The International Cessna^® 170 Association

Serviceable TCM IO-360 engines of a suitable dash number for the conversion are VERY difficult to find. I was very fortunate to find one for about $10,000 from Don George down in Florida. I had been looking for about two years. I paid $500 for a test stand run and inspection plus freight to CA. from FL.
It was a 50 hr. since TCM factory OH front engine out of a C-337 from Mexico and I traded him the 24V starter and generator(or alternator) for the C-337 rear engine mount. Tom Anderson gave me a discount on the $4,995 STC/Engine Mount package for the rear C-337 mount. I was going to retain the 12v C-170 electrical system anyway.
My first FP prop cost me $1,000 plus shipping from OK.to CA.
I later found a CS prop governor in a junk yard for $300, and boufgt a McCauley 82 in. CS prop for $2,500 plus shipping from SC. to CA.
The exhaust system built by Knisley cost me $1,500.
I found a Maule header tank and firewall SOV for $100 in a junk yard.
Throttle, Prop, and Mixture controls, return fuel check valve, fuel hose and fittings from Spruce, and on and on and on-----.

$$$$$$$$$$$$$$$$$--------- All It Takes is MONE. But, It sure makes a helluva nifty airplane!

Well after seeing an earlier post in this thread, I thought possibly I might have just had bad luck finding an engine for my XP (rather than paying the 34K bill) but maybe I'm not alone. Its a bit of a mugs game trying to find an engine in good shape, with time and at a price that makes sense. Having said that, the truth is I haven't found a single IO-360KB engine in years of looking. When I've called the wreckers, they just say " Yeah we will keep it on file" which I've interpreted to mean good luck buddy.
There is presently an add in Barnstormers for one but the owner has not replied to my inquiries and as well there's also a very good (IMO) ad for a pile of parts ($4500) with a good crank. All you have to do is build it...and maybe add a few parts which likely means 30K later plus the $4500.
So there's some hope and most would agree the mod would make a great airplane climb like nothing else. All I can say is I'm taking my hat off to those that presently are carrying the torch. They obviously have more Blueldr git-her-done attitude than I think I could muster.

I keep trying to think my way into doing this for a reasonable sum, but fail repeatedly. My AME tells me to just sell my plane and buy one with the engine I want, but I really like my plane and can't bear to part with it. And my 0-300 does 99% of what I need.

Getting back to the gentleman"s first post, I think if I was faced with his quandary, I might go Skoot's http://www.stootsaviation.com/Cessna_170___172.html
The conversion looks simple, straight forward and likely paperwork clean. Yes, you get ugly bumps. Yes, you end up with the shakes but if the mission needs more horsepower, then that's some of the " down the road" maintenance costs.
I'm just suggesting the Skoot's conversion but I really have no first hand experience. It would be interesting to find a member that has been down that road.

That Stoots set up is a nice looking deal,

How muh does it cost?

Lycoming four bangers shake like a dog trying to pass peach pits.

Has anybody had any experience putting 85 hp pistons in their 145 Continentals? I've heard that it raises the hp to around 170. Curious if anybody has anything to add as far as problems, longevity, etc.. I know that it's not legal....just saying....

Joe Moilanen wrote:Has anybody had any experience putting 85 hp pistons in their 145 Continentals? I've heard that it raises the hp to around 170. Curious if anybody has anything to add as far as problems, longevity, etc.. I know that it's not legal....just saying....

The first issue is that the piston needs to be modified so that it doesn't strike the cylinder at TDC. You need to make a 0.25"x45% chamfer on the top of the pistons.
The second issue is that you need to adjust the timming for the new compression ratios.
The third and certainly not the least is, none of this is approved for a certified airplane.

I can't find anything that states the actual gains from bumping the compression like this but it makes sense that the motor would be more efficient with 100LL.

If this provided such a measurable gain, I'd think that someone would have made an STC for it by now as it really is a simple mod.

Modified C85 pistons in an O-300 engine work just fine using stock ignition timing.
A slight increase in static runup RPM will be about the only indication of added horsepwer.

