Why do manufacturers detune engines?

