How do I get 4-2-4 cycle

LAST EDITED ON Feb-03-04 AT 12:57 PM (CDT)
 
I have a friend that flies in all the contests with a 36 size engine can't remember the engine name. He buys a brand new engine then mails it to someone and for $150.00 they modify it and send it back. The engine sounds like a low RPM 4 cylinder with lots of pulling power. His airplane flies so slow it looks like it would fall out of the sky.

I was told to file a tiny 45 deg angle on the top inside of the cylinder wall intake port and file a tiny 45 deg angle on the top back side of the piston to match the angle of the intake port. I was also told to debur all the shape edges on the inside of the crankshaft fuel port. Add some extra head gaskets to reduce compression.

I can't seem to get my engines to run 4-2-4 cycle. My engines all run the same speed all the time. I adjust the needle slow or fast makes no difference once the airplane is in the air the RPM never changes even during a climb straight up.

I am not sure why I can't get a 4-2-4 cycle?

How long have you been out there in left field??

Who told you that and what engine are you refering to???

If you are not a machinist or have some training in machining model engines, stay away from them with a "file". Gary, just buy a good known brand of stunt engine, break it in properly and fly it.

What TY Said

>I was told to file a tiny 45 deg angle on the top inside of
>the cylinder wall intake port and file a tiny 45 deg angle
>on the top back side of the piston to match the angle of the
>intake port. I was also told to debur all the shape edges
>on the inside of the crankshaft fuel port.
>
>I don't want to screw up my engine what really works?

Generally, buying one that's already powerful enough, or one size bigger, is a much more reliable way of getting more power than anything you can do with a file or Dremel tool as a one-off.

If you want performance, there's plenty of external items to work before taking the engine apart. Propellors are almost magic - find the right prop and it's like you have a 46 instead of a 35. I also suggest fuel. Most people are hesitant to try more nitro. I regularly run 15% in hot weather and I have seen very few cases where stunt engines become over-compressed. It's not like they are generally setup up "on the edge" in the first place. 15%, 29% castor in a Fox is like running a turbocharger. You might need Randy's new crankshaft, but that's just an indication that it works and now you are overstressing the motor.

I would also suggest that you can make the airplane act as if it has more power by trimming the airplane better. Most airplanes I see are far enough out of trim that they are wasting power in droves.

I urge you to explore these areas in full before even attempting what appear to be "simple" engine modifications. If you could "get more power" with simple internal modification (like drilling a hole in the piston skirt, filing the baffle, or any of the other erzatz mods you sometimes hear about), the manufacturers would generally have already done it. The engine business is very competitive, and they know far more about it than you and I. In any event, most stunt engine modification is directed towards *taming* the power, as opposed to pumping it up. In many cases, I am not a major fan of this approach either, as it's frequently possible to use them out-of-box if you know how to go about it, and keep an open mind.

I can tell you from vast experience watching the rise of rampant enigne modifications in stunt, that by far the cheapest and shortest path to getting more power is buying a better engine. You'll ruin enough engines experimenting that $70 for a Magnum 36 and $15 for a venturi begins to look like a charity operation.

What Brett said! Buy something from Len, or one of the other known engine guys, and haunt them if it doesn't work. I don't even want to add head gaskets.....

See Ya

Well said, Brett!

I never get tired of telling this story:

Some years ago I bought me an OS.32F, a helluvan engine, more ponies than a .40.

Of coure I was having serious runaway problems. And everybody was messin with then 32's, even Bob Hunt got Dean Papas to raise the ports, reducing the blowdownd (and also the power).

Brett knows that this ain't the smartest thing to do on such a high performance jewel.

I gave the engine to a machinist friend of mine, and some minutes before my nice .32 was gonna be "castrated" I got this e-mail from Brett screaming "blody murder" on messing with the sleeve.

I called my friend at the exact moment he was turning on his machninery.

A smaller venturi, a low pitch prop, more revs and it was pulling a 275 sq" plane like superman. If I want I can hang it on a 600 sq " bird, just out on a bigger ventury and It'll handle it, no sweat.

PLUS if I put a pipe on the sucker it'll run like a .50, I believe.

You want a 4-2-4?
Get an LA, it can do it. It has the boost blocked, which Len has been doin' for ages.

I only resent the fact that Len did "it" on a OS.40VF that later was offered to me for peanuts.

Darn you, Len, don't you ever again dare to do that to any engine thta I might possibly want to buy (get a cristal ball)!!!

