Angles and parallels - why?

Flying Scotsman · #1 07-11-2010, 12:22 AM

OK, this is probably an insanely stupid question, but here goes...

After reading another thread which indicated that some angle valve engines had a different rear plug than parallel valved engines, it occurred to me that a lot of discussions reference the angle-valve this or the parallel-valve that engine, for things that seem to have no relationship to valves at all (like rear crankcase plugs). So I got to thinking...I've never really heard a good explanation of *why* an engine would have angle valves, or for that matter, parallel valves. Everybody just seems to "know" which engines are which, but I've never heard a reason why...

e.g., Why is the Lycoming IO-360 w/ 200 HP an angle-valve engine, and the 180 hp model is parallel? What's different about the engine that makes that choice? (And what does it have to do with rear crankcase plugs?

). Etc...

Anyway, like I said...probably a really dumb question with a stupid, simple answer, but I'm not an engine guy...all this is new to me LOL!

TIA!

G-force · #2 07-11-2010, 02:19 AM

I'm no aviation engine expert, but in general, parallel valved heads are easier and cheaper to manufacture and a simpler, cheaper valve train setup. Pushrods are the same length, rocker arms can be on a common shaft (less parts, fewer machining setups during manufacture.) The benefit to angled valves it typically you can design a more efficient shaped combustion chamber.

pierre smith · #3 07-11-2010, 05:05 AM

It was so named because it has a hemispherically shaped combustion chamber
due to the angled valves, which, when open, move away from the cylinder, allowing intake air to flow inwards, all the way around the valve. In a parallel situation the valve remains close to the cylinder wall as it opens, restricting flow in that area.

Obviously, angled valves can't share a common rocker shaft as in a parallel valved engine, accounting for the extra parts count,

....short quickie on this

Best,

deene · #4 07-11-2010, 08:27 AM

The "angle valve" and "parallel valve" nomenclature for Lycoming engines relates to the angle between the rocker arms...not the angle of the valve stem to the cylinder.

When the 200 hp 360ci engine was developed, a larger exhaust valve was needed leading to spacing the valve heads such that the rocker arms could no longer parallel be to each other.

Other changes to the 180 hp engine to get to 200hp for the IO-360-AlA include a horizontal front mounted fuel injector with a tuned intake and 8.7:1 compression ratio. Other design items which are added due the additional horsepower: piston cooling nozzles, stronger crankshaft, tongue and groove connecting rods with stretch bolts, and rotator type intake valves.

AK4x4 · #5 07-17-2010, 09:45 AM

Steve, the angle valve engines have cylinders with a "Hemi" style combustion chamber. The paralell valve cylinders have flat or traditional combustion chamber. In the experamental world either type of cylinder could be bolted to the base engine provided the cylinder bore is the same size. Engines from Lycoming do have differances in the base engine. The paralell valve cylinders are less expensive and lighter weight. The angle valve cylinders are more expensive, heavier, and flow more air making more horsepower. The IO-360, 180 and 200 horsepower numbers are Lycoming factory power numbers. These numbers don't mean much to experamental engines. The Lycoming paralell valve IO-360 is 180 HP and the angle valve IO-360 is 200 HP. But the experamental ECI IO-340 paralell valve with 9-1 compression is 190 HP. Lycon in califorina has built angle valve IO-360 engines with 250 HP. The "Best" engine for your aplication depends on budget, desired power, and desired installed weight. Talk with your engine builder/supplier. Remember the performance of an aircraft is based on its power to weight ratio, not installed Horsepower. Good luck, Russ

Bob Axsom · #6 07-17-2010, 08:46 PM

What does Lycon want for the 250 hp 360 - sigh.

Bob Axsom

Flying Scotsman · #7 07-19-2010, 12:50 AM

Well, there's already a brand new Lycoming YIO-360-M1B attached to my airframe

so that decision has been made...basically went with Van's "stock" solution.

I was just wondering what design/engineering decisions drove the implementation towards a parallel vs. angle valve setup, and I think I get it (partly) now...

(still wondering about that other thread where the crankcase plug somehow was related to valve geometry LOL!)...

Steve