Engine choice-190 or 200 hp for 8a

My new Superior io-382 is scheduled for Sept. delivery for my rv-8a. The 190 hp version is warrantied for low lead. The 200hp uses 100LL only. Where I live, l premium gas without ethanol is available at regular gas stations.

I'll be running a constant speed Whirlwind 74rv prop. The prop calls for a minimum 200 hp but Whirlwind advises that it should be fine with 190.

I'm trying to decide between the two versions.
Shortish fun flights with the fun of takeoff is my primary use. Occasional long cruises. I'm skipping the 3 blade prop this time around although I loved the acceleration.

So, my question is, how much would I be giving up by going with an engine rated at 190 hp vs 200 hp for an rv-8a?

I am assuming a CR difference between the two, so the extra fuel burn per HP from the lower CR 190HP is going to affect range.

Go for the HP

Where are the specs for these?

Not enough info available. If I were you, I'd go with the unleaded option - *if* I had a reliable supply of non-EPA/ADM contaminated gasoline. The hassle would be worth the cost savings. 10 hp will not be missed. Especially if you've never had it.

This is a personal decision as much as performance, imo.

Engine choice

If you were talking about the heavy angle valve I0360, I'd advise the lighter engine. But since weight is not a factor......In the words of Tim the tool time Taylor,......More Power! That said, experience has taught me that 9 to 1 compression ratio is as much as you should go. After that, it's more cubic inches.

Specs on the io-382 aren't available yet. Will be on display at Oshkosh. Info is from discussion with Aerosport.
8.3 cr for 190hp. 9.0 cr for 200hp.

Lots of upsides to no-lead fuel. Minimal to no plug fouling, potentially lower egt's (more of the fuel burns in the combustion chamber), oil stays cleaner longer, slightly higher energy content, etc, not to mention better 'PR' with the non-flying 99.6%.

Charlie

The XP-382 spec sheet is posted here.

http://www.vansairforce.com/community/showthread.php?t=111501

tomhanaway said:

Specs on the io-382 aren't available yet. Will be on display at Oshkosh. Info is from discussion with Aerosport.
8.3 cr for 190hp. 9.0 cr for 200hp.

Click to expand...

Since an 8A has the extra weight of a nosegear up front, I'd rather have a 190-something HP parallel valve engine to help save some weight up front over a heavier angle valve engine. Just a personal preference, but my friend's RV-8 with a 192hp parallel valve ECI Titan IO-360 sure is a well-balanced delight to fly.

Engine choice

You didn't say for sure if parallel vs angle valve was in the mix but i suspect it is. After working on these engines for years my feeling is that with all other factors being equal the parallel valve motors have the edge on reliability and longevity. On the other hand if you'll never put more than 800-1000 hrs on a fresh engine (especially if it has real Lycoming cylinders) and you don't mind some added wt and cost go for it. 10 more HP won't change your life either way but it will climb better and probably use less fuel. YMMV

Don B

RV- 9. Rebiuld in Progress

Additional info,
The io-382 is a parallel valve engine. Based on the 360. HP difference is solely from the piston compression.
Latest hp numbers from Superior dropped 5hp for the lower compression their S&F flyer. Either rating will have a counter balanced crank.

I'd go with the mogas-compatible engine, and I'd go further by ensuring that the fuel system is ethanol-compatible and minimizes vapor lock potential. You need not burn E-gas, but it sure would be nice to have the capability there if you need or want it later.

IMVHO, the double-digit cost savings per flight hour (even leaving the no-fouling benefits aside) far outweigh the loss of 10 hp and a knot or three in cruise. And should 100LL be discontinued, or replaced with an even more expensive alternative, the mogas-capable engine would leave you even better off. I'm still years from flying, but at current prices and with my projected average use, that cost differential should pretty much cover local hangar rent every month. Those dollars add up...

Notes below in red

rv7charlie said:

Lots of upsides to no-lead fuel.Yes Minimal to no plug foulingyes, potentially lower egt's (more of the fuel burns in the combustion chamber) No, see notes below, oil stays cleaner longer Yes and maybe a Mobil 1 could be used again!, slightly higher energy content See Notes below, etc, not to mention better 'PR' with the non-flying 99.6% ABSOLUTELY!!!.

Charlie

Click to expand...

Notes:
1. EGT is a function of the expansion of the gases and this is from the CR and the latency of the fuel (all other things being equal. A suitable UL avgas such as G100UL will have an EGT ever so slightly higher and so far all the test pilots can't pick it and even then only just pick it in data when it is pointed out to them. So it is not noticeable. Some notable UL options have a much higher EGT and this is a bad thing for the Turbo guys. Rules them out altogether.

2. Energy content? Well no, this is one funny thing, the overall variation in all fuels over the last 100 years has been +/-2% at the max. G100UL for example is marginally less BTU's but is denser so the end result is you do get less per pound but more per gallon. Oddly enough 2%

Hope this helps!

