360 vs. 320

[az_gila]

Originally Posted by Steve Sampson

.... 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.

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

[gmcjetpilot]

Originally Posted by Steve Sampson

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.

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...Guide/320.html

Look at O-360-A (265 lb) IO-360-B (270 lb)
http://www.lycoming.textron.com/main...Guide/360.html

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

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" (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/communit...4&postcount=19

[osxuser]

I'll take an extra 25lbs for an extra 25HP... but thats just me.

[kevinh]

Originally Posted by osxuser

I'll take an extra 25lbs for an extra 25HP... but thats just me.

Especially on a 7, which tend to be slightly tail heavy.

[szicree]

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.

[Steve Sampson]

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.

[Brian Denk]

Originally Posted by jclark

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

James

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.

[chaskuss]

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

[glenn654]

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

[Steve Sampson]

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