H O F T E C
Your Homebuilt is now far enough along that you are contemplating the other 50% of your airplane's cost - an engine purchase.
Statistically, for homebuilders a Lycoming 0-320 is the most popular choice. After all, the 150-160 HP they produce is good power to fly one or two people around the sky. Decision: let's find us an 0-320.
You see an ad in your favourite publication: " 0-320 for sale - $3000". That is your engine! You call the vendor and are told it is an -H1AD model. That doesn't mean anything to you, and you are satisfied that as long as it is an 0-320 at a good price you will worry about the details later. But hold on: what are you buying? Better still, what did you want to buy?
What do the dash numbers mean anyway?
First, the '0' in the 0-320 means horizontally opposed, and not an injected engine or else it would have been labelled IO-320. An AIO-320 is an aerobatic injected version. An LIO is a left hand rotation injected engine. The '320' is the displacement in cubic inches. Then things get complicated, and there is no easy pattern to follow for all the dash numbers.
The first letter after the '320' gives the Power Rating. The '-A' is 150 HP, the '-B' is 160 HP, the '-C' is 150 HP, the '-D' is 160 HP, the '-E' is 150 HP, and the '-H' is 160 HP.
The 0-320-A1A is a 150 Hp engine, using controllable prop and designed for 80/87 gas, has 7.00:1 compression and Bendix mags with the spark advance set at 25 degrees.
The 0-320-B1A is a 160 HP engine, otherwise the same as the A1A but using 100 octane gas and has a compression ratio of 8.5:1.
The 0-320 C1A is the same as the B1A except that it is a 150 HP field conversion to low compression and 80/87 gas.
The 0-320 D1A is the same as the B1A (160 HP), except that it has 7/16" propeller bolts, a straight riser in the oil sump, a -32 carb, and Type 1 Dynafocal mounts. Whew!
The 0-320 E1A is the same as the A1A (150 HP) except that it has 7/16"" propeller bolts, a straight riser in the oil sump, a -32 carb, and Type 1 Dynafocal mounts.
There were no -F's made, so don't buy one. The only -F was an IO-320 F1A, in other words a fuel injected engine, a development from the -C1A engine.
Nor buy a 'G' for the same reason.
The 0-320 H1AD was a 160 HP engine, designed for 100 octane, had 9.00 : 1 compression, an integral accessory case, front mounted fuel pump, external mounted oil pump and an impulse coupled dual magneto.
When you inspect a list of these engines it appears that the numbers in the group after the first letter following the dash, e.g. A2A, refer to the propeller data, or the nose section. A '1' indicates constant speed propeller capability, a '2' indicates fixed pitch, and a '3' 7/16" prop bolts.
The last letter in the group of three gives details about the accessory section and riser tubes in the sumps; an `A' indicates a 'Z' shaped riser tube, a 'B' a straight riser as well as a -32 carb, and a 'C' Retard Breaker points. A 'D' can indicate conical mounts, different sumps and intake pipes, horizontal carburation, `Slick' mags and an assortment of other features. An 'F' indicates that the prop governor drive is on the left front crankcase, a 'G' has 0-320-A intake pipes, the 'H' is the same as the -E2D but has 'Bendix' mags, and finally the 'J' is the same as the E1F but with 'Slick' 4000 series mags. Are you with me.
Numbers after the last letter in the group of three give details about the Counterweights, and a letter after that number details about the magnetos. An "A" on the end of the engine serial number designates a "wide deck" engine, so check the serial number on the engine in addition to the model number.
Do you still want to just buy that engine over the phone without asking further questions about the model engine? Probably not.
Nor should you as a homebuilder say that the variations are unimportant because the engine is going on a homebuilt. You should not interchange parts, even though they may fit. Piper had problems with very early magneto failures on some installations. The cure ultimately was to go to a solid crankshaft, i.e. from an -A3A to an -A4A engine. Vibration, fatigue, thermal stresses etc. cause havoc. Engines are shaky things! (Excuse the pun.)
Also, remember that not all models manufactured by Lycoming were successful - i.e. maintenance free - some require the timing to be checked every 25 hours. The 0-320-H2AD engine was known for cam follower failures. Talk to a mechanic to get a feel for which models to avoid.
If you are hunting for an engine, best get the Lycoming guide to establish the details of a particular model, (Certificated Aircraft Engines, SSP-289, July 1989) and also find out for which airplane installation that dash number was originally meant. It may give you a clue what the engineers were addressing in choosing that particular dash number. Remember: it is not a question of will it run, but rather for how long will it run!