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| [GMCnet] Cad 500 EGT [message #244238] |
Wed, 19 March 2014 08:32  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Is anyone else measuring EGT on a Cad 500? Hubert Rowell and I installed a
new set of thermocouples and a dual 4-digit display last Sunday.
http://www.auberins.com/index.php?main_page=product_info&cPath=5_21&products_id=357
http://goo.gl/fLm6ED
It's a neat system, and went in pretty easily. Just one problem with the
installation: After about 15 minutes of running, on of the thermocouples
decouples -- the temp readout drops about 800*F. I'm sure they'll replace
it with no problem when I get home from Montgomery, but for now I'll have
to be content reading the Left EGT.
The question is, "What EGT should I be reading 1" below the exhaust
manifold flange on the Cad 500?" Everyone else I know who's reading EGT
are running an Olds with headers. That arrangement places the thermocouple
considerably farther from the nearest exhaust valve than my arrangement,
and the headers cool the gases faster. So their common 1400*F redline may
be (hopefully is) below mine.
On the 600 mile run we've had so far, I'm cruising at 60 mph, 18-19" Hg,
14.7 AFR, 196*F H20, with EGT about 1440. My NASCAR engine buddy says
that's fine, but I'd sure like to hear of similar experience.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #244559 is a reply to message #244238] |
Fri, 21 March 2014 17:11  |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
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What gear ratio are you running?
18" to 19" Hg is what only about 10% load? Seems pretty light.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] Cad 500 EGT [message #244588 is a reply to message #244559] |
Fri, 21 March 2014 20:47 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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3.55 final drive. That 18"-19" is near sea level, level road, steady
speed, for the X-Birchaven pulling a CRV at about 3500#. It is, indeed, a
pretty light load for the Cad500. But during last summers' 12000 mile trip
during which I pounded the exhaust valve seats into the head up to 1/16', I
didn't consider the 500 heavily loaded most of the time. The A/F ratio
during heavy load periods was usually in the 9:1 range as opposed to the
normal cruise at 14.7. During that trip I had Lean Cruise (LC, AKA Highway
Mode) implemented so that under the conditions above it would have been
running near 16:1. That's disabled now for fear of that causing the
damage. As soon as I gain some confidence and knowledge about the EGT's,
I'll re-implement LC.
Ken H.
On Fri, Mar 21, 2014 at 5:11 PM, jerrod winter wrote:
>
>
> What gear ratio are you running?
>
> 18" to 19" Hg is what only about 10% load? Seems pretty light.
> --
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #244595 is a reply to message #244238] |
Fri, 21 March 2014 21:22 |
cbryan
Messages: 451
Registered: May 2012
Location: Ennis, Texas
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Ken,
I'm interested in your results. I found a way to add one more gauge in the panel. Double needle air pressure gauge leaves an extra for EGT. Do you have one of those double needle EGT gauges with needles going every which way? Like a semaphore on the trains? I know, it reminds you of the T-38. I figure one gauge with two thermocouples and a switch between just to keep me moving my appendages. Sorry for the language. I am tired but happy from GMCing today, hope to make Montgomery tomorrow!
Best,
Carey
Carey from Ennis, Texas
78 Royale, 500 Cadillac, Rance Baxter EFI.
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| Re: [GMCnet] Cad 500 EGT [message #244604 is a reply to message #244595] |
Fri, 21 March 2014 22:15 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Carey,
No, I don't care much for the appearance of the dual needle gauges so I
went digital -- a stacked pair of 4-digit readouts:
http://www.auberins.com/index.php?main_page=product_info&cPath=5_21&products_id=357
http://goo.gl/fLm6ED
I had to quickly fabricate a temporary add-on panel for it. All of the
real estate on my instrument panel is occupied, plus the fact that the
square face of the instrument is not quite as large as the diameter of the
2-1/16" round gauges. That means it will probably never go on the cluster.
But it will get a more complete enclosure when I get home in April.
We'll be looking for you tomorrow.