HP output is a direct result of RPM....regardless of any compression increases.
You can achieve the same thing with a lower-pitched prop...and stay legal too. (The downside will be slower cruise speeds...but the piston mod may force you to operate at lower RPM to remain within red-line at cruise...so you're back to square one ...illegally, in the latter scenario.)

The real fix is a variable pitch prop..and we all know what that means.... (Steal Dave Bengston's)

(I didn't notice a lot of gain with Dave's adjustable pitch prop, so I don't think it's worth the money/effort/trouble/mx.)

Bottom line: To gain significant performance gain.... requires significant money.

George,

1. The first line of your above comment is absolutely WRONG!
2. The three things that make horsepower are DISPLACEMENT, RPM, and BMEP.
3. All other things being unchanged, raising the compression raises the BMEP.

The more I read about BMEP, the less I believe that.

http://www.epi-eng.com/piston_engine_te ... dstick.htm
BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

BMEP is a more correct way to express a motor's power but it's a theoretical number not based on actual compression ratios.

Increasing the compression ratio allows the engine to develop the same amount of power for a given RPM with less fuel.
http://en.m.wikipedia.org/wiki/Compression_ratio

I can't find a source that states increasing compression increases power for a given RPM. Everything I read about compression talks about thermal efficiency and lower EGT.

Can someone cite a source that explains this?

Power equals torque times rotational velocity (RPM). Increase either or both and you've increased power.

Would you agee that increasing the compression ratio will increase the pressure on the piston head?
Would you also agree that increaseing the manifold pressure also increases the pressure on the piston head?
Now install a CS prop and set the rpm at any given amount. Now open the throttle and raise the manifold pressure. Does the working pressire on the piston head go up? And does the power power go up? Of course it does.
The three things that determine power in an internsal combustion engine are DISPLACEMENT, BMEP, and RPM.

bagarre wrote:The more I read about BMEP, the less I believe that.

http://www.epi-eng.com/piston_engine_te ... dstick.htm
BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

BMEP is a more correct way to express a motor's power but it's a theoretical number not based on actual compression ratios.

Increasing the compression ratio allows the engine to develop the same amount of power for a given RPM with less fuel.
http://en.m.wikipedia.org/wiki/Compression_ratio

I can't find a source that states increasing compression increases power for a given RPM. Everything I read about compression talks about thermal efficiency and lower EGT.

Can someone cite a source that explains this?

You are correct. I do not have a source to cite, but I did thoroughly research how compression ratios relate to horsepower (in automotive engines). What I remember finding were several articles on the WWW, and several "horsepower calculators". You plug in all the specifications of your engine, or one you intend to build. What I found is that bumping the stock compression ratio of a Chevy 283 from 8.2 to 9.8 only increased HP 2%.
The reason for the lower EGT is that the combustion event occurs more efficiently; faster, and more completely, reducing the amount of fuel continuing to burn and exiting the exhaust valve after the power stroke. I had to replace the original 160 degree thermostat with a 192 to get the heater to work good. I'm not an engine guy, these are my personal observations, and during a very brief period of research. We still have the engine. It's now installed in a 1982 1/2 ton Chevy 2wd pickup. It gets 23 mpg. Better than any of the late model V-8's we have. As for power, it has plenty pulling itself down the road. Hook it up to a trailer and it won't pull a greasy string out of a cats azz, but I can say the same about my Chevy 5.3 1/2 ton

blueldr wrote:George,

1. The first line of your above comment is absolutely WRONG!
....

My comment was predicated upon the C145/O300 engines installed in our airplanes (since we were only considering a piston changeout.)
This engine's output is measured based upon the RPM generated. Now, having said that, it is certainly possible to increase RPM by improving the efficiency of this engine....but that will provide an increase primarily because it may provide slightly higher RPM.... at least that is how it will manifest itself.... and THAT is why more HP might result.

You can do it a lot cheaper ...and legally...with a prop change.