Chris300s

My Feedback: (1)

I've got a couple of pipe issues. I had the solutions from the former forum but now can't find them. I'm hoping that some of you can help me out with dimensions (Mr. Auger...).
On a Shrike .40 I've got an older O.S. 46 VFR? Rear exhaust with a MACS kick up header and pipe. What length should I be going for to start tuning? I'm running an AP 9x9 but could run an 8X8 which I think is the optimal prop.
On a Shrike .10 I've got an MVVS .21 with the silencer muffler bolted directly to the engine (no header length). What prop and pipe should I be using? Before I go and modify the fuse for the silencer I'd like to know if a non-silencing pipe is advantagious. I also have an MVVS .26 Combat Special that I could put oon instead but need to come up with a pipe for it.
On a Direct Connection F-20 (F-5) .40 size, I've got a Jett .50 side exaust with the Jett sport muffler. Would it be worthwhile to put it on a pipe and what prop?
Summer's on it's way and we'll start airshow racing soon, I just want to go fast. Are there pre-set headers and pipes availible?

Thanks for your help,
Chris

FlooredCOBRA

I can help out with the MVVS 26. That is what I am running also but on a .10 size Shrike. I am using a APC 7x7 on mine with the MVVS pipe set up. I have the rear exhaust so the pipe clips directly onto the short header supplied. The 7x7 seems to work very well like this.

On the other hand buddy of mine is running same set up but using a 8x6 on his. His launches and gains altitude a bit faster but does not run as fast. It tops out a bit quicker than the 7x7 does. Also flying side by side you can see the difference in speed.

combatpigg

My Feedback: (3)

HI CHRIS! It is helpful before you start tuning to have a supply of head, and liner shims to alter compression and or exhaust timing with. You will also need a tach, paper and pencil. Get the best open exhaust rpm you can by trying different shims. When you make a change that forces you to open the needle more to maintain the right mixture, you are moving in the right direction. Y ou won't know how far to go, until you go too far.The open exhaust readings is to get a baseline set up and tach reading. Now hook up your pipe and get a reading with the longest length your coupling allows, keep trying shorter setups until the rpm goes down, then get your coupling back to the last good length you were at and go fly. If your initial pipe reading was less than your open exhaust reading, then the system is tooo small, so dont cut anything, you need a bigger system.If you aren't willing to go through these steps, then you aren't going to know if you have optimized your set up. It helps to know going into one of these sessions what other guys have been able to acheive with similar setups. Engines that fall into "in between" size catagories will be more difficult to find that "just right" prop for. I doubt if you will ever find an off the shelf prop for the .26 that is optimum, but if you are willing to put in the time it is almost a whole seperate hobby to rework wood pylon series props to find the best size. Keep us posted on your project and it's progress!