Re: Tuned pipe on a four stroke 120

This may be true but I just wondered what other modellers experience of running 120 size (or similar) on tuned pipes was ? I mean are they hard to set up, finicky on needle setting, peaky or what. Also how much (if at all) does it affect the power output ?

I'm not dissing JE but they are in the market to sell stuff, I just wondered what "real peoples" experiences were ?

Thanks,

Tuned pipes provide a boost in power for most two-strokes.

The only people running tuned pipes on four-strokes are those that are saddled with strict noise restrictions.

While it is true that a divergent cone "can" provide some scavenging effect for a four-stroke engine if tuned properly, I doubt that the whole tuned pipe set-up is worth its weight unless noise reduction is figured into the equation.

Ed Cregger

Umm. A tuned pipe works, AFAICR, by using the fact that on a 2-stroke teh exhaust and inlet effectively overlap, and teh tining dras unburnt fule into the exhaust and then rams it back into the combustion chamber.

There is very little overlap on most 4-strokes, so I am dubious it would actually make much difference in performance at all..certainly nothing like as dramatic as on a 2-stroke that is desined to use it..

Get a turbocharger. That should work :-)

Thanks ed, that was my recollection as well. I am pretty sure that racing 4 strokes do get some gain on tuned pipes in the car world, but its not dramatic, and their valve timimgs are wild anyway.

AFAICR which confirms your opinon, its more about reducing exhaust back pressure, than pre-chatging the combustion cyle - that is, on very high gas flows, it makes teh silencing system look like less of an onstructin than it otherwise might.

I am sure there should be a market for tiny turbochargers :-)

Don't tell the top fuel and funny car guys [and gals] that tuned exhaust doesn't work! Those may look like random pieces of pipe bolted on the head but size and length are very critical.

remove my-wife to reply :-)

Valve timing is too conservative on 4 stroke engines. I bet they would throw prop nuts like popcorn if timed radically enough to use a pipe.

Bob

That is exactly what the Macs pipe did on my OS .91 Surpass. In fact, it made my engine TOO quiet! While racing, I couldn't hear my plane above the others!

Hi Paul,

Does this mean you've actually tried a tuned pipe on a fs engine ? At last ! Real people's experience ! Can you tell me what, if anything, it did to the revs on a given prop ?

Thanks,

Cannot speak for model engines, but I had a 1968 Honda CB-450K motorcycle that I fitted with shorty megaphones. With these megaphones all of the power went into making noise and the engine didn't run worth a crap, especially at higher rpm's. The stock pipes performed much better. We tried an experiment by lengthening the header pipes incrementally and we reached a point where the bike actually would run better than stock. But it was LOUD. In conclusion, we found that the length of the exhaust does make a difference in 4-stroke engines. However you will pay a penalty at either end of the rpm range depending on the length of the pipes.

RCFlyr sed that!!

I am specifically referring to the tuned pipes used on model airplanes.

My bike had a set of two into one Hooker headers that absolutely increased its grunt. My AMX used a set of Doug's headers and gave me the worst traction problem I ever had. Too much low end grunt.

However, a hodge-podge collection of two-stroke pipes on a four-stroke engine is hardly comparable to either of the above examples.

Ed Cregger

It made no difference on my engine. I was running a 12.5X9 APC and 40% nitro. The engine tached 10,900 with the standard exhaust and with the pipe.

Tuning the exhaust to get ALL the exhaust out out of the engine is one thing,but tuning it to help pull in an intake charge is entirely different. Using atune pipe on a 4 stroke probably helps O........

Automotive, or Motorcycle tuning is of little use here, due to size limitations and Reynold numbers. Exhaust tuning works on pipes with at least 7/8" diameter, and a length of about 2 feet, for a range at around 9000 rpm. It should have an intake duct of about 9" to assist intake charging. This again needs ducts of sufficient diameter to work well. With the 3/8" dia pipes on our fourbangers, aided by corrugated bends, tuning with the pipe is hardly an option, because the wall resistance will be way too high.

BTW/FWIW, the tuned pipe should be smooth and of constant diameter, or end in a diverging cone. Due to the slowing down of the pressure wave, the cone length to replace about 3/2 its own length of the straight pipe. i.e. 12" cone replaces 18" straight pipe. (thumb rule) Muffling behind tuned pipes needs exhausting into a large volume plenum chamber of at least 40 times engine displacement.

Ok thanks all for the answers, it sounds as if tuned pipes on four-strokes are not worth the expense unless for silencing reasons. I'll probaly skip it as we don't have any major noise problems at our club site and it'll make rigging the plane a little harder.