I'm about to bolt a TH .75 engine to a new airframe. I have a Macs header and tuned pipe for the engine. The airframe is not designed to go fast. I'm building a sport plane and I hope to have good slow speed aerobatics and even some mild 3D capability.

The main goal is to increase the size/diameter of the prop - go up 1 or 2 prop sizes - and maintain good mid range throttle

I've only had one tuned pipe on a glow engine and it was for a speed plane. The prop was small diameter with a lot of pitch. I tuned it by cutting the header off in 1/4" increments until it peaked out. Simple enough. Plane was fast. I was happy.

I have read about people tuning a pipe for mid range throttle but I am confused on how to do this. Isn't a tuned pipe designed for all out RPM? How would you tune it for mid-range performance? If you could tune it for mid-range performance - how on earth would you know that you were in the sweet spot? Seams to me you'd need to have 2 headers and be willing to cut both of them up.

Here's my issue:
The TH .75 engine usually turns a 13-6 prop very nicely at my altitude. I'm usually taching these engines around 10,000RPM with the 13-6 Pro Zinger wood prop and 5% fuel. I want to try and turn a 14-6 or maybe even a 15-6 with this engine on a tuned pipe. But I don't know how to accomplish the tuning process.

Here is what my brain is thinking:
Buy a 13-6 prop
Buy a 14-6 prop
Buy a 15-6 prop

Run the engine with an open header and tach each prop.

Assume (we all know where that usually leads [sm=lol.gif]) the engine will gain 10% - 15% power with the pipe. Pick the prop thats turning about 8500- 9000RPM. Install that prop and the pipe. Tune for max RPM. Fly it. That sounds reasonable, but is the pipe going to be a dog if the engine isn't at full throttle? I don't necessarily want all out RPM and speed. I want thrust from a big prop disc and I want nice throttle transition in the mid-range.

How do I get the engine to spin a 14-6 or a 15-6 prop and have nice mid range performance? Am I totally screwed up and should just set the pipe aside? Or can I accomplish the performance goals with the pipe?

Only thing I know for sure - is I'm really confused and don't want to start cutting up $40 headers until I know what the heck I'm doing.

I'd really appreciate any help from some of you guys that have practical knowledge of tuned pipes and tuning experience. I can read theory until I'm blue in the face. That gets me nothing. I need help from you guys that actually know how to do it - not somebody who is guessing - I can guess on my own.