Trying to get my YS 91 into my top flite P-47 and I need a 45 degree stack to get the exhaust out the bottom. I was told performance specialties makes one, is a bit pricey. I didn't see one on their website, but haven't called yet. Do stacks from any other engines fit this motor. I think the thread is 13mm by 1 mm pitch.

Go to your local welder and make your own. Fourstroke pipes are a nobrainer, no expansion chamber to deal with or special pipe routing. Might save yourself some cash.

1)Call macs products or google products in San Jose Cali
2)He makes simple 90 degree bends that screw in , you then add exaust tubeing(screws ins ) and you can even add your stock muffler on the end of the exaust tubeing .
Look up warbirds and look for "My second VQ P40 " I have this set up shown in pics with my OS 91 .
You can even tap the 90 degree bend so you can add your pressure fitting and presurize the tank

Macs Products (916)456-6932 / fax(916)456-7414 e-mail ([email protected] is out of order) use [email protected]. Macs Products 7935A Carlton Rd. Sacramento, CA 95826 ...
www.macspro

I'm running a YS-91 in my TF P-47 ARF. I just did a straight pipe. I had a 90 degree header from Central Hobbies on hand so I took the flare nut off of that, discarded the pipe, lightly flared a piece of 3/8" steel tubing and installed it on the engine using the flare nut. I angle cut the pipe it so it just sticks out of the cowl. There is a small hole in the side of the cowl but nothing drastic.

You could also bend 3/8" steel tubing into just about any shape of pipe you want to exit just about anywhere.

ChuckW- How does that thing sound with no muffler? I was thinking of doing that and since I fly in the middle of no where loud is OK.

It sounds great. Kind of pops at idle like a little Harley Davidson engine or something. Full throttle sounds great too. It isn't that much louder than with the muffler to be honest. Maybe a little more raspy but not extremely loud.