The Murphy Builders Site

My 0320 E2D with the speed cowl (modified with two access doors) and Ellision
Throttle Body carb, runs hot on the CHT's. The hottest hangs around 400 F if
I "don't" lean with EGT's at 1350. And 415 F if I do lean with EGT's at 1500.
This is all at around 75% power. Walter told me it will get worse on floats.

All baffling is MAM specs, tight with no leaks. I'm thinking of putting a
baffle at the front behind the flywheel like RV's and certified aircraft do.
There is a lot of escaping air there. I'm not convinced cutting giant exit holes
is the only answer although it seemed to cure Walter's temp problems.

Lycoming says keep the CHT's under 400 F at 75% and under 435 F at high
performance. I could almost just deal with it now but I'm concerned if it gets
worse with the floats I'll be forced to fix it then anyway.

I didn't think EGT's were effected so much by the CHT temps as much as they
are by leaning. Probe location should not be a factor if they are calibrated
and placed as manufacture specs. Could the Ellision Carburetor effect the EGT
temps or is the speed cowl just a poor design all together?

Bruce 357R



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Hi Bruce,
Just my two cents worth. Tommy Jones in Nfld had the same problem with high
temps. I built up his engine for him - 0320B3B. I believe he was in the
230's on oil temp hot and heavy during climb. I suggested he enlargen his
duct to his cooler and to open up the bottom of his cowl.. He was reluctant
to do this but did with results of much lower temps. Just back up and think
of what the words "high speed cowl" refers to when you apply it to a float
configuration. Do they belong together?

Steve W. #637.

From: Legeorgen@aol.com
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Re: CHT's Date: Sat, 14 Jun 2003 10:40:19 EDT

My 0320 E2D with the speed cowl (modified with two access doors) and
Ellision
Throttle Body carb, runs hot on the CHT's. The hottest hangs around 400 F
if
I "don't" lean with EGT's at 1350. And 415 F if I do lean with EGT's at
1500.
This is all at around 75% power. Walter told me it will get worse on
floats.

All baffling is MAM specs, tight with no leaks. I'm thinking of putting a
baffle at the front behind the flywheel like RV's and certified aircraft
do.
There is a lot of escaping air there. I'm not convinced cutting giant exit
holes
is the only answer although it seemed to cure Walter's temp problems.

Lycoming says keep the CHT's under 400 F at 75% and under 435 F at high
performance. I could almost just deal with it now but I'm concerned if it
gets
worse with the floats I'll be forced to fix it then anyway.

I didn't think EGT's were effected so much by the CHT temps as much as they
are by leaning. Probe location should not be a factor if they are
calibrated
and placed as manufacture specs. Could the Ellision Carburetor effect the
EGT
temps or is the speed cowl just a poor design all together?

Bruce 357R



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I think you are putting things backwards here Bruce! It's not EGT's that are
effected by CHT's when leaning., it's the other way around. Your CHT's are
rising because the flame coming out the exhaust port is 150+ degrees more
than it was before you started leaning. OF course some of that heat is going
to raise the CHT's and this is why you should always go full rich before a
climb so the extra fuel acts as a coolant. Also remember that a carbureted
lyco can have as much as 200*F difference between cylinders, on CHT's, due
to different length intake runners etc and fuel injected systems around
100*F differential between cylinders. Yours would fall under the 200*F
category even with the throttle body as it's still not fuel injected. Are
you monitoring all the cylinders or just one. Maybe you need to move the
probe around and find you hottest and coolest cylinders.

Also, with you stating 1500* EGT's I suspect that you have your probes
tooooo close to the exhaust port. They should be at least 3 inches away and
somewhere between 3" and 4" is better. I know as we had Howard's about 2
inches or so away and he was showing 1580 or so and his monitor was always
going into alarm when you put the power to it (that of course threw the
flame a little further out the ports). Moving the probes to about 3 1/2"
from the exhaust flange settled down the large increases and decreases due
to throttle postion changes and made monitoring 1000% more consistant.

From the Lyco "Flyer" - Key Reprints - Cylinder temps are alright anywhere

between a minimum of 150*F and MAXIMUM of 500*F for a direct drive normally
aspirated engine (475*F for some higher power complex engines). Engines do
benefit by keeping below 400*F and in cruise/climb it's fully normal to
operate between 350*F and 435*F .

Remember also that Lyco only recommends the bayonet CHT probes that thread
into the cylinder heads tapped hole in the bottom fins of the cylinder. If
you are using under the plug senders these usually read 25 to 50*F higher
than the bayonets. That reminds me that I have under the plug ones so my
375/385 may only be 325 to 350*F!! If you have the under plug senders then
you are fine as well. If you have the bayonets then maybe opening your
cowling outlet will pull them down the 25* or so you are looking for. We
"pulled" Howard's temps down by over 75*F opening his MAM stock cowling to
the way the pics show it on the archives.

Wayne


----- Original Message -----
From: <Legeorgen@aol.com>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, June 14, 2003 10:40 AM
Subject: Re: CHT's

My 0320 E2D with the speed cowl (modified with two access doors) and

Ellision

Throttle Body carb, runs hot on the CHT's. The hottest hangs around 400 F

if

I "don't" lean with EGT's at 1350. And 415 F if I do lean with EGT's at

1500.

This is all at around 75% power. Walter told me it will get worse on

floats.

All baffling is MAM specs, tight with no leaks. I'm thinking of putting a
baffle at the front behind the flywheel like RV's and certified aircraft

do.

There is a lot of escaping air there. I'm not convinced cutting giant exit

holes

is the only answer although it seemed to cure Walter's temp problems.

Lycoming says keep the CHT's under 400 F at 75% and under 435 F at high
performance. I could almost just deal with it now but I'm concerned if it

gets

worse with the floats I'll be forced to fix it then anyway.

