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

 

[patprimmer]

G whizz Carl

You should tell the factory engineers about it. They never thought of investigating fuel required for maximum power vs a downside like hydrocarbon emissions, smoke, smell and NOx

Regards

eng-tips, by professional engineers for professional engineers
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[carl0s]

This is what I want to know though. Is it really just emissions and economy that is affected? Or is there a chance of pre-ignition or some other catastrophic engine failue? If it's just emissions, then my argument that "these things should be avoided at all costs" is not going to have quite the desired effect.

 

[SomptingGuy]

Just turn your scroll plates a bit.

- Steve

 

[carl0s]

Thanks SomptingGuy. I am not looking for ways to gain power on my diesel engine though.

Some people on the Honda forum have fitted these boxes. Some feel they work, when they "set the knob to 30". The check-engine light comes on when they "set the knob to 45".

A user said he feels they are a rip-off waste of time, and he asked "I just don't understand why the engine supposedly has to 'learn' to work with the box', to which my comments were:

"It has to learn how to cope with the duff sensor readings it's getting. Put it on "45" and the ECU decides the sensor is well and truly fubar'd, hence the check-engine light.

It strikes me that these boxes are "one for all" with only the plugs on the end being swapped for different cars.

I'm no engine expert either, but IMO this sort of thing is very bad.
It's the diesel equivalent of a lambda resistor, which is a bad thing too. Apparently diesels work the opposite way to petrol, in that a richer fuel mix increases power, whereas petrol motors make more power when running leaner. The fuel mix has been carefully set right by Honda, unsurprisingly

I suppose you could argue that the fuel mix has been set right for reasons of economy and low emissions, over power, but I'd rather be safe than sorry thanks, and there does tend to be a "correct" air/fuel mix with engines. I don't think it's typical to use the air/fuel mix to alter emissions of an engine.

The problem with the richer mix is higher EGTs, and probably all sorts of other problems that I don't know about on diesel motors. Remember the primary reason why petrol cars (other than latest Porsche 911 turbo) have not had these nice VNT/VGT (variable vane/nozzle) turbo chargers is because they cannot handle the high EGTs of petrol motors.

Without wanting to hurt feelings of those who have bought them, I think a responsible community like this should be point blank telling people to avoid this sort of thing.

I'm sure it won't be long 'til somebody develops an easy to remove proper ECU remap chip or piggyback unit."

I am just looking for some technical feedback as to whether they are dangerous to the health of the car, or whether my suspicions are totally wrong and the only downsides are emissions related. Emissions are hardly a concern to people who are trying to increase their car's power - these are the sorts of people who would just pull out the CATs if it would increase power.

Nobody with a half a clue would go leaning out their petrol turbo car with a 2p resistor, but it seems to be a different world with diesels. I hear talk that there's no actual "safe mix", or "no mix at all.. just fuel" etc.

 

[JSteve2]

carl0s:
Most production diesels are de-tuned and can handle far more torque and fueling than they come away from the factory with. The same engines are sold at a variety of ratings with no physical part differences. If you turn the fueling up without the whole engine being designed for it, you are mostly looking at unfavorable fuel economy and emissions impacts, but in most cases you can get a significant increase in torque and power. There are instances - for example the engine is at the high end of the rating ranges - where your turbocharger or other system can be limiting and you will actually not get a power increase (the ECM responds to the fuel increase by de-tuning to protect those parts). However, increasing the fuel may reduce the part life of some components below design, and will probably void the warranty if any. Further, if your system has an aftertreatment system, you should not do anything to negatively impact the emissions because that can be very damaging.

This is usually done instead with an electronic box for modern diesels, not with turning up the fuel pressure.

Having said all of that - merely increasing the fuel pressure will have little effect on fueling. Some engines don't depend upon rail pressure and in those engines increasing the fuel pressure does nothing (actual injection pressure is generated within the injector). For common rail systems, I don't think you will be able to increase the pressure very much because those systems are basically designed for maximum pressure anyway. Increasing the injection pressure will have positive impact on emissions so they are already doing about what they can. Significantly increasing the pressure might be a good way to test your system for pinhole leaks.

 

[dgallup]

I don't know anything about the Honda engine or the black boxes in question. However, I spent the early years of my career in the engine development lab of a heavy duty truck manufacturer. It is true in the heavy duty market that the same block is sold at many power levels. However, we changed pistons, rings, turbos, intercoolers, rods, bearings, cams, injectors, fuel pumps, etc. as the power ratings went up. We also added piston cooling oil squirters, main bearing tie plates, etc. for the highest outputs. Many truckers bought the cheapest (lowest power) engine and cranked up the fueling & timing (easy to do in the bad old mechanical injection days). They also blew up a lot of engines. Even if they got the engine replaced under warranty they lost a lot of down time. Not smart.

Now I expect the Honda engine is only offered in one power rating and that rating is as high as they can get it while meeting emissions & all the other regulations they have to comply with. I expect a small increase in power will not compromise structural integrity but I doubt that an automotive engine has very large safety margins. If it were mine & I bought it for long life & good economy I'd leave it alone. If I wanted performance I wouldn't buy a diesel in the first place!

 

[carl0s]

This is all very interesting, thanks guys. What surprises me most is that these boxes are just attempting to increase the fuelling, but they are not increasing turbo pressure.

Does it not hold true for diesels that actually the turbo boost pressure needs increasing, and then the fuel supply needs increasing to match the increased air, as is the case for petrol motors? What you have said above seems to refer to just increasing the fuelling, which was my question, but I had expected something along the lines of "increasing fuel alone will do nothing except damage a,b,d & d.".

