Tuning with EGT

hombre

Nitrous
Joined
Dec 31, 2006
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Horsepower is a product of heat. An EGT gauge gives you an indication of where you are in the heat curve. This is a bell curve... as you lean out the engine the temperature will increase, peak, and start down the other side. If you are on the wrong side of the curve you are in trouble.

Like all tools, you need a full tool box to do the job. The EGT is only one of the tools that you need. I think an EGT is worthwhile for long pulls like Bonneville. Even at Maxton they can provide decent information. IMO, on a short run like Maxton you can run an EGT of 1500 and get away with it.

An aluminum piston is going to melt in the 1200 range depending on the alloy. But the piston actually sees much higher temps than the EGT indicates on the power stroke... like 4800 degrees. Then it gets cooled by the incoming charge. Your gauge reads the average at the EGT probe. :eek:

The distance, type of thermocouple, open or closed tip, and other things keeps it from being an absolute tool. As a relative tool, being able to compare run-to-run helps.

At 1200 you are giving away HP. At 1300-1400 you are close. Over 1500 it better be short!

An oxygen sensor (AF meter) coupled with the EGT gives you a really good tool set. The amount of oxygen exiting the engine should be zero. In a perfect world that would be the case. In the dynamic environment of the cylinder, you can't get a perfect mix of fuel and oxygen because of the short time for that to happen. Excess fuel is required to make sure that you get peak HP.

Now we must also consider fun subjects like detonation, the effect of compression ratios on flame temperature, incoming charge temperature, and humidity. :cool:
 
I love techinical stuff.............

Horsepower is a product of heat. An EGT gauge gives you an indication of where you are in the heat curve. This is a bell curve... as you lean out the engine the temperature will increase, peak, and start down the other side. If you are on the wrong side of the curve you are in trouble.

Like all tools, you need a full tool box to do the job. The EGT is only one of the tools that you need. I think an EGT is worthwhile for long pulls like Bonneville. Even at Maxton they can provide decent information. IMO, on a short run like Maxton you can run an EGT of 1500 and get away with it.

An aluminum piston is going to melt in the 1200 range depending on the alloy. But the piston actually sees much higher temps than the EGT indicates on the power stroke... like 4800 degrees. Then it gets cooled by the incoming charge. Your gauge reads the average at the EGT probe. :eek:

The distance, type of thermocouple, open or closed tip, and other things keeps it from being an absolute tool. As a relative tool, being able to compare run-to-run helps.

At 1200 you are giving away HP. At 1300-1400 you are close. Over 1500 it better be short!

An oxygen sensor (AF meter) coupled with the EGT gives you a really good tool set. The amount of oxygen exiting the engine should be zero. In a perfect world that would be the case. In the dynamic environment of the cylinder, you can't get a perfect mix of fuel and oxygen because of the short time for that to happen. Excess fuel is required to make sure that you get peak HP.

Now we must also consider fun subjects like detonation, the effect of compression ratios on flame temperature, incoming charge temperature, and humidity. :cool:

Walt:
Horsepower and torque are a by product of the inherent heat of the combustion process. Other things like reciprocating mass need to be taken into account as well. While alloy pistons will stand temperatures above 1500 degrees for short periods. the crown area will start to deform and detonation will occur with resultant metal transfer, usually depositing itself on the plug electrode and the upper cylinder walls. You have one advantage in the R3 engine and that is it has factory under crown oilers. Oil is squirted, under pressure into the lower crown area of the piston, carrying away excess heat just like is common practice in turbocharged diesel engines. I've re-bored and re-sleeved a number of engines, both 4 stroke and 2 stroke and the result is always the same. The search for the optimum AF ratio usually leads one to the machine shop ultimately.

You are correct in the theory that the piston gets cooled by the incoming charge but if you improve the AF ratio too much on the lean side, you loose the cooling effect and meltdown will surely occur. If I were you, I'd err on the side of being slightly rich. Granted, any internal combustion engine will produce maximum horsepower and torque on the ragged edge of detonation but that edge can and will be very expensive.

