Anyone have any information or thoughts about these? Are there any benefits when used for bracket racing? If yes, how could knowing your exhaust temperature help?

http://www.jegs.com/cgi-bin/ncommerce3/CategoryDisplay?cgmenbr=361&cgrfnbr=850

Thanks
Aaron

Exhaust gas temp is used to help determine carb set-up. Exhaust Gas Temp (EGT) tells you if the engine is rich or lean and will help to avoid burning pistons. Maximum acceptable EGT on a gas engine is around 1500 Degrees F (we get nervous at 1550 and shut a dyno down.) EGT's above that indicate piston damage is not far behind. EGT's in the 1200 range would tell you that your engine is way fat and down on power.EGT's also help diagnose air/fuel distribution issues. It is not uncommon for the range accross cylinders to be 1350 F to 1500 F on a carb'd V8 engine.Bottom line, EGT is one of the best tuning tools available. Combine it with wide band O2 and you can really tune an engine.

Gary

Aaron,

I have to vary from Gary's explanation because high EGT temps don't always mean a problem in the combustion chamber.


Here is a RE-Print of Information from PRO-systems

http://www.pro-system.com


The A, B, C's of EGT's and Oxygen Sensors

As most of you know we have a video out that explains the proper use of E.G.T. (Exhaust Gas Temperature) information and how to properly use the information this type of sensor supplies. But we still receive calls from misinformed racers about the use or potential misuse of this data.

Since onboard data-logging systems are now becoming pretty mainstream most people are under the impression that they can bolt these systems on and burned pistons, detonation, and incorrect jetting are a thing of the past. Not true.

EGT and Oxygen sensors are wonderful inventions, but they are not an end all be all of tuning. Here's why.

Every engine has a thermal signature. Meaning it will create "A" amount of combustion heat, it will burn "B" amount of fuel in a given span of time and it will expel "C" amount of unburned or currently burning gases.

"A" is "in the chamber" combustion. Allow me to explain. One of the teams I work with has a system that actually measures the combustion temperature. This is an "in the chamber" reading not and "in the pipe" reading and you can directly correlate chamber efficiency, fuel distillation curve selection and even cylinder head temperature to assist you in burning all the fuel "in the chamber" as opposed to a residual burn. Its really quite an eye opener and it really taught our company a lot about droplet size and fuel preparation.

"B" is the amount of fuel required to match up fuel and air to get proper combustion. Now everyone knows that 14.7:1 is stoic, but this is not a perfect world. Piston tops and intake to exhaust scavenging percentages will alter the required air to fuel ratio for proper operation. Now don't panic, just because your engine requires .8 more of an air to fuel ratio or EGT's that are 100 degrees lower than your buddy's car is not a bad thing. Some engines make excellent power with lots of fuel and although they may seem to be wasting it, you can't deny proven on track performance. For example: We have a particular carburetor design that makes no more power on the dyno, but for some reason its very quick on the racetrack. When the fuel curve is altered to supply what the engine builder deems is a proper air to fuel ratio, the vehicle slows down. So there are no set rules and EGT and Oxygen sensors have to thought of as base-lining or reference tools. Remember that statement.

"C" is the amount of residual unburned or currently burning gases that are expelled into the exhaust pipe. One of the nitrous teams that tests for our company currently has EGT numbers in the 1760 degree range. You may think that's high and that sure seems excessive, but it's a World Record holding tune-up and you don't deny that. The engine gets torn down regularly and to quote the racer "Its so nice inside this engine, I could even reuse the bearings if I wanted to". So don't panic if you're seeing real high EGT numbers. Oftentimes its residual fuel burning and if you roll some ignition timing into it to get it to burn in the chamber, you could end up hurting parts.

Oftentimes an Oxygen sensor will show you a cylinder that requires more air to fuel ratio than its opposing cylinder or even its direct neighbor. Let the cylinder have the fuel. Don't get caught in a numbers game. The same thing goes for EGT data. If your engine performs better with higher or lower numbers than someone else's, look at the A,B,C's and you can probably pretty accurately determine what's different from your combination than his/hers.

Also remember, when mounting EGTs or Oxygen sensors symmetry is VERY important. An EGT sensor mounted on the bottom of a header pipe will typically record data 100 degrees lower than the same sensor mounted on the top of the pipe. If you're using a single oxygen sensor, remember a misfiring cylinder will exhibit an over-rich condition and you may think less fuel is required, so don't forget to look at everything when you're tuning.

When you open the hood there is a lot of stuff under there and something as simple as a fluctuating fuel pressure regulator can create surging and just plain unusable data. That's when the real tuner earns his pay. EGTs and Oxygen sensors are tools that can lie to you, but they're great for educating you on what to look for, so pull that header off or pull out that sparkplug when the car is running good. Get a good look and remember what you see. Sparkplugs and header pipes are harder to read but they rarely tell a lie.

Thanks for reading. Have a great season everyone.

