S

szicree

Well Known Member
I'm hoping to get some opinions regarding using 360 vs 320. My plane is a day vfr fixed pitch 4. I'm leaning towards a Catto prop, but might go metal. I know the 320 is a small bit lighter and also maybe a bit less stressful on the airframe, but more power is also nice to have. I'm also curious about whether my 360 cowl would work with the 320. I would love to hear from anybody with an opinion on this. Thanks.
 
You can always pull the throttle back on the 360. You can't go past the firewall on a 320. My driver's ed instructor had a brake on his side - he said he wished he had an accelerator instead.
 
That new IO-390X...or whatever it's called, sounds like DA BOMB for the two seat RV's. Built on a 320 core, jazzed up to put out 185hp or so. Sounds like a sweet deal. This, coupled to a constant speed prop would be a smokin' hot setup.

IMO, for mostly at or near sea level ops, the 320 is a fine engine. Where I live, where density altitudes during the summer can reach 9,000', I opted for the 360 and am glad I did. Coupled to the 83" pitch Sensenich, it climbs like crazy and still will do 200mph at 8,000' and 2700 rpm. I typically dial it back to 2550 rpm for cruising, save some gas and still get there at around 175-180mph. An O-320, constant speed RV8 of similar weight is very close in overall performance with maybe a bit less climb available.

I fly with a guy who has a -4, with a Catto (I think), on a healthy O-320 and we fly formation just fine. I set my power to 2350 rpm which leaves us both plenty of power to keep it tight. He runs maybe 1000 rpm more. His ship is smooth, light and fast. A perfect combination.

Choose your mission, fit it to your budget, and don't let anyone else tell you otherwise. Not even me.

:D
 
Brian Denk said:
<SNIP>

I fly with a guy who has a -4, with a Catto (I think), on a healthy O-320 and we fly formation just fine. I set my power to 2350 rpm which leaves us both plenty of power to keep it tight. He runs maybe 1000 rpm more. His ship is smooth, light and fast. A perfect combination.

Choose your mission, fit it to your budget, and don't let anyone else tell you otherwise. Not even me.

:D
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Brain, is this a typo? (1000 RPM more ...) You really meant 100 RPM more right???

James
 
Steve - first off VANS sell a 320 and a 360 cowl for the -4. The air box I think is bigger and makes the 320 cowl unusable with a 360. If you put injection on a 320 you also need the 360 cowl. To my mind the 360 cowl is not so pretty, but some would view that differently.

Next point the -4 is not underpowered with 160 hp. Top speed is a function of the cube root of the power so I guess you will get about 4% more speed at the top end.

Fuel/ Well it only gets more expensive.

The 360 weighs I think abot 11lbs more. To me on a -4 that is a key issue.
1) It is 11lbs of luggage you wont have with you on a trip.
2) It is going to affect your stall speed and ground role on landing. Depending where you fly from this might be important. It is to me. See http://gikonwhy4.blogspot.com/
3) It will move your CofG. This may /may not be beneficial. Since I am putting an MT on the front I view it as unhelpful to have even more weight forward.
4) The engine mount / fuselage junction on the -4 is not its strongest point! Minimising the weight out there must be helpful.
5) Light aircraft are more fun to fly.

Lots of people will say its only 11lbs. Each of the weight decisions is only a few lbs but that is how two seemingly identical aircraft end up weighing 100lbs apart.

Oh, one other thing. Aircraft engines like hard work. They dont seem to respond well to low power operation over a prolonged period. To me there is merit in having a smaller engine where the throttle will be open a little more rather than less.

Well you have my view and its pretty clear, but there are no absolute truths in this. Have fun.
 
I agree with Steve. In many cases the smaller engine will perform better. Most of the RVs that I inspect now days have a big engine, constant speed prop, autopilots, etc. Most empty weights come in over 1100 lbs. without paint. An RV that weighs around 1000 lbs. will fly MUCH better.
Another minor thing to look at; Have you noticed how many people complain about the ADs and service bulletins on the O-360s? How many have you seen on the O-320? The O-320s have a history of running well beyond TBO when operated properly. My engine had 2500 hrs on it when I bought it. I flew it another 300 and when I took it down for overhaul, everything was within servicable limits at 2815 hrs.
 
