Performance Flowmatch Cylinders

[MontanaBird]

I have a '56 170B with the O-300, probably 300 SMOH. I think it's clearly the perfect plane. But, is it possible to make it even more perfect by getting (some) percentage of xtra hp from flowmatching the cylinders?

I perhaps should have done this when I o'hauled the engine; oh well.

But if anyone does have experience with the pre/post flowmatch differences in performance I would greatly appreciate hearing from them.

Thnx!

MontanaBird

[HA]

you could dump some $$ into flowing the cylinders but it won't fix the very imbalanced intake system and low-budget exhaust system, so IMHO you'd be wasting your moola. if you want more power maybe you could hang a Seneca turbo on there, now that would be a cool experiment! the brute force method

[blueldr]

It's pretty darn dificult to make a silk purse out on an O-300.

[GAHorn]

There are a lot of companies who've taken a lot of money from owners after convincing them that flowmatching, porting/polishing, exhaust-tuning, "blue-printing", and painting their engines pretty colors makes more horsepower.
(And the fact is that even if you did those mods..... the proof they worked would be more fuel burned and more heat generated.... two things you do not want or need in your airplane.)
While NASCAR might in those race-car engines... it is a waste of money on most aircraft engines, and a violation of the engine mfr's rebuild instructions which is based upon proven (and approved) data.

To make more horsepower with a fixed-pitch propped engine.... you must increase RPM. The simplest and legal way to do that is re-pitch your prop or go to a variable-pitch prop. (The more complicated and expensive way to do it is thru turbo-charging/normalizing, but I don't know anyone who does that on this installation.)

[davevramp]

Performance in any application may defined by power were you want it. 0-300 and c145 are limited by rpm, red line. Making ports bigger slows down the speed of the incoming charge and may not fill the cylinder as well as a stock port if the rpm does not increase.. Taking out any casting flash would be an improvement. But bigger ports are not always better when limited by rpm. Newer castings are so much better that the old ones.

The intake track looks like a good and economical place to start looking for improvements. Is there a flow balance data on the intake runners of manifolds? The exhaust mufflers could be another place to look for increase in flow by lowing resistance. Why did Cessna go from 5 inch to 6 inches cans on the 172? Does anyone have a drawing or picture on the internals of the muffler? There are a few camshafts available for the o-300. Which one is the best for our application? Any specifications available? Information like this could be put into a program and come up with theoretical improvements and show weak area to make improvements. This could be a good topic of discussion. I believe that someone has profiled this engine group and this data should be available some were. But I have not found it, yet.

[GAHorn]

...Why did Cessna go from 5 inch to 6 inches cans on the 172? ....

Improved cabin and carb heat. (The real purpose of the "mufflers" is not to reduce sound such as in automobiles,... it's to extract heat. Think of them as heat-exchangers. For that reason (and a few others) is why "tuned" exhausts are ridiculous money-burners in aircraft.)

[blueldr]

I know a guy who spent a small fortune having a "Donkey Dick" exhaust installed and approved on his C-170B with a Lycoming O-360. He is convinced it gives him a tremedous horsepower incease.
If I had spent that much money on an exhaust system, I would convince myself the same way, even if only to keep from crying myself to sleep every night.

[minton]

I agree with BL and Horn. You are shoveling good money at a bad idea. If your insurance company, the FUZZ and the manufactures' get hold of this issue someday it's going to get ugly. When you make more horsepower within a FAA cerified engine without express written premission (STC) and that STC must authorize "MORE" horsepower output you are flirting with a hornets nest full of grief.

[Showboatsix]

For God's sake......... you have 7 to 1 compression ratio, NOTHING will help the c-145/ 0300 make power.

At best it only makes 130 -135 HP at take off and cruise, it only makes 145 @2700, if it will rev that high.

[Jimmy M.]

we've had good luck with 9 to 1 pistons from Lycon......makes about 160 hp.
Engine life of may be questionable........and of course these are NOT certified.
( but a person could always sneek them in )

This should open a whole can of worms .......right george ??

[GAHorn]

we've had good luck with 9 to 1 pistons from Lycon......makes about 160 hp.
Engine life of may be questionable........and of course these are NOT certified.
( but a person could always sneek them in )

This should open a whole can of worms .......right george ??