I didn't think EGT's were effected so much by the CHT temps as much as

they

are by leaning. Probe location should not be a factor if they are

calibrated

and placed as manufacture specs. Could the Ellision Carburetor effect the

EGT

temps or is the speed cowl just a poor design all together?

Bruce 357R

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Hi Steve,

My oil temps are OK, it's just the CHT's that I'm concerned with. I think of
the speed cowl as a looks thing as it doesn't add any speed that I'm aware of.
I do like the looks of the speed cowl but if it cooks my engine I'm sure to
change my mind real quick.

Bruce 357R



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Wayne,

I monitor all cylinders with the bayonet type and they do run around 125*
spread. I will remember to measure the EGT probes next trip to the plane but I
believe they were more like 1/2" or 2" from the port. The cross over exhaust
came with the engine I bought with 125 hours.

Running rich will keep the CHT's about 15* to 20* cooler. So ... is it OK to
cruise at 75% power and 415* CHT's on the Lyc. or is it better to bring them
down to 390* or so by what ever method?

Bruce 357R



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Yes, Bruce, I would say if you're cruising at 415 on
wheels, you're going to have trouble on floats. I just
got back from the lake, and today mine was running at
380 - 390 in cruise, but it wasn't a hot day either.
Last weekend, though, I put it to the test as we had
32C degree (90 F) plus weather here. My cruise then was
around 400 which is marginally acceptable. I also was
doing some climbs from sea level to 8500 ASL for some
sight seeing and it would heat up to 450 before I would
back off and let it cool a bit. I had to do that twice
in a climb, but once I got past 5000, I could keep
climbing without having to back off.

I am still tweaking my cooling, and the latest is a
lexan eyebrow riveted to the top lip of my left inlet.
I think it helped a bit, at least in climb, maybe 5 or
10 degrees. Not much else for me to try, as I've got
the giant opening with lips at the bottom as you
described, my bottom firewall flange is faired, top
cowl front is sealed, and I have the inlets all
smoothly ramped top and bottom.

Having said that, I am thinking of raising the inner
tops of the inlets to make them bigger. My neighbour at
the hangar is tired of hearing me complain, and seeing
my futile tweaking attempts, so has offered to help. He
is a real fibreglass expert, unlike myself. Hope it
doesn't ruin the looks, though, as that's about all the
speed cowl had going for it. Not sure what else there
is to try.

I should mention that I run mine at LOP EGT in cruise
which does cool it slightly from peak EGT. It saves
more on fuel, too. I used to run it at peak or ROP and
it ran about 5 or 10 degree CHT hotter. In my case, the
hottest CHT cylinder also reaches peak EGT first when
leaning, so running it LOP helps balance my temps. This
is at 2350 RPM (65% power). I wouldn't do that at
higher power settings. This is all with regular Mogas.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
Legeorgen@aol.com
Sent: Saturday, June 14, 2003 8:21 PM
To: murphy-rebel@dcsol.com
Subject: Re: CHT's


Wayne,

I monitor all cylinders with the bayonet
type and they do run around 125*
spread. I will remember to measure the EGT
probes next trip to the plane but I
believe they were more like 1/2" or 2" from
the port. The cross over exhaust
came with the engine I bought with 125 hours.

Running rich will keep the CHT's about 15*
to 20* cooler. So ... is it OK to
cruise at 75% power and 415* CHT's on the
Lyc. or is it better to bring them
down to 390* or so by what ever method?

Bruce 357R



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As Walter says it would be better to get them down below 400 if you can. I
think Howard's are still running the + side of 400* though and so far no
detriment seen to his cylinders, as his compression is still a lowest
cylinder of 77/80 on his Cermichromes. Will ask him when he comes in for
fuel next what temps he is seeing, now that last year I changed his EIS over
to the newer model that watches all 4 CHT and EGT's at the same time and
installed bayonets for CHT after removing his under plug senders (so he has
some true numbers instead of the fictitious ones we were chasing originally
while cutting and expanding his cowl exits due to the high numbers shown by
the under plug senders).

Wayne

----- Original Message -----
From: <Legeorgen@aol.com>
To: <murphy-rebel@dcsol.com>
Sent: Saturday, June 14, 2003 11:21 PM
Subject: Re: CHT's

Wayne,

I monitor all cylinders with the bayonet type and they do run around 125*
spread. I will remember to measure the EGT probes next trip to the plane

but I

believe they were more like 1/2" or 2" from the port. The cross over

exhaust

came with the engine I bought with 125 hours.

Running rich will keep the CHT's about 15* to 20* cooler. So ... is it OK

to

cruise at 75% power and 415* CHT's on the Lyc. or is it better to bring

them

down to 390* or so by what ever method?

Bruce 357R

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Hi Bruce,
Don't know what Tommy's cyl temps were exactly but do remember they were up
off the scale for safe operation. I am not really familiar with the speed
cowl but if it was built for higher cruise in mind, the inlet holes are most
likely smaller than the conventional cowl thus lesser cooling ability. I
got the standard cowl as I had floats in mind right from the beginning. I
agree the speed cowl looks really nice. I fly a C-210 for a living and
could get use to having cowl flaps on my Rebel! There are not really
complicated. Large open area for climb and a sleek belly in cruise. . ..
take care

Steve W.

From: Legeorgen@aol.com
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Re: CHT's
Date: Sat, 14 Jun 2003 22:28:49 EDT

Hi Steve,

My oil temps are OK, it's just the CHT's that I'm concerned with. I think
of
the speed cowl as a looks thing as it doesn't add any speed that I'm aware
of.
I do like the looks of the speed cowl but if it cooks my engine I'm sure to
change my mind real quick.

Bruce 357R



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