Numbers

320 cu-in Vs. 360 cu-in

160 hp Vs. 180 hp

$21,200 Vs $21,300 *

259 lbs. Vs. 293 lbs. ** (corrected on following post)


* Mattituck raised prices :( and odd enough price diff between O320 and
O360 are nil. Also 320's with FI are the same price at Carb versions. There is
a little more price delta between IO320 and IO360 but not much. My
prefrence is Carb.

** This is a swag based on Lyc weights.


Based on new prices the 360 seems an obvious choice. However the weight
comments above are very valid. A 1000 lb RV flys differnt than a 1100 lb one.
Than again 20 HP is 20 HP. Van says RV-4 w/ 180 HP is good for 8 mph and
400 fpm more than a 160 HP dash 4.

Can you handle the extra 30 lbs or so for the 360. If you're buying used you
get what you can find. 160 HP is plenty of power. Good luck. I would go 180
hp. At some point if you sell the plane, 180 hp is a plus or goodness on the
used market.
 
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What about the IOX-340 from ECI? Lighter than a 360 and 185HP... that'd be my choice for a 4 or 8 right now. The -7 that I'm building needs the weight on the nose... so 360 for it.
 
Thanks for all the great info; keep it coming! I'm curious about the weight difference estimates that I'm reading. Seems like its somewhere between 10 and 30 lbs? For what it's worth, my plane should end up very light. I have no interior beyond seats and carpet, no lights, no gyros, no vacuum system, probably a 4-pipe, and most likely a composite prop.
 
George - like for like I doubt the weight difference you have there. I dont understand the source you are quoting. The only difference between an XP-320 and XP-360 except for the crank (which presumably has a negligable weight difference) is the 4 cylinders. They are slightly larger on the 360 and that I think accounts for 11lbs in total that you cant get away from. I was given that number by an engine builder in the UK.

Cheers.
 
Steve Sampson said:
.... The only difference between an XP-320 and XP-360 except for the crank (which presumably has a negligable weight difference) is the 4 cylinders. .....

Cheers.
Click to expand...

I'm not sure this is a good assumption.... The crank has a longer throw, so the "meat" between the journals is longer, and I would have thought it might be a little thicker for strength with the extra HP....

gil in Tucson
 
Good Catch, weight correction

Steve Sampson said:
George - like for like I doubt the weight difference you have there. I don't understand the source you are quoting. The only difference between an XP-320 and XP-360 except for the crank (which presumably has a negligible weight difference) is the 4 cylinders. They are slightly larger on the 360 and that I think accounts for 11lbs in total that you cant get away from. I was given that number by an engine builder in the UK.

Cheers.
Click to expand...
Yea Steve good call I used a IO-360-A, C (200 hp) weight. Here is my source.


Look at O-320-B, D (255 lb) and IO-320-B, C (259 lb)
http://www.lycoming.textron.com/main.jsp?bodyPage=/productSales/engineSelectionGuide/320.html

Look at O-360-A (265 lb) IO-360-B (270 lb)
http://www.lycoming.textron.com/main.jsp?bodyPage=productSales/engineSelectionGuide/360.html

So the weight diff is about ** 11 lbs as you say according to the links above. So I stand corrected, thanks. :D

However word of caution that many of the 360 clones weight more in general than the Lyc equiv like the O-360-A, which is a light weight engine. May be Mahlon or someone can chime in but the clones are a bit heavier especially the Superior XP-360, which I believe uses a counter weighted crankshaft. Superior list their XP-360 weight as 290 lbs / 287 lbs (FI/Carb). That is about 20 lbs more than the listed Lyc dry weights. I don't believe anyone uses counterweight cranks on 320's so my original weight I posted of a little over 290 lbs is about right for a XP-360.

Bottom line these are all estimates and you don't know until you put it all on a scale. Of course these are dry weights.

** My "research" :rolleyes: (ref.1) of over 100 actual finished empty weights of flying RV's shows that 320 RV's weigh at least 20-36 lbs less than RV's with 360's. Here's an excerpt.

