IO-360 -> Maximum safe HP?

A forum to discuss the installation and maintenance of the O-320, O-360, & O-540 engines and their variants.
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N200PF
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IO-360 -> Maximum safe HP?

Post by N200PF »

I have been looking in to who will provide the power-plant for our RV-7 (I know it's early but we're budgeting...) and we're interested in the most HP for the least amount of weight. In our search, we're learning that there are some AMAZING things that can be done today where you can have a new IO-360 built and have it dyno around 230 to 235 HP.

The last company I spoke to said there will be very little additional maintenance involved with this and says it more about the 10:1 pistons, (which I don't understand yet) how carefully the engine is balanced and built and the Ti roller tappets etc. They specialize in high performance engines and have some famous clients but I don't know if I'm getting myself in to a situation where I have to be an A&P for 2 hours for every hour of flight or if we can just fly it if we take care of it with regular maintenance.

Any thoughts on this? What are the down sides of this type of performance? ...or how the "High Comp" pistons actually help? Mahlon?

- Peter
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Post by captain_john »

Two facts of (engine) life that I have learned during my tenure in tinkering.

1) The flame which burns twice as bright, only burns half as long.

2) There is no replacement for displacement.

Now, I am new to aviation engines, but whenever I got an engine up to it's maximum potential "power-wise"... it became fickle and tempermental.

Also, the only way to get RELIABLE power was to make a BIG ENGINE! An engine is an air pump. Suck, squeze, bang, blow... do it all over again.

The more air you move through it, the more power (combined horsepower and torque) comes out of the crankshaft.

How does everyone else's life experiences add up?

:roll: CJ
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N200PF
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Post by N200PF »

CJ -

Your fear is the same as mine which is why I'm asking! They have the IO-390 dyno out consistantly at 255 to 260! :o

They also said you don't have to use it at full power all the time! ...just at altitude and on climb out.

- Peter
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Post by captain_john »

Yup... you see my point.

I am in no way looking for THAT kinda hoss. The advertised and honest 200 hosses in a low compression, long endurance, heavy breathing, torque monster is what I am looking at/for.

All that at under $15,000 and we got a deal!

:bow: CJ
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Post by cjensen »

I'm sure you've thought of this, I know I have, but Vans max power RECOMMENDATION for the -7 is 200. That being said, the IO-390 or IO-400 will put out about 210, which isn't too terribly much more than they say. But getting in to 230-250 on to the -7 may be stretching the envelope a bit.

The differing compressions come from different length pistons. They way I understand it (and this may be completely wrong--Mahlon??), is that the longer piston creates a higher compression due to the same amount of air being brought in and squeezed a little tighter-more power.

I do like the 390 and 400, but with that comes a weight penalty. More cubes typically equals more weight. I wouldn't be suprised to see similar numbers from an IO-390 powered -7 and and IOX-340 powered -7. :dunno: Of course, like CJ pointed out, the smaller engine producing more power may equal less time before work is needed (LTBWIN). :mrgreen:
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Post by captain_john »

Chad, au contraire'...

These engines are on a very similar block as the 360 (as you probably already know) and this means they will weigh about the same. More cubes means a larger hole where the piston goes back and forth in! They are putting more pi$$ in the piston!

:lol:

Anywhooooo, any ideas as to WHY the plane is rated at 200? I did run iit past the guys in the Van's booth while out at OSH and got some interesting replies. None of which compelled me to disregard the big bore design.

...and I was under the impression the higher compression was earned with the piston RINGS ability to hold the pressure in the chamber.

When you increase displacement from lengthening STROKE, it is an entirely different situation than increasing BORE, like these designs.

:) CJ
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Post by Wicked Stick »

I used to have a 160 hp O-320 in my grumman that used to run great at near redline. It was very smooth too.

The 160 in my RV-4 seems to be the smoothest at around 2,450 rpm.

I guess it all depends on how well the engine is built, balanced, and flown.
I think the key is to balance everything as much as possible, make sure it's flown regularly, and leaned properly.

I think making TBO on the bottom end is much easier than expecting the top end (cylinders) to make TBO. I don't see that happening much, but then again it is an air cooled cylinder.
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Post by cjensen »

Well, the compression ratings on the bigger bore engines may be different than dropping a set higher (or lower) pistons in a 320 or 360. I'm sure when Mahlon sees this thread he will straighten this out.

The weight issue does hold true to an extent. A bigger bore means more piston to fill that hole, and more piston means more weight. It's probably not much, but I can't see it being the same or similar. It is the exact same block as the 360, bigger jugs. We all like bigger jugs right? :lol:

The reasoning behind the 200hp limit that I've been told is because more hp was causing the airframes to get to Vne too easily...
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Post by cjensen »

One huge draw for me on the big bore engines is the lower compression, and the ability to run on 91 Octane. Avgas is supposed to be around for quite some time, but it won't be here forever, and the longer it's here and still produced in the small amounts, the price will continue to rise pricing me out of the flying market. I have to find somthing that will have the ability to outlive avgas, and the price of said product. That's why I've been considering an auto conversion, and the big bore engines. I love the idea of the IOX-340, but with the requirment of avgas, it will probably be out of the running for me...
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Post by captain_john »

Yup, Vne and flutter.