RV10inOz said:

Notes below in red



Notes:
1. EGT is a function of the expansion of the gases and this is from the CR and the latency of the fuel (all other things being equal. A suitable UL avgas such as G100UL will have an EGT ever so slightly higher and so far all the test pilots can't pick it and even then only just pick it in data when it is pointed out to them. So it is not noticeable. Some notable UL options have a much higher EGT and this is a bad thing for the Turbo guys. Rules them out altogether.

2. Energy content? Well no, this is one funny thing, the overall variation in all fuels over the last 100 years has been +/-2% at the max. G100UL for example is marginally less BTU's but is denser so the end result is you do get less per pound but more per gallon. Oddly enough 2%

Hope this helps!

Click to expand...

Aren't those points comparing apples & oranges? I was trying to compare typical 100LL to typical USA-based no-alcohol auto fuel, since characteristics of certified unleaded avgas is just speculation at this point. If he was looking at a direct 100LL replacement no-lead, then there'd be no need to worry about which engine to buy.

In general, don't octane enhancers displace energy producers in fuel? I suppose that you could make a case for the extra energy content driving higher combustion temps, which might drive higher egts. But I think that most mogas users here in the USA have seen higher CHTs and lower EGTs when running mogas vs 100LL.

Charlie
Never even played a chemist on TV, but I do run mogas in a Lyc

Scientific pontification aside the chosen prop wants 200hp+ (Whirlwind told me more like 210+). It was specifically built for that purpose. If you wanted under 200hp, why not go with the 200RV prop which is built specifically for that power? With the 74Rv being a prop built for high power, high speed...I have to wonder if you haven't purchased the wrong prop considering your stated mission is short hops. I have a 74RV and love it, but wouldn't have given up the ground clearance or weight penalty (it's 2" longer than the 200rv and heavier) if my engine wasn't perfect for that prop and my intended mission matches the design intent (high speed cruise). If you already have a 74rv, get the engine for it. Just my opinion.

As for the never ending debate about 100LL disappearing....do a google search. If you read a post from a decade ago, it will read exactly the same as today's. The sky is falling...oh dear lord. You can change your pistons in a weekend, why spend so much time being afraid of that? Get the extra power...and use it. That's my .02

I am with Bill, go the extra CR, it has all the benefits of HP and the better range.

Charlie,

You did not specify, you just said "no lead fuel", neither an UL Avgas or Mogas. And your suggestion was a lower EGT was a good thing, when in fact it is not, and mostly it does not matter in itself, but the other factors that it is attached to might be good or bad. Confusing just to type that

Yes on ordinary car gas the CHT is higher and the EGT lower, and that is due to the latency of the fuel being less. Oddly enough there is nothing better about that scenario and actually it is the opposite unless you adjust other things for it, like spark timing, and retard it.

Did that help?

The one time I tried to use autogas in my -8, it vapor locked. The engines run pretty hot under that tight cowl. I've never had a problem with AvGas. I'm sure somebody will say that they use it all the time with no problems but it didn't work for me. I never tried it again. Another thing HP=Heat. Two cents.......

Steve, you are quite right. Except that HP does not directly equate to heat. But lets say that is near enough for now. You can generate the same HP but with vastly different CHT's under the same conditions.

When selecting an engine for our aircraft I went through a decision-making matrix of the options available for our aircraft type. Those options included O- and IO-360 at 180hp, IO-360 at 200hp, and IO-390 at 210hp. After years of successfully flying with mogas and running the numbers, I could not justify losing the ability to burn mogas, so my default selection was the O-360-A1F6 counterweighted crankshaft engine. We lucked into a partially-completed kit which came with a factory-new certified Lycoming O-360-A1F6.

Now, several years later (and still building) I don't regret one little bit having purchased this engine. The most I've paid for 91 octane, ethanol-free premium mogas so far is CAD$1.50/litre (about USD$5.10/US gallon) while our on-field 100LL sells for CAD$2.05/litre (about USD$6.97/US gallon). At a savings of about $18/hour, I can't justify not being able to burn mogas. I also like having the ability to land at an airport, and, after discovering they're out of fuel, drive into town and pick up a few jerry cans of mogas in order to be able to safely return home. Mogas = flexibility in this part of the world.

We RV Builders & Fliers are so spoiled!

We are wondering about the significance of 10 HP here.

Did we forget that there are a number of four place airplanes flying around with 145 HP engines? (Early 172's, for example.)

Stuffing a 190 HP or 210 HP or 160 HP engine in a light aircraft, such as our RV's, reducing the number of seats by 50%, and reducing the frontal area significantly still produces a screaming airplane.

The only time you are going to miss that extra 10 HP is when racing against another plane with a more powerful engine. Even then, if you went with the 200 HP, you could end up next to Kahuna and his 260 HP Super-8, and he could end up next to a Rocket.

Go with the flexibility of the 190 HP, you won't miss the extra HP. Besides, you can make up that HP with dual electronic ignition.

(This coming from a guy who put a 180+ HP O-360 in his -9.)