Fudging turbo-diesel fuelling for more power. 1

[carl0s]

Hi.

There are boxes for sale which screw with the fuel pressure of modern turbo-diesel motors in order to over-fuel the engine.

It strikes me that these boxes are the diesel equivalent to those 5p lambda resistors that are sold on a certain auction site. They are screwing with the fuelling to increase power.

I understand why this is bad on a petrol motor, but I am having difficulty finding proper information about why this might be a bad thing on a cutting-edge turbo-diesel engine, (for example Honda's 2.2 i-CTDI), if it is at all. All I have found so far is that a richer mix in a diesel motor increases power and raises EGTs, which can damage the turbocharger.

Does anybody know anything about the subject? Should these overpriced resistors-in-a-box be avoided, and if so, why?

Thanks for your time,

Carl

 

[curtis74]

Many diesels have little or no boost limit other than compressor surge. So, in addition to having an excess of air at all points, as you add fuel, you are adding mass flow to the turbine as well. More fuel, more turbo pressure, which means more air. Of course if you add 30% more fuel, you don't get 30% more air, so depending on the setup (and if there is a wastegate or other boost control) you will reach a point where other mods are necessary.

Typically on a common turbo diesel, the first things you want to do are remove restrictions in the intake and exhaust. Both will lower EGTs. Then add an EGT gauge. Then as you add those tuner boxes you can add fuel.

Eventually you will reach a power level where a stock turbo just runs out of range and an aftermarket turbo may be helpful, but its not uncommon for an LB7 Duramax to put 450 hp and 900 lb-ft to the wheels with an intake, exhaust, and tuner only. The capabilities of many stock setups leave a TON of room for more fuel.

 

[Ffoxy]

Thanks everyone for the replies, I'm happily enjoying fuel saving benefits from my re-map as well as potential performance gains, I know the power is there if I need or want it. The car was rolling roaded before and after, showing the standard MJet produced 144 bhp at the flywheel (est from the RR torque figs)and now shows 194bhp, key improvement for a diesel being the increase in torque for low revs use.