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SJ Cowling Cooling issues

R

rvbldr3170

Active Member
I posted previously on this issue, but I'm interested in some "real world" answers. I am looking for some feedback from people actually using a Sam James cowl on an RV-4 with an 0-360. Mine is an 0-360 A1A with 9:1 pistons, chrome cylinders, 2 mags, and a carb.
I have been chasing high CHT's since first flight, and I can't seem to get 2 of them down below 400 degrees without drastically reducing power. I have flown when OAT was 40 degrees and I still get high CHT's on #2 & #3. That's the confusing part. The hot cylinders are the left front and right rear (as viewed from the cockpit). I have taken the plenum off and checked and remade the inter cylinder baffles twice. I also verified my CHT probes with boiling water, and they seem to be OK. Is there anything on the exit end of the cowling that anybody has tried with any success? My oil temps are fine (never over 210), and my EGT's seem good with no major spread. I am about to scrap the Sam James cowl and go back to Van's, but I want to do everything I can to try to make the SJ cowl work before I do that.
Sam??
 
The heat is on...

Hi Merle,
I have helped several 0-360 RV4 owners install the SJ cowl and talked many out of it. I have raced them before and after the conversion and kept very close tabs on speeds and power settings. The cowling conversion is roughly $250.00 per knot gained. With the pants, leg fairings and wing root fairing it goes up to nearly $1000 per knot.
The high CHT's are not unusual while tweeking the cowl. Make sure there are no leaks and then you can experiment with the lower cowl lip removing 1/4" at a time. Send me an email and we can chat anytime.

Smokey
[email protected]
 
smokyray said:
Hi Merle,
I have helped several 0-360 RV4 owners install the SJ cowl and talked many out of it. I have raced them before and after the conversion and kept very close tabs on speeds and power settings. The cowling conversion is roughly $250.00 per knot gained. With the pants, leg fairings and wing root fairing it goes up to nearly $1000 per knot.
The high CHT's are not unusual while tweeking the cowl. Make sure there are no leaks and then you can experiment with the lower cowl lip removing 1/4" at a time. Send me an email and we can chat anytime.

Smokey
[email protected]
Click to expand...

$250/knot is CHEAP!!! Think no airplane to 180 knots for $45,000

$1000/knot; now you're up in RV10 territory...:cool:
 
Have you inspected the cylinder cooling fins around the spark plugs. I have seen most Lycoming cylinders with flash blocking airflow in that area.

It takes a close inspection to find it. If there is any, it needs to be removed as it is THE hot spot. I hace cured many hot 360's by removing the flash from that area.

At Reno one year we looked at the 360 Lycomings in each tent all displaying great paint jobs, and much chrome. 100% of the 360 engines we looked at had some flash there.
 
Sam James Cooling Issues Volume 3

OK, I'll admit it. I reduced my CHT's enough to fly in the colder weather of winter, but now that the OAT's are up, so are my CHT's. How much is too much to remove down on the exit side of the cowling? I have cut it back to where it is shorter than the fuselage bottom where it turns up, and I built an exit ramp (like a non movable cowl flap) that lowers the bottom of the cowl 3/4" and I'm still seeing CHT's over 400F at 2450RPM in cruise flight,(OAT 82) and I'm wondering if I should cut it any more, or work on the inlet side.
As I stated before, there is no leakage in the baffles, I have gone over them 5-6 times and RTV'ed them
From my previous post 0-360, 9:1 pistons, chrome cyl's, carbureted, 23 hours to date.

Gettin' tired of all this messin' 'round!
 
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carb heat?

Merle,

Do you have the standard Vans carb heat door installed in the airbox? Is it connected to the exhaust system or open to the lower cowl plenum? If it is open try this:

Apply carb heat full open prior to take-off

recored CHTs during a Vy climb every 1000 ft and average them.

compare to same data with carb heat closed (off).

at a nominal 2400 rpm during climb the engine consumes approx.. .31 lbm/sec mass flow (standard SL density) which equates to about 12% of the 2.5lbm/sec required to maintain CHTs at about 370 degress (from O-360 lycoming cooling chart). That mass flow into the engine comes from the lower plenum which should drop lower plenum pressure and increase mass flow through the cyl fins hopefully resulting in lower CHTs.

The air is still filtered if you have the standard Vans FAB so no harm in trying this.

Honestly I have not done so myself and just thought of it. Maybe someone else has tried and knows the answer. Somebody might check my math I used a lunch napkin.

This isn't the real solution to your problem but may give you a managable work-around until one is found.


I'll do the same test myself this evening.
 
Pix & Fuel Flow

DanH said:
Merle, post some pictures.
Click to expand...

I'll take some pix tomorrow when I'm over there.
Also the fuel flow varies I've tried not leaning, and that helps, but only incrementally. The Dynon shows between 7-7.5 GPH at 2450 RPM when leaned to peak.
 
RV8R999 said:
Merle,

Do you have the standard Vans carb heat door installed in the airbox? Is it connected to the exhaust system or open to the lower cowl plenum? If it is open try this:

Apply carb heat full open prior to take-off

recored CHTs during a Vy climb every 1000 ft and average them.

compare to same data with carb heat closed (off).

at a nominal 2400 rpm during climb the engine consumes approx.. .31 lbm/sec mass flow (standard SL density) which equates to about 12% of the 2.5lbm/sec required to maintain CHTs at about 370 degress (from O-360 lycoming cooling chart). That mass flow into the engine comes from the lower plenum which should drop lower plenum pressure and increase mass flow through the cyl fins hopefully resulting in lower CHTs.

The air is still filtered if you have the standard Vans FAB so no harm in trying this.

Honestly I have not done so myself and just thought of it. Maybe someone else has tried and knows the answer. Somebody might check my math I used a lunch napkin.

This isn't the real solution to your problem but may give you a managable work-around until one is found.


I'll do the same test myself this evening.
Click to expand...

Ooops disregard this idea - doesn't work - tried it. While the idea I believe has merit the implementation in our current configuration won't allow it. The seal between the FAB and the intake inlet will not support the total pressure (static plus dynamic) which results in blow-by and flow directly into the lower plenum through the seal. If we could find a way to positively secure the seal from FAB to intake inlet then I believe using CARB heat may actually help increase mass flow through the cyl by reduction in lower plenum pressure - effectively this increases the exit size of the cowl by pumping lower plenum air through the engine and out of the exhaust. We need to seal that junction first!!! Anyone have a method to do this? I suppose creating an access panel on the lower intake inlet area to allow for a hose clamp around the seal would work? This may have the added benefit of increasing MAP in level flight when carb heat is turned off again.

My average CHTs increased from 352 to 357 under similar ambient conditions with CARB heat on in a Vy climb from SL to 8000.
 
too Lean

rvbldr3170 said:
The Dynon shows between 7-7.5 GPH at 2450 RPM when leaned to peak.
Click to expand...
Pretty sure you are running too lean. What is your carb set up? what model carb, etc. Are you getting full travel on your mixture control cable? The problem is most likely not the James cowl, it is a basic fuel flow problem.
A lot of o-360's came with 10-3868 carbs and are too lean. The 10-4164 is the corrrect one for the 0-360 in an RV. Lots of info in the archives about this topic.

http://www.avweb.com/news/pelican/182179-1.html?type=pf
Link to John Dekin's articles found on AVWeb under Pelican Perch...#63 Where do I run my engine. Read the whole article but focus on the Fuel Flow part.
 
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