. It is a very different aircraft at the ends of the CG range, and ultimately you cannot have the best of both worlds :eek:

A rule of thumb I was told and I think valid - the RV-8 becomes (relatively) "unpleasant" to fly/land forward of 80.00". So put your solo weight into a CG calc and see where you need the basic CG to end up 80.00" or aft. Try and specify / build using other's experiences to target that basic CG ;) I am sure others will disagree :(
 
Engine

I'm not sure of how much time you put into your project each day , you might not need an engine for a few years . I have an Angle Valve and a Hartzell ( Constant Speed) came in at 1094 complete with all fairings , pants and paint .CG is at the forward edge . First flight in a few weeks , will report back .
 
The extra money is hard to justify. I have a 180 hp and my buddy has the 200hp it's hard to see any difference in Performance even he says he would install a 180 if he did it again.
 
Andy nailed it. Carefully consider your mission, then choose. The mission drives the choices, because good design is a matter of reasoned compromise.

If primarily a sport plane, flown mostly solo, choose a light engine. The preference is response and stick feel.

If primarily a hauler, take the big motor. The preference is great climb rate at factory gross or more, and stability at rear CG.

A fixed pitch is viable in the first case, but a constant speed is a practical requirement for the second. In a drag race from the ground, a big motor w/CS will leave a parallel valve w/FP like it's tied to a tree.

My chosen mission was two-up cross country with a lot of baggage, with a quick climb to cool air. Even my business missions tend to be two-up. Solo, the 390/metal Hartzell just nearly requires two hands for a 3.5 G pull into a loop. On the flip side, I'm good with crazy loads like a 180lb passenger and a whole Rotax 582 in the baggage compartment (CG 86.07").
 
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Brian,

The 8 drivers will have to help with the c.g. issues of parallel v. angle, which might wind up being more important to you than 20 hp.

But I wouldn't spend the money for an angle valve. A basic 360 parallel engine is easily bumped to ~200hp. One of the sweetest engines I've flown was a O-360-A1A with 8.5:1 (standard) from LyCon, flowed and polished, with dual P-mags. Relatively inexpensive, particularly if you are happy with a carburetor.

If you spring for the proprietary pricing of a 375, it starts with a basic 360 at 7 or 8.5 and stroking bumps it to 8 or 9.6. Bart (when at ASP) told me you can use 91 mogas in a 9.0 motor, so I had him face off the pistons of an 8.5 to yield 9.0. Barely affects horsepower, but you do gain a tad of thermal efficiency.

Personally, I like horsepower for going up. Even my non-pilot wife understands it makes the pine trees get smaller quicker. We cruise 10K or so, at low rpm; fuel consumption is <8 gph, truing ~168k in -7s.

Pleasant View, huh? How about and HR or F1 for eastbound departures?

Bolt on a CS unless all you want to do is cruise, then get an appropriate FP (and consider, again, the effect on c.g.).

John Siebold
 
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OK Ill Bite.
Ive flown all variants of the RV-8. From 150 FP, to 300hp Super 8's. Lycoming, continental, and Subies. 320's, 360's, 390's, 520, 540 etc. All prop combinations, ignitions, and engine variants I can imagine.
As others have mentioned, your mission is the first question. By far most settle into the 180 c/s.
I have removed motors of owners that had angle valves and were being out climbed and out run by their parallel valve counter parts. The weight does not justify the horsepower on this platform. The parallel engine is the easy winner.
With price being a constant pressure, the parallel valve higher compression stroked motors are quite the balance. Price premium is minimal. Compressions to suit your desires. Power to weight and reliability to match. TBO with Titans to 2400. Engine selection is a balance like everything else.
While the FP/CS debate continues, I have never met an owner of a conversion of a FP to CS, that wanted to go back for any reason on an RV-8. I have worked with some that went CS to FP for odd personal reasons, all regretted it terribly.

I now see 2 choices today. 370 non-counterweighted 195hp 9:1, or the 371 counterweighted 9.6:1 at a $1500 premium to 205 hp.
 
I'd like to place an order soon for an rv8 fuselage and finishing kit but I just can't settle on which engine. I've been looking into the 200hp IO 360, IO 375 or the IO 390. I think I'm sold on a CS prop. I'm looking for an ideal power plant for my plane. None of these engines seem ideal when I look at cost, weight, well proven, RPM restrictions, each has its own downside.

1.) Are there insurance implications for using "Non-vans approved" engines (ie 390)

2.) Are there insurance implications at or above 200hp?

3.) Would any of these power plants work better for the RV8 airframe /CG?

4.) Is there a significant seat of the pants performance feel vs a 180 hp IO360 or is it just a waste of money given the added weight?

Advice needed from those with experience. Thanks!