EMPTY WEIGHT BY PROP, ENG or ENG/PROP
Total; Eng/Prop; MIN; MAX; AVG

60; FIX;..........874; 1170; 1041
55; CS;.........1010; 1244; 1111
41; 320;..........874; 1168; 1034
60; 360;..........986; 1189; 1084
14; IO360;.....1103; 1244; 1151
32; 320/Fix;......874; 1106; 1019
28; 360/Fix;.....986; 1170; 1066
09; 320/CS;....1010; 1168; 1084
32; 360/CS;....1026; 1189; 1101
14; IO360/CS;.1103; 1244; 1151

Fix or CS = no breakdown of brand, blade material, most popular: Sensenich & Hartzell
320 = 150 or 160HP Carb or injected
360 = 180 HP Carb or Injected
IO360 = (200HP)

Of course doing statistical analysis and trying to filter out all the variables is not easy with the info available. The prop was fairly straight forward to factor in, since that is usually reported; however paint, upholstery, panel and so on is harder to do. Clearly there are 320 RV's that weigh more than 360 RV's, but by in large equivalent 320 powered RV's are lighter, for the obvious reason of engine weight.

I think a good safe number for the 320 Vs. 360 weight delta range is 18-50 lbs. The builder has to be careful with every ounce they put on their plane. Why do the 360 powered RV's weight more than the 11 lbs dry assy weight Lyc post? Probably heavier accessories: prop bolts, oil cooler, air filter and so on. It all adds up.


(ref. 1) http://www.vansairforce.com/community/showpost.php?p=784&postcount=19
 
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Isn't it funny how much time, thought and money goes in to trying to shave 10 or 11 pounds off a finished airplane, but nobody stops to think about the amount of extra weight savings that could be accomplished by skipping the beer and cheeseburger once in a while? I figure at 175 lbs I've already saved the difference between a 320 and a 360 over some of my more "bubba-ish" fellow pilots. :D
 
George - an interesting post. While there clearly is a weight difference between the two engines, I think if you take a statistical approach you get two other effects. 1)There are people like me who say which is lighter. There is another school of thought, which asks which has more power. The first of these groups tend also to have fewer 'toys', so their aircraft are lighter for that reason also. 2) Each decision has a knock on effect. As I indicated before I will put an O-320 in my -4 and save (I think) 11lbs. However, I will save more than that because if I went with an O-360 I would also have to use the next size up MT prop since the one I will use is rated for a 160hp engine. Of course the next one up is also heavier. I forget the exact numbers but I think together the weight difference is in the order of 20 lbs.

The good news is we can make our own decision. If 'toys' and HP float your boat stick em in.
 
jclark said:
Brain, is this a typo? (1000 RPM more ...) You really meant 100 RPM more right???

James
Click to expand...

You are correct! Sorry, 100 rpm or so. Interestingly enough, I also flew with another -4 a few years ago, with the same power/prop but maybe pitched more for cruise. We both took off one morning with full tanks, flew the same speeds, same route, landed, taxied, had breakfast, and did the repeat on the way back then topped off our tanks. I burned .5 gallon less for the flight. Sure, lot's of variables here, but I think it illustrates that the bigger engine can be economical too, as long as you don't always go blasting along with your hair on fire. I've been taking very short flights recently (with my 4 year old son in back, so he stays interested instead of bored!). I'm throttling back a lot and just cruising around gently to keep the noise down and to just enjoy the time together. It's amazing how much fun you can have at 120mph when you're not in a hurry to get anywhere.
 
Steve,
I'm not sure where George got his 259 vs 293 pound weight differential. He sure isn't comparing similar parallel valve engines with that statement. 293 pounds is the weight of the 200 hp IO-360-A1A angle valve 360. See

http://rvimg.com/tcds/lycoming-io-360.pdf

scroll down to page 13 to see the weights of the various 360 cu fuel injected engines.

The O-360-A1A engine commonly installed in RVs only weighs 258 pounds. See

http://rvimg.com/tcds/lycoming-o-360.pdf

Scroll down to page 11 for weights

The O-320-A1A weighs 244 pounds, according to Lycoming. See

http://rvimg.com/tcds/lycoming-o-320.pdf

Scroll down to page 7 for weights.