There are those who have proclaimed installing C-85 pistons in the O-200/300 engines raise compressions significantly and make more horsepower. I've never seen that mod or operated it and, of course, it's not legal for certificated airplanes, but it makes one wonder .... if it's so good and safe....then why has no one STC'd it? (or at least obtained a one-time approval for their own airplane?)
You cannot change one component significantly without changing the reliability of the whole machine.
This subject is so encompassing that it is beyond the scope of our ability to discuss it accurately in an online forum, but I recommend that anyone interested in the subject, read Chap. 3 of the Sky Ranch Engineering Manual where porting/polishing is cussed and discussed at length. One cannot simply polish the ports of cylinders and expect to significantly overcome the turbulence and wildly-variable affects of this engine's carburetor air-box and associated plumbing. Nor can one expect polishing to improve fuel atomization, which depends upon turbulence in the intakes. (The early C-90 engines had polished intake ports, which was discovered to counteract necessary "swirl" of the fuel-atomization and actually REDUCE volumetric efficiency of the engine. Continental stopped porting/polishing subsequent to that discovery.)

[Jimmy M.]

I tried the C-85 piston route but didn't like it because you have to relieve the bottom of the skirt to clear the opposing connecting rod bolt. Pistons available from Lycon fit better and are stronger.
This was on a C-85 to O-200 conversion I did a few years ago.( it did go up almost 300 static rpm with
the same prop )That engine is still running and happy at 400 plus hours.
A friend of mine did the same conversion and is at 600 hours and using about a quart in 6 hrs
You need an oil cooler 'cause you're making more heat, you're baffles have to be really good

Two more guys up here have gone 9 to 1 pistons in O-300 with marked power increase. and no problem so far( couple hundred hours each )...........porting etc does very little and is pricey........lots of labour.

We are all on floats, and with a gazillion lakes in the area we almost always have a place to land.......
THESE AIRPLANES ARE NOT CERTIFIED

I'm not suggesting anyone try this.......I'm just saying I know it works
And I'm certainly not looking to get into a pissing match with anyone.

The best way to improve performance in these aircraft is to install a bigger engine......360 Lyc, 360 Cont, etc
I fly a homebuilt and a Cessna......both Lycoming powered


Do you have any idea how long it took me to type this ..with one finger ???

[ghostflyer]

When I had a Continental o-300 in my 170A ,We modified it with 4 inch mufflers and did heaps of work on the cylinder assemblies. The cylinders were cleaned up by port and polishing and the cooling fins cleaned up. They were flowed checked. There was a great difference between cylinders due to different manufacturers. The cylinder head castings must have been cast in some kids sand pit. High compression pistons were fitted. All rotating masses were balanced. The airbox was "repaired" to smooth out the flow. The intake manifold internally is a design nightmare. This was smoothed out as best it could be. the engine was placed in a test cell and run under a calabriated load ,power output was 165 hp. The engine would spin easily to 2700rpm and was smooth as a drink of Jack D. All mods were to "Engineering orders "or STC,s to make it legal in my country. A Airwolf oil filter kit was fitted with a finned fitting around the filter. I fitted a brand new carby but this engine loved fuel.
CHT,s were not a problem but it had very bad carby ice problems when throttled back. I did about 450hrs until some nutter went around the airport tampering with the aircraft and my engine seized on takeoff. He disconnected my oil pressure line to the gauge.
I have now fitted a Lycoming clone [Superior] o-360 . Using Harrys STC. The Continental was painted Gold and not red but still kept up with 172,s

[ghostflyer]

Some exhaust sytems are junk. Due to old age and broken baffles . I have seen some tuned exhaust systems return some good economy fuel figures also. People neglict their exhaust systems and allow leaks and cracks to develope. In my view the pancake and the 3 inch muffles are too restricting on the o-300 . When the 4inch muffles went on I had to modify the lower cowl for clearance. Messy but worth it. We have just fitted a "Power flow "system to a Cardinal with a o-320 lycoming. What a difference. A far better climb rate and fuel cosumption is down about 3 gals a hour. I have done many hours in this aircraft before the new exhaust . The old exhaust was a shocker. Many or too many repairs.

[GAHorn]

... The cylinders were cleaned up ... and the cooling fins cleaned up. ... The cylinder head castings must have been cast in some kids sand pit. ... CHTs were not a problem ...

I'm surprised CHTs were not a problem because TCM specifically advises AGAINST polishing/"cleaning up" the cooling fins. The "sand cast" appearance of those fins actually HELP cylinder cooling, and polishing them up degrades cooling by encouraging cooling air to whizz on thru instead of inter-acting with the fins and absorbing heat.