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  #11  
Old 12-29-2014, 06:08 AM
Adam Adam is offline
 
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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.
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  #12  
Old 12-29-2014, 06:41 AM
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DanH DanH is offline
 
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Location: 08A
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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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Last edited by DanH : 12-29-2014 at 06:44 AM.
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  #13  
Old 12-29-2014, 07:38 AM
RV7ator RV7ator is offline
 
Join Date: Jan 2005
Location: Boise, ID
Posts: 1,007
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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

Last edited by RV7ator : 12-29-2014 at 07:43 AM.
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  #14  
Old 12-29-2014, 08:43 AM
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Kahuna Kahuna is offline
 
Join Date: Dec 2004
Location: Gold Hill, NC25
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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.
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  #15  
Old 12-29-2014, 09:14 AM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
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Quote:
Originally Posted by FlynBrian View Post
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.
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  #16  
Old 12-29-2014, 11:23 PM
FlynBrian FlynBrian is offline
 
Join Date: Jun 2014
Location: Pleasant View UT
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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.
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  #17  
Old 12-29-2014, 11:35 PM
FlynBrian FlynBrian is offline
 
Join Date: Jun 2014
Location: Pleasant View UT
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Quote:
Originally Posted by RV7ator View Post
Pleasant View, huh? How about and HR or F1 for eastbound departures?
Now your talking! I started wanting a -4, almost purchased a HR kit but landed right in the middle with the -8.
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  #18  
Old 12-30-2014, 07:11 AM
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Saville Saville is offline
 
Join Date: May 2014
Location: KBVY Massachusetts
Posts: 1,100
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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
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  #19  
Old 12-30-2014, 03:45 PM
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flyboykelly flyboykelly is offline
 
Join Date: Jun 2006
Location: Port Orange, FL (7FL6)
Posts: 274
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Quote:
Originally Posted by N941WR View Post
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.
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  #20  
Old 12-30-2014, 07:57 PM
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claycookiemonster claycookiemonster is offline
 
Join Date: Oct 2007
Location: Old Saybrook, CT
Posts: 201
Default 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?
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