TD5 tuning and stress

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robhtid

robhtid

Well-Known Member
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Location
Blackpool
Senario.....A td5 under load going up a hill say holding 2800rpm in 2nd to maintain speed

The same car but now with a remap going up the same hill at the same speed not accelerating but maintaining, now the engine has more power is it under more strain and higher exhaust gas temps or with it having more power is it working less hard and under less strain and lower EGTs?
 
IMO it depends very much on the quality of the remap, with a good one it should have lower EGT or max the same at the same speed but better throttle response... the gist of a good remap is to gain power and throttle response without increasing the EGT... so with a good remap the EGT should be lower at the same power or the EGT the same with more power if you see what i mean

....at least that's what i observed on mine
 
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lynall said:
I reckon with same egt, you would have same output, so speed the same.
Click to expand...
then what's the utility of a remap ? ... according to my own measurements with many different remapped chips when a good one was in action at the same EGT the speed was higher, usually the EGT goes together with the throttle demand not with the speed and with a good remap the vehicle goes faster with same throttle.... it happens when it's an AFR based remap cos if it's on the injection duration maps the power gain goes together with EGT.
 
sierrafery said:
then what's the utility of a remap ? ... according to my own measurements with many different remapped chips when a good one was in action at the same EGT the speed was higher, usually the EGT goes together with the throttle demand not with the speed and with a good remap the vehicle goes faster with same throttle.... it happens when it's an AFR based remap cos if it's on the injection duration maps the power gain goes together with EGT.
Click to expand...

I have no idea, it just seems to me if you ask X from anything and you get X, then to get X, you must have the same ingredients in the same quantities, seems logical to me?
It is like the old saying, nothing is for free.
 
lynall said:
I have no idea, it just seems to me if you ask X from anything and you get X, then to get X, you must have the same ingredients in the same quantities, seems logical to me?
Click to expand...
IMO if on standard map X throttle = X power/speed with a remap you should get X = Y (where Y is better than X) :)... though i've had chips with X = Z(where Z meant EGT in the sky... though the vehicle flew like a rocket)... many circumstances are involved
 
IMO, exhaust gas temperature (EGT) is not a good indicator of engine stress as it only records the heat energy released during the exhaust stroke, when the cylinder is under relatively low stress. Also, a high EGT could simply point to an inefficient combustion where most of the energy is being wasted instead of transformed into mechanical work. Tuning such as advanced timing usually elevates engine stress and brings down EGT whereas the opposite (i.e. with timing retardation) is also true. EGT is also affected by the air-fuel mixture and reaches its peak when the mixture is optimal (Stoichiometric) and full combustion can be achieved. Hence, a mixture that is either lean or rich will lower the EGT (lean = less fuel and therefore less energy, rich = excess fuel that remains unoxidised and which will absorb heat energy when vaporised).

Cylinder head temperature (CHT) is considered a better indicator of engine stress since it measures heat energy wasted during the power stroke, when the cylinder is under maximum stress. There is a direct correlation between CHT and power delivered by the engine, cooling system efficiency and volume of airflow.
 
NPG said:
Hence, a mixture that is either lean or rich will lower the EGT (lean = less fuel and therefore less energy, rich = excess fuel that remains unoxidised and which will absorb heat energy when vaporised).
Click to expand...
Aren't these "lean"/"rich" terms specific for petrol engines though? AFAIK diesel engines are running lean by default and excess fuel in a diesel will always raise EGT not reduce it.... but i'm not gonna go deeper in this cos it's above my knowledge.
 
sierrafery said:
Aren't these "lean"/"rich" terms specific for petrol engines though? AFAIK diesel engines are running lean by default and excess fuel in a diesel will always raise EGT not reduce it.... but i'm not gonna go deeper in this cos it's above my knowledge.
Click to expand...

You are correct in saying that diesel engines always run on lean air-fuel mixtures. My mention of lean and rich was a reference to the ideal Stoichiometric air-fuel ratio and not the actual ratio or the equivalence (λ). I don't know what this is for the TD5 but I would assume it would be somewhere between 1.65 and 1.10 with λ = 1 being the ideal Stoichiometric mixture that can produce a complete combustion with no unburnt fuel present in the exhaust. The λ range of 1.65 - 1.10 tells us that air is always in excess, that fuel combustion is never complete and that the mixture is made richer by injecting more fuel. This is when λ starts moving towards the 1.10 mark (lowest fuel consumption is obtained around λ = 1.65), at which point we get peak combustion and exhaust temps. So you are correct in saying that there is a region when additional fuel will raise the EGT but it is unlikely to be the case when λ < 1.10 and certainly not when λ < 1 (i.e. rich mixture relative to the ideal Stoichiometric air-fuel ratio).
 
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