Anybody who really likes to discuss and share power mods to engines - any brand -any tricks.
Throw your hat in the ring---

Diablo wrote in the "Taurus engine prices" thread:

>>A rotary valve or a reed valve engine both have good potential for top end horsepower

Yes, a reed and rotary valve can be tuned to produce great high RPM horsepower.....but this is not the strength of either of these designs, their greatest strength is producing power over a wide power band. In other words, relative to other engine designs, you can get great peak power without sacrificing all your mid-range power. What that means in r/c applications is (theoretically) you can tune the good peak power for wherever target RPM range you want, without having it being a peaky motor.

You have said before, as you imply here, that our motors don't need low end torque, only power over a very narrow band. I say again, I don't agree. A wide power band from down low to your peak is essential for good throttle response and fast acceleration to peak RPM, such as pulling out of a hover.

To continue -BUT the prop load is very small at low revs- because the prop is not really hooked into the air at low revs.
For example - imagine this -or try this.
make a pull test setup - (however).
Now run the engine up in 1000 rpm increments .
read the thrust at each 1000 rpm step.
What does the curve look like.
If you were hooked in water -the curve would - and here I am guessing, be quite different. No?yes?
My point is that as long as the carb is functioning as desired - the first 3000 rpm should come up fast.
The exception would be a very heavy prop.

Bpryor: This is pipes and power thread. a tunned pipe on your Taurus engine may work very good. Take a look a the webb site that Dick Hansen has. P.S. I changed this post quite a bit. I read the previous thread wrong and put my foot in my mouth(that hurts). Please keep the facts comming in. They are vauable to all. We would miss you if you didnt .(Really) Best Regards C. John

captinjohn:

Here's my retraction. Thanks for yours, I appreciate it.

BTW, I picked up a MACS Quiet pipe a while back to try on the Taurus. I didn't mention it because I haven't had time to get it hooked up. It's more just for ground testing as I don't think I would ever put something this big on a plane the size of the DP Extra. The total length of the pipe with header is over 3' and 2 1/4" in diameter. The weight isn't (relative to the size) bad though at about 12 oz.

I am very interested to see how it runs with it though, both for noise, power and transition.

I also want the Taurus to be well broken in before trying this out. I will report when I get it on the test stand.

Bill

Dick
What kind off muffler have you found to give the best all around performance?

If using a tuned pipe do gas engines get peaky, like the glow versions do? I ran a g-23 in my boat. i had a water cooled head, higher compresson, big bore carb and a tuned pipe. The engine really wasn't crisp untill mid range. From there on up it hauled butt.
I haven't tried a tuned pipe on my ZDZ-60's. I am running a bison pitt's style muffler. Would i get better performance by making a header pipe that has smoother bends. Then have the header go into a 1 1/2" diameter pipe about 7" long. then have 2- 5/8" tail pipes. How long should the header be before the muffler? Making it look like a bison muffler. Noise is not a concern.

As far as engine mods go, it seems preety hard to improve the ZDZ line right now so i am looking at the exhaust.

Pardon please -whilst I interject one thing -What I was really after --was power mods - for all engines -not who has the most power - best prices - etc..- power mods - power tricks - tests that show how to improve performance- that kind of stuff.
anything else - well count to ten first then see if it really fits.
I know there are power mods for piston ported engines - I have done them- at least on one - the G62-and I had a twin custom made -a 4.8 that was very nice, smmoth engine -reed valve setup -it was , however just not a design which lent it'self to smokin! it turned a 24 x10 Zinger at 6200 as I recall.and weighed five lbs- so - It got sent on to a home where it could be better appreciated.
(meanwhile, back at the ranch--)

The best all around muffler is kinda like picking the best car to buy-
But my own qualifications are
1 It does not have to fit in the cowling -
2 it should muffle quite well
3 it should enhance power IF possible.
4 For aerobatics - peakiness is not acceptable nor is a flat spot in midrange.
So - here is my take on it.
A header and a can or tube is just about a forgone conclusion.
The best setup for simply ease of doing the job, is a very large , low backpressure , NONTUNED device.
The Europeans have developed a few of these and basically they are like the RCS can called the JMB and the German can called the PIFA.
These quiet the exhaust note but simply do not enhance thru a tuned backpressure (wave) .
If someone has found otherwise - please correct me!
Some engines are not fussy and actually like and need some backpressure to really run correctly.
The easiest exhaust setup to obtain for these is simply the K&S and do it by the book - basically a header abut 12" long seems good for the setups I have tried.
There are more- the Chapman Vtech setup is a real booster but you better have an engine which likes it - It really can build backpressure.
Mac's has some full length pipes large enough for 40cc and I think has an even larger one .
The forty one I tried - was no better than the K&S -but I am going to re- vist the whole tuning program -now that I found out that the durn carburetor can be switched to give better midrange--this discovery was simply from cut and try - but it really worked .
It will probably work on other engines too -but WHICH carb will improve the midrange -on WHICH engine -is a mystery to me.

