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320 vs 360 for an RV-7

DaleB

Well Known Member
Up until now I've been pretty much settled on a 180HP O- or IO-360 for my plane, mostly because that seems to be the norm for a -7. Today, though, I got to looking at the actual performance numbers, and figured out the actual difference in flying time to various destinations we'd be likely to fly to regularly (or even infrequently) with 160 and 180 HP. Using the numbers published on the Van's site, I come up with a worst case difference in flight time of about 15 minutes at economy cruise settings, not adjusted for winds. That's on flights from here in the middle of the country to pretty much either coast; most flights were 5-10 minutes difference.

So now I'm re-considering. It seems that O-320s are quite a bit more plentiful and less expensive than O-360s, although most of the 320s seem to have solid cranks for FP props. I have not yet changed my mind, but I'm certainly thinking I may expend my engine search pool.

I see some difference in takeoff and climb performance, but certainly not enough to be a deciding factor - it looks like an RV-7 pushed along Fred Flintstone style would perform well. I'm not looking to wring every last knot out of the plane. An RV-9 would probably have fit my mission just as well if not slightly better, but I liked the options I'd have open with the 7 - and I got a great deal on the kit. Resale value aside, are there reasons to go with the 180HP or higher 360 vs the 320 -- or vice versa? At the same speed, for example, would one burn significantly less fuel than the other?
 
"I wish this thing had less power." Said no one. Ever. :D

Look at the price difference between a 320 and 360 (or 340). It may be significant enough to make up your mind for you. The hit on resale value is a legit concern though if you plan on selling.

A 320 with a fixed pitch catto and minimal panel would be nice and light though, the way Van intended. Think about it this way... it's the same engine/power as a C-172 with 1/2 the weight and 1/3 the drag.
 
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It's true: more power buys little speed (for an idealized airplane speed is proportional to the cube root of power, so a 10% power increase gets you a 3% speed increase).
But you climb on excess power: you will see a significant difference in climb rate.
I see you live in Omaha. If you plan to head west when it's hot and you're heavy, you'll like the bigger engine.
 
If you ever intend to fly very much in the mountains, you'll really be wishing for that extra 20 hp.

My O-320 in a fairly lightweight RV-6 was a dog at the high altitude mountain airstrips... even solo and keeping the fuel and baggage weights down to a minimum, I was glad I had all those years of experience of flying a Cherokee 140 on hot Texas days at full gross :eek: :D.

The O-340 option sounds like it might be a pretty good compromise.
 
Up until now I've been pretty much settled on a 180HP O- or IO-360 for my plane, mostly because that seems to be the norm for a -7......

Leave it at that.... I posed the same questions many moons ago at OSH during a
Van's banquet to the table full of experienced builders/ flyers. They pretty much all said go with the 180hp for all the reasons the experienced VAF builders are stating in this thread.
 
320 vs 360

I thought my first RV, a 6 with a 0-320 150 hp fixed pitch was really great until I rode in a constant speed 360. That required me to build yet another airplane. I am very happy with my 0-360 powered RV-7......my advice, go with the bigger engine you won't be sorry.
 
Gotcha. We do live in Omaha, where the DA seldom exceeds 3000 but we have friends in CO and family in southern CA. Hot and heavy would describe accurately some of the flying I hope to do... well, it describes a lot of things I'd like to do, but that's a different matter.

I do like the idea of the 340, but if I'm going to shell out for a new engine the 370 or 375 looks nice too. :D
 
I have a friend that had a 7A with the IO 360, 200hp. He could definately get me in climb, but flat out, we were neck & neck. Probably that nose dragger held him back a little. To me, the 180 seems to be the best all around choice. Good luck with whatever you decide.
 
Resale will suffer with an O-320. My biased suggestion to a friend looking to buy a RV-7 with an O-320....forget it.

Same airspeed (O-320 and O-360) means almost identical fuel consumption.

O-320...forget flying with O-360 powered RVs for breakfast/lunch. Unless you leave five minutes earlier.

Stay with the O-360 or better.
 
Same airspeed (O-320 and O-360) means almost identical fuel consumption.
This, right here, is what I was wondering. If the fuel consumption at the same airspeed will be the same (and I think I've heard that before) then it's an easy choice.
 
All things considered, the 360 series 180 HP engine is a better fit for the RV-7/7A. The W&B, engine mount, cowl, and extra performance all make the 360 engine a better fit for the aircraft. If you want to limit yourself to 160 HP, just pull the Black Knob out a little...:rolleyes: CS or FP props are your choice.
 
fuel burn comparison

I regularly fly with a friend with a RV-9A and the 340, I have a 0-360 in my -7. We both have Catto FP props and at cruise power setting we pretty much have the same fuel burn rate.
Also the -7 tends to aft CG particularly if you go FP, so with the 320 I think people put a different mount to move the engine forward a bit, just more things to think about.
 