They of course haven't tested this scenario, but there are the Super 7's and 8's running around out there and some REAL heavy breathing IO-360's pushing some crazy HP's!

These guys routinely push the limits and sometimes exceed them, I am sure. I don't want to do that.

Now, I aren't a en-ganear... nor a "real" mechanic, but I did stay at a Holiday Inn once this past year.

The additional metal in the top end doesn't add up to much. I hear it is about an 8 pound gain. A good trade for reliable power if you ask me.

I am looking forward to seeing these engines put into use!

:) CJ
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Post by cjensen »

Me too CJ! I'm toying with the idea of a 390 or 400 more and more these days.
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Post by captain_john »

Chad, cool... As much as I would like an alternative, I am not sure it exists yet. The Mogas thing has me wrapped around an axle too!

Peter, Hot thread!!!

Good call!

:) CJ
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Post by cjensen »

No kiddin'!!! My wife isn't here, and I'm typing on the computer rather than working on fuel tanks! What am I thinking!!?? I gotta get out to the garage! You guys are great, really, but I gotta get some work done! :lol:
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Post by N200PF »

GOOD STUFF GUYS! Sorry to cut in to your build time tonight Chad! :mrgreen: Great discussions!

This all started as I was dead set on the IO-390 and the 210 HP mark. Then Dick Martin said if it's put together right it should Dyno at 215. COOL. Then this place said the 360 built right will be 230...then he said why not a 390 built the same way to give you 260... :bang: ENOUGH!!! I want to be able to buy food next year too!

Chad and CJ, I don't know a thing about compression or how it relates to longevity but the idea of building up an IO- 390 to make a solid 210 to 215 will be MORE than enough juice to get me far enough in to the yellow arc to be happy buy not so far that I'm puckering. Vne just plain scares me in anything I fly. I leave the playground above 200 Kts to the daredevils out there.

- Peter
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Post by cjensen »

Not a problem Peter! I love the info sharing we do here as much as anything, and this IS a part of my build, so no worries PF!

CJ and I talked on the land line tonight about running the 390 or 400 de-rated using a self imposed RPM restriction. The rest is for emercengies. Run the 200 hosses at a lower RPM, extend engine life, burn less fuel, and things are quieter! How can you go wrong! :thumbsup:
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Post by Lorin Dueck »

Guys -
I'm all for performance.. and this is not to be negative -> but don't forget that power output also equals heat rejection from your engine.
I've not looked into it ... but my gut tells me no sense having all that power if you can't keep your CHT/EGT under limits....
Custom cowls & exotic plenums probably start to play in here somewhere.....
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Post by Maxwell007 »

I'm new here....been "lurking" for some time and took my $30K demo ride last week at Van's so I thought it now appropriate to join the group. I'm gonna' do this!! That RV-7A was a hoot!
Anyway, I have an extensive automotive background and have built many, many engines both stock and racing so I thought I'd add my two cents worth to this horsepower issue.
First of all the compression ratio is just that...a ratio. It is the ratio of the volume of the cylinder filled with air when the piston is at the bottom of the stroke (at the bottom of the cylinder) vs. the the volume when the piston is at TDC (top dead center). You can get a higher ratio by either increasing the volume at BDC (bottom dead center) or decreasing the volume at TDC. The former is usually done by going to a longer stroke. The latter is done by making the combustion chamber area smaller, usually by putting some kind of a dome on the top of the piston. This dome fills up the combustion chamber with metal causing the air to squeeze further, thus increasing the compression ratio. While this usually increases power it also causes other problems.
High compression engines are more prone to detonation, more sensitive to timing, mixture control and ambient air temperatures and are sometimes tempermental when it comes to starting them.
I know that this is long winded for my first post but I thought it might help to shed a little light on the issue. I hope I didn't ramble too much.

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Post by Lorin Dueck »

Max (if I may be so bold)...
Welcome, and glad to have you with us!! :yay:
Stay awhile.. listen ... and post.
We can all learn from each other. :)
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Post by captain_john »

Lorin, I see cooling as an achievable task. Especially in a low compression engine. Although SLIGHTLY larger on the exterior, baffling should be typically similar.

Max, Welcome!

What you say brings me back to my initial 2 laws of performance. I am always in favor of a nice, solid conservative buildup!

:) CJ
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Post by Spike »

Baffling might be similar CJ but thermal output of the engine will not be if its producing more power. The question is will you have sufficient airflow to cope?

As for why Van's doesn't want more than 200HP, thats because you are much more likely to approach Vne with altitude. Van's had a good article, actually a few, about this very thing in their RVator. Vne is measured in true airspeed, not indicated airspeed. Remember, the AI is just an airpressure differental gauge , not a true airspeed gauge. This is like coffin corner, where the higher you go, the closer your stall speed in true airspeed gets to Vne.

Me, Im going with just a lowly 160HP FP in my 9. Im not ashamed, Ill arrive 10 minutes after you do with a smaller fuel bill. Well, that is if you don't have to stop for gas enroute, then Ill get there first :)
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