From past experience with 2 stroke gas engines (motorcycle related), I know there is usually a lot of clean up and fine tuning available on mass produced engines. Things like matching ports, cleaning up casting marks, matching gaskets to the ports, setting an accurate squish band, etc. Are these things still an issue on our model engines or are they pretty well taken care of in manufacturing? The two specific motors I am thinking about are the Brillelli 40cc and the ZDZ 40. How much improvment is usually realized by sorting these out on an otherwise stock engine?


Thanks,
Mark

There are many things that can be done to RC airplane engines to gain more power. Things like you mentioned. The thing to remember is racing engines for motorcycles, boats, and cars for that matter are modified for top end power. If you were building a gas engine for somthing like a pylon type plane this would be fine. But for regular flying like most of us do, that kind of engine is impractical. We need an engine that runs well in all of the rpm and throttle range, and not just flat out wide open. Many hopped up engines make great power at top end, but do not do well at much more than full throttle. Also engines like racing go carts and such make thier top HP at well above 10,000 rpm. That is an unusable power band for us. We need low end torq. As an example. Take a .15 car engine for a remote control car. It puts out 1hp + in some cases, but will not turn a prop for crap because it hits it top HP at almost 30,000 rpm.
You can change port timing, compression, and other things as well. As I am sure you know, port timing changes can do a lot of good, or a lot of harm. It is a fine line between too much and just right.

Just my opinion. I have built over 500 RC airplane engines so far and have learned the wrong way to do things on them for sure I am still learning though.

I understand. I am not thinking of changing the basic engine specs, just cleaning up the junk left behind by manufacture. Like cleaning out casting flash from the ports, matching the ports so there are no sharp edges (between the cases and cylinder) and trimming the base gasket to match the ports instead of sticking out into them. I am not interested in raising the peak torque rpm point, just shifting the entire curve upwards a bit. This is just basic blueprinting and is free horsepower with no effect on the general engine behavior. I certainly don't want a nasty, tempermental high rpm motor that is no good for weekend flying.

Any experiences with how much improvement to expect?


Thanks,
Mark

I'd expect little if any measurable improvement. The best place to spend your effort is a better exhaust system - that can give you around 25% more power.

I have found the best power increase I could get was by enlarging the transfer ports. On most engines they are allready large enough or can not be enlarged.

Go to the Conversion Engines Forum here on RCU. Those guys are always converting Weedies and Chainsaws. They know just how much exhaust duration you can get away with and how much you can mill the jug down to increase compression without going to far on the squishband.

Matching the cylinder transfer ports to the case is not going to hurt you in any way. Just matching the ports will not hurt the engine. It will help out a bit, but I couldn't say how much. You know that if you take too much out of any transfer ports, then you are increasing the swept volume and effectively slowing down your transfer charge velocity. Thats not good, unless you stuff the case or make other modifications to counteract the larger and slower port velocity.

I think your on the right track if you just want to clean it up a bit. When you start raising transfer ports for increased transfer duration, or changing the intake duration--thats when it gets tricky.

Go to the Conversion Engines Forum and ask your question there. Those guys do conversions because they like tinkering with motors. Most guys who fly your off the shelf engines have no interest in modifying their engines.

1/2 of them can't even tune a carb.

[sm=47_47.gif] Did I say that out loud?

Porting is where the big power is, all right. But I don't want the hours of testing and research that goes along with it... I was just wondering about the finishing of the engines that are out there and if there is much left to clean up. Given the industrial usage design intent of the conversion engines, I would expect there to be a few rough edges that could use cleaning up for some free power. I guess I will have to wait and see what it looks like when I get in my shop and pull the cylinder off the cases to really know what I've got.


Thanks,
Mark

I will check out the Conversion Engines forum and see what I can get.

Thanks,
Mark

ACK!!

It's not the conversion guys who can't tune a carb. Thats not what I meant. [sm=confused_smile.gif]

Now I gotta go find my flame suit. [sm=angel_smile.gif]

I got what you mean, it was just the way I snipped the message that made it look bad. If anyone needs the Nomex, it should be me...


Mark

That's what the SALA mods do, clean em up, match the ports, etc. XIPP gets all my motors for port work, he is the Man on these things!!

Tom

Looks like he only does DA engines and no others.

I say if your the kinda of guy who has a hard time tuning a carb....stay away from mods or maybe conversions. Although if you get a engine free....if you fingers do crazy things to whatever....your not going to loose much. May learn something!

I thought he did 3 Dub as well.

And how much of an improvement do you see, for what work done?


