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Old 08-07-2022, 10:47 PM
cjjohns79 cjjohns79 is offline
Join Date: Aug 2022
Location: Edmond, OK
Posts: 1
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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Old 08-07-2022, 11:30 PM
Mike S's Avatar
Mike S Mike S is offline
Senior Curmudgeon
Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,616
Default Welcome to VAF

Chad, welcome aboard the good ship VAF
Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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Old 08-07-2022, 11:43 PM
Robert Sailor Robert Sailor is offline
Join Date: Nov 2018
Location: Nanaimo BC Canada
Posts: 176

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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Old 08-08-2022, 11:45 AM
N82VM N82VM is offline
Join Date: May 2017
Location: VA
Posts: 244

It will reduce the weight of your wallet about $12,000 more than a 180hp io-360
RV-8A Project
2022 Dues Paid
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Old 08-08-2022, 12:02 PM
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Tim 8-A Tim 8-A is offline
Join Date: Mar 2009
Location: Colleyville
Posts: 319

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.
Tim Blake
Colleyville, Tx
RV8a Purchased flying (many changes) Sold
RV-10 Purchased flying.. Panel upgrade complete.
G3X/Dynon/TT all new interior. Flyin like a dream. Sold
RV8a Purchased flying Let the changes begin

Last edited by Tim 8-A : 08-08-2022 at 12:07 PM.
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Old 08-08-2022, 12:03 PM
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Ironflight Ironflight is offline
VAF Moderator / Line Boy
Join Date: Jan 2005
Location: Dayton, NV
Posts: 13,310

“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.
Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
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Old 08-08-2022, 12:38 PM
Freemasm Freemasm is offline
Join Date: Nov 2017
Location: Orlando
Posts: 957

Parallel valve:

Stroked to 370-ish CIs
better breathing sump

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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Old 08-08-2022, 01:02 PM
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Carl Froehlich Carl Froehlich is online now
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 4,028

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.

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Old 08-08-2022, 01:28 PM
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Gash Gash is offline
Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 988

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!
Karl, Goodyear, Arizona (KGYR) ATP, CFII
Yak 50 Red Thunder Airshows
=VAF= donor 2023
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Old 08-08-2022, 01:56 PM
Mikeyb Mikeyb is offline
Join Date: Nov 2018
Location: Pasadena ca
Posts: 242

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.
SN 83764
Hartzell Composite CS
Phase 1 complete 10/29/22

Last edited by Mikeyb : 08-08-2022 at 02:33 PM. Reason: Added condition
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