Dick

What carb did you switch on What engine???? ZDZ?? I was sick that day and missed it!! hehehe

This is a little out there, but I recently read in one of the automotive engineering journals about a new power boosting, variable displacement and variable compression ratio design. They put a linked rod between the crankpin and the connecting rod. The link is moveable with (hydraulic control maybe?) Anyway they can change the stroke of the motor while it runs. Also the piston lingers longer at TDC, so there is more complete burning of the mixture - more power and better efficiency.

You hit on my favorite topic-
rod length vs stroke-
The DA is the only engine which mentions it .
The increased rod length is an idea accepted by some race tuners and rejected by others but the advantage -as mentioned --is that IF the cumbustion which starts at -say 15 degrees of crank rotation BTDC- the amount that the piston will rise is lessened -also th piston spends more time at the top -before starting down.
It then moves relatively faster at mid stroke.--
All of this can assist in the gas flow INTO the crankcase-on a two stroke.
Another advantage is that more compression can be used - giving more torque.
Why? well the problem that can exist in some engine designs is that the combustion chamber -if squeezed after the flame has started-will autocombust at the far side of the chamber - and this is detonation - Not pre ignition -not Pre detonation(?) a term oft heard.

I agree with you on the long rod setup. The higher you can get the wrist pin to the top of the piston the better. At the same time You can also increase the stroke of the crank to get more torque at a lower rpm range. You would have a very flat torque curve(Ideal for our use)
As far as detonation, you can control that with compression(More is best) and hi octane fuels (110 low lead). and ign. timing (like multiply spark) Piston design now comes into play to help stop detonation. A design like the nascar guys are using. Swirl technology and fast burn cylinder design is now coming of age. The better we can atomize the fuel charge the more power we get without detonation. no detonation, more torque!! And to top it all off we would get longer run times / oz of fuel.

I will problably be one of the first to buy a stand alone fuel injection unit for Gassers when they come out. It's just a matter of time before they do.
ttyl

bpryor Bill: Will you have to make a special header to hook up the Taurus to the Macs Quite pipe? Or is there headers made that will bolt to engine. Best regards Cap. John

Hi Cap. John,

You've hit on one of the problems of hooking these pipes up. Typically they aren't turn-key kits that are ready to bolt on. You have to get all the parts and hope you know someone like DH that can help you out with a starting header length...and in many cases you need pay a professional welder or have access(and skill) to your own heli-arc setup(I've noticed DH uses mild steel headers, so in that case you wouldn't need the fancy welder).

For the Taurus, MACS(www.macsproducts.com) has a Sachs header that will fit. For other engines, if you don't fit one of the ones available, you'll have to ask the people that carry them to measure the ones available to find a fit(I bugged the heck out of Dave at DA to try and find a KS one for the Taurus, but I could only find a close fit). KS makes quite a few header adapters. Desert Aircraft(www.desertaircraft.com) carries them in the U.S. and you can see a partial list on their site. MACS is also a good source of headers even if you don't use their pipes.

Here's one more point to consider. MACS uses a one piece header that curves and runs back several inches. They sell them with 3 different radii. KS does make a one piece header, but their typical setup uses an exhaust flange with a variety of curved and straight sections, and flex tubing, you can buy to make up a header that fits your application. This makes it much more difficult, but gives you total flexibility in your installation. Look at DH's site for examples.

HI Bill P. Thanks for the reply. I wonder if the people who make the Taurus line of engines have tried pipes or tunned exhaust? If I new what flying field they fly at, I could take a drive this summer and join the fun. I think I will try to see if they have a email address and ask them. Take Care Captin John

Along these lines....I work on some 290cc opposed twin cylinder ex military drone engines..We use them in Reno style pylon races..The manufacturer has a dyno for testing..
The combustion chamber is off set in the cylinder, for a better angle on the rod..He says there is a measureable improvement on the dyno when the cylinders are set up so that the offsets are opposite for the best push on the rods...Something to try someday....
We get about 30 hp on methanol, 9000 rpm with a 24-28 carbon prop..234 mph...
Gasoline gave about 400 rpm less, with half the fuel consumption...
Our rules don't allow tuned pipes, just 8" stacks..I would really like to see what one of these would do with pipes..
The engine is piston ported, modified for 170 degrees intake duration and higher compression with extra boost ports..
The manufacturer tried a reed valve system, didn't like the way it worked for his application...
the drone flew 6 hour missions, so fuel economy was a consideration..

I used to work on old muscle cars. In those days, we always used to say there is no replacement for displacement. Obviously this means more CCs. Another HP gainer was compression. By shaving a few thou off the bottom of the heads we gained in compression ('course this causes more heat.) I think if the engine manufacturers, BME 3W DA and so on, would make optional rebuild kits with slightly bigger pistons then you could gain in the CC area. I took an OS .60 and bored out the sleeve and made my own piston once. I had good results, but the materials were not the best for this application. This bumped the engine up to a .71 if I remember correctly. On the same prop that I had ran I gained 800 rpm and aother 200 rpm after 36 ounces of fuel. I haven't ran it in a while afraid the materials will break down.

Jeff