Ion (sorry for ratting on you, Len) Muniz

PS Len said the wisest thing on the subject: If it's gonna run like a fox and sound like a fox it'll probably have the power of a fox.

Instead of messing with schneurle engines get one of those foxes Larry makes, no .36 is gonna do a better 4-2-4

PS 2 - Slow turn has nothing to do with 4-2-4, if you don't have the speed (momentum) the plane neeeds to do a wingover don't expect no tight lines just because the engine bursts into a 2 cycle run.

LAST EDITED ON Feb-03-04 AT 01:11 PM (CDT)
 
Different engines will behave differently.
Some aren't meant to be flown with a 4-2-4 break
(e.g., a Fox Combat Special). Others are famous for it
(e.g., the Fox 35). I mention Fox in both cases to
emphasize that it's not the manufacturer.

What engine are you playing with?

>I was told to file a tiny 45 deg angle on the top inside of
>the cylinder wall intake port and file a tiny 45 deg angle
>on the top back side of the piston to match the angle of the
>intake port. I was also told to debur all the shape edges
>on the inside of the crankshaft fuel port.
>
>I don't want to screw up my engine what really works?
>
>Gary Weaver [email protected]

Just adding my own comments here, there is no magic formula that will work on all engines and suddenly improve them. That doesn't mean they can't be improved. Most all of the mass produced engines we have available to us today are designed for RC. There can be modifications to timing, porting, compression, etc. that will improve certain characteristics of some of these engines and make them better suited for our purposes. But everything is a compromise. And you need to know what you are starting with and where you are going with it. And what your objectives are. Wouldn't it be nice if every engine manufacturer made it possible for us to put a 45 degree bevel in his engine and make it run better?

That said, engine modification is kind of a cut and try, hit and miss proposition. As I said, there are no magic formulas that work with every engine. I have ruined a lot of heads getting no improvement and a lot of times making it worse. I have ruined a few sleeves along the way trying to find that magic elixer as well.

So, if you have followed me this far, how sure are you that what you were told is just exactly what you need to do to your particular engine? And then, how sure are you that you could even cut a 45 degree angle in the sleeve or head? (I couldn't by hand) Cutting anything by hand is really a gamble. Even when trying to cut the ports flat it is hard to get them within ten thousandths of an inch doing it by hand. The manufacturers using CNC machinbery can only count on getting them within about two thousandths. But this angle thing just compounds the error. You change the angle, and you change the timing considerably.

And did you know that different engines have different thicknesses in the sleeve? The 35 FP and the 40 FP have the same stroke and the same timing, for instance. the difference is in the bore. They also use the same case which means the sleeve on the 35 is much thicker. Thus even if you were to cut the angle perfectly, you would raise the porting on the 35 much higher than you would on the 40. And who came up with this magic number that 45 degrees will do it? And why are you cutting the the top of the piston as well?

Some people will cut a bevel in the piston because it accomplishes the same thing as raising the intake ports and is easier. It does change the combustion chamber, however, so there is another compromise. But both together?

Let's go back to that 35 FP that I was talking about. With the stock porting on the sleeve of this engine the exhaust port is 62 thousandths of an inch above the intake ports. The sleeve on this engine is 65 thousandths of an inch thick. So if you beveled the port a perfect 45 degrees as suggested, the intake port would open before the exhaust. And that is without beveling the top of the piston which was also suggested. Bevel the piston as well, and you have raised the intake porting even higher. Do that--do it perfectly--and you have made a paper weight out of the engine. YOu would have done exactly what was suggested and destroyed the engine. You want to know why you want to change the timing, exactly how far you want to change it, and that you can do it accurately. If you do not know the answer to all three of those, stop right there unless you are willing to sacrifice the engine for the sake of experimentation. When I was a young lad I once decided to experiment with a cake recipe. If adding a little baking powder makes the cake rise, I wonder what would happen if I put twice as much in. I found out. It ruins the cake....and you get to clean the oven.

Oh, and as for deburring the crankshaft intake, or the inside of the case, etc., that may sometimes help a speed engine. But our stunt engines can actually benefit from having a few square edges. You get a little more swirl of the mixture without making it flow quite so smoothly. Even here we can sometimes outguess ourselves thinking we are going to improve things when we aren't.

Did I discourage you? I hope so.

I found no mater what engine you choose. whether it runs 4-2-4 or just 2. Propeller choice plays a big part in how the engine wants to run and how the plane is going to perform in the pattern. Even on my RC planes I will at times try up to 6 different props of different brands and pitches to find just that sweet one that fits the complete package. I've found control line planes even down to my 1/2a ones are even more sensative to prop changes. So before you start cutting at anything I would suggest playing with an assortment of props if you already haven't.