This is my expereince from this past summer

I have EGT probes in 2 of my cylinders (1 and 8)and experienced excessive temperatures in the 1900 F range. This was do to fuel burning in the header tube and giving me false readings of combustion chamber temperature. I knew or should I say "I thought" I had the carb setup rich as a starting point since this was a brand new motor, so I jetted up and the temps maxed out the meter. in both cylinders. From these results I realized I did have it rich and now it was way too rich.

I proceeded to jet her down and my mph was going up and EGT temps were going down to the 1500 range.

As my 2003 season was getting close to ending I decided to stop tuning the car because I wantred to try and win a few so I started to race for consistency only.

I am still on the rich side and need to keep tuning, but that's what next year is for.

The units like the Percy will measure temps in two cylinders, BUT here is the catch..it will only record One at a time..very misleading.

You can tune your carb by mph and the EGT is just a tool and as Patrick discusses they are not an instant tune all for a quick tuneup. I am glad I purchased my kit and look forward to seeing how the EGT readings compare to my changes in mph. I will be sure to report on the results come next year.

The dragstrip is the best tuning tool out there.

I highly recommend

http://www.motorsportsinnovations.com

for the EGT kit they sell and the real support they will give you.

....and I must disagree with Tom (mostly because he disagreed with me and I haven't had my coffee yet.) High EGT's are a problem on the types of cars that are being driven by the members of this forum. You can't compare a 2500 HP Pro Mod engine or some other high end exotic like an IRL engine to the street/strip types of engine built and driven by our friends on this forum. And trust me I'm very familiar with combustion chamber temp data, fuel burning in the pipe and all the rest of it.Bottom line, if you work for a living, build you car to play with on the weekends and don't have money to throw away, then you had better be leary of EGT's over 1500-1550, no matter what the root cause.

GP

I agree about the temps Gary. When I first installed the probes and it hit 1900 to 1999 I wanted to panic. I was already jetted 90 front with a PV and 96 rear with a plug. (The 850 DP carb came out of the box with 80/78 with PV's.) So I was way over box stock which most of the time is pretty close. I do have 540" but then again only turn max of 5950+/- RPM.

One should start with a known overly rich condition and jet down from there, Even though it didn't seem reasonable by experience, I jetted up (thinking I was lean) to 90 and 98 and had black smoke at WOT and now the EGT meter was maxed out in both #1 and #8 (I made 2 runs to check each cylinder), mph was off a litttle even though the air temp was dropping slightly. There was no sign of spark plug damage or bits of aluminum on the plug, so I kept scratching my head.

A fellow older racer who runs a 10.80 SB street nova said I was burning fuel in the header pipes and to jet it down. I tried it and went down to 88 and 94. the mph picked up and the EGT temps starting coming down. I jetted down to 84 and 92 and the temps came down again to 1500 +/- and I have run my best mph's (so far) with this jetting. That is where I stopped and decided it was race time...(Hi Gene!) :D

EDIT: - Also, My part throttle cruise temps went down to 1300/1400 with 84/92.

I understand there are two sides of Max EGT and that max EGT is not necessarily the temp of peak performance. It is very important to start on the rich condition side of max EGT and work backwards to peak torque and mph while staying within the limits of 1500 max.

Gary, please add anything to this and provide some info I may not be aware of. We are all still learning.

Thanks

Gary and Tom,

Good posts!!!

Tom is right on regarding starting on the rich side and sneaking up on lean. This is always true, we call it "piston protection." And you always put a little "piston protection" on a new engine. When GMPP sells a crate engine, it's jetted so that it can run rich at sea level at moderate ambient air temps. This is done to ensure that a customer doesn't burn a piston during start-up and break-in. Piston protection is especially important on engine with cast or hypereutectic pistons as they will not take the heat that a forged piston will and are fit in thew cylinder with less piston to wall clearance.

Ya'll have a merry Christmas.

GP

I started this thread before I went to bed. I was surprized to see this much writen about it. Gary and Tom thanks for replying graemlins/thumbsup.gif . I basicly understand the ABC as you put them. Tom how much ET and MPH did you gain by tunning with a EGT

Too lean an AFR can give you high EGT's as well. which can make using them a bit hard to do unless you have a baseline. using TC's with a WBO2 makes life a LOT easier when you dont have a baseline & you want some kind of sounding board (as well as MPH of course). these are great tools when used with a bit of caution. one thing is for sure, Pluges & pipes NEVER lie.

Bob

Aaron,

I can't say positively that I picked up any ET because my 60 foots were not changing enough to confirm a benefit, but my mph was consistently 123.8 to 124.4 and I didn't break the 125 mph barrier until right after I dropped the jetting to the current settings.

I am no where near done tuning this combination and that includes jetting as one of the many.

I am also going to screw up all the tuning so far by throwing on a performer RPM, one stock and one port matched.

Tom let us know how the tunning goes. I'm interested in the progress you make with the EGT.