This would be for use on 4-stroke engines, They use these on real cars and signifigantly increase power, so here it goes:

I hope you know how a 4 stroke engines works and differs from a 2 stroke, otherwise you will be really confused.

When the intake valve on a 4 stroke closes, air piles up behind it because it slamms shut all at once, then the air bounces off and travels back through the carb and wherever it came from. If you could attach something that timed it so that the air bounced off, and then bounced back off something again, and then came back right as the valve opened back up the second time, it would force more air into the chamber, effectivly supercharging the engine.

I'm not sure if this could be done or not, but it works on real cars, and signifigantly increases power.

Hardlanding, That may work, but only at a certain rpm. If made to work at 5000 rpm, then at lower speeds it wouldn't get there in time and at higher speed it would have already been there and reflected back off the valve again.
What I was wondering, if a boost bottle would work? Like what is used on 2 stroke racing buggy's. Hooked up on the intake, it would empty it's self on intake and fill up when the valve shut. Thus..mild supercharging. ??? What do you think???
Suptter

It could be done but I'm not sure how much extra power it would give. The big problem is that it would need to be very long even given that you'd only be tuning for maybe 10K on a 4 stroke. Look at the length of a tuned intake runner on a modern car (or if you're very lucky, the runner on a 50's Mercedes 300SL )and compare the difference in revs.

yeah, hmmmm, i will think about that a little more. But you were talking about it working only at certain revs? Well, how does it work in real cars then? Their ranges vary greatly, almost changing every second, yet it still is an effective means to produce more power, so I think u could get around that

Ever heard of the air chamber on a YS .91 AC/FX or a 1.20 AC?

John

Hi,

Well, actually a similar idea is currently used by YS engines. The carburetor is not open to air but connected to crankcase. As the piston goes up, air comes into the crankcase from outside and as the piston goes down, the pressure is used to push air into cylinder. They have disc valve on cover-plate to make airflow directional.

By this mechanism, YS engines have about 20% more power compared to other engines of same size. The famous FZ91 model still has air chamber attached on the cylinder head. FZ120 does not have one but instead it uses inside of cylinder head to get some space.

OS engine once had a model FS120SP which was also equipped with supercharger. Seems they are now working on 140 model to beat YS FZ140 or the strongest DZ140. I doubt if it is possible but if they really make one THING customers will be pleased again. Especially the F3A competitors.

Good luck!

Michael

Somewhere in this process you would need to straighten out the intake track otherwise the 180 drgree turn at top of the intake pipe, 90 into the head and 90 through the intake port would negate any gain, a pressure wave would not survive that turn as the pressure from the YS plenum does. Many cars, Ford Taurus SHO for example use unequal length intake tubes and a computer to control when each is open and closed. Way too much complexity to be practical on a model engine. The very best option is of course a bigger engine.

Not true. Ever seen a header pipe on a helicopter engine? Some bend 270 degrees plus an additional 90 in the opposite direction before they ever get to the pipe.

John

We're talking intake and fourstroke, you're talking exhaust and two stroke.

A pressure wave is a pressure wave is a pressure wave.

John

How about variable cam timing instead. Very easily done, like Honda's 4 stroke M/cycles and cars. The bikes cam have simple weights that fly out and move a cam lobe over on a ramp that over rides the org. lobe. This could be done with minimum hardware and size. An overhead cam/4 valve head would be nice too!
Suptter

I have two OHC four strokes, one is two valve and the other four valve, neither is as powerful as a Saito 120 Hemi.

Hobbsy, Ah...but I bet they "could" be made to make a lot more power. Let's face it, 2 intake valves will flow more than 1 , given the same area in the head. (more surface area). Maybe the one's you have don't have the cam needed to make the horse power. Most 4 stroke engines are capable of more power than what the designer wanted it to make for reliability. It's a shame that someone out there doesn't make a couple of different grinds, maybe for torque, mid-range and top end for our engines. Just a thought.
Suptter

So Danny, you want a hopped up cam?
I guess someone with experience in the welding trade and a 'good' welder could put a dollop on top of each of the cam's lobes. These 'dollops' could then be filed and honed to match one another.
With the piston at TDC a valve may be manually pushed open and the distance of max travel measured. (High rpm extended piston travel must also be taken into account.)
One may also measure the existing valve travel and hone/file the 'dolloped' lobes for an increase in valve travel.
This idea I believe is feasible for a possible performance increase.

Would the extended lobes, even though extended by only several thousandths of an inch, still rotate freely within the cam housing? Would the weld material stand up to frictional punishment?

Now to find someone with the time, patience, and equipment to implement it...