Comparing apples to apples, we see that the O-360-A1A engine weighs 14 pounds more than the O-320-A1A engine.

The 360 cubic inch engines vary quite a bit in weight. This is due to the fact that there are both parallel and angle valve (200 hp) models. The angle valve units weigh 18 to 30 pounds more than the parallel valve (180 hp) models.
Either engine will work quite well. Let me give you some more info.
The crankcases, timing gears, rocker arms, valves, springs and accessory covers are essentially the same on both 320 and 360 cubic inch parallel valve engines. The 360 cubic inch engines have the same bore (5.125") as the 320 models. They differ in stroke. The 320 cu engines are 3.875" stroke. (The 340 engine has a 4.125" stroke) The 360 cu models have 4.375" stroke. That is a 1/2" difference. Because of this, the crank throws on the crankshaft are 1/4" longer, the connecting rods are longer. Most importantly, the steel barrel part of the 360 cu cylinders are 1/2" longer. (You can spot the difference in cylinders by counting the number of steel fins on the barrel. 320s have 15 fins, 360s have 19)
This extra length in the cylinders means that a 360 engine is 1" wider than the 320.
If you live near sea level or a "flat lands" area, the 320 will be more than enough motor. I have several friends with RV4s. They all use the old Prestolite (can you say "heavy" boys and girls?) starter. They do this for CG perposes, not because it's a great starter. If the 360 is near the same price, I'd rather install the bigger engine with a light weight starter, myself, but that's just me. The light weight starter will retreive 8 of the 14 pounds you give up compared to an O-320 with the standard starter.
FYI, ECI has managed to save 7 pounds off of the weight of their 360 engine. They did this by tapering the steel fins on the barrel part of the cylinders. I learned this while visiting their tent at Sun N' Fun this year. ;-)
Charlie Kuss
 
-320 vs -360

Hey Steve,
I have an RV-4 w/ O-320-D1A, 160 HP w/ Ellison TBI and 3 blade Catto prop and have been very happy with this combination. Since I live in the SE, high altitude is not a problem. My -4 is fast (8500',WOT=196 MPH in calm air) my friend in a 180 hp/RV-8 is faster but not by much. My fuel burn is good and if I power back to 65% and less and aggressively lean is surprisingly good. At high altitude (8500' and up) can get 6.5-7 gal/hr and 170+mpg....works for me. My -4 is a little heavy (1057lbs) but I plan to put it on a diet soon and shead a few lbs. The TBI is far superior to a carb in every measure...CAFE likes it too. I have also been very happy w/ the Catto prop.
Very smooth, quiet, light and simple and great performance plus it looks great too. I'm using a Landoll Balancer which makes for lower, smoother idle and reduced vibration. Obviously, I am very happy with my set-up and this may be somthing you may want to consider.
Hope this helps and feel free to contact me if you have any questions.

CAVU,
Glenn
N654RV @ OKZ
 
Glenn - could you be a bit more specific as to how you find the TBI superior? I looked at it a while ago and got the impression it was fussy. Also I could not get answers from them but thats a different issue.

Thanks
 
Ellison TBI

Steve- Here are my 2 cents, the TBI is physically smaller, lighter and much more simple than a typical carb. It creates a fog of fuel across the throat of the intake through the fuel metering tube giving much more even fuel distribution to the cylinders.The intake diameter is adjusted with a sliding block, changing intake flow based on throttle position/fuel flow. And because of that it is possible to lean more aggressively than a carb. Initial adjustment is not very complicated but I did have to make another adjustment on either the mixture or idle (can't remember which) within the first 10 hrs but have not had any squawks since. You would need a primer for starting....that's a minor item. Also it can be mounted in any orientation and is unaffected by aerobatics.
That's all I can think of for now...let me know if I can help with more info.

CAVU,
Glenn
RV-4 N654RV @ OKZ
 
Ellison TBI

Steve,
Something else I remembered...Ellison says you will get .5-1.0 inch of extra MAP @ altitude....this has been my experience when cruising @8500'.

You're going to LOVE your -4 when you start flying.

Glenn
 
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