O-320 hybrid from O-360, O-290

[Andy_RR]

In my idle hours whilst dreaming about wish-list powerplant ideas for my soon-to-be RV-8, I wondered why the O-320 doesn't appear to give anywhere near the fuel consumption advantage over its O-360 cousin.

Having a look at the bore-stroke ratios of the engines, it is easy to see why this might be. An O-320 has an estimated combustion chamber surface/volume ratio of more than 10% greater than the O-360, which translates pretty much directly into a 10% greater loss of heat during the combustion cycle -> inefficiency!

If I was to take an O-290 head and barrel (and all other things being equal etc) but with an O-360 crank, I can get an O-327 within 1% of the surface/volume ratio of the O-360, so I might start to see some of the fuel consumption gains that a smaller engine should offer, not to mention better knock resistance and potentially lower weight.

So, does anyone know much about the O-290's? There doesn't seem to be a wealth of info on the web about them, although a VAF search suggests that replacement parts may be hard to come by, except as second-hand GPU's

I wonder if the results could be good enough to convince some of the Lycloners to do a 4.875" bore kit to suit an O-360 crankcase?

Thoughts?

Andrew

[Steve]

An A&P bud told me I could replace my worn 290 cylinders with 320s. It would require minor modification to the bottom of the cylinder to clear the crank throw. It sounded intriguing in light of the scarcity of 290 parts and the engine would be "experimental" and not to be used on my old TriPacer. I decided to cut bait and sell the plane. I never did the math to figure the displacement.

Steve

[N941WR]

Originally Posted by Steve

An A&P bud told me I could replace my worn 290 cylinders with 320s. It would require minor modification to the bottom of the cylinder to clear the crank throw. It sounded intriguing in light of the scarcity of 290 parts and the engine would be "experimental" and not to be used on my old TriPacer. I decided to cut bait and sell the plane. I never did the math to figure the displacement.

Steve

I have looked into this as I have a line on a 2nd O-290-D2.

Here is what is required:
Mill the case to accept the O-320 crank
Then you need a bunch of O-320 parts:
Crank
Connecting rods
Pistons
push rods
cylinders
etc.

By the time you are done, the only O-290 part left will be the case.

The advantage is that you save about 20 lbs when finished over an O-320.

I might do this but I'm going to wait and see how my O-290 holds out.

[RVbySDI]

Well this is not exactly in line with your thinking but close. Why not look at ECI's stroked 320. It is their O/IO-340. Same bore but longer stroke as the 320. It has tapered cylinders that shave quite a bit of weight off the engine. The fuel injected engine has a cold air induction system and ECI reports 185 HP out of this engine. I will be using this engine in my airplane.

Here is a link to the ECI IO-340 website.

[LifeofReiley]

I must say, every O-320 I've been behind has never burned anywhere close to the same amount of fuel as an O-360. But... there are too many variables to make a general comparison here.

[Andy_RR]

Steve,

I have been looking at ECI's O-340. As a 'standard' engine, that is what I will probably plump for, but I was just wondering out loud at some more radical surgery to get into the properly 'experimental' theme.

The O-340 ?s only half as bad as the O-320 in terms of surface/volume ratio - it's about 5% larger than the O-360.

Darrell,

Interesting what you say about fuel burn. That makes for conflicting reports on what I have read around the traps, a lot of which is here on VAF. If you do a search on "should I choose an O-320 over an O-360" here, you get the general impression that you won't save much in fuel or gain in range by going O-320.

I guess an O-320 at 75% will burn less fuel than an O-360 at 75% simply because it is producing less power. If they produce the same power, i.e. enough to achieve the same IAS/TAS how do they compare then? In theory, the O-320 at the same speed and a higher MAP should deliver better fuel consumption, but I have yet to read where this appears to be borne out by experience.

A