All things considered, the 360 series 180 HP engine is a better fit for the RV-7/7A. The W&B, engine mount, cowl, and extra performance all make the 360 engine a better fit for the aircraft. If you want to limit yourself to 160 HP, just pull the Black Knob out a little...:rolleyes: CS or FP props are your choice.

Well... I guess you'd know what you're talking about. :)
 
When I replaced the O-290-D2 in my RV-9 I went through the same thought process.

The (I)O-360 doesn't weigh much more than an O-320 and the cost difference was only $500 at the time. $500 for 20 extra HP, sign me up.

I also looked at the IO-340 and it cost more than the O-360 and even though I'm sure it is a great engine, it is still a bit of an oddball.

You can always buy your 360 with a hollow crank and start life with a FP prop and change it over to a CS prop later on.

These planes are so over powered that unless you are doing a lot of formation flying or are really into acro, there is very little need for a CS prop. (Note, I said need not want.)
 
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These plans are so over powered that unless you are doing a lot of formation flying or are really into acro, there is very little need for a CS prop. (Note, I said need not want.)

Well, we really don't need these planes either, but

I always say.......don't believe everything you read. Personally, I just wouldn't care for an RV without a C/S. It's all the difference in the world, unless you're really into that...."as Van intended" lightweight no frills stuff. I'm not, as I like the performance difference, which is very, very noticeable.

Had a 6A with a 180HP and Hartzell C/S
 
I chose an O-320 because i found a great deal on a good core. If i was buying new i would go 180 hp. I saved a bunch of money overhauling that 320.
 
Resale will suffer with an O-320. My biased suggestion to a friend looking to buy a RV-7 with an O-320....forget it.

Same airspeed (O-320 and O-360) means almost identical fuel consumption.

O-320...forget flying with O-360 powered RVs for breakfast/lunch. Unless you leave five minutes earlier.

Stay with the O-360 or better.

What's 5 minutes between friends?
 
Depends, build the airplane you want (ultimate performance or ultimate budget). I attempted to save for a new engine while shopping for a decent deal on a used engine (320 or 360). $$ was my biggest obstacle to the entire build, i ended up with a decent deal on a 360. If I would have found a decent 320 for 5K less i would have been happily flying last year with a 320. Vans makes a longer engine mount to accommodate the 320 W&B.

A O-320 Rv7 is not underpowered.

$$ savings on new doesn't make sense to buy the 320, a good used O-320 for $$ less than a O-360? I say go for it.
 
I've flown 2 RV-8s with 160HP - nothing wrong with them at all. Only "disadvantage" to me seems perception, resale and if you fly alongside 180HP+ RVs a lot :eek:

Far more difference in all round perf will be FP v CS Prop. In the Flt Testing I have done, I use 110KIAS for climb, and a 180HP VP prop tends to climb ~7000' @ MAUW, FP props nearer 5500'. The latter obviously closely depends on type of FP Prop and RPM achieved. At 2350RPM (higher end of the RPMs I have seen @ 110K) your 180HP engine only gives 155HP and the prop is not at peak efficiency.

For what I use RVs for, I would pick 160HP VP over 180HP FP every time. But only you know what you want the RV for, where your priorities are, and your budget ;)
 
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Hmm

I am watching this thread very closely as I am building an RV-7A and have a hollow crank O-320 sitting on an engine stand in the shop. I have been debating heavily on whether I should just sell the 320 or commit. Hearing how much work it will take to change the plane from a 320 to a 360 after its flying is a big factor to weigh, especially after hearing "Man, I wish this plane had less power" said no one, ever. Oh yea, I live in South Texas, also a factor.
 
Dale,

With "hot and heavy" in your planned missions, don't even think about the 320. Nearly all my cross countries make me re-appreciate vertical ability, both up and down, not just horsepower for climb, but a constant speed for quick let-downs. Speed is not always first priority. Your opening post didn't hang your decision on dollars, so what's your hesitation regarding performance?

Also, pack as much weight forward in the build as you possibly can. The 7 quickly runs out of rear c.g. with little weight in the baggage area without a forward empty c.g. bias. Another blow in favor of the 360/Hartzell. Then there's resale, expectations, grin, etc.

Every time I've ridden a fixed pitch, especially a 320/FP, I'm left with the impression it's a pig compared to a 360/CS.

John Siebold
 
Actually there is a well-known story about an RV owner wanting to change from an O-360 to an O-320. The story quickly spread from internet forum to internet forum and achieved a life of its own.

Eventually it was determined to either be a story like the Lock Ness monster or something some hypoxic guy in Colorado made up.
 
If someone wanted a 320 from the beginning, and not too much into acrobatics. Would that make a good case to build a RV 9 instead?
 
