I got bored today and started looking at old dyno sheets to have my ECM reprogrammed.

What is the difference between analyzing the Air Fuel versus the Exhaust Gas Temperatures?
My big questions is what are normal EGT's in a boat at WOT?

most people tune their engines by reading the AFR ratios whic is combineing all the cylinders gas's..egt's is theexhaust gas tenpertures.. a safe number for egt would be between 1300 to 1500 degrees depending on the engine..here is a good read to help explane better..

There seems to be a lot of mystery and misinformation about using exhaust gas temperatures to tune engines. Claims by many EGT gauge manufacturers about it being the best way to tune an engine must be qualified. The BEST way to tune an engine is on an engine dyno- PERIOD. What EGT is good for is a reference for where the engine made maximum torque at wide open throttle. Once removed from the dyno, a similar air/fuel ratio can be established at a later date by dialing in the mixture to achieve the target EGT. It is really the AFR that is important, not the EGT. Most engines will make maximum power at an AFR of between 12.0 and 13.5 to 1 however, the EGT may vary from 1250F to 1800F and is dependent on many factors.

It should be mentioned that the target EGT is valid only on the same engine configuration as was used on the dyno. If you change the ignition timing, cams, pistons, headers etc., the optimum EGT may also change. Raising the compression ratio with no other changes will drop the EGT at the same AFR. Retarding the ignition timing will generally raise the EGT at the same AFR. One engine might make best power at 1350 degrees while a very similar engine might be happier at 1500. You can't guess at this or you are simply wasting your money on the instrumentation. Wankel engines have higher EGTs than comparable piston engines due to their lower thermal efficiencies. 1800F is not uncommon here.

Some gauge manufacturers say you should tune to achieve maximum or peak EGT for maximum performance. This is incorrect. Peak EGT generally occurs at an AFR of around 14.7- 15.0 to 1 on gasoline. This is far too lean for maximum power and is dangerous under continuous WOT conditions. Many people think that the leaner you go, the higher the EGT gets. This is also incorrect. Peak EGT occurs at stoichiometry- about 15 to 1 for our purposes. If you go richer than 15 to 1, EGT will drop and if you go leaner than 15 to 1 EGT will ALSO drop. It is VERY important to know which side of peak EGT you are on before making adjustments. It is safe to say that peak power will occur at an EGT somewhat colder than peak EGT.

You can sometimes feel a lean of peak condition as the mixture is hard to ignite and power will be down a bit as well. Once the AFR gets close to 17 to 1 at WOT, generally the engine will start to lean misfire. Most tuners always recommend to begin jetting or programming from a known very rich initial setting and carefully leaning until torque falls off slightly, then going back richer to the point of max torque. Note the EGT at this setting. Be aware that altitude, barometric pressure and ambient air temperature may affect this optimal temperature to some degree.

Are EGT gauges better than AFR meters? Conventional narrow band oxygen sensors and digital LED meters are not the best devices to measure AFR in the richer ranges but they certainly warn of a too lean condition immediately and obviously, without translation by the driver and they are affordable. Meters combined with wide band sensors are supposed to be highly accurate and everyone has jumped on the bandwagon with these lately. Unfortunately the naive and impressionable often don't question the accuracy of these devices. We have seen some dyno plots indicating best power was achieved at AFRs of 9.7 to 1 on gasoline. This is PHYSICALLY AND CHEMICALLY IMPOSSIBLE and shows that either the sensor was bad (leaded fuel used possibly) or the meter was not calibrated properly. Again, the wide band sensors have the same limitations as the narrow band- leaded race gas quickly fouls them. We have heard and read many stories now indicating that certain brands of wideband meters differ as much as 2 points AFR in readings between each other. In other words, the accuracy of some of these devices is highly questionable. Extensive testing with laboratory quality instrumentation on aircraft engines universally indicates that best power is NEVER made at AFRs richer than 12 to 1. Airflow and fuel flow rates are independently measured and each cylinder is instrumented with EGT probes.

We recently dynoed a shop road racing Celica on a DynoJet equipped with a wide band meter. The meter was saying that the engine was going super lean (17 to 1) at high rpm so we kept upping the fuel there. The engine lost more and more power as we added fuel. The dyno operator was convinced that the meter was right but logic told us with no serious dip in power on the curve and the fact that the engine was still alive that the meter was not correct. We started leaning the engine down more and the engine started gaining power. Finally, when confronted with this information, the operator checked the water trap for the wide band sensor. Once this was emptied, the AFRs looked reasonable again. We didn't need the wide band to tell us this, only the torque curve from the dyno.

We have heard of several other instances with people using wide bands getting erroneous readings and tuning their SDS based on these readings. Then they phone us saying that the system is crap. Look at the dyno curve, when the engine makes its best power at a given rpm, that's where it likes the AFR irregardless of what other instrumentation is telling you. Remember, a bad sensor whether O2 or EGT equals bad information. When the engine sounds crisp and makes great power, you're there.

I would suggest that mixture meters and EGT gauges are complimentary. EGT gauges have the advantage of working long term with leaded fuel which will clog oxygen sensors. EGT gauges are widely used to set mixture on engines used for steady state high power applications where operation has been carefully documented such as in aircraft. The choice would depend on the application. Both are better if you can afford them.