Ken H
On Fri, Mar 21, 2014 at 9:22 PM, Carey Bryan wrote:
>
>
> Ken,
>
> I'm interested in your results. I found a way to add one more gauge in
> the panel. Double needle air pressure gauge leaves an extra for EGT. Do
> you have one of those double needle EGT gauges with needles going every
> which way? Like a semaphore on the trains? I know, it reminds you of the
> T-38. I figure one gauge with two thermocouples and a switch between just
> to keep me moving my appendages. Sorry for the language. I am tired buthappy from GMCing today, hope to make Montgomery tomorrow!
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #244621 is a reply to message #244588] |
Sat, 22 March 2014 00:09 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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| Ken Henderson wrote on Fri, 21 March 2014 20:47 |
3.55 final drive. That 18"-19" is near sea level, level road, steady
speed, for the X-Birchaven pulling a CRV at about 3500#. It is, indeed, a
pretty light load for the Cad500. But during last summers' 12000 mile trip
during which I pounded the exhaust valve seats into the head up to 1/16', I
didn't consider the 500 heavily loaded most of the time. The A/F ratio
during heavy load periods was usually in the 9:1 range as opposed to the
normal cruise at 14.7. During that trip I had Lean Cruise (LC, AKA Highway
Mode) implemented so that under the conditions above it would have been
running near 16:1.
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Under no circumstances should exhaust temps in the port or a few inches downstream ever exceed 1550F. With that said pulling a total weight of approx 14-15k lbs on level ground at about 3000 rpm I'm not surprised by exhaust temps of 1440F at 14.7 A/F. I think I'd err on the side of a little enrichment (maybe 1 A/F) at this speed and load and you could bring your EGTs down by 50-100 degrees. Also what ignition timing are you running? If you are several degrees retarded that could be adding 50-100 degrees to EGT. It does not surprise me that you had some valve seat recession if you run sustained operation at this exhaust temp.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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| Re: [GMCnet] Cad 500 EGT [message #244622 is a reply to message #244604] |
Sat, 22 March 2014 00:30 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Ken,
Here is my experience on EGT.
On a gasoline aircraft engine we teach students not to lean below 5000 feet. Above 5,000 feet and at 75% of power or less (cruise) we then lean out the engine looking for peak the EGT on the leanest cylinder. We then richen the mixture to get a 50 to 75 degree EGT drop on the leanest cylinder. So on mine the hottest cylinder is usually in the 1525 F. range. I richen the mixture until I see about 1450 degrees and go. It will run all day at that temperature and power setting. Well actually it will run at about 5.5 hours. After that it will fall out of the sky. So mine runs about 4.5 hours (550 nautical miles) at that setting and then I stop for more fuel.
You can take the above numbers and try to interpolate them to a 500 Cadillac. Obviously the applications are very different. On the GMC you are constantly varying the power setting and I doubt that you are running at 75% of power very often. If you have some way of setting say a 65 or 70 mph cruise (85 if you are Jim K.) and then varying the mixture, you could find the leanest cylinder and establish a base line. From there you could richen the mixture on the leanest cylinder say 100 degrees and probably be safe.
Altitude really does not really make much difference on EGT. It is the mixture that makes the temperature difference. The only reason we teach students not to lean below 5000 feet is because it is difficult for them to screw up and burn a valve above 5000 feet because they can not get above 75% of power.
I wonder how fast I could go with a 500 Cadillac in my airplane. I'm just dreaming. It would weigh so much that I would never be able to get it off the ground.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Cad 500 EGT [message #244629 is a reply to message #244622] |
Sat, 22 March 2014 07:30 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Ken,
Thanks for your comments. Even though I'm a little surprised by some of
them. As you know, I've got little light aircraft experience, being a
turboprop driver most of my flying career. But, I thought the standard
mixture control protocol for the past quite a few years was to lean to max
temperature, then, rather than enrich for 75*F or so lower EGT, to LEAN for
a temperature drop. And, in fact some of the current flyers here have made
comments to that effect -- i.e., lean cruise runs oooler at 16:1 than at
14.7:1.
Are you just "old school", or am I confused again?
I'm not sure how to extrapolate your individual cylinder temperatures,
probably measured within an inch after each of the exhaust valves, to my
4-cylinder melds measured 6" from the closest one. I'm already hoping that
the 3" or so difference between where Randy and George, and I, measure, and
the different dissipation characteristics of thin steel and thick iron,
will account for my readings running 150*-200*F above theirs.
