RV Baffles - Mod to Reduce CHT

Hey Folks,
I have been happily flying my experimental for over 200 hours now. The airplane has been a joy to fly. One thing that has been an nuisance is my #3 CHT. It oftens runs extra hot compared to other cylinders, especially in summer time. It hangs out around 385-390F while the others are 350 and below. In an extended climb, #3 will go up to 425F-450F pretty quickly in the summer. I have been trying all kinds of fixes, like ramp angle, extra outlet air, etc. None were very effective.

I have the RV baffles on my Cub. In talking to some folks at JC, it seems that RV baffles run hotter than the stock Cub style baffles. I would imagine this is because they are tuned for a 200mph airplane and not so much Cub speeds. None of my friends with stock style baffles said they had a cooling problem. As I looked at various Cub baffles, the only major difference I could find was around the #3 cylinder. I don't have a cooling problem with my other cylinders. The RV baffle is angled and pulls in very tight around #3. So I modified my #3 RV baffle area to be more like a stock Cub, which is more boxed and has around a 2" air gap behind the cylinder.

I tested my modification yesterday and the results were immediately evident, my #3 CHT now is about 30-35F cooler. In fact #3 is no longer the hottest cylinder, #4 is 2 or 3 degrees hotter. During an extended climb, both #3 and 4 stay below 400F. So I was very happy with this modification. I posted this mainly to help those with experimentals who want to run the RV baffles and still have good cooling performance. The RV baffles are around $500 cheaper than the certified kits.

To modify, made a vertical cut in the rear baffle to seperate that section behind upper cylinder. I then flattened the rear baffle, added some sides/ducting, riveted closed. Siliconed the joints. It took me two evenings to complete. Would be a lot easier to modify if the kit wasn't installed yet. Hope this info helps!

Just to add, I have no idea why this is better and improved the CHT. It would seem the RV style is more efficient, but I guess for the Cub speeds it is not. Baffles are a mysterious thing.

lower speed means lower pressure...

my guess:

larger volume of air is able to travel past the cylinder now, as the air won't 'back up' as much on top trying to pass down.

My guess is the #1 temp went down a shade also?

Cool solution, thanks for brining this up. Glad you are having so much fun with it, I look forward to seeing it again at JC next year.

The old baffle on #3 looks plain wrong! Your modified (new) rear gap makes perfect sense to me. Thank you for the details and the fix. Good post.

(Air compressing goes slower and heats -- Air expanding goes faster and cools)

I also used the RV Baffles on the O-320 in my E-AB Cub. When I built the cowl sides, I opened up the cowl cheeks quite a bit to help draw more air through. Knowing that #3 is typically the hottest cylinder, I only used a CHT on #3 cyl. It tops out at 375* in a hard climb on a summer day, then drops back to 340* for normal cruise, or 300* for just putting around at 2200 rpm. I don't have the other cylinders instrumented, but I expect they are likely running a bit cooler than desired. The oil cooler is mounted to the left rear baffle with similar results. It might get up to 205* on a summer day if I really hang it on the prop, but will immediately drop back to 180* as soon as I pitch over.

BTW, Bugs, your web site was immensely helpful to me while finishing my Cub.

-CubBuilder

I think my #1 is running cooler now also, side benefit but it rarely got over 325, usually hangs around 310 or so. Will be flying it some more this weekend when expected OAT is 90F and will report back here.

CubBuilder, interesting, like I said baffles are mysterious. I think there are a lot of variables for the entire cooling system. I have O-360 baffles, do the RV O-320 baffles look the same? All I can say is this mod helped me the most so far. Thanks!

What's up with that #3 picture. Is that nut and cotter key part of the spring, ball, & seat housing? Doesn't look right is it pic or me

EXCELLENT and INFORMATIVE post Christian. Just what us experimental guys need. I had the same issue with the Vans baffling and tried numerous fixes all to no avail. I was looking at that very section as well. Glad to know that was the problem. Thank you!!!

Bill

Bugs66 said:

CubBuilder, interesting, like I said baffles are mysterious. I think there are a lot of variables for the entire cooling system. I have O-360 baffles, do the RV O-320 baffles look the same? All I can say is this mod helped me the most so far. Thanks!

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The O-320 RV baffles are very similar to the O-360 baffles. I've got some pictures on my web site at <http://jscott.comlu.com/Cub/firewall_forward/Firewall_Forward%202.html>, but not any close detail of the area you modified.