Thanks! That was a really good read.

I know 1500 is high EGT in a car but isnt 1500+ typical in a boat? I assume this is why we need better valves than a street application?

I know cruising on the highway in my highly modified Subaru I would run about 1200 but under boost I could easily pin the gauge at 1600 @ 21 lbs of boost. Never came close to running lean. Good thread.

Awesome read thanks.

Both are important in their own respect. The problem with tuning solely on EGT's, is that elevated EGT's may mean the engine is lean, or it may mean the engine is rich. If the engine is to rich, combustion will still be taking place in the exhaust pipe, which is where the EGT probe is located. This is where AFR's come in. There really is no discreptancy about lean or rich with AFRs. The tune of the engine will directly affect the AFR's.

EGT's can change with timing. When tuning an engine on the dyno, I will give it timing until it either stops making more power, or it gets on the knock sensor(efi engine) That, along with the combo itself, will pretty much determine what the EGT's are. Then you can tune in the AFR's. The EGT's are what they are at that point. Some engines will have 1300 EGT's and others will have 1500+. I use the EGT's as a tool, but rely more on AFR's for tuning. If I only had one to use, it would be AFR's.

This is a pretty simplified version but I hope it helps anyway.
Eddie

on another note the only real way to tune your engine is if each header tube had a egt and a o2 bung welded into it like the race car i use to work on..we ran 4 stages of nos so it was really needed..the cars data logger would tell up what the engine did after each run..each cylinder is color coaded and one graf was for egt and the other was for afr's..i see now people are useing the data logger in boats with high boosted power..

You may get an acceptable (or what one thinks is acceptable) egt readings on a dyno pull, even on a boosted engine, with a somewhat lean AFR . But these are marine engines, the egt readings on a 10 second dyno pull, may not tell the story of what happens when the engine is held wfo for a few miles. It gives a indication of what the engine is liking, but the number itself IMO is moot, and not something to base the Overall tune off of.

The combination of enough timing advance without detonating, and enough fuel (AFR) will keep things cool on long runs. Too little timing, too little fuel, will melt things. Too much timing , will detonate.

In this day and age, the proven recipe is a safe AFR number, combined with timing advance that the engine wants. The dyno will tell you what timing the engine wants. That's why I often cringe when I see guys on the forums telling others what timing they need to run, based off a guy saying he has a custom engine running a supercharger, but no other details provided. Over the years, the old theory was keep it fat as heck, coffee brown plugs, and keep timing to 30* if you had a supercharger. At the time, that was a safe bet.

Nowdays, we have access to technology. There's no need to guess anymore. No need to wash rings out of engines, fill the crankcase with gas, transom looking like a diesel locomotive, and glowing red headers from lack of timing.

My advice, get a wideband. The tool pays for itself. Not just for wot readings either. It tells the story from idle to wot . If you have a lean spot, you'll find it. If you have a fuel supply issue, you'll find it. I've seen several carb engines dyno with a target AFR on the dyno. Then it gets installed in the boat, and end up being substantially fatter due to several circumstances . Properly tuned you will save fuel, have a happier better performing engine, and not have a transom that looks like a diesel exhaust, or melted pistons. I've ran mine as fat as low 10's on AFR at wot (was still tuning), and even that rich, transom was fairly clean, and plugs looked fat, but not what I would have called good years ago. I've got a few buddy's who tune the old fashioned way, without a AFR meter. Black transoms, dark dark brown plugs, and pull the dipstick and wreaks of gas within a hour of run time. My guess is if we slapped a wideband on those engines, we'd probably be off the chart rich.

For marine stuff, I wouldn't concern myself with a AFR number for "power". The hp difference say at 12.0 and 13.5 is null. 10-15 hp from leaning things down isn't worth the damage that 13.5 might do in a marine engine. On my blown stuff, I'm targeting low 12's at cruise, and low 11's at wot. If I was N/A, I'd target 12.5-12.7 at cruise, and 12.0-12.2 at wot. I'm sure with port injection, you can get away being a little leaner , since fuel distribution is better, but on a carbed setup, IMO it's better to be a little fat since the o2 only reads a average of the 4 cylinders on that bank . One cylinder can be quite a bit leaner than the next .

My efi gas dually truck with stock gm tuning, dips to 12.5-12.7 at anything over about 75% throttle. Idle and light throttle , 14.6. They try to get as close to stoich for emissions purposes , but in a high load scenario, stoich won't cut it. The ECM keeps it targeting stoich , until a certain throttle position is achieved , then it switches to a pre determined mixture to keep things together. 14.7 with your foot to the floor pulling a trailer uphill ( like a boat on plane) will melt things.

A dyno tune will get you close...but not perfect...the dyno environment is nowhere like the real world where the engine is run, air, load, and the amount to time its under load...this best deal is AFR under the operating conditions you running...period

I got a snow performance universal water/meth injection kit I bought to try out on my diesels, since I only run about 840 degrees cruising and 1050 wide open it didn't really make much of a difference for me, but it looks like you could use it! The 50/50 water methanol mixture did give me some extra hp though.