newbie with an engine question
 

I recently received a super tigre 61 x series engine in near perfect condition. I also received the exhaust tube and a pipe with it but I am new to racing and don't know much about using a tuned pipe. I know if the pipe isn't right the engine will never step up on it. I'm going to mount it on a hangar9 t-34 that I reserected after the last speedworld warbird race. I put the plane on a major diet and cut anything off that wasn't absolutely necessary. I'm also not sure what prop and fuel I should use. I know there are alot of pattern guys out there with alot of experience in this area so any advice would be invaluable. I have plenty of time on this, I'm not planning on competing with this plane till next october, but R&D time is crutial. Thanks guys.

RE: newbie with an engine question
 

Crash, I know that there are alot of opinions on pipe tuning and they vary from time to time . The Pattern guys were basically using a long pipe to gibe lots of torque and swinging props designed to give them a good constant speed in all directions, with the torque range for pulling veritical manuevers. In pylon , we are wanting speed so the long pipe isnt quite what we are going for, we want RPM and speed. what you need to do is figure out what diameter and pitch is going to be correct for the airplane you are flying. When you finally get that magic size, buy a prop that is smaller in diameter for tuning purposes.
Mount the engine and pipe combo on a good test stand and run the engine at WOT and get a good RPM reading at peak. Now comes the fun part, start cutting the header length 1/4 inch at a time and re check the RPM after each cut! you should see and increase in RPM .the RPM risesas the header gets shorter. When the RPM peaks or doesnt improve any, I would add 1/2 " back to the rubber coupler and race it at that length. You need to remember that the pressure tap needs to be located at the largest diameter of the pipe. You can NOT locate it at the header because it will be a negative pressure at that location and cause the engine to go lean when it comes on the pipe. My experience is from the mid 80's when we were running tuned pipes in Q500 before the rossi became the standard engine. we also ran crank case pressure but pipe pressure will work just fine.
I hope this helps some but I would like to see if anyone else has a different method , I am sure there are others and maybe they can give a better idea.
Good luck

RE: newbie with an engine question
 

Just to add to Storm's advice. You will need to adjust the needle after every cut you make on the pipe, usually richer. Also, if you find that your blowing glowplugs every bench run or flight you will need to add a head shim, .004-.005 thick will usually be enough, sometimes switching to a colder plug helps too. As RPM increases, more head clearance is needed to prevent detonation. If your using a digital tach and the readings are jumping around by 200-300 rpm at full throttle, this is an indication of detonation. In my experience with some 40 size engines, going over 17k rpm requires more head clearance, and increasing nitro content also requires more head clearance to prevent detonation. The real test is in the air, you should hear a noticable increase in rpm at about 3/4 throttle as the engine comes on the pipe. Once you have a good combination of prop, nitro and pipe length, changing anything will require re-tuning the pipe.

RE: newbie with an engine question
 

Thanks for the advice guys, I test ran the engine today (my neighbors weren't happy), and I was able to swing a 12/9 prop at 13,500 rpm concistently, I did notice, however, that the engine did not get that pipe scream and step up, the plane did start life with a YS 110, but I am currently using it on a zero. I flew it with a 13/10 prop at 12000rpm w/45% fuel, with this new engine on the old plane should I reduce the diameter of the prop and increase pitch, or just go with a smaller diameter with the same pitch. I need to stay as close to a square prop as I can, I don't much care about idle, after all it only stays there long enough for the "idle requirement" to be fulfilled. Again, I really appreciate the help, I'm having a blast with the tuning.

RE: newbie with an engine question
 

For racing applications you generally want less diameter and more pitch, as an example I have a DagoRed with a .91 4 stroke and run a 12x10 prop on 30% fuel and turn 11.5k on the ground.
Your rpm numbers seem low and with a pipe and correct prop I would expect to see at least another 2 or 3k rpm. You might ask some of you questions over on the Extreme speed plane forum here on RCU to get some prop recommendations, something likean 11x9 or 10x10 might be better. You should really flight test the props because the overall drag on the airframe comes into play also.

RE: newbie with an engine question
 

Thats alot of prop. I was thinking you would be using something like a 11X7.5 or 11X8 to fly with. I am not an experienced 60 size engine man so I might be off on that. I would tune it with a prop that is atleast 1" diameter less that what ypu will fly with to simulate an unloaded condition.
ckecking in the xtreme threads might be a good idea.