-CubBuilder

Lance said:

What's up with that #3 picture. Is that nut and cotter key part of the spring, ball, & seat housing? Doesn't look right is it pic or me

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Adjustable oil pressure relief valve. Attached parts catalog page for O-360-A1A.

Interesting that it made that much difference. I need to make that change as well. Thanks for the information.

Christian, If I am not mistaken the RV6 baffles for the conical mount O-320 that I have used were straight up on the rear. These are some pictures of my Dad's baffles on his Clipper. It is always interesting to me how this stuff works and what changes effect what.

Lance said:

What's up with that #3 picture. Is that nut and cotter key part of the spring, ball, & seat housing? Doesn't look right is it pic or me

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Lance, That is the late model adjustable oil pressure relief valve.

Figured that's what it was, just never seen one like that

In the pic it looks like you can just turn the whole thing with a screwdriver. If that nut is a lock or jam nut, I can't see how it's working.

No big deal. Not loosing sleep over it , was just curious.

Sorry for thread creep

Lance

Did you put the baffling in that goes across the front of the case right behind the nosebowl? This is the key to getting good cooling because if you leave it out it will let a lot of air out around there lowering the pressure through the cylinders and increasing the pressure under the engine. I have the stock RV7 baffling on mine with a hot rod O-320 and never see high CHTs or oil temps even on 100* days. The pics show a little of it , I don't seem to have a real good one. Don

pittsdriver said:

Did you put the baffling in that goes across the front of the case right behind the nosebowl?...

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I put the front baffles on earlier this year. It helped a little but not enough. If you look at stock Cubs they don't have it and cool fine. Glad yours are working ok, that's what you want!

Steve Pierce said:

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Steve, What's with the upside down cylinder casting numbers?? Lycoming has them right side up.

Narrow deck O-320.

Steve, how about the #3 side?

This is the best picture I could find of #3.

pittsdriver said:

Did you put the baffling in that goes across the front of the case right behind the nosebowl? This is the key to getting good cooling because if you leave it out it will let a lot of air out around there lowering the pressure through the cylinders and increasing the pressure under the engine. I have the stock RV7 baffling on mine with a hot rod O-320 and never see high CHTs or oil temps even on 100* days. The pics show a little of it , I don't seem to have a real good one. Don

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Sorry, more thread creep..... What exhaust system have you got there?

Andrew.

MainlandCub said:

Sorry, more thread creep..... What exhaust system have you got there?

Andrew.

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I got it from Steve Tubbs and would have to look in my receipts. Just after I got this one Vetterman came out with an almost identical system for half the price and the same quality. That's what I would go with today. Don

MainlandCub said:

Sorry, more thread creep..... What exhaust system have you got there?

Andrew.

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I have a similar exhaust on my Cub which I got here http://www.customaircraft.com/

It is well built and fit perfectly.

Looking at all the sheet metal used for Supercub baffles makes me appreciate the simplicity and easy cylinder access of my Crosswinds baffles.

skywagon8a said:

I have a similar exhaust on my Cub which I got here http://www.customaircraft.com/ View attachment 7536

It is well built and fit perfectly.

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That's what mine is. The Vetterman is identical and the same quality for about half the price. Don

Vetterman Exhaust also has a light weight, dual muffler system available that weighs just under 10 lbs installed. Sorry for the thread creep thought I'd throw that out there.

Pittedriver, where did those baffles for the front of your engine come from, they look good, and I want a set. Thanks

Tim

I too got my exhaust from Tubbs. It was probably built by Custom. Fit great, no problems,....... except........ I FROZE MY ARSE OFF. I could not get enough heat out of that thing to even tell if it was working. Welded in 30% more studs and still froze. Could hold my hand in front of the cabin heat box all day without getting hot. Other cubs I have flown would melt your boots (or gloves) if you put it in front of the cabin heat box for more than a few seconds. I doubt I'll use either of those exhausts next time. I am open to other ideas.....need a muffler.....

Bill

I have the custom exhaust and it's so hot, I can barely open the heating valve. The muffler has the heating studs. Carb heat works great. I also put in the heated seats you can find auto-aftermarket, every little bit helps.

Tim said:

Pittedriver, where did those baffles for the front of your engine come from, they look good, and I want a set. Thanks

Tim

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The baffles are the RV6/7 from Vans. Don