No matter how fast the sampling rate is on the EGT probe, it will only give you an approximation of actual combustion chamber temperatures. The charge actually cools substantially after combustion as the actual temperature is absorbed by the mass, the piston, liner and the head and the exhaust valve....see below.

You can't control the relative humidity, or the flame front/path. You have to rely on your ECM to adjust for humidity and the flame front and path is inherent to the combustion chamber shape, valve placement and crown shape which are all inherent design aspects of the motor. Incoming charge temperature is entirely determined by the ability of the air-to-air cooler dropping the charge air temperature below the point of detonation as well as the basic compression ratio, again, adjusted by the ECM to optimum conditions.

The engine mass itself cools the combustion temperature, the heat is transferred through the liners and head to the coolant which transfers the BTU's through the air to water cooler. Problems occur when the mass of the engine cannot dissipate the inherent heat of combustion fast enough, when your incoming charge is so lean that it actually has no heat transfer effect and combustion chamber temperatures reach above what the alloy will withstand.

One thing you aren't taking into account is the exhaust side of the equation. Your exhaust valves are solid stem. If you want to explore that ragged edge (I know your pocketbook can do that, mine can't), I'd seriously consider sodium filled exhaust valves. The liquid (at exhaust temperature) sodium will carry away the searing heat from the valve head and prolong the life. There is a real chance, with solid stems, running an optimum AF ratio, to loose a valve head. Drop a valve at 6,000 rpm and you might as well use your expensive motor for an anchor. If, at Maxton at speed you drop a valve, you'd better be prepared to test your leathers. Not something I'd want to do.

You consider Maxton a short run as compared to say Bonneville, which it is. Therein lies a problem. At Maxton, you are going to stress the engine in an abrupt heat cycle whereas at Bonneville, you can stabilize the engine temperature prior to running it at WOT. The spike in temperature in the combustion chamber is very abusive. Basically, you are going to pre-warm the engine (which will not bring the combustion chamber temperature anywhere near a load condition) and then make a WOT run with a short shut down. Alloy's don't like that abuse and will move in relation to the heat. Hopefully, they won't move the wrong way.

Again, I'd stay on the side of the bell. near the top but not precisely at the top. I don't believe the engine will stand it. I've studied the R3 engine internally over some time now. Just putting a compressor on the inlet and cooling the charge air, I don't believe, will allow the engine to make 300 RWHP even with cams and porting. It may for a very short time, a very, very short time but without any reliability.

I'd also seriously consider sodium filled exhaust valves.

If I were you (and I'm not), but if I was going down the road you are traveling, I would have turbocharged with charge air cooling, maybe even compound turbocharged. You blow all the energy out the tailpipe while using a parasitic supercharger but then, I'm a turbocharger guy. You aren't.

I'm more than interested in how the beast runs at Maxton. I'm sure you will keep us apprised of any and all results whether positive or negative I'm sure.

By the way, chatting with you on this site is much better than farming or mowing the lawn. Both mundane tasks that I'd like to train my wife to do but I strongly suspect that will never happen.:eek:
 
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Flip, I'm not much on farming either. ;) Most of the "farm" here is forested, with excellent deer & turkey hunting.

Actually I have a sodium filled valve sitting right here on my desk... use it as a paper weight. It's a spare from the days when I had a pair of Wright 1820-76Ds... on an aircraft, of course. It's amazing to me how all this "hot rod" stuff was actually developed for radial piston engines way back in the 1940's! :eek:

I absolutely agree that by the time the EGT tells you you're too hot... it's too **** late! It's a tuning tool, to be used with a good AF sensor. For this Fall, I'll keep my "tune" in the 1400 range... a margin for safety for 4 runs at Maxton. Then I'm looking to grind some new cams over the winter, and may consider new valves as well. Where does one source sodium filled R3 valves?? :confused:

I know of another R3 currently at 280 RWHP, and I'm not far behind. I think 300HP can be approached with caution. How long it will live is another matter. Look forwards to meeting you at Maxton some day... you would dig the huge spectrum of land race vehicles.
 
