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Thread: Fixed My CHT Problems, Thanks Fobjob

  1. #1

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    Fixed My CHT Problems, Thanks Fobjob

    Was running high CHT's with an O-320 B2B, rear oil cooler. Baffling tight as a duck. Used a light in a dark hangar to totally darken the upper deck. Could not climb out without going to about 420. After much research I took fobjob's idea of ramps and installed some of my own in consultation with my very cooperative IA. Also put a fence on the right one to help out by the alternator belt. Result? I climbed 5000' at Vy without going over 385 on #4. Front cylinders went up about 20, the rear down about 20. Total delta between all 4 is now 12 degrees. #3 is now the coolest cylinder followed by 4, 2 and 1. Opened up the right ramp a little bit now they all track very nicely together. I will post pictures of the ramps I built after I get them out of paint and reinstalled. This site pays for itself again! Thanks again.

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    Yes pics Please

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    fobjob's Avatar
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    Does the fence on the right one serve the purpose of preventing some air from spilling down the front of the engine? That is where I got my biggest gains....found myself in the unusual situation the other day having to increase my power setting to keep my CHT above 300F...OAT was 20F...

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    That is the idea. How well does it work? I don't know because I have not been without the fence. On the other hand, it may need to be bigger but I am satisfied where I am at right now. I think if I make the fence too big it might start to buzz.

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    Ruffair's Avatar
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    Quote Originally Posted by GeeBee View Post
    Was running high CHT's with an O-320 B2B, rear oil cooler. Baffling tight as a duck. Used a light in a dark hangar to totally darken the upper deck. Could not climb out without going to about 420. After much research I took fobjob's idea of ramps and installed some of my own in consultation with my very cooperative IA. Also put a fence on the right one to help out by the alternator belt. Result? I climbed 5000' at Vy without going over 385 on #4. Front cylinders went up about 20, the rear down about 20. Total delta between all 4 is now 12 degrees. #3 is now the coolest cylinder followed by 4, 2 and 1. Opened up the right ramp a little bit now they all track very nicely together. I will post pictures of the ramps I built after I get them out of paint and reinstalled. This site pays for itself again! Thanks again.
    What CHT gauge are you using..?

    Kem

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    I am using an Insight G2 engine analyzer.

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    Not much problem with high temp up here, but same cyl head temp range problem. looking forward to pictures or any info to duplicate the ramps on my PA-12

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    fobjob's Avatar
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    The ramps by themselves are good for 20F.....block off the flow down the front of the engine and you add another 27F to the 'wonderfulness' department. If you don't want the front cylinder to heat up 20F, then drill about ten 1/4 inch holes in the ramp.

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    would appreciate any tips , pictures and advice, new great lakes bipe running rear pots hot (up to 430f) on climb and at 24 /24 for aeros. All the obvious done plus some tweaks to cowl outlet lip but would be happier to get those rear cyls cooler.


    Mart

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    Quote Originally Posted by fobjob View Post
    The ramps by themselves are good for 20F.....block off the flow down the front of the engine and you add another 27F to the 'wonderfulness' department. If you don't want the front cylinder to heat up 20F, then drill about ten 1/4 inch holes in the ramp.
    Thinking about a fix for the front using Sugru.

    Fobjob, what about the rounded lip on the bottom of the firewall you denote in your drawings? Does it help and if so how do you fabricate it?

  11. #11
    fobjob's Avatar
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    I haven't tried it yet. But, I would take some 2024T3 sheet, (torch it to make it T0) coax it into the appropriate shape, then take about a month trying to make cutouts in it to miss all the stuff on the firewall it would interfere with. Better to make it out of cardboard first, then transfer it to metal. (AFTER you decide whether it works or not) About three inches radius would be minimum, but I'll bet it would be tough to get everything to fit....it's only theory so far. *

    * In theory, theory and practice are the same. In practice, they aren't....

