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Fixed My CHT Problems, Thanks Fobjob

GeeBee

Registered User
Lake Lanier, GA
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.
 
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...
 
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.
 
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
 
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
 
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.
 
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
 
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?
 
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....
 
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
 
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....
 
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.
 
That is interesting, thanks for the link. I was not aware of that. I need to check my numbers.
 
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.

DCP06101.JPG
 

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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
 
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.
 
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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....
 
... 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 New Fuel Nozzle.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? :crazyeyes:

Cheers
 
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
 
Here are some photos

Here is the left side parts

left_side_parts.JPG

Here is the left side install details

Left_side_intall_1.JPG

Left_side_intall_2.JPG

Left_side_intall_3.JPG

The right side was tougher.

Here are the parts

Right_Side_parts_2.JPG

A pivoting bracket was required

Right_side_parts_3.JPG

Here is all the right side brackets installed

Right_side_brackets.JPG

The ramp, note the fence

Right_Side_parts_1.JPG

Right side fully installed, it is very secure


Right_side_intall.JPG
 

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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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