Mogas: what happens to EGTs?

Stu Gotts
shared these priceless pearls of wisdom:

-Before this morfs into how the innkeeper built his homemade fuel
-pumper, I thought I would post the answers. I'm surprised many more
-didn't take a shot at this but then again, it's not regular hangar
-chat. How well did you do?

The innkeeper built his homemade fuel pumper after seeing the plans that a
sparky gave him at an Oshkosh forum, but to the point...

Now to the point -- I thought you said that your source had DONE the experiment
and HAD data. People who have been there and done that don't say "SHOULD" and
"PROBABLY", they say "DID". I think you've dicked the problem without hard
data.


Jim


-
-EGT = Exhaust Gas Temperature
-CHT = Cylinder Head Temperature
-ROP = Rich of Peak
-LOP = Lean of Peak
-(and I should have listed this earlier, sorry!)
-
-
-The lower octane should cause a faster overall burn time and short
^^^^^^
-interval to peak pressure - - and that should result in lower EGTs.
^^^^^^
-
-For the same reasons, the peak pressure increase should cause higher
^^^^^^
-CHTs.
-
-And the horsepower ?? It probably would not change much... 1-2 % .
^^^^^^^
-
-The overall effect is the same as if you had improperly advanced the
-timing 3-7 degrees.
-
-Regards, George
-
-Contact George at gami.com for any further explanations.
-
-
-
-
-
-
-Ok... little MOGAS quiz for you.
-
-You run the Left tank dry and fill it up with premium unleaded car
-gas.
-
-Right tank has 100LL.
-
-Takeoff on the RH tank and climb, level off, and set up the mixture
-for
-cruise flight. Either ROP or LOP. Your choice.
-
-
-THEN, you switch to the LEFT tank. You change nothing else.
-
-Later you download your JPI and plot the data.
-
-1 What is it going to show happened to the EGTs when you switched
-tanks?
-
-2 What is it going to show happened to the CHTS when you switched
-tanks?
-
-3 (not in the JPI, but: ) What is the airspeed going to do? Increase?
-Decrease? Stay the same?
-
-Why?
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"Newps" wrote in message
news:1UQ2c.82422$PR3.1197113@attbi_s03...


Jim Weir wrote:

-
-1 What is it going to show happened to the EGTs when you switched
-tanks?

The EGT should show a very slight increase. The higher the octane, the
smoother
and cooler the burn.

I don't think I agree with this last sentence. First of all the burn may
be just as smooth with a lower octane with a low compression engine. High
octane fuel like 100LL has no benefits for an A-65 Continental engine with
6.3:1 compression ratio and loves the 80 octane gasoline it was designed
for.

And if the burn is cooler when 100LL (rather than 80) is run through the
carb, why is it the engine must have special 100LL exhaust valves, which are
designed with high-temperature alloys?


You have gone from 100 octane to (arguably) 87 or 93
octane and the car gas should burn hotter.

Are not the auto and aviation octane scales different?


I don't know the answer but I tell you what I suspect. I suspect the egt
of 100LL will be higher. Think about it and correct me if I'm wrong. The
low compression Continentals when they are rebuilt -- the A-65's, O-200's,
and O-300's --- have optional 100-octane exhaust valves available from the
parts supply houses like Fresno Airparts. Now WHY is that, other than
because the mix is still burning when the exhaust valve opens? My
suspicion. You (anyone) tell me, with an intelligent explanation, if I'm
wrong.

Higher octane gasoline like 100LL, furthermore, is a little less volatile
than mogas and burns more slowly because of the higher RON numbers, so that
when the exhaust valve opens combustion is less complete than with the same
charge of mogas -- in the low-compression O-300. So if you're running
100LL in an O-300-powered 172, why do you need 100-octane exhaust valves,
whose faces are something like inconel or another exotic alloy designed for
temperatures much higher than the stock exhaust valves?

" jls"
shared these priceless pearls of wisdom:

-
-And if the burn is cooler when 100LL (rather than 80) is run through the
-carb, why is it the engine must have special 100LL exhaust valves, which are
-designed with high-temperature alloys?

