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  #1  
Old 08-07-2022, 09:47 PM
cjjohns79 cjjohns79 is offline
 
Join Date: Aug 2022
Location: Edmond, OK
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Default IO-390 vs IO-360

Im 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!
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  #2  
Old 08-07-2022, 10:30 PM
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Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,451
Default Welcome to VAF

Chad, welcome aboard the good ship VAF
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Flying as of 12/4/2010

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  #3  
Old 08-07-2022, 10:43 PM
Robert Sailor Robert Sailor is offline
 
Join Date: Nov 2018
Location: Nanaimo BC Canada
Posts: 153
Default

I suspect youll notice a bit more speed but probably not a lot however the additional hp will really show in takeoff and climb.
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  #4  
Old 08-08-2022, 10:45 AM
N82VM N82VM is offline
 
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Location: Warrenton, VA
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It will reduce the weight of your wallet about $12,000 more than a 180hp io-360
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  #5  
Old 08-08-2022, 11:02 AM
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Tim 8-A Tim 8-A is offline
 
Join Date: Mar 2009
Location: Colleyville
Posts: 308
Default

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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Last edited by Tim 8-A : 08-08-2022 at 11:07 AM.
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  #6  
Old 08-08-2022, 11:03 AM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
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Default

“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.
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  #7  
Old 08-08-2022, 11:38 AM
Freemasm Freemasm is offline
 
Join Date: Nov 2017
Location: Orlando
Posts: 759
Default

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.
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  #8  
Old 08-08-2022, 12:02 PM
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Carl Froehlich Carl Froehlich is online now
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,741
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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
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  #9  
Old 08-08-2022, 12:28 PM
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Gash Gash is offline
 
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Location: Goodyear, Arizona
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Default

Quote:
Originally Posted by Ironflight View Post
I wish I had less horsepower!..said no pilot, ever!
That gave me a good chuckle Paul. So true!
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  #10  
Old 08-08-2022, 12:56 PM
Mikeyb Mikeyb is offline
 
Join Date: Nov 2018
Location: Pasadena ca
Posts: 145
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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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Last edited by Mikeyb : 08-08-2022 at 01:33 PM. Reason: Added condition
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