Diesel Tuning (beyond just a remap).

[Lowtechguy]

Hi Guy,

I searched your forum and noticed there is no discussion on diesel tuning.
I am purchasing the 156 2.4 JTD diesel engine shortly and would like to learn more on the diesel side of tuning.
Are there any books/authors you can recommend or are there any basic principles you advise I should follow.

For example exhaust tuning, same as petrol turbo, head tuning etc?

I don't expect you to write a book just for me but your thoughts on the subject are highly regarded.

Many thanks,

Cristian.

[Guy Croft]

The diesel -whether electronically injected or mechanical is markedly different from the petrol engine in that:
1. It runs 'excess air' in other words it ingests far more air than it burns
2. The ignition quality depends on the compression ratio and fuel atomisation. The fuel auto-ignites when the droplets are small enough and each surrounded by superheated air to provide a chemically correct mixture of fuel-oxygen.
3. The speed and thus power of a diesel is limited by the viscosity of the fuel - getting it in faster via common-rail and electronically controlled injectors was a huge step forward.

I have considered your question with great care and as far as I know there are a very limited number of ways to get more power from a diesel:

1. Bigger cubic capacity
2. Turbo/supercharging
3. Improved in-cylinder mixing and optimisation of burn.

You can certainly forget petrol engine techiques like porting, valve and seat work, modified exhaust headers etc.

Methods 1&2 above certainly require detailed recalibration of the fuel system to provide more energy. Method 3 may simply improve the use of the existing amount of fuel going in, or it may offer the possibility of increasing the injection rate. It can lead to significant power gains but the chances of being able to do that outside of a highly developed research facility are zero.
Turbocharging and higher boost is of course the norm, with high power tractor-pulling units (eg: John Deere) in E coast USA running triple stage turbos up to 10 bar boost or more.

I don't have any more faith in the 'remapping' thing with diesels in the aftermarket than I currently do in the petrol engine market, except to say that I do know some highly reputable firms - like JE Engineering in Coventry - have been into this issue in very great depth and achieved good results from engines like the Land Rover Discovery, but I would guess they are in a minority.


GC

[Lowtechguy]

Wow, that is interesting.

Since my post I have bought the car and was told it was already remapped but like you I have my doubts on the 200bhp and 300ftlb that was claimed. I am having a rolling road after work (if I get there in time) and will post results (if you are interested of course).

To be honest though, I am shocked.. I thought some minor modifications like over bore of the exhaust to reduce lag and shorter/striaghter induction for the turbo again to reduce lag.

But no flowing mods? or is this simply because you'd just argue to up the boost? 0.5psi of flow for ‚£‚£‚£ or up the boost for free etc?

The version I have is with solid lifters so I was hoping something could be done to the cam at least to promote what the driver thinks its lacking (power or torque)...

At the moment it performs very well, turbo lag is something I want gone for good and I want to make sure it never smokes (partly because of the fine i'll get - thanks K Livingstone!).

I think 10bar boost might be alittle too much for this engine but with nobody I'd trust (only BS remap companies make claims) nobody has done their homework to see what the engine can handle.

I know the gearbox is breaking with more than 330ftlb but the claimed 300ftlb I doubt is much more than 250ftlb from what I can tell.

I'll post the graph tomorrow.

Thank you for your time.

Cristian.

[Lowtechguy]

Striaght on the rollers as bought;


Standard map put back for comparison;

[Lowtechguy]

Blue (torque at wheels)
Black (BHP flywheel)
Red (BHP wheels)

[Guy Croft]

OK, but in order that it's not just another set of dyno curves you need to explain with a decent technical expose what we are looking at here, eg: before/after? Same car? Mods done etc!

GC

[Lowtechguy]

Sorry Guy, things always make more sense in your own head...

It is the same car, same day.
There are no mods other than a remap.

The car was sold to me as 200bhp and 300ftlb with a remap (a common claim from many companies).

I rolling roaded the car as it was... It made alot less power than promised.

I then put the standard map back on; just to see what it does standard, it would of been obvious if it made considerably less power than standard with the standard map that something is wrong with the car. The standard map produced the standard power.

The objective for the rolling road was to see everything was running well, it seems it is but not at the levels alot of people with this car expect.

Next I will be removing the complicated induction which imo is far too long and heavily restricted for a turbo application and have a straight of silicone pipe with a cone filter in the wing.

I have also discovered now the boost peaks at 28psi, I am told I can increase safely to 32psi but would like to do other things first before it is set-up finally. The pipework from the intercooler is very soft so with its expansion I suspect it creates more lag.

I will want to address the exhaust properly also but unfortunately I am getting typical boy racer advice from companies (remove cats and silencers), I don't believe things to be that simple.

I would like to find an off the shelf replacement turbo from the same family for easy sourcing of replacements but to increase boost without over working the turbo.

I want to increase fuelling (fuel makes the power) but I don't want to over richen the mix to then cause problems with overheating the turbo, cracking the head in extreme cases and so on.

I also want to get some sort of probe in the exhaust so I can monitor the temperature so I can ensure everything is above board. I am certain this equipment exists but I'm a complete novice to diesel thinking and have alot to learn.

Sorry again for making a confusing thread, I tried to give feedback but didn't put enough thought into it.

Apologies.

Cristian.

[Guy Croft]

Well done, a response very much in the vein of this website.

It's plenty powerful - leave it alone is my strong advice!!

GC

[Lowtechguy]

I just read my post "I want, I want, I want"...

I will service, address the induction and maybe tinker the exhaust if I think it needs it but I think that will be all as you say.

Alot of big claims with this engine but no proof.

Amazing how you can have an engine with double the power but no rolling road ever... :!:

Thanks for the advice as always.

Cristian.

[Guy Croft]

Sanguine approach! Always best..

GC

[mtbr]

Christian,
A word of caution about running your car with the non std. fuel map. One of the most critical parameters for a diesel engine is exhaust gas temperature. The engine manufacturer will have determined the opperating limits very carefully, because the margin for error at full load is usually very small. Exceed these limits and you run a high risk of destroying your exhaust valves and or the valve seats.

Almost any diesel engine will produce more power than std. if you increase the amount of fuel being injected. This is because the fuel limit is determined by exhaust temperature and smoke production, rather than reaching a point where the torque no longer increases as more fuel is aded.

The aftermarket fuel map you have, will almost certainly be capable of exceeding these limits under some driving conditions. e.g. climbing a hill for a long time or prolonged high speed running. The company that produced this map is "hoping" that road conditions will prevent you from opperating the engine in this damaging regime.

I would recomend that you install an exhaust temperature gauge in the car and deterine the highest temperatures you can achieve with the std fuel map. You could then use these temperatures as a kind of "red line" for the aftermarket map.

You will find exhaust temperature is a very sensitive parameter, which is to say, it changes almost instantly with load.

Mark

[Lowtechguy]

Thank you. I will.