The alloy of a valve in a low-compression Continental engine is precisely the
same alloy as the 100LL exhaust valve. The 100LL valve has had some machine
work and clearance work (mainly in the stem area and in the angle of the valve
seat area) done to make it compatible with the excess 100LL lead that jams
valves.



-I don't know the answer but I tell you what I suspect. I suspect the egt
-of 100LL will be higher.

You suspect wrong. I have made this exact same measurement on several
low-compression Continentals before I started using mogas (primarily the O-300D,
but a couple of more engines to a lesser extent. Mogas burns hotter according
to the EGT.


-Higher octane gasoline like 100LL, furthermore, is a little less volatile
-than mogas and burns more slowly because of the higher RON numbers, so that
-when the exhaust valve opens combustion is less complete than with the same
-charge of mogas -- in the low-compression O-300. So if you're running
-100LL in an O-300-powered 172, why do you need 100-octane exhaust valves,
-whose faces are something like inconel or another exotic alloy designed for
-temperatures much higher than the stock exhaust valves?

You predicate your entire argument on the fallacy of "exotic alloy" valves, when
in fact, the only difference is in the settings of the lathe that cuts them.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Before I would buy into any of this (this runs hotter/cooler than that) I would
like to see some kind of quantitative study, i.e. a quantity of different size
engines from the same manufacturer and then different manufacturers. Other
things also like what seasonal additives the mogas may or may not have. After
13 years of dynomometer testing on air cooled VW engines I have seen the same
motors react ever so slightly to things like different fuel, etc. due to things
like, for example, timing (ignition, valve, whatever) being a tick different.
What I'm saying is that one engine may seem to run hotter with a different fuel
while another may seem to run cooler with the same switch.

Jim

"Jim Weir" wrote in message
news
" jls"
shared these priceless pearls of wisdom:

-
-And if the burn is cooler when 100LL (rather than 80) is run through the
-carb, why is it the engine must have special 100LL exhaust valves, which
are
-designed with high-temperature alloys?

The alloy of a valve in a low-compression Continental engine is precisely
the
same alloy as the 100LL exhaust valve. The 100LL valve has had some
machine
work and clearance work (mainly in the stem area and in the angle of the
valve
seat area) done to make it compatible with the excess 100LL lead that jams
valves.

I stand corrected, then. Thanks for your lecture and I note that you
rubbed it in a little too. OK, all in a day's fun. I can take it.
Sniffle I had read that the 100 octane valve was a different alloy but
always wondered if it were so. It sure is a comparatively expensive little
bugger.

-I don't know the answer but I tell you what I suspect. I suspect the
egt
-of 100LL will be higher.

You suspect wrong. I have made this exact same measurement on several
low-compression Continentals before I started using mogas (primarily the
O-300D,
but a couple of more engines to a lesser extent. Mogas burns hotter
according
to the EGT.

Thanks. I will find out soon with respect to my own O-300 which will have
EGT sensors and will compare results. Btw I enjoyed the poke you took at
the poor guy who had chickens in his sparkplugs. He was right gentlemanly
about the poke too.


-Higher octane gasoline like 100LL, furthermore, is a little less
volatile
-than mogas and burns more slowly because of the higher RON numbers, so
that
-when the exhaust valve opens combustion is less complete than with the
same
-charge of mogas -- in the low-compression O-300. So if you're running
-100LL in an O-300-powered 172, why do you need 100-octane exhaust
valves,
-whose faces are something like inconel or another exotic alloy designed
for
-temperatures much higher than the stock exhaust valves?

You predicate your entire argument on the fallacy of "exotic alloy"
valves, when
in fact, the only difference is in the settings of the lathe that cuts
them.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir wrote:

Stu Gotts
shared these priceless pearls of wisdom:

Now to the point -- I thought you said that your source had DONE the experiment
and HAD data. People who have been there and done that don't say "SHOULD" and
"PROBABLY", they say "DID". I think you've dicked the problem without hard
data.


