What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Baffle Mod

I went with a mini-duct per a later DanH post ..it was easy to make and gives more cross sectional area for the air to get through. YMMV, but my #3 has no cooling issues. I did a similar thing on the front of #2, tucked behind the IO-360 snorkel. The only cooling mod I had to do after break-in was to remove the dam in front of #1.

(photos prior to sealing with RTV)

051219-IMG_0041-L.jpg


051219-IMG_0037-L.jpg


051219-IMG_0042-L.jpg
 
Thanks for posting

Thanks for posting. I am going to copy you.

As my college teacher said: plagiarism is good. Oh wait, that was my college roommate. Never mind.
 
Yeah, but...

Perfection is the enemy of good enough.

I've heard that quote just about every time I've tried to fix something that was giving us problems at work in my career as an aerospace structural engineer. My response? "Yeah, but first you have to be 'Good Enough'..." :D
 
My CHT issues weren't terrible on #1 and #3, but in level flight my #2 ran hot compared to #4. I did a similar mod to the front of the baffle on #2 and it cured my temperature imbalance with #4. Now they are within a degree of each other. I wrote up what I did on my blog.
 
I went with a mini-duct per a later DanH post ..it was easy to make and gives more cross sectional area for the air to get through. YMMV, but my #3 has no cooling issues. I did a similar thing on the front of #2, tucked behind the IO-360 snorkel. The only cooling mod I had to do after break-in was to remove the dam in front of #1.

(photos prior to sealing with RTV)

051219-IMG_0041-L.jpg


051219-IMG_0037-L.jpg


051219-IMG_0042-L.jpg

Bill, This is the exact mod I used in 2015.

Here are the flow areas based on the starting gap at the centerline (.4") then below, as the head wraps around. The chute above has .20"+ at the centerline and has the flow area plotted in post #56 above. 8 fins (1.9") is about the max there are 8 fins that get deeper down to the bottom. The other fins remain constant as they are limited by the exhaust port. The chart plot for .063 is the flow area for a washer. Note the area difference for the chute. I ran no temperature data for the difference, only present the area comparison.

2015 Baffle MOD plot.jpg

Template for the chute. Just print, verify your printed circle is 4", make a poster board prototype, then when satisfied, use some .032" to make the final. Note the need for CS rivets to eliminate interference. See my posts beginning at #56 for more photos.

View attachment RR_Baffle_Template.pdf
 
Last edited:
Bill, This is the exact mod I used in 2015. A template is posted somewhere here for it.

Here is the flow areas based on the gap at the centerline and below as the head wraps around.

View attachment 23669


Thanks for the data, great information.

As for the template for this mod...If anyone could post a link or share a photo, please do...I came up goose eggs on a search.
 
So how do the certified planes handle this issue? Ignore it or do they have some sort of bypass too?

I've seen one OEM install with a bypass tube. Photos below are from a Grumman.
.
 

Attachments

  • Grumman Tiger LF.jpg
    Grumman Tiger LF.jpg
    92.7 KB · Views: 257
  • Grumman Tiger RR Top.jpg
    Grumman Tiger RR Top.jpg
    106.4 KB · Views: 249
  • Grumman Tiger RR.jpg
    Grumman Tiger RR.jpg
    80.6 KB · Views: 254
Perfection is the enemy of good enough.

Same can be said for "over-engineering". We seem to think of these somewhat crude little airplanes as akin to the Saturn V command module. I'd say spend 10 minutes putting a washer in there and enjoy the rest of the day out flying.
 
So how do the certified planes handle this issue? Ignore it or do they have some sort of bypass too?

One thing to remember is that the 2 low flow areas (In front of #2 and behind #3 or #5 (depending)) are on the intake side of the cylinder. That side of the cylinder is cooled by the internal airflow (and fuel flow) and doesn't need as much cooling as the exhaust side. Lycoming engineered the fin depth with that in mind.

But to answer your question - the approaches vary. Some manufacturers do nothing, others build in ducts and the like.

The washer solution is a very low effort mod that helps if you have a need for more cooling on the back of the aft cylinder on the right side of the airplane. If it doesn't do enough, you can always add ducting.
 
Same can be said for "over-engineering". We seem to think of these somewhat crude little airplanes as akin to the Saturn V command module. I'd say spend 10 minutes putting a washer in there and enjoy the rest of the day out flying.

The best got that way detail by detail.

I've been side by side with another RV8 which was burning 50% more fuel and running 80 F warmer.
 
One thing to remember is that the 2 low flow areas (In front of #2 and behind #3 or #5 (depending)) are on the intake side of the cylinder. That side of the cylinder is cooled by the internal airflow (and fuel flow) and doesn't need as much cooling as the exhaust side. Lycoming engineered the fin depth with that in mind....

The bypass duct is not to allow "cooling" on the side of the cylinder, rather, it is to supply air to the bottom fins. Without an adjacent cylinder to provide that air path, the lower fins are starved of air. The baffle wrap we all install needs air from above to function. The "washer trick" gets you part of the way there but spills a bunch out the sides in the process. Kind of like trying to fill a wine bottle by pouring from a 5 gallon paint bucket. Messy.
 
Same can be said for "over-engineering". We seem to think of these somewhat crude little airplanes as akin to the Saturn V command module. I'd say spend 10 minutes putting a washer in there and enjoy the rest of the day out flying.

Curious why this after the thread's been inactive for over a year... in any case I was glad to run across it a as it's a fairly simple mod - not over engineered though maybe over-analyzed (hey, that's what engineer types do :rolleyes:). Not rocket science but on warm days my #3 gets hot on climbout like with a lot of us here, every little bit helps.
 
It looks like the cleanup on the cylinders after the casting could have been better.

Is there any reason not to remove what looks like it shouldn’t be there?
 

Attachments

  • IMG_0869.jpg
    IMG_0869.jpg
    146.5 KB · Views: 111
Last edited:
It looks like the cleanup on the cylinders after the casting could have been better.

Is there any reason not to remove what looks like it shouldn’t be there?

I think a bypass duct is less risky then touching a cylinder. I think the price of a Lycoming is about the same as a Ferrari engine. JMHO
 
On my -14 I think that a little 3/8 duct from the top of the baffle shelf aft of the filter down to the front of the #2 cylinder lower fins would be the final answer to dropping the #2 temps. My Arrow had that on its engine. What I cant quite figure out is how to do it with the way the shelf is built. I don’t want to just open a path to the back of the snorkel.
 
The airflow was completely blocked on cylinder #3…….not anymore. Thank you everyone for the ideas on how to tackle the issue.
 

Attachments

  • IMG_1528.jpeg
    IMG_1528.jpeg
    4.2 MB · Views: 110
Back
Top