Even Matt, with his lab experience isn't making me feel real comfortable
with my temperatures -- 'though he too has no directly applicable
experience.
At least in USAF R&D I didn't have to personally do the greasy stuff! :-)
Ken H.
On Sat, Mar 22, 2014 at 12:30 AM, Ken Burton wrote:
>
>
> Ken,
>
> Here is my experience on EGT.
>
> On a gasoline aircraft engine we teach students not to lean below 5000
> feet. Above 5,000 feet and at 75% of power or less (cruise) we then lean
> out the engine looking for peak the EGT on the leanest cylinder. We then
> richen the mixture to get a 50 to 75 degree EGT drop on the leanest
> cylinder. So on mine the hottest cylinder is usually in the 1525 F. range.
> I richen the mixture until I see about 1450 degrees and go. It will run
> all day at that temperature and power setting. Well actually it will run
> at about 5.5 hours. After that it will fall out of the sky. So mine runs
> about 4.5 hours (550 nautical miles) at that setting and then I stop for
> more fuel.
>
> You can take the above numbers and try to interpolate them to a 500
> Cadillac. Obviously the applications are very different. On the GMC you
> are constantly varying the power setting and I doubt that you are running
> at 75% of power very often. If you have some way of setting say a 65 or 70
> mph cruise (85 if you are Jim K.) and then varying the mixture, you could
> find the leanest cylinder and establish a base line. From there you could
> richen the mixture on the leanest cylinder say 100 degrees and probably be
> safe.
>
> Altitude really does not really make much difference on EGT. It is the
> mixture that makes the temperature difference. The only reason we teach
> students not to lean below 5000 feet is because it is difficult for them to
> screw up and burn a valve above 5000 feet because they can not get above
> 75% of power.
>
> I wonder how fast I could go with a 500 Cadillac in my airplane. I'm just
> dreaming. It would weigh so much that I would never be able to get it off
> the ground.
> --
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #244637 is a reply to message #244629] |
Sat, 22 March 2014 08:22 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Ken,
I do not know the relationship between air/fuel numbers and EGT numbers. I thought the magic 14.7 number was for minimum emissions and not necessarily maximum efficiency.
You can run on the lean side of peak but you are running close to the detonation point. Saving a little fuel at the expense of ruining an engine is hardly worth it. We are trying to get the smoothest running and most fuel efficient mixture without destroying an engine. When Dick Rutan and Jenna Yeager flew around the world non-stop without refueling, they ran those Continental engines on the lean side of peak for maximum economy.
So it can be done, but the recommendation is still to run on the rich side of peak for engine longevity. What is interesting to me is to watch the EGT on all cylinders and see the leanest cylinder change between cylinders at various power settings.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Cad 500 EGT [message #244724 is a reply to message #244621] |
Sat, 22 March 2014 22:18 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Chris,
Thanks. Your comments reassure me a little bit. At least until I can get
the thermocouples working on both banks and a more reliable computer
monitoring the EFI, then I'll be able to do some more experimenting. I'm
definitely not running retarded timing. Based on the Cad's reputation for
liking lots of timing, I've got the maximum set somewhere around 48*, and
under the cruise condtions i mentioned, I actually see 40*+, with NO knock
counts (I couldn't HEAR Tom Henry under there with his hammer).
Among my experiments I'll be looking not just at enriching but at leaning
the mixture. Some indications are that lean cruise at 16:1 or so may
result in lower EGT's at light loads -- certainly not a heavy load though.
I'm going to change computers for the trip home, so maybe I can experiment
a little next week.
Ken H.
On Sat, Mar 22, 2014 at 12:09 AM, Chris Geils wrote:
>
>
> Ken Henderson wrote on Fri, 21 March 2014 20:47
> > 3.55 final drive. That 18"-19" is near sea level, level road, steady
> > speed, for the X-Birchaven pulling a CRV at about 3500#. It is, indeed,
> a
> > pretty light load for the Cad500. But during last summers' 12000 mile
> trip
> > during which I pounded the exhaust valve seats into the head up to
> 1/16', I
> > didn't consider the 500 heavily loaded most of the time. The A/F ratio
> > during heavy load periods was usually in the 9:1 range as opposed to the
> > normal cruise at 14.7. During that trip I had Lean Cruise (LC, AKA
> Highway
> > Mode) implemented so that under the conditions above it would have been
> > running near 16:1.