Oh, and as for deburring the crankshaft intake, or the inside of the case, etc., that may sometimes help a speed engine. But our stunt engines can actually benefit from having a few square edges. You get a little more swirl of the mixture without making it flow quite so smoothly. Even here we can sometimes outguess ourselves thinking we are going to improve things when we aren't.

Leonard Neumann

Len,

I beg your pardon.

Speed engines, Stunt engines, all engines are, at one level, nothing but air pumps.

Are you saying that you *intentionally*--through omission if not commission--block or restrict or trip the flow through a Stunt motor?

The Saito 30 and 40 both feature two 90-degree turns in their intake plumbing. Is this good or bad?

I would be most interested in any empirical data you may have which demonstrates the validity of your statement, quoted above.

Especially as I am fixin' to install some flow trippers in the bypass of a favorite Fox 35, am considering cutting some trips in a hemi head, maybe even adding vanes to the back of a Fox 35 'wheel.

LAST EDITED ON Feb-06-04 AT 07:21 AM (CDT)
 
What Leonard is saying makes perfect sence to me. I have built street rod engines and racing engines for cars, go karts, trucks, boats, motor cycles and I know for a fact if you build a 350 chevy small block engine with a stock 282 head for street service it will out perform a ported and polished racing head on the street but with the tables turned the same engine on a race track is worthless with stock heads. It all has to do with the laws of physics. Use the laws of physics to your advantage don't try to change them. There is a huge difference between a speed engine and a torque engine.
A stunt engine has less air flow than a racing engine just like a stock 350 chevy head has less air flow than a racing head. The tiny sand casting bumps inside a stock chevy head stirs up the air fuel mixture to give you a better fuel/air mix. A high speed engine isn't so critical when it comes to a perfect air fuel mix its more important to get the fuel air mix IN the cylinder. Bumps of any kind are a restriction for high speed air flow. Low speed air will love those sand casting bumps. If you polish the sand casting bumps out of a stock 282 head you will loose 10% or your horse power and torque. Airplane engines are no different than car engines just smaller.

Gary,

Neither you nor Len have addressed my comments. My primary point is that **all** engines, from rat motors to Cox 049s, are at one level merely air pumps. As such, it is always a real good idea to let the air/fuel mixture flow, whether for maximizing low-end grunt, mid-range torque, top-end horsepower or even an over-rev capability for those times when shifting up a gear is not an option.

We are not discussing, for example, the ongoing debate between intake surfaces polished to mirror-like condition versus a very slightly rough finish.

Do you perchance mean a "283" Chevy head?

282 is the casting number. All chevy heads have casting numbers. There are charts available that will tell you the port size, CC rating, valve size, air flow rating for the intake and exhaust ports, chamber size of each casting. There are several 100 different casting numbers. Any small block chevy head can be swapped to any small block chevy engine you like. Heads for a 283 engine are different than 282 casting number. A 282 cast heads will fit any chevy engine with a 4.001" diameter cylinder bore including a 400 small block which as a 4.125" cylinder bore. A chevy 302, 327, 350 all have a 4.001" diameter cylinder bore. A 283 and 307 engine have a 3.876" diameter cylinder bore. The 283 engine has a 3.00" piston stroke. The 307 and 327 engine have a 3.25" piston stroke. The 350 engine has a 3.48" stroke.

GM came out with the 283 engine then the 307 and then the 350 engine. GM put a 283 crank in a 350 block and came out with the 302 engines what were very popular engines in the hot rod street cars like the camaro. GM put a 307 crank in a 350 block to get a 327 engine which were also very hot short stroke engines that would turn quick RPMs with lots of torque.

283 engines are very hard to find these days you can build one yourself by putting a 302 crank in a 307 block using the 302 engine heads.

GM engines are neat you can swap the pieces around to get differene stokes and different bores to make any cubic inch engine you like. A very popular race car engine is the 383 which is a 350 block with a 400 crank. You have to buy a regrind 400 crank from the speed shop to make it work. Use the 400 rods on the 350 pistons. Use the 350 heads.

If you want to build an 650 HP chevy engine buy dish pistons with a dish deep enough to get a compression ratio of 6 to 1. You can turn a stock 350 engine into 650 HP just by changing the pistons and putting a blower on the intake.

Well now we know the history of small block chey engines (even though the 262 cubic inch and 267 weren't metioned) but what makes a model engine do the 4-2-4 break?