Hello fellow evo members!! My car currently goes up to around 700 while cruising and goes near 900 upon full throttle 4-5th gear pulls. Cross referring to my supra numbers, I would be very concerned with these EGTs in the above mentioned circumstances. Do these cars normally run hotter?

I have noticed that these cars warm up quiet quickly for a 4 cylinder in the winter months and thinking may be these cars do run hotter!!

Any kind of input will be appreciated guys and thank you very much in advance for your help!!

Note: The probe for the EGT is mounted on the second runner (near cam gear).

 

Incidentally for the metrically impaired(like me), 900* Celsius=1652* Fahrenheit.

 

its not massively hot that but i thought 850 was more the limit ?
sustained high egt like top speed runs are the killers

 

First to substantiate my claims let me say that I am a graduate engineer and my full time job is combustion and performance calibration of internal combustion engines. And when it comes to EGT's most newbies don't realize how much complexity and information there is behind EGT's. There are a dozens of variables that have an impact on it and many different ways to address it.

Around 900-930C is flirting with the safe limit for 93 octane. For the sake of reliability and knock/preignition mitigation it is a good idea to try to keep egt's down. 750-800ish is a better place to be. I think most people are in the 750-850 range and getting up to 900-930 is pretty extreme. Here are a few of the implication of high EGT's:

The highest adiabatic flame temperature occurs just slightly on the rich side of stoichiometric. One would think that this would mean that peak EGT would happen when AFR is just slightly rich. However due to fast flame propagation due to good combustion conditions, a maximum amount of work is extracted from the charge under these conditions and in reality there is another factor that complicates the EGT temperature: unburned gasoline.

When you run lean, combustion conditions are poor and flame propagation is slower. As a result, combustion can still be occurring even as the Exhaust valve opens to evacuate the cylinder. This continued combustion in the exhaust manifold accounts for the very high EGTs on lean A/F.

Another way of explaining it is that given an amount of fuel and enough oxygen to burn it, a certain amount energy is extracted by piston movement and converted into work. When combustion is slow, not as much energy is converted to work, and it has to go somewhere. It ends up being rejected as heat, often melting components and causing overheating high EGTs.


There are a handful of ways to address high EGT's.

1) You can check your A/F ratios. If you are running 12-12.5 AFR try riching it up a little bit to maybe 11:5ish. Running rich does NOT make more power, just because you are adding fuel. When you significantly richer than about 14.5:1 there is no oxygen left to burn the excess fuel. Instead it just vaporizes (remember you grade school science) and in the process it absorbs a lot of heat out of the charge cooling it down. The reason we want to run so rich 11.5-12 AFR on high boost is to take advantage of this charge cooling effect.


2) You could adjust timing. Retarding timing a bit will reduce your peak temperature significantly. The trade off is you will loose some power. There is no free lunch in engine tuning, fixing something will always cost you something else.

3) This is more advanced and would be used in conjuction with the other 2 but you could adjust (if you have adjustable cam gears) your cars exhaust valve open event to happen a bit later. This will ensure that the piston extracts the maximum amount of energy out of the charge, before the valve opens. Again there are trade offs. This will cost you some top end power due to poor blowdown (woosh of exhaust out the valve when it first opens due to pressure differential) and reduced scavenging (intake air pushing out exhaust air) at high rpm.

 

From my own tuning experience retarding timing will net you hotter egt's. Advancing timing will lower the egt's. The catch is on 93 octane you can only control the egt's so much with timing before you begin to see knock from the advanced timing.

 

I’m sure what he meant was retarding timing a bit but still within the acceptable rage of “advanced” timing. Going lower than MBT and retarding into the negative will skyrocket your EGT's. That’s the how anti-lag works to keep the temps in the turbine high and spin the turbo.

On my own shop Evo I have run up to 1100C on 105 Octane. (AKI) It’s not great and temps this high were always at the end of a few hard pulls on the dyno testing the engines limits. The stainless headers were almost translucent that’s how hot this tem is in case you’re wondering. Exciting but dangerous.


A well tuned 4G63/4 should be in the 800 - 880C range when pushed through the repeated gearing cycles on a track. Keeping the engine at peak power RPM for a top end run may see these temps spike higher into early 900’s, but this happens slowly enough so you can back off if need be. Temps drop instantly to 600C and then from there even lower. Most OEM temps ive seen are below 800C.

Sorry I don’t do imperial, just metric.

 

To the OP: What thermocouple are you using?

 

What effect does water/alcohol injection have on EGTs? Has anyone observed a cooling effect in their logs?

 

Ah yes, my apologies for the confusion. Popadel is correct, I meant retarding the timing while still keeping it on the advanced side. Retarding timing all the way back to TDC or later will definitely heat up your EGT because of late combustion occuring when the exhaust valve opens.

Under most conditions, with a properly setup motor it is not necessary to retard timing all the way back into the negative. That sort of very late spark is sometimes used as a special technique to manage exhaust emissions and NOx formation. But it will cost you all kinds of power and torque and result in a terrible increase in BSFC. Luckily aftermarket tuners don't have to worry about such things


Both water and alcohol injection are implemented to cool the intake charge during vaporization to increase the safe knock limit. All things fixed, cooler charge temps would result in lower peak in cyl temperatures and given good combusiton conditions, a cooler EGT.

However, in real life, people don't just inject water/alcohol and then call it a day. Pretty much everybody who does supplementary charge cooling uses the increased knock margin to up the boost and/or advance the timing a little bit to make more power

As a result, the effect of supplementary charge cooling on EGT would pretty much be overshadowed by the effects of increased boost and/or timing.

 

Water has a direct effect on lowering EGT´s, whereas alcohol only cools the intake charge. A one degree drop in intake charge temps does not equate to a one degree drop in EGT´s. The ratio is not 1:1.

Water, unlike alcohol fuel, changes state from a liquid and becomes steam during the combustion process. This stream removes heat from the combustion chamber. A one degree drop in combustion chamber temps translates directly into a one degree drop in EGT´s.

 

just got an evo8 last week, and for some dumb reasons, the previous owner had mounted the egt probe on the downpipe, i thought it was only meant to be mounted on the exhaust manifold...is there another benefit to mount it on the downpipe? I notice that cruising it sits around 600* but full throttle it will jump to 900*, but wouldnt that part of the exhaust be hotter right of the downpipe?