>
>
> Under no circumstances should exhaust temps in the port or a few inches
> downstream ever exceed 1550F. With that said pulling a total weight of
> approx 14-15k lbs on level ground at about 3000 rpm I'm not surprised by
> exhaust temps of 1440F at 14.7 A/F. I think I'd err on the side of a
> little enrichment (maybe 1 A/F) at this speed and load and you could bring
> your EGTs down by 50-100 degrees. Also what ignition timing are you
> running? If you are several degrees retarded that could be adding 50-100
> degrees to EGT. It does not surprise me that you had some valve seat
> recession if you run sustained operation at this exhaust temp.
> --
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #245056 is a reply to message #244238] |
Tue, 25 March 2014 16:56 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
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Is this a situation where egr might help lower exhaust temps? Low load at 3000 rpm steady. I think the efi manifold has egr built in.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] Cad 500 EGT [message #245091 is a reply to message #245056] |
Tue, 25 March 2014 20:15 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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I've never had any occasion to learn anything about EGR, except that there
are such passages in these heads. What I'd add to implement it and how it
might improve the situation is beyond me. Any suggestions?
Ken H.
On Tue, Mar 25, 2014 at 4:56 PM, jerrod winter wrote:
>
>
> Is this a situation where egr might help lower exhaust temps? Low load
> at 3000 rpm steady. I think the efi manifold has egr built in.
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cad 500 EGT [message #245095 is a reply to message #244238] |
Tue, 25 March 2014 21:04 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
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From what I've read it was used to reduce NOx emissions. A side effect is that it reduces egt and pumping losses at light load. You also have less detonation and can pull more timing advance. I don't have experience with tuning an engine with egr but it seems like an opportunity for this scenario.
It usually gets bypassed along with other emmissions schemes for the sake of performance. In a motorhome application like ours the benifite may have been small due to heavy constant load. Your rig is running at around 10% load so it is more like a car.
I look forward to some discussion on the topic. Seems like a easy light cruise option.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: [GMCnet] Cad 500 EGT [message #245121 is a reply to message #245095] |
Tue, 25 March 2014 23:08 |
mrgmc3
Messages: 210
Registered: September 2013
Location: W Washington
Karma: 2
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EGR or exhaust gas recirculation is as it says, recycles exhaust gas back into the intake stream. The purpose of EGR is to dilute the fresh charge of air and fuel with an inert substance (exhaust is inert and readily available). It's primary result is the lowering of the peak combustion temperature, and as a result this lowers NOx formation. A secondary result of diluting the mixture is that at a given rpm the throttle blade will need to be open slightly more to make the same amount of torque. This creates a slight fuel economy benefit due to the reduced pumping losses (please note this also corresponds to a lower vacuum level, contrary to the common wisdom here that higher vacuum means better fuel economy - it does not necessarily mean so). Also as you introduce EGR you slow down the burn rate which requires / allows more spark advance. The advance does not give you the improved economy in this case, it compensates for the slower burn rate.
Now the hard part for our GMCs - introducing the right amount of EGR and coordinating with the right amount of additional spark advance. The EGR valves of the 70s were crude devices that were unreliable and difficult to meter. Ideally you want to dilute the charge with about 10% EGR, at light to medium loads, none at heavy load, but this is difficult in practice - too much and torque will fall off and you can get ignition misfire, too little and you see no benefit. Then you need to meter in a coordinated amount of additional vacuum advance. Too much and it will knock. Engine calibration engineers spend many hours coordinating the EGR and spark schedules, or at least they used to. Variable valve timing has effectively obsoleted EGR valves by forcing exhaust gas into the chamber with overlap at light loads.
Chris Geils - Twin Cities / W Wa
1978 26' Kingsley w/ very few mods; PD9040, aux trans cooler, one repaint in stock colors, R134a, Al rad, Alcoas, 54k mi
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