Mark

The ports in our two strokers -- are the heart of the potential power and how the manufacturers cast them -pretty well dictated the effective ANGLES OF FLOW
We can buf n clean em but from a purely practical standpoint - not do much
The new engine designs with huge bulging ports were possible due to new casting techniques -much like lost wax -
these allow the flow to be better directed
Note that the intakes actually crossfire on some engines-- with little or no boost port involment
and the exhaust ports are small but directional
Flow is such a black magic thing
On Chevs- the really effective trick is to raise the intake runners and effectively get the approaching flow looking right at the backside of the valve-- this lets the charge flow all around the valve and remain as a "tulip" -increasing flo
What looks good on paper can turn out to be absolutely worthless .
Lots of guys grind out ports to make em bigger - and wreck directional control of the flow
Best bet as previously noted-- work on the exhaust system - It is really the control point for flow into the engine.

Well put. Especially flow in a 2 stroke, crankcase scavenged engine.

Which is why all I am wondering about is cleaning up the junk and not altering port shapes or port timing. I don't have enough time in my life to do the testing required to get that working properly... I just want the optimum version of what the manufacturer started, with no flash, no gaskets sticking out and no sharp edges from port mismatch between the cases and cylinder barrel.


Mark

You can't go wrong cleaning it up inside. Do just exactly what you described. Take off the flash and match the cylinder transfer ports to the case. Clean up the case/cylinder gasket to prevent any disturbance in the flow.

I've done it with some of the little conversion engines and even did it once with a Poulan 54cc conversion. I did notice a few more RPMs, but nothing to brag about. Maybe 100RPM. I thought the Poulan 54 idled smoother after I cleaned up the case to transfer ports and matched them up. I didn't really take off that much material. I just knocked off the dog ears here and there and used some fine paper to smooth it up a little bit where I worked it with the dremel.

The really cool thing about the Poulan 54 was it had a split case. I bolted 1/2 the case to the cylinder and matched the ports exactly. Then took that side of the case off and bolted the other side onto the cylinder. Cleaned up that side and polished it just a little. When it was all done--I had the match between the case and the cylinder just about dead on.

My friend and I have done things to the twin ring Ryobi 31cc engines that you can't imagine. The mods work, but that little engine has such a week rod, it can't take much hopping up. We didn't put enough prop on it and the engine let go after about 2hrs run time at 8800RPM. Just bumping the compression by lowering the cylinder does a lot. Then bring the exhaust port back up to stock and maybe a little more. Slap a bigger carb on it and bend the reed stop out a bit. We started running high octane pump gas. 91 octane and 40:1 mix. It works, but you really don't want to take them past 7500--7800RPM on the bench. We had one turning 8800RPM with an 18" prop. It broke after 8 flights on the Lanier Stinger 120. [sm=confused_smile.gif]

looong ago butnot so faraway-- I put together a Ford flathead - stroked to 4" bored to 3 5/16" big cam -Mallory and HC ignition headers- ported and the valve transfer areas relieved - blah blah- it ran great - 274 cubes- would easily blow off the then new Chev V8's -which was a real trick back then.
Next rod was a heavy303 cu in Olds sedan - with one simple mod:
a blower -12 lbs boost and a mag ignition no headers - no clean up - nothin--
getting max flow into the cylinders was worth far more than all the sweat on the flathead
very sobering revelation
flow is what it's all about
Next rods - Chev V8's - these could be made to really flow - my little mouse engines stomped all over bigger stuff.
Now the litle furrin stuff -- Hondas etc., have taken this even further- incredible power just from great flow .
it is fun blueprinting an engine - the real beanstho- are from new port designs which really ram the cylinders FULL .

Our peak rpm is too limited to gain much from porting. All of our chainsaw cylinders will support more rpm than we can use efficiently with our big and slow airplanes. A tuned pipe will let you place the peak torque anywhere you want it. If performance is important then get a tuned pipe or a bigger engine. Porting an engine that will use a muffler is a waist of time.

He's done a couple 3Dubs for me, 200 and a 80 single, smoother operation, better midrange, extra 100 RPM's or so, well worth it!!

A good example is the G26 compared to the G23...Transfers on the G26 are almost as large as the G62...Good for almost 1000 rpm on the top....
I wish we could enlarge the G62 transfers, but the casting is too thin...

One thing I have found in altering 2 strokes is to raise the top of the exhaust port a bit, if the bottom of the piston when at tdc blocks the intake port at the top shave it off until it on longer is in the way, Polish everything to a mirror finish, all of the ports, inside the crankcase and what ever else you can see on the inside if the motor. An engine is nothing more than an air pump. The less resistance air has to get in and out will make it a more effecient motor

Nothing in the intake tract should be polished, it should have a matte finish similar to a beadblasted surface or slightly rougher. The exhaust port can be shiny for a bit better flow. You have to be careful about raising ports, it all depends on what RPM the engine is timed to work at. The entire system must be matcehd together to work properly or you get poor results. This means intake timing, intake tract length, case volume, port timing, size and shape and exhaust pipe must all be tuned to work at the same rpm range or power will suffer.


Mark

All of the internal mods one can think of -won't make as much difference as a decent exhaust system - the little box horrors (in cowl exhausts) many use - simply stops the intake tract from flowing- The outbound exhaust is either badly restricted or the box acts as a reflector -in any case - many are really bad power robbers.