O-320 how do we decide which engine model?

I'm building an RV9A for long distance cruising and have access to auto gas at the hangar. The IO-320 or the O-320 seems to be the logical choice with low compression pistons so we can use auto gas. For 20 cents more per gallon, I'd use premium auto gas if I can get 160hp versus 150.

There are a variety of versions of these 320 engines and I was curious if folks could steer us straight concerning the model numbers I read about.

Second, in auto engines, I've used hypereutectic pistons for better sealing, emissions and economy. Does that apply to Lycoming too?

Any guidance would be appreciated.

First, this should probably be in the 'Engines' section of the forum.

But other than that, i'll try to answer your questions. The O-320 is the highest power engine that Van's suggests using in the -9A, therefore, it is always the logical choice. A few people are putting O-235 or O-290's in, but with the higher overhaul costs of both of these, they don't make sense in the long run, and the O-320's are plentiful on the market.

The one engine you probably want to stay away from is the O-320H2AD. This engine was a 160HP, single mag drive engine used in the 1977-1981 ish 172N's. These engines, while decent performers now, don't have much in common with the rest of the O-320 series, therefore they cost more to overhaul, have a dual-mag off one drive (which is also pricy to overhaul) and generally have more reliablity problems than the other O-320's. They are relitively plentiful on the market, and are pretty cheap for a run-out one however.

When choosing an engine, you really have to decide what you want ahead of time. If your looking for value, you might want to consider a vertical induction carburated O-320, if your looking for better performance, a fwd facing induction with Fuel Injection might be what you want. Since you could be running Mogas sometimes, it's probable that you would want a carbed engine, with lower compression ratios. This leads me to say that an O-320E2D would be ideal. These were used on pre-1977 172's, are rated at 150HP, and can run on Mogas with no problem.

Lycoming has a PDF that explains the differences between all the engine designators, unfortunitly, it's not really intuitive to use. But can be viewed here:
http://www.lycoming.textron.com/main.jsp?bodyPage=/support/publications/keyReprints/maintenance/modelCode.html
and here:
http://www.lycoming.textron.com/productSales/engineSpecifications/SSP204.pdf
if those help at all.
In Lycoming's, it is my opinion that the tolerances are so loose anyway, because they are aircooled, that piston coatings won't make a big difference, but others here might think differently. I feel that putting on plain steel cylinders (like Superiors) will seal up really well, and be effiencent and reliable throughout their lifetime.

My 2?

Which Lycoming 320 model to use?

Thanks for the links and info Stephen. Another friend sent this suggestion.

Whaddya think?

One option I was thinking about is a low compression, FP prop, IO-360. I am considering buying a new engine from Mattituck or PennYan so the cost and weight are not much different. As for the issue of too much HP I don't think that is an issue. The 7:1 compression 360 produces 170 HP at 2700 rpm. A FP (cruise) prop won't turn 2700 rpm. I haven't worked the numbers but this set-up should be ~160 hp at WOT. Also I like fuel injection so I can run LOP.

Good suggestion in my view. The IO-360 is the smallest engine I heard of running LOP operations. Running a heavily cruise pitched prop should allow all the benefits of the CS on TO (Running about 2400RPM is 160HP) and allow you to keep that HP up a little higher. Many people have install this type of engine with positive results. You'll probably want to consider that with FI this engine will probably weigh a bit more than a 320, perhaps 15-20 LB's but the FP prop would make up for quite a bit of that.

I would also tend to recommend horizontal induction if your going to go to FI, more because the cowl looks a lot nicer with the filter coming off the fwd baffle and no induction holes in it. Kinda like Dan's.

What you would want to do if you did this is make sure to restrict all your power settings to 160HP, not necessarily because the airframe won't take more power, but because if you ever sell it, your operation procedures (which YOU as the manufactor should define before phase 1 is done with) won't allow them to run at powersettings of more than 160HP. This allows you to say you stayed within the kit designers recommendations if someone ever sues you.

Auto Gas, don't worry about compression

MrNomad said:

I'm building an RV9A for long distance cruising and have access to auto gas at the hangar. The IO-320 or the O-320 seems to be the logical choice with low compression pistons so we can use auto gas. For 20 cents more per gallon, I'd use premium auto gas if I can get 160hp versus 150.

Click to expand...

Sorry if I don't give you an exact model number of a 320 Lyc to use but you mention Mogas or Auto gas as some kind of criteria I would like to address.

Auto gas is not widely available at every airport, and in some regions may cost as much as 100LL or MORE! Check it out. Do a cost survey country wide of 100LL, 87-Mogas.