Here on RCU a similar idea was proposed some time ago. It involved changing the fulcrum point of the rocker arms thus effectively increasing their ratio.
One would have to make new rockers with the fulcrum closer to the push rods. The rockers' 'swivel pin'? would also need to moved the same distance toward the rods.
The effect would be the same but the machining more difficult.

Hmmmm. Could one reduce the distance from rocker fulcrum to push rod?

Thoughts?

You don't need to weld onto the cam. Just grind some metal off the backside of the lobe, then reshape the lobe for higher RPM.

Screw the tappet adjuster in a bit to make up for the smaller base-circle.

Gee. Now that is much easier!

(Man, I feel stupid for not seeing it.)

But, but, but... It isn't even complicated!!!

Well if you grind down the base circle then make sure you also put back in the accelleration/decelleration ramps into the cam profile (assuming they even use them to start with ).

Modifying or attempting weld and machine a small camshaft such as those used in model engines would be difficult.. Many reasons for this assertion. One could offset grind the camshaft [so to speak] from its intended base circle by turning down the outside diameter of the pins or journals located at either end of the camshaft typically supported by bearings. Then simply replace the bearings with with new units sized to the new journal size. This would effectively provide more lift to the valve train. At a minimum of effort without compromising the camshafts metallurgy and or messing with the profile.

OR:
Changing the engines rocker arm stand-off installed height would provide similar results.

OR:
Modifying or fabricating a new rocker arm would provide similar results.

OR:
Shaving or milling the head and or cylinder Assembly would provide similar results.

OR:
Longer or taller push-rods and or valve lifters would provide similar results.

OR:
Or longer or taller valve stems or possibly lowering the valve into the head slightly would provide similar results.

BUT:
With all these considerations one must consider and observe weather or not valve spring coil bind is or maybe present. And lets not forget about piston to valve clearance...

And after all these secondary methods, will increased lift without thought for duration effectively change the engines performance? Cam profiles have several specifications, lift is only one of them. Duration, ramping and timing are keys to increased performance.

Larger valves maybe of some benefit without all the other headaches...

Or how about simply using higher nitro content or purchasing a YS Engine if you really feel the need for performance with a minimum of effort.

Personally, I think the cam profile would be the easiest thing to do. With extended lobes, I don't think would be a big problem in the cam housing, most have a lot of room because of the cam gear. And like Phil said, just regrind the lobes, don't weld them to get the right duration, lift or timing. The difference can be made up on the tappet adjuster. And heavy duty valve springs wouldn't be a big problem either, there very easy to change.
All this is done on larger engines, so why not our smaller ones? I think there are a lot of people out there that would spring for a "hotter" cam. It happens every day for car or motorcycle re-builders, why not us? Think about how many 4 stroke engines are sold everyday in this country. Just the most popular brands, like OS, YS, etc... I wish I could do this.. I think there is a market for this, even though it maybe small, you never know until you try.
Suptter

Questions: Is there enough intake and exhaust flow to warrant increased lift and/or duration? Would the port timing have to be adjusted to compensate for the increased duration? Would it still idle reliably?
Dont you think the manufacturers have taken the cam profile into account and optimized it?

That said, I think *if* you could improve intake flow, the engine might respond better to larger valves rather than a different cam profile.

In my opinion the only way to anyone is going to gain from these mods is to let the engine rev higher than stock, this will require a smaller prop, ei less pitch, less diameter or both. Additional torque is hard to come by, in fact with many mods you lose torque and narrow the rpm it is spread over, as in peakier, to gain a few rpm. I've worked on my brothers stock car engines and read enough dyno charts to know, there ain't no free lunch. If you want to gain a little here you have to give a little there.

amen

Those engine makers must really be stupid to turn their backs on all this easy horsepower !

The simplest method of extracting more power from these engines is to use HIGHER content nitro fuel... However this is a double-sided sword. Higher fuel expense and accelerated wear and tear on the engine components. There is no free ride.

The most effective method of increasing lift with the least machining effort would be what I mentioned with regard to turning down or offset grinding the camshaft's bearing journals and replacing the bearings with smaller ID units...

We have experimented with different cam profiles from other 120 and 140's, didn't seem to offer any power improvements at high rpm.

Ladyflyer is right, the engineer's have taken all of these things into consideration and have offered a combination that is the best for all around use.

The YS engine is capable of living through many abusive high rpm runs on high nitro fuel. We do it all the time on 65% at 11,000rpm with 120 SC's and the 91's can see 13,000rpm. We often burn higher nitro fuel as well. The guys that come and race with us from Arizona are master's with the YS engine and often burn in excess of 80% nitro. Do you know the sound of top-fuel engines??? It's an incredible sound on the course...