So, are you really saying that *just* increasing fuelling (whether that actually happens through increased rail pressure or not) is a good and safe way to obtain additional power?

The fact that increasing the rail pressure may not even affect fuelling is an interesting side thought..

I personally do not want more power. I have a lightly modified mk4 Supra twin turbo sat on the drive. The diesel Honda is my everyday car. As I said before, I am just trying to get to the bottom of whether or not my concerns about these trick-boxes was valid (i.e. have I been talking rubbish when telling people that these boxes should be avoided).

 

[SonyAD]

They should be avoided because they often fool the ECU into raising the rail pressure over the design limits of the injection system. To pressures where if the ECU knew what was going down it would shut the engine off immediately.

The worst that can happen is injectors rail and pump being compromised, maybe even timing belt failure with all the fun things that come with that.

 

[JSteve2]

I don't know that anyone said it's a good and safe way to get additional power. You will generally get additional power because there is excess air available to make more torque if you add the fuel (but again not if you hit a measurable limit that the computer responds to like a temperature or pressure somewhere in the system).

If anyone does this, it should not surprise them if something breaks or if it fails much sooner than it would have otherwise (see dgallup's list as a starting point).

 

[dgallup]

Again, I don't know any specifics on the Honda engine but I think all turbo diesels these days have excess air at all power levels including peak power to keep smoke & emissions down. So yes, more fuel will give more power. Diesels always run very lean at low power levels because they are essentially unthrottled. They can never get up to a stoichiometric A/F ratio where gas engines typically operate because they don't mix the air & fuel well enough to get complete utilization. As you approach stoichiometric the smoke starts going through the roof but power keeps going up. I once did an unofficial "low idle" test on a 1000 cu in V8 turbo diesel where we just kept adding fuel at 600 RPM. Eventually it was so rich that the power & exhaust temps started to go down. At that point the soot was so bad the smoke went down instead of rising. I think it was putting out over 200 HP.

 

[Bribyk]

Yikes! BMEP = 264 psi (18.2 bar). Did you manage to finish your low idle test or did it just stop on its own?

 

[Bribyk]

Or was it a two-stroke?

 

[BrianPetersen]

On another website dedicated to VW turbo diesels, generally the "sensor-fooler" boxes are frowned upon, in favor of properly re-mapping the ECU.

As for the reliability of such a modification ... it depends more on driving habits and maintenance as long as the modification remains *reasonable*.

My TDI got re-mapped for more power at 26,000 km, and all is still well at 197,000 km. The one I had before this started getting "tinkered with" (we didn't have access to proper re-mapping in the early days) at around 160,000 km, and I sold the car with the engine still running fine at 462,000 km. And I tow a trailer a lot in both cases ... although I try to avoid pedal-to-the-metal for extended periods.

No change in fuel consumption in either case during normal driving, and the earlier car went through what passes for an emission-test a few times without any issues.

By the way, the internals of the previous 90hp North American spec TDI are the same as the European 110hp except for the oil cooler and the injector nozzles. These engines are quite a bit under-tuned from the factory.

 

[Ffoxy]

Hi guys, new here, interested in theviews on Tuning boxes and ECU Re-maps. I have a re-mapped 1.9 FIAT Turbodiesel that shows genuine improvements in performance and economy, any views at all?

Also, I understand the stresses placed on a cylinder block within a diesel engine cused by rotational mass and compression ratios, but why cant a car diesel engine be made from a light alloy with hefty cylinder liners to reduce the engines sprung weight for handling benefits and improved economy?

Cheers guys... Keith

 

[BrianPetersen]

Honda diesels use aluminum-alloy blocks as that is that company's specialty - that's how Honda builds engines, doesn't matter gas or diesel. It CAN be done that way. VW's special 1.2 litre 3 cylinder TDI used in the "3-litre" (per 100 km) version of the Lupo also used an alloy block. But cast iron is less expensive, and in the auto industry, money talks above all else.

Aluminum requires thicker cross-sections and you need to do something special with the cylinder liners that need not be done with a cast-iron block, so the weight savings might not be what they first appear.

 

[SonyAD]

Alu block (and head) diesels are nothing new:

"The 1.6-litre HDi/Duratorq TDCi’s all-aluminium construction has maintained its weight at a very low 120 kilos. It is equipped exclusively with a 16-valve cylinder head derived directly from the head used on the 1.4-litre HDi/Duratorq TDCi, whose engine block displacement was increased to 1,560 cc by increasing both the stroke (by 6.3 mm) and bore (by 1.3 mm). The engine block of the 110 hp version is made of pressure-cast aluminium."

http://www.peugeot.com.au/PEUGEOT/AU/clientdocs/asp/minisites/hdi/technical.pdf

http://paulaxford.com/suzuki/misc_docs/8-valve engine description.pdf

http://www.sae.org/automag/techbriefs/05-2003/1-111-5-30.pdf

http://www.psa-peugeot-citroen.com/document/presse_dossier/feuillets_magique_uk1045567497.pdf

 

[SonyAD]

"The DV6 TED4 engine has a diecast aluminium block and head with cast iron bearings and liners inserted at the foundry."

 

[Ffoxy]

Great replies thanks guys, so its just FIAT pennypinching.

Good stuff and by the way, great informative site thanks.

 

[GregLocock]

"its just FIAT pennypinching."

I think you meant to type "it's just that FIAT's engineers performed an attribute based cost benefit analysis and decided to retain the quieter, cheaper, more reliable and not necessarily heavier option".

Unless of course you actually know better.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.