SpeedAddict62

I figured some of you would like to see my latest project, custom 13B exhaust sleeves. I didn't like the stock one much, and figured it would be a fun project to develop a new one, and this is what I ended up with:

- inlet same as stock, but with a much smaller gap to the port
- much thicker to allow for porting and port matching
- removal of the stock air holes
- outlet to match the ID of a 2" x .065" wall tube

These prototypes are laser sintered out of Inconel 625. If I make more for another engine build, I'll probably get them machined out of 321 stainless or similar.

And, pictures!

Kenku

Very nice fitup on those, good work! Did you do anything to play around with the rate of area change compared to the stock ones? I did the low-buck version of that once with some crushed stainless tube but it was a heck of a lot more fitting to get everything to nice close tolerances.

SpeedAddict62

Very cool! I can't imagine the time you had into that to get it just right.

I didn't play with the rate of change, partially because it's a pain in the *** to model, and partially because I don't have any reference for what an ideal expansion is. My main focus was matching the stock port and smoothly transitioning that to a 2" tube ID. That way I don't have to play with crushing the tube to size when I try to match it up to the port. The one improvement I could make there is to make the exit flow perpendicular to the cross section. That would get rid of a sudden turn at the exit but would mean a faster expansion.

Kenku

It wasn't too bad actually. Squeezed the tube in a vice then made the curve on a belt grinder - lathe turned the ring thingie, TIG welded them, a bit more grinding, voila. All depends on the tools you have. What I was trying to do was cut the opening size down to have less expansion to keep exhaust velocity up more. Another thought I had was to 3d print a mold, then use some castable ceramic and fire it. Probably be a bit tricky to get all the pre-shrink sizing perfect, but what's the fun if it's easy?

I love the sintered Inconel one you made though, if that wasn't clear. Where'd you have it done, and was it big bucks, or a friend deal?

SpeedAddict62

That makes sense. I guess I meant it could take a while if you are as **** as me when it comes to the finer details. I've got many, many hours into the CAD model of that sleeve...

The ceramic is a good idea, I hadn't thought of that. I wonder if cracking would be a concern or not. Regardless, making the molds would be pretty easy now that I have the CAD model. I prototyped the sleeve out on my home FDM printer before sending it out.

I had Stratasys do it. They are significantly cheaper than other companies capable of doing DMLS and good people too. And yes, I paid big bucks. Since these were just for me, it made more sense to print them, and bonus that I could print them from Inconel. If I were to go into production with them, I would have them machined out of something less exotic.

Kenku

Depends on the ceramic? I know that ceramic lined exhaust ports have been done before in production cars, and something like silicon dioxide is supposedly more thermal shock resistant than others but obviously it's unproven for rotaries.

SpeedAddict62

Yeah, I figure making a thinner piece should minimize thermal stresses. Should help insulate the exhaust and reduce heat rejection to the coolant though.

Did you ever do testing on your piece, or was it all butt dyno?

Kenku

Not even much on the butt dyno - that race car got crashed before we even finished jetting. Probably going to redo the header and throw it in another project though, so we'll see.

SpeedAddict62

Damn, sorry to hear that. Well I'm excited to see how it turns out. Keep me updated when you get them installed again and I'll let you know how it goes with these. Although I won't have much of a baseline to compare to, so not sure even dyno numbers will be very meaningful.

Unless I was able to figure out a way to remove the sleeves without disassembling the engine. Then it would be easy to pop the header off, swap out sleeves and run again.