Jim

I agree, but that's not in character for him. But if I may be so bold
to correct the Great Weir, "Shall" must be used rather than "Should".
You're a big boy, call him up and ask him. My "source" is George
Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
etc. He wrote it, he sent it, he answered it. You may be surprised
to hear how he arrived at the answers.

I don't give a DAMN how he arrived at the answers other than doing the
experiment. Obviously he hasn't. I don't know what is in "character" for a
person of this magnitude other than to tell it right up front HOW he measured it
and under WHAT conditions. Then others can repeat the experiment and show it
valid or not.

Every scientist from the dawn of time through Newton and Einstein published
their theory, and then the proofs, and then the experiments to prove them right
or wrong. If Brother Braly isn't willing to give us hard numbers as to his
measurements, then we are just whistling in the wind.

Try again, and no, I'm not going to waste my time with phone calls. If the
"probably"s in this newsgroup were laid end to end, it would be a good idea.

Jim





Stu Gotts
shared these priceless pearls of wisdom:

-On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir wrote:
-
-Stu Gotts
-shared these priceless pearls of wisdom:
-
-Now to the point -- I thought you said that your source had DONE the
experiment
-and HAD data. People who have been there and done that don't say "SHOULD"
and
-"PROBABLY", they say "DID". I think you've dicked the problem without hard
-data.
-
-
-Jim
-
-I agree, but that's not in character for him. But if I may be so bold
-to correct the Great Weir, "Shall" must be used rather than "Should".
-You're a big boy, call him up and ask him. My "source" is George
-Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
-etc. He wrote it, he sent it, he answered it. You may be surprised
-to hear how he arrived at the answers.
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Too bad your scope doesn't include an open mind and open ears. What
seems to be your problem? Something you can't claim to know anything
about? Poor baby!

For those that realize Weir can hurt as much as he helps (old age
assaholism, I guess, or maybe he's still ****ed that a foreigner could
beat him in the election), and would like to pursue this, a simple
email to George will give you any answers yo o may need to justify his
quiz Q & A's. I know the guy and his company and his work, and I'll
take him at his word. I'll drop him an email to see if he claims to
know anything about manufacturing electronics (other than the PRISM
system), but I somehow bet he'll leave that to the real experts in
the field without questioning them about what they eat for breakfast.

On Mon, 08 Mar 2004 19:47:05 -0800, Jim Weir wrote:


I don't give a DAMN how he arrived at the answers other than doing the
experiment. Obviously he hasn't. I don't know what is in "character" for a
person of this magnitude other than to tell it right up front HOW he measured it
and under WHAT conditions. Then others can repeat the experiment and show it
valid or not.

Every scientist from the dawn of time through Newton and Einstein published
their theory, and then the proofs, and then the experiments to prove them right
or wrong. If Brother Braly isn't willing to give us hard numbers as to his
measurements, then we are just whistling in the wind.

Try again, and no, I'm not going to waste my time with phone calls. If the
"probably"s in this newsgroup were laid end to end, it would be a good idea.

Jim





Stu Gotts
shared these priceless pearls of wisdom:

-On Mon, 08 Mar 2004 08:08:58 -0800, Jim Weir wrote:
-
-Stu Gotts
-shared these priceless pearls of wisdom:
-
-Now to the point -- I thought you said that your source had DONE the
experiment
-and HAD data. People who have been there and done that don't say "SHOULD"
and
-"PROBABLY", they say "DID". I think you've dicked the problem without hard
-data.
-
-
-Jim
-
-I agree, but that's not in character for him. But if I may be so bold
-to correct the Great Weir, "Shall" must be used rather than "Should".
-You're a big boy, call him up and ask him. My "source" is George
-Braly of GAMI. You know, injectors, turbo normalizing, PRISM, APS,
-etc. He wrote it, he sent it, he answered it. You may be surprised
-to hear how he arrived at the answers.
-

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"Jim Weir" wrote in message
news
" jls"
shared these priceless pearls of wisdom:

-
-And if the burn is cooler when 100LL (rather than 80) is run through the
-carb, why is it the engine must have special 100LL exhaust valves, which
are
-designed with high-temperature alloys?