  12. #12
    Tim's Avatar
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    Some guys I know are building an RV-8. At the bottom of the firewall on the engine side is what looks like 2" tubing cut in half length ways. It's about 14" long. I guess it has something to with air flow out of the cowling. I'll get a pic. Anyone ever see something like this

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    Sounds like fobjob's drawings of creating a low impedence situation.

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    gdafoe's Avatar
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    Check this picture of the lower firewall air exit. It is part an interesting thread on the same subject.

    http://www.vansairforce.com/communit...6&postcount=39
    Gerald

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    fobjob's Avatar
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    That's what I love to see: Data!
    Bear in mind, this is a 20 deg gain at dang near 200mph, so the gains for us might only be 10....or 40....??? see how much mechanical interference there is with existing 'stuff' sticking out of the firewall....
    I slowed down my efforts when most of the low hanging fruit had been sampled, but if you like to fiddle, more can be had, but at a cost....

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    Agree it most likely works, but I would avoid that design on the RV. The problem being sheet aluminum edges near engine mount tubing. I almost lost an engine mount on a Commander 112TC when the edge of the sheet metal heat shield fretted almost all the way through the tubing. I was out over water (west of the Golden Gate) made for some pensive moments. If one were to do that I would have a large radius around the tubing sealed with some cowl saver material.

  17. #17
    TirolCub's Avatar
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    ... just an idea to check also the Marvel Schebler SB-22, if you have high or split CHT/EGT temperatures with a Lycoming O320 equipped with relatively new MA-4SPA 10-3678-32 carb ...

    http://msacarbs.com/pdf/SB-22_O%20Ne...l%20Nozzle.pdf

    Cheers

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    That is interesting, thanks for the link. I was not aware of that. I need to check my numbers.

  19. #19
    irishfield's Avatar
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    Keep in mind that the picture of the Van's RV mod is to clean up the lip forward firewall (that causes air flow blockage), that isn't an issue on a SCub as the firewall is smooth at the bottom. This lip is the same issue on the Murphy line.. and picture attached of how I drop the temps in a fiberglass speed cowled Elite by doing something similar.

    Click image for larger version. 

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  20. #20
    Tim's Avatar
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    Wayne, my 2+2 has a lip that sticks out 1/2 to 3/4 of an inch ( I haven't measured it ) and I want to do something like in the pic you posted. My problem is I have a bunch of stuff sticking out in that area. I think I can work around it with much fiddeling. On a 100 MPH airplane how much difference do you think it would make on CHT temps.

    Tim

  21. #21
    irishfield's Avatar
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    This dropped the Elite (on Amphibs) CHT's about 25F and the oil temp (rear mount cooler) about 10F if memory serves me correct... and IF the owner was telling me the truth both before and after.
    Last edited by irishfield; 01-04-2015 at 09:04 PM.

  22. #22
    Tim's Avatar
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    Those CHT numbers are impressive. Thanks

    Tim

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    aviationinfo's Avatar
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    Can someone post a picture of what is meant by "fences" ?

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    Ruffair's Avatar
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    Quote Originally Posted by aviationinfo View Post
    Can someone post a picture of what is meant by "fences" ?
    Maybe a photo of the "ramps" too plz.

  25. #25
    fobjob's Avatar
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    quote:"On a 100 MPH airplane how much difference do you think it would make on CHT temps." unquote// Tim, my best guess, and it's only a guess, that if you did all three sides of the firewall, it probably would be in the 10-15 deg range...
    I'm willing to be surprised, though....

  26. #26

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    Should have photos tomorrow PM guys.

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    TirolCub's Avatar
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    Quote Originally Posted by TirolCub View Post
    ... just an idea to check also the Marvel Schebler SB-22, if you have high or split CHT/EGT temperatures with a Lycoming O320 equipped with relatively new MA-4SPA 10-3678-32 carb ...

    http://msacarbs.com/pdf/SB-22_O%20Ne...l%20Nozzle.pdf

    Cheers
    ... had spoken to Marvel Schebler concerning the SB-22. The answer was that changing the nozzle is only for the experimental engine CC340 and not for the O320 series. They have not tested the change in a O320 (both engines are running exactly the same carburetor MA-4-SPA 10-3678-32) But if it helps in a CC340 why not in a O320?

