more hp for o-235c

have guestion about 235c originaly 100hp and 78 oct fuel,how can i change it for 100ll and more hp thanks for any info

100ll

put 100ll in your fuel tank and enjoy your flight..
you only need higher octane if your already running
high compression pistons.. I suppose you could put
higher compression pistons and get a little more hp..


Danny..

There are at least 3 different "Stock" compression ratios for the O-235. You've got the low compression, there is an 8.0:1 or 8.25:1, which will deliver up to 118 hp. There is also a higher compression piston set that will net 125 hp.

A piston swap may be all that is required, but I wouldn't bet on it. I'd guess a carb switch would be necessary and the 125 hp conversion requires an oil cooler on certified installations. The 118 hp version doesn't require an oil cooler, but my experience (Tomahawk) was that an oil cooler would have been a Good Thing in warm weather.

Power

For the relatively small difference in weight, and size, more power can be had with a 320.
Higher octane will not make more power. Octane numbers indicate resistance to detonation/pre ignition.
With modern electronics. compression ratios and octane number corrolation are no longer valid. One engine with 12.5:1 uses 87 octane. Many with 10:1 also use 87. the list is long.
T88
RV10
IO540 w/87 mogas

To gain more power out of any engine there are a few simple rules.

1) "There is no replacement for displacement"
2) Increase compression ratio, which allows you to take better advantage of the fuel burn. I once read there is actually less energy in higher octane fuel. It is just refined better to eliminate pre-ignition in high compression engines. One advantage to low compression engines is they can run regular unleaded auto gas. 87 Octane for me, thank you very much.
3) Think of your engine in terms of an air pump. The easier it is to get air in and out of an engine the better power it will make. (Example, replacing the stock air box on my 1.8L Miata with a mass flow air intake and K&N air filter gained just under 5% more power at the rear wheels, dyno proven.)
4) The "stock" Van's exhaust seems fairly good, probably better than what the O-235 originally lived with, so you probably won't see many gains there.
5) Electronic ignition would be good. Better spark timing and a hotter spark will help the flame propagate much better and will reduce the problem of plug fouling from 100LL and produce more power.
6) Fuel injection will help. Carbs are ok, but fuel injection will be better. You have two real options here, Ellison and the Aero-Carb. Both require a fuel return line, which will be no big deal. I seriously looked at the Aero-Carb and was all set to use one until I found the correct carb for my O-290-D2.
7) Forced induction! Very cool but building a turbo or super charger setup might be beyond what you want to do.

Now for the important question; why do you want more power?

If the answer is to go as fast as an O-320 powered plane, get the O-320. If the answer is because you have an O-235 that you would like to use and you want a little more power, do the things above, keep the plane light and clean, and you will have a great flier.

235

thank you guys the reason is have both engines o-290g and o-235 c and when i check the weight there is big difference around 20 pounds if i want go light i will chose the o-235 if i want go fast will go with o-290g ,both engine have from my instructor so will probably first check witch one is in better shape

Neither

Not sure if any one mentioned it, but parts for the O290 are expensive and not supported well or at all. The O235 also think suffers from the same low volumn deal, thus cost of parts are not as good of a deal. Easy to check out.

I wound not use high compression pistons above the stock 118HP in the O235. The STC for 125HP is pushing the detonation margin. Lyc stopped making the 125HP version for a reason. I have good reason for saying this. Lets just leave it at that. Of the two engines you list I would sell them to some Long EZ guys or other folks and get a O320. G

DON'T go with the O-290G. The O-290G is a conversion from a ground based GPU. It has machining done to the case, and much of the time the workmanship isn't all that great. I have TWO of these that my hanger mate has for his tailwind, and they are both troublesome. One because it has the wrong carb on it (try finding the right one... for less than 1K) and the other because it is missing some parts and they are a bear to find.

The other reason is that the O-235 can make as much power as the -290G, High comp pistons and EI. Now if you had a O-290 D or D2, that MIGHT be worth the hassle, but those are still unsupported engines (No lycoming parts).

gmcjetpilot said:

Not sure if any one mentioned it, but parts for the O290 are expensive and not supported well or at all.

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osxuser said:

Now if you had a O-290 D or D2, that MIGHT be worth the hassle, but those are still unsupported engines (No lycoming parts).

Click to expand...

Neither statement is 100% true. I have found that about 40% of the O-290 (-D2 in my case) are the same as those used in the O-235, 40% are the same as those used in the O-320 and about 20% are unique the O-290.

For example, the sump that you will need for the O-290-G is the same for all current production 4 cylinder Lycomings and the accessory case is the same as that used on the O-235. (I think the case you have is milled for the fuel pump.) The cam gear and plunger you will need to drive the fuel pump are standard O-320 parts and may be the same as those used on the few O-235's that had fuel pumps.

Unfortunately the big items are unique to the O-290; case, cylinders, and crank shaft, etc. Piston rings, OH gaskets, etc. are still readily available. Cylinders can be found but they won't be new. You can raise the compression by switching to helicopter pistons, which are still a current part. If you want new cylinders, the case can be milled to accept O-320 cylinders, crank, etc.)

The carburetor is the biggest challenge. I bought mine from an air boat builder in Florida. It was then sent out to be overhauled/yellow tagged. Yes it was expensive but not any more so than buying a new carburetor for an O-320. Actually, mine was less costly than buying a new one.

Look at this way, parts are available. Not all the parts may be new but they will be serviceable. Heck, they keep P-51's, Stearman?s, and T-6?s flying; when was the last time someone built new parts for one of those engines?

That said, if you have the choice, go with the O-235. I got a great deal on my O-290-D2 and I'm sure I will be very happy with it when I'm finished. If and when it is no longer servicable, I'll either build it into an O-320 or find another one.

235

those engines i have were free ,so i still have time decide if i want use one or no i cannot afford engine for 19000$ and more

The 235 will be a great starter engine, and if you want to upgrade later, it should be no big deal to bolt up a 320 or something.

235

thanks thats what i was thinking

osxuser said:

The 235 will be a great starter engine, and if you want to upgrade later, it should be no big deal to bolt up a 320 or something.

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Good point. Just remember, that to upgrade later will require a new engine mount, cowling, and exhaust.

The cowling and engine mount I have are unique to the smaller engines and my exhaust is for an O-320 but will be cut down to fit the O-290.

It can be done but those parts alone are almost $3000. Add to that a different prop, spinner, etc. and the price keeps going up.

Free engine equals a simple answer, go for it.

I helpd a friend buy a KIS Cruiser with an O-290-D2 last year. It had compression problems on the first annual (it's an older airplane, and he suspect it). He ended up doing a top-end overhaul. While the parts are availabe, he paid extra in time and money. He waited over three months to find the parts then another month to get them on/off the airplane. I didn't buy them, so I wont venture to say how much extra he paid, but he complained a lot about it.

Put all that aside, it's really just a hastle. Either a 235 or a 320 would simply be less pain.

-Bruce