Tip: Go-fast baffling: RTV & glass
 

I?ve had a couple people email me asking how I constructed my RTV & fiberglass baffing for my VariEze. I found that this was a great way to keep my hopped up O-200 cool & the drag low. The goal of this was put all the air where you want it & not let any leak to where you don?t want it. It?s a very messy process, but gives an amazing seal around the cooling fins. Here's a writeup I did on the process dug up from my personal VariEze archives (from 1998):

This is how I did my RTV/glass cylinder baffling for my O-200 powered VariEze. This worked for me & really helps cool even my hopped up motor efficiently...no guarantees on your installation though. :cool:

Some aluminum is still required, but not really around the cylinders. I have some between the skinny parts of the cylinders that I re-used from my old baffling installation, but you could actually lay up a solid glass piece to put there or maybe a smaller aluminum piece than I have. If you got a little creative, you could even put RTV/glass there. The front, side & back baffling pieces still have to be made of something rigid. Aluminum or epoxy/glass or carbon should work fine.

I bought Hi-Temp red (looks orange) RTV from Autozone, PepBoys or some such auto parts store. They sell it in big tubes that you can put in a caulking gun. I used several of these tubes to finish the project. I think they cost about $10 a piece (maybe less - can't remember exactly). The red RTV is the highest temp stuff they sell, but you could maybe get away with a cooler temp RTV if you wanted a better color. Not sure on that one, but the temps at the outside of your cooling fins shouldn't be all that hot.

I used 1 layer of 5oz BID fiberglass in my RTV layups.

• First, I cut fiberglass pieces to fit. I used different pieces for the barrel & head since their size is so different. The RTV/glass layup is easily cut once dry, so don't worry about making your parts too big. Just make sure it's big enough to cover all the cooling fins.
• Once the pieces were cut, I layed down Saran Wrap (wax paper might work too) on a flat work bench. I coated the Saran Wrap with about 1/8" of RTV then laid the glass down on the RTV. Then I put another 1/8" layer of RTV on the glass. This makes an RTV/glass/RTV sandwich with Saran Wrap on one side.
• Now lift the piece off your bench & place it on the cylinder. I used a plastic spackling spreader & my hands to push the RTV/glass sandwich onto the cylinder. The idea here is to make the RTV on the non-Saran Wrap side get in between the cooling fins so the whole mess will stick to the fins once it's dry.
• Once you've done the previous step, never pull this piece off your cylinder. If you do, you'll have to remake the part because the RTV will no longer be stuck to your cooling fins.
• Continue putting the layups on your engine until you get everything covered.
• Once dry (many hours later - read the label on your RTV container), peel off the Saran Wrap.
• You can use a straight single edged razor blade to trim any excess layup off & set the proper gaps on the top & bottom of your cylinder air holes. I can't remember exactly how big I made the holes on the top & bottom, but you can use the pictures as a guide. Be careful not to score your cylinder fins (or anything else) while you are trimming the RTV/glass. Extra deformities anywhere on an engine are probably not good.

I'm not exactly sure how much extra cooling this style will get you. I did mine during an engine rebuild where I pumped up my motor considerably, so it's tough to tell the benefit exactly. Before the rebuild, my engine ran at about 425F CHT in climbout & about 400 in cruise. After adding at least 30hp to the engine (should make for hotter CHT's) and the RTV/glass baffling, I now run about 380 on climbout & about 350 in cruise. By my math, the RTV/glass baffling helps.

WARNING - NON-RV PICTURES BELOW!!











While I did this project on a plastic plane, I think it could yield the drag-concious builder a little less drag in his/her RV. Hmmm...maybe it's time for me to start another project on my plane. :D

Moderators: You may have to move this thread..."general" seemed to be the best fit I could find, but "Tips" might also be a good place.