Thread: ENGINE TUNING - EGT, Psi and Wideband AFR

twice half its length!~

Originally Posted by Kaaaiju

Have mates who have ran 850c egt at the dump for 45min straight and no damage to the motor and others at 1000c for months and no damage just how long is a piece of string

Didnt your friends pick it up before the turbo by any chance?... cos if it was after the turbo then IMO it's silly to drive it for months knowing it's 1000*C as it means that something is very wrong... 1000 after the turbo can be above 1200 in the head which is close to it's melting point

One had before the turbo and one had after the turbo, just saying td5s can cop about if abuse with boost and egts and survive, not as fragile as most people think they are

The amount of information regarding the EGTs is one that no doubt leads to confusion, agree that the TD5 is a robust design and more so with the Turner head.

Have read that Garret 'talk' (this is anecdotal of peoples with Garret Engineers) about 950C the limit for transient temps with the VNT but they never qualify it with pre or post turbo, though I believe they are talking pre as this is the most accurate means of measuring. This is seemingly high but the 700-720C limit seems to stem from the early 2000's when the technology was wastegates and much lower boost pressures.

Of course petrol engines run higher EGT's than diesel but the they run at higher engine speeds with greater flow speeds and corresponding lower heat soak levels, the higher boost levels of the VNT as far I can discern mimic / match this flow and hence the higher allowed safer EGT's. The choice of manifold can also play a part herein, certainly the Darkside Development blokes are unequivocal as to higher safer EGTs available with their manifold and VNT combination.

To qualify that, it is common knowledge / hearsay, to lower high EGTs by changing down a gear for higher gas flows.

Originally Posted by RRT

To qualify that, it is common knowledge / hearsay, to lower high EGTs by changing down a gear for higher gas flows.

Going back a gear for higher RPM doesn't necessarily change the air flow through the motor.

As the same amount of power ALWAYS requires the same amount of Airmass for the same result, (100kw is always 100kw and requires enough Airmass for 100kw no matter the revs or size of the engine or turbo) the only likely change will be the pressure ratio.

A lower pressure ratio will lower the charge air temp going into the engine via the intercooler.

Lower IAT will always lower the EGT.

With a TD5, the bottom end is remarkably robust, the issue is with the head, turbo and exhaust manifold.

The problem is finding what sort of power can reliably be made, as the tuning method used for the last 20 years has generally been injector duration hacks.


This means that many higher output tunes have end of injection far too late, this causes high EGT which can damage the turbo and manifold, and is also inefficient economy wise.

I very occasionally see hacks to the injector timing to try and compensate, but again this is inefficient when the duration tables have been hacked... And also can create extremely high peak cylinder pressures, which can cause head and head gasket problems, and create too much "negative work" and also reduce fuel economy.

I always laugh when I see comments regarding high boost wrecking head gaskets and heads... It's never the boost, it's peak cylinder pressure.

Extra boost just lifts air charge /mass figures which can allow higher inject quantity at healthy AFR's, it's the inject quantity and the timing of it that does the damage.

Originally Posted by shack

Going back a gear for higher RPM doesn't necessarily change the air flow through the motor.

As the same amount of power ALWAYS requires the same amount of Airmass for the same result, (100kw is always 100kw and requires enough Airmass for 100kw no matter the revs or size of the engine or turbo) the only likely change will be the pressure ratio.

A lower pressure ratio will lower the charge air temp going into the engine via the intercooler.

Lower IAT will always lower the EGT.

With a TD5, the bottom end is remarkably robust, the issue is with the head, turbo and exhaust manifold.

The problem is finding what sort of power can reliably be made, as the tuning method used for the last 20 years has generally been injector duration hacks.


This means that many higher output tunes have end of injection far too late, this causes high EGT which can damage the turbo and manifold, and is also inefficient economy wise.

I very occasionally see hacks to the injector timing to try and compensate, but again this is inefficient when the duration tables have been hacked... And also can create extremely high peak cylinder pressures, which can cause head and head gasket problems, and create too much "negative work" and also reduce fuel economy.

I always laugh when I see comments regarding high boost wrecking head gaskets and heads... It's never the boost, it's peak cylinder pressure.

Extra boost just lifts air charge /mass figures which can allow higher inject quantity at healthy AFR's, it's the inject quantity and the timing of it that does the damage.

Nearly all turners I have seen just wind fuel in and see you later

Having the timing and fuel done correctly makes the car amazing to drive at any throttle position

Originally Posted by shack

Going back a gear for higher RPM doesn't necessarily change the air flow through the motor.

As the same amount of power ALWAYS requires the same amount of Airmass for the same result, (100kw is always 100kw and requires enough Airmass for 100kw no matter the revs or size of the engine or turbo) the only likely change will be the pressure ratio.

A lower pressure ratio will lower the charge air temp going into the engine via the intercooler.

Lower IAT will always lower the EGT.

With a TD5, the bottom end is remarkably robust, the issue is with the head, turbo and exhaust manifold.

The problem is finding what sort of power can reliably be made, as the tuning method used for the last 20 years has generally been injector duration hacks.


This means that many higher output tunes have end of injection far too late, this causes high EGT which can damage the turbo and manifold, and is also inefficient economy wise.

Literally gold here mate, the black art of ECU reprogramming is now a very very dark grey.

Have been looking at this issue of lowering air temps and once you have a larger intercooler and more efficient turbo, the simplest way of achieving it is water misting. Spraying a mist of water across the intercooler face was used in the Subaru STi but for mine this is way too cumbersome and sure it could be set up at a trigger temp but the idea is get cooler air at all times, not just at the extreme.

Water injection into the airstream would need a whole lot of education as to the worth of such.

Anecdotally the new gearbox will be running at lot lower temps than the 4HP and should remove a little of the heatsink at the front of the vehicle, but you still have the air-conditioning there. Even looked at the possibility of a top mount intercooler but under the bonnet there is not much height there.

Not sure how the Patrol airbox will make a difference as the surface area of the comparative filters are roughly equal but there may be a gain there in flow as the round filter spreads the 'fins' out and certainly wont be going back to reusable. The 4" snorkel should ensure adequate air supply, have the design but this will have to wait till the shoulder is better.

Patrol Airbox and 4 inch snorkel I have on my daily disco still goes into decent vacuum which isn’t good so needs another upgrade , it’s ok for a standard setup