A 160HP which needs a min of 91 octane is not suitable for 87 octane Mogas you can get at the airport. Also electronic ignition and the high flow intake and exhaust? Probably a bad idea to use low octane auto gas at all.

I don't know where you are going to by "premium" Mogas? I guess you can go to the local gas station and tanker it to your hanger, provided it does not have alcohol or Ethanol in it.

If you decide you want to use car gas or Mogas, I believe you should use than use low compression 150HP engine. That is the only way you can expect to get any "mileage" out of Mogas when you can buy it. However I can't emphasise how little the price differnce really is. In the big scheme of things it's peanuts. If all you did is local flying it would make sense, but you said you want to cross country as you main flying.

The economics may be different if you already have your own storage tank and have a truck or some way to tanker fuel already. However that is only for local flying and most do not have the equipment to transport and store fuel, which both have safety implications in itself.

The 160HP needs 91 octane minimum. The hole issue is a little convoluted and the article I linked to at the bottom of this post talks to the subject fairly well. After reading the article you will know why I think RV's in general are not good candidates for auto-gas and the 160HP is just worse. I suppose purchase of premium will help. Where are you going to get that on a cross country.

http://www.webworksltd.com/autofuelstc/pa/faq.html (read the 1st question)


Also in general auto gas in a tightly cowled airplane's like a RV may be a bad combo. Auto gas can cause seal problems and vapor lock. Some RV'ers I have heard run auto gas in one tank and Avgas in the other tank, for takeoff and landing, because they has LOSS OF POWER ON TAKEOFF with the Mogas Look, if the gas is not good for t/o and ldg, than I don't want to use it at all. I just think its false economy with hassle and risk. You need to really look into it. Mogas STC's my work in a C182 or C150, but a RV?

The Mooney and Comanche also have tight cowls and do not have Mogas STC approval. Why? http://www.webworksltd.com/autofuelstc/pa/faq.html ( read the 4th question! )

In RV's in general it's my opinion its a bad idea overall. Feel fee to debate me. Again I am no expert, I just see very limited use in a "HOT" hombuilt like a RV.

You say you have auto gas in your hanger, but that does little good on a cross country. You will not be buying much Mogas on a cross country. You will take what ever is at the airport. Most of the time it will be 100LL ONLY. Some times I have seen Mogas cost more then the 100LL. Why I don't know. Some say then why have Mogas at all than. Why indeed, but don't forget there are some real low compressions engines certified to run on 80/87 octane and don't run well on 100LL.

Availability of suitable gas from an auto gas station without additives is getting harder from what I hear. Alcohol in the gas is a no-no. Ethanol, forget it, that's also a common additive and a no-no.

Just from a price stand point at today's prices the savings you think you will get is questionable from my analysis, not to mention safety, the real issue. I can't tell you how many auto gas users have reported problems in their RV's.

It sounds like you have lots of money and are going to buy a new engine, than go with a new 160HP (carb or FI). Since you are going to be cruising a lot than FI may pay for itself. However a O320 Carb setup is cheap and reliable, but if you live in a wet climate or fly IFR a lot, FI is better since it's not subject to Carb ice. Of course FI cost a lot more; it's not only the cost of the engine but the installation which is about $1000 more due to expensive fuel pumps. However if you are like most and looking for a bargain in the form of a used engine, O320 150HP is still a great choice, especially in a RV-9A and if the price is right.

The big question is will WE have gas at all or at a reasonable price. I have a O360 with stock compression and intentionally kept it that way when I rebuilt it for several reasons, but Mogas use was not in mind. If you know how they distill gas and get the octane rating, I don't think it will be a matter of high octane availability, but it may be an issue of getting gas at all.

Regardless 100LL will be around for some time to come because large aircraft needed it. However there is pressure to "get the lead" out. Clearly lead boosts octane. There are other ways to get octane but lead is cheapest. The cost of gas now a days is from the basic crude barrel prices not the processing. Also Federal and State Tax add a big part of the cost. Processing from barrel to pump and additives are really a bargain.

It's unlikely 100LL will be phased out anytime soon. In Europe they now have 91 octane no lead Avgas, which could be the future for some of us. However when it comes to extream high compression engines (hot rod engines with real high comp pistons), they may be out of luck if 100LL goes away. I still would not buy a 150HP engine over a 160HP engine on this basis 100LL might go away.

Here is one Auto gas article:
http://www.eaa.org/education/fuel/autogaspart2.pdf

George

George....

What RV do you fly? And by the way, have you seen the new rules that you need to add to your signature, who/what and where you are? Just curious.