Your opening post didn't hang your decision on dollars, so what's your hesitation regarding performance?
John,

My thinking was that used 320s are cheap and plentiful (though maybe not so much the CS models). If the 320 would give me good-enough performance and be substantially less expensive to feed, it might be the way to go. I'd gladly give up a few knots in cruise for lower fuel burn.

According to what I'm hearing, though, the fuel burn at the same speeds would be the same, or very close. If the fuel burn is not substantially different, I'll go with the bigger engine.
 
If someone wanted a 320 from the beginning, and not too much into acrobatics. Would that make a good case to build a RV 9 instead?
I was -><- that close to deciding on a 9 anyway... :) Found a great deal on a 7 kit, and I do like the idea of being able to (safely, and within designer's recommendations/limits) do some acro if I decide I want to.
 
If the fuel burn is not substantially different, I'll go with the bigger engine.

Depending on the prop-------dont forget that part of the equation. A 360 with a C/S vs a 320 fixed is not going to be a fair comparison. In fact, I suspect the 360 C/S will be more fuel efficient at the same airspeed over most of the envelope.
 
I am watching this thread very closely as I am building an RV-7A and have a hollow crank O-320 sitting on an engine stand in the shop. I have been debating heavily on whether I should just sell the 320 or commit. Hearing how much work it will take to change the plane from a 320 to a 360 after its flying is a big factor to weigh, especially after hearing "Man, I wish this plane had less power" said no one, ever. Oh yea, I live in South Texas, also a factor.

Bird in the hand. The price difference switching to a 360 will buy a lot of avgas. Building it straight, light and clean will make up for a lot of horspower.

Put a CS prop on it, and enjoy!

If someone wanted a 320 from the beginning, and not too much into acrobatics. Would that make a good case to build a RV 9 instead?

If you don't want to go upside down, and are looking for economical cruising and tooling around, I'd build a 9.
 
How many RV-6s are out there flying on 150/160 HP? It was the standard years ago. An 1100 lb airplane with 160 HP nearly doesn't exist outside of experimental..... I guess it all depends on your point of reference. Personally, if I had a 320 sitting in the shop it'd be a no brainer for me.
 
My RV 7A and 0-320 FP numbers

I have 140 hours on my RV 7A with the 160 hp/fixed pitch Sensenich propeller, (2600 RPM restriction), combination. As far as performance, with the exception of climb rate, My cruise and top end numbers are pretty close to Vans specs. My rates of climb on hot summer days in South Alabama are around 1300 ft./m..... Up to about 1000-1500 feet. At that point I have to level off and throttle back a little to allow the number two cylinder head temperature to come down some. Had I installed 180 hp my climb rates would have been better but I probably would still be restricted by the cylinder head temperature, (My baffling is excellent). Cylinder head temperatures are a common problem. With that said, let me add this, most of my flying is solo. So here are my thoughts. If you're going to be flying at Max gross weights or high density altitudes definitely go with the 180 hp. Fixed pitch versus constant speed.... Only way to look at that is the mission, complexity and cost. If I had it to do over I would probably go with 180 hp and a fixed pitch prop however I would not go with the Sensenich because of the RPM restriction. A few years ago when I was making my decision, the single biggest factor that weighed in my mind was what someone mentioned earlier about the Cessna 172. The 7A is much lighter and a whole heck of a lot less drag. Whatever you choose, you're going to love your new airplane! Mine is a hot rod compared to the Cessna 152 I owned for 10 years.
 
I have 140 hours on my RV 7A with the 160 hp/fixed pitch Sensenich propeller, (2600 RPM restriction), combination. As far as performance, with the exception of climb rate, My cruise and top end numbers are pretty close to Vans specs. My rates of climb on hot summer days in South Alabama are around 1300 ft./m..... Up to about 1000-1500 feet. At that point I have to level off and throttle back a little to allow the number two cylinder head temperature to come down some. Had I installed 180 hp my climb rates would have been better but I probably would still be restricted by the cylinder head temperature, (My baffling is excellent). Cylinder head temperatures are a common problem. With that said, let me add this, most of my flying is solo. So here are my thoughts. If you're going to be flying at Max gross weights or high density altitudes definitely go with the 180 hp. Fixed pitch versus constant speed.... Only way to look at that is the mission, complexity and cost. If I had it to do over I would probably go with 180 hp and a fixed pitch prop however I would not go with the Sensenich because of the RPM restriction. A few years ago when I was making my decision, the single biggest factor that weighed in my mind was what someone mentioned earlier about the Cessna 172. The 7A is much lighter and a whole heck of a lot less drag. Whatever you choose, you're going to love your new airplane! Mine is a hot rod compared to the Cessna 152 I owned for 10 years.

There is no restriction on the Sensenich 180 hp prop.
 
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