    Cheers

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    I called them also, the jet size is .106 in case anyone wants to know. The pepperbox nozzle was used in some of the other carbs this is the first one I found for the MA-4-SPA. Do a image search for cub crafters nozzle and the picture pops up.
    DENNY

  29. #29

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    Here are some photos

    Here is the left side parts

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    Here is the left side install details

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    The right side was tougher.

    Here are the parts

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    A pivoting bracket was required

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    Here is all the right side brackets installed

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    The ramp, note the fence

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    Right side fully installed, it is very secure


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  30. #30
    aviationinfo's Avatar
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    Thanks for the great pics!

    I have often wondered how well I should seal up that right side immediately behind the nose bowl. Is there any concern with getting enough cooling air to the alternator if that gap is closed ?

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    If it's completely closed, yes. The fence won't block it much...I built mine very similarly(only not as nice), and completely closing it added 27 deg to the total. Added a separate air scoop and scat hose to supply air to the generator.

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    Is there a source for these "ramps" or "fences"? I would like to try that before buying a complete baffle kit

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    Self fabricated.

  34. #34
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    Do you have drawings/dimensions you would consider sharing?

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    Fabricated on the fly. No drawings, sorry.

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    Put new ramps on the front this year. This has been a 2 year long workup to get it right. Started with aluminized tape on the front cylinders to get the CHTs in line and some other work. Than moved to flat metal plates in front of cylinders last year and this year added the ramps. With just flat plates/tape I was able to get 1-3 and 2-4 within 5-10 degrees of CHT. With a 10-20 degree spread from side to side. I think the ramps which are about 3/4 of an inch lower than the flat plate will do close to the same with a overall drop of 15-20 degrees. I can run at 2500 RPM and keep CHT's below 350 with no problem. I would recommend ALL the changes posted above to help with temps.
    I would not attempt any front baffling changes without a 4 cylinder CHT/EGT!! 1 tape on the front cylinders can change temps to where 1-2 become the hot cylinders. The other thing is to fly it for a year to make sure you cover all the temps you will encounter.
    file:///Users/dennis/Pictures/Photos%20Library_2.photoslibrary/Masters/2015/12/16/20151216-165905/IMG_1724.JPGfile:///Users/dennis/Pictures/Photos%20Library_2.photoslibrary/Masters/2015/12/16/20151216-165905/IMG_1723.JPGfile:///Users/dennis/Pictures/Photos%20Library_2.photoslibrary/Masters/2015/12/16/20151216-165905/IMG_1718.JPGfile:///Users/dennis/Pictures/Photos%20Library_2.photoslibrary/Masters/2015/12/16/20151216-165905/IMG_1717.JPG
    DENNY

  37. #37

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    Well that did not work will try again.
    DENNY
    file:///Users/dennis/Pictures/Photos%20Library_2.photoslibrary/Masters/2015/12/16/20151216-165905/IMG_1724.JPG
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  38. #38

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    OK that is better notice I did not seal the top of the plate with RTV, I wanted air to flow over the plate and down the front of the front cylinders. I left the flat plate I put in last year (cut down 3/4 inch) and hooked the top lip over that. Just need to fly another year to see what the results will be.
    DENNY

  39. #39
    Tim's Avatar
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    By accident I reduced my CHTs 15 to 20 degrees. I took off my sen. wood 80X44 prop and put on my cruise prop a Warnke 74X56 also a wood prop. The hub on the Sen. is much fatter that is the only thing I can think of that made that much difference

  40. #40
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    It is generally assumed that the pressure side of the cowl is set only by ram air pressure. However, I compared my cub (climb prop, 54", sensenich) with another cub, which had a 56" prop. His was a higher pressure, while under cruise power.
    More pitch=higher pressure=better cooling....

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