The alloy of a valve in a low-compression Continental engine is precisely
the
same alloy as the 100LL exhaust valve. The 100LL valve has had some
machine
work and clearance work (mainly in the stem area and in the angle of the
valve
seat area) done to make it compatible with the excess 100LL lead that jams
valves.

Now that I have done some homework, I find your statement here to be in
error. Please look up the alloy formula for stellite, which is the exotic
alloy coating on expensive 100-octane aircraft engine exhaust valves. I
bought several of these exhaust valves recently for a small Continental
engine. I had earlier told you that I stood corrected but now must refute
what you have said here after having studied your arguments and contentions.
As for most of the typical exhaust valve surface it is chromium-plated and
the stellite added to the 100-octane exhaust valve is plated onto the
seating face.



-I don't know the answer but I tell you what I suspect. I suspect the
egt
-of 100LL will be higher.

You suspect wrong. I have made this exact same measurement on several
low-compression Continentals before I started using mogas (primarily the
O-300D,
but a couple of more engines to a lesser extent. Mogas burns hotter
according
to the EGT.

Yes, then, a negligible number, like 9 degrees as stated by a later poster
flying an O-360 powered 172 with avgas in one tank and mogas in the other.
'Net homework also shows, as this poster found, a negligible increase in EGT
with mogas.



-Higher octane gasoline like 100LL, furthermore, is a little less
volatile
-than mogas and burns more slowly because of the higher RON numbers, so
that
-when the exhaust valve opens combustion is less complete than with the
same
-charge of mogas -- in the low-compression O-300. So if you're running
-100LL in an O-300-powered 172, why do you need 100-octane exhaust
valves,
-whose faces are something like inconel or another exotic alloy designed
for
-temperatures much higher than the stock exhaust valves?

You predicate your entire argument on the fallacy of "exotic alloy"
valves, when
in fact, the only difference is in the settings of the lathe that cuts
them.

I am afraid that the manifest weight of authority is against you and
completely refutes you on your contention here. I just looked up those
stellite constituents for the typical 100-octane stellite exhaust valves
sold for Continental engines. They are pretty exotic, as in: manganese,
molybdenum, chromium, silicon, nickel, and cobalt. That doesn't sound to
me like enhancing a steel valve with a lathe. That stellite stuff sounds
like "exotic alloy" hardening to me.

You do YOUR homework now, fella. I'll respect your authority on the issue
of radios and antennae, however. I have now retracted my earlier statement
admitting error and saying that I stood corrected. The floor is yours now
to resurrect your case, if that is possible.

Jim

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

" jls"
shared these priceless pearls of wisdom:

-
-
-Now that I have done some homework, I find your statement here to be in
-error. Please look up the alloy formula for stellite, which is the exotic
-alloy coating on expensive 100-octane aircraft engine exhaust valves.

I know well the formula for stellite. If you are nuts enough to buy stellite
faced valves, I know there are people willing to take your money. If you want a
plain-jane 100 octane valve, there are those, too. I can tell you that I've
done enough work inside Continental engines to understand the difference. Have
you?


- You suspect wrong. I have made this exact same measurement on several
- low-compression Continentals
-
-Yes, then, a negligible number, like 9 degrees as stated by a later poster
-flying an O-360 powered 172 with avgas in one tank and mogas in the other.
-'Net homework also shows, as this poster found, a negligible increase in EGT
-with mogas.

An O-360 is a Lycoming. I said NOTHING about Lycomings of any persuasion. Read
the post. And I can tell you that the EGT showed a perceptible rise. I never
thought to record it to make a point in the newsgroups.



-I am afraid that the manifest weight of authority is against you and
-completely refutes you on your contention here. I just looked up those
-stellite constituents for the typical 100-octane stellite exhaust valves
-sold for Continental engines.

There are people who will sell you gold-plated speaker wire for your stereo,
too, and some people flat out believe that it makes the music sound more mellow.
P.T. Barnum had it pretty well nailed.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com