Is an EGT thresh hold standard across the board? I have a wide band O2 in my cat on my turbo car showing about 9-10 AFRs @ redline. I'm pushing about 22psi max (about 14-15psi @ redline on 9.5:1 compression with a direct injection head (1600psi fuel pressure) 1 full throttle spurt 1st,2nd,3rd usually results in about a 1500F EGT. Another romp soon after and I'm into 1600F territory.

I've been doing so for a while with no notable side effects.
 
Is an EGT thresh hold standard across the board? I have a wide band O2 in my cat on my turbo car showing about 9-10 AFRs @ redline. I'm pushing about 22psi max (about 14-15psi @ redline on 9.5:1 compression with a direct injection head (1600psi fuel pressure) 1 full throttle spurt 1st,2nd,3rd usually results in about a 1500F EGT. Another romp soon after and I'm into 1600F territory.

I've been doing so for a while with no notable side effects.

1. What kind of automobile is it?
2. Where is the physical location of the EGT probe and what kind of probe is it or the sampling rate?
3. Is the EGT readout digital or analog and what is the sensitivity of the readout itself, in other words the accuracy.

If you are running an actual (sustained)(indicated) 1500F and the probe is on the hot side of the turbo between the exhaust manifold flange and the turbo inlet, you should be okay. You are right at the point of crown deformation with aluminum alloy pistons. Your statement that you are in 1600F territory soon after tells me the sampling rate on the probe is not nearly fast enough. When you get off the fuel, the EGT should drop right off, right now. If it hangs, you need a probe with a faster sampling rate.

You can find out really quick if, indeed, you are too lean. Do a plug chop.

HB....my suggestion to you is that on your next oil change, do a spectroscopic analysis. There are a number of on-line labs that do it. Blackstone Labs in Indy has a nice 22 dollar mailer and they do a fast turnaround. You'll be able to quickly ascertain everything from stability in grade to metals present and if you are moving the alloy, it will show up as elevated AL.

I bet Walt does spectroanalysis on his oil even though he never talks about it. Aviation has relied on spectroscopic analysis for years.

I tend to do spectroanalysis on all my vehicles on every third oil change. Lets you know of pending problems, coolant leaks, head gasket problems and even mixture problems. Everything winds up in the oil, everything.

We all tend to take oil for granted other than expounding it's virtues that we think it has, in various oil threads on froums everywhere. It gets dirty (so we think) and we change it and replace the filters and so on and so on, but, your oil is a book with many chapters that can be unlocked with a controlled spectroscopic burn. It tells you everything you need to know about what is going on inside the engine.

A good example is I use 5w-40 Rotella Synthetic in my cars. I was changing it and filters at 5K. I did a burn and the viscosity numbers and base index as well as the soot content came back well within range. I've extended the interval to 10K. At 10K, the viscosity index is down 5 points and the soot content is at 5ppm. Just where I need to change it..
 
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Is an EGT thresh hold standard across the board? I have a wide band O2 in my cat on my turbo car showing about 9-10 AFRs @ redline. I'm pushing about 22psi max (about 14-15psi @ redline on 9.5:1 compression with a direct injection head (1600psi fuel pressure) 1 full throttle spurt 1st,2nd,3rd usually results in about a 1500F EGT. Another romp soon after and I'm into 1600F territory.

I've been doing so for a while with no notable side effects.

A particular EGT limit IS NOT standard across the board. It depends on many things... probe placement, probe type, piston alloy, and in your case turbine inlet temperature.

From the AF you are seeing (9-10) I'd say your car's tune is set that rich to keep your TIT cool... therefore your pistons are also safe. Adding an intercooler could enable you to run a leaner AF (say 12), make more power, and still keep TIT and EGT within the same limits. Oil analysis is always a excellent idea... smart insurance!
 
THanks for the replies fellows. It's intercooled. I have a fairly large bar/plate set up.

Sidecar, it's a mazda 3.

I read the booklet for the gauge last night and apparently, the EGT parameter I was monitoring is actually listed a Cat temp. I would imagine that's probably different than actual EGT. I tried to see what the refresh rate was on the data and didn't see a listing. I know it changes display readings every second or so.

I've been meaning to do a spectroscopic analysis. This might be enough to actually get me to do it.
 
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