Perhaps if the criteria were more focused and not so broad, the choice would be easier to make.

For example - I want most power and performance. I want lightest possible weight. I want least cost. I want a proven, reliable engine.

When you throw all these factors together in the pot it is difficult to come up with a best engine selection.

Narrow what you want and the choice becomes a manageable process. And don't rely on advice as to which way to go. We each have made choices based on personal preferences. They will not be yours.

The engine selection here was easy - Barrett - reliable, proven engine. Total no brainer.

The airplane objective was minimum weight - no bells or whistles or counter weights - parallel valves and it had to be a Catto prop. Total no brainer.

If you like head aches and spending money, go for an odd ball engine. Stay away from what we know works.

And you've already got reservations. That's what I mean by doing your on process. What suits the gander does not suit all geese.

The process gets simpler if you narrow the choices, but don't think for a minute that someone has invented a better wheel when it comes to an engine. Been there and done that, it is not so.
 
So much great advice in this thread. So well spoken by so many! I have a much clearer view now of what the trade offs are. As far as my mission, I really like the idea of light and nimble machine for aerobatics. Climbing performance is also high on my list. From what I've read it sounds like a parallel valve with a cs up front is the ticket. It was also very good info on the resell demand for lower compression engines. No final decisions yet but I'm narrowing in on what best suits my needs.
 
Great thread. Timely too. As I look at airplanes they all have varied versions of an O-320 or O-360. The *impact* of the differences escapes me and I would appreciate some pointers. For example there's:

straight riser in oil sump

-32 carburetor.

retard breaker magnetos.

7/16 inch propeller bolts (vs 3/8" etc)

Slick instead of Bendix magnetos

a horizontal carburetor and induction housing

Integral accessory section crankcase,

front-mounted fuel pump

external mounted oil pump

D4RN-2O21 impulse coupling dual magneto
 
There wasn't for me. The insurance company never asked why kind of engine the plane had.

I went as far as asking one broker what they did for RV's with auto engines and was told that they lump the airframes together and don't look at the engine installed. YMMV

My insurance company did ask, but even with the radial engine I was able to get full coverage.
 
Me too

I'm quite a ways from facing this decision, but it seems to me things have gotten quite a bit more complicated recently with the various "Stroker" engines. I'm building an -8 and I'm aware of the forward CG issues with a heavy engine out front, so I'd always planned on a parallel valve IO-360 with 180 hp. Fair enough, but what CG issues do the various IO-370/71/75/90 or even 400/409 create? Aren't they all just over-jugged IO-360's? How much extra weight do they bring to the table?
Yes, too much horsepower used imprudently can get you into VNE trouble, and I'm sure fuel economy suffers to feed all those extra horses; anything else? More heat in a tight cowling? More stress on motor mounts? Might we need larger rudders? Larger oil cooler? More cubes can bring compression ratios down, bringing Mogas back into the picture without sacrificing hp.
Economics of fuel & purchase cost aside, what disadvantages come from these stroked IO-360's?
 
The RV-8 I helped a friend build, and got to fly for a couple years before I got my own RV-6 has a 192hp ECI Titan IO-360 9.2:1 compression (parallel valve) with Hartzel BA prop. The lighter weight up front makes it a delight to fly. Takeoff acceleration and climb performance make it what I'd call a "muscle plane". Taking off from high density altitude airports on warm days in the mountains in Idaho, and Utah on our trips to Johnson Creek, loaded to full max gross, he had no problems at all while my 160hp fixed pitch RV-6 wallowed like a fat Cherokee 140.
 
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I just received my engine from Titan. Its an IOX370 parallel valve with standard compression cylinders pushing 197 HP. Basically the same HP as an IO360 without the added weight. Could have gotten over 200 HP if I went with high compression, but I didn't think it was worth losing the flexibility of using unleaded fuel. Give Kevin a call. Great group of people to work with.
 
Titan 370/375 best bang for the buck, hundreds flying!

ECi started selling the 370 (Aerosport continues to call it 375) many years ago and there are hundreds of these flying. This past year this was Titan's best selling engine next to the 340.

There are two reasons that I believe this specific engine works so well in our airframes:

1. The stroked engine doesn't just increase hp, it moved the peak torque down exactly where we want it. I can easily get over 200hp by spinning a high compression 360 way up, but what I want is peak torque around 2550 rpm exactly where the stroked 370 is.

2. Second is the weight. A angle valve 360 while it produces 200hp weighs well over 330 lbs. A comparable straight valve 370/375 comparably equipped usually goes out the door around 285lbs.

The last point I want to make about lowering the compression; rather than lowering the compression on a standard 180hp 360 and compromise hp why not start out with a 204hp 370 and lower to around 185-188hp and have the flexibility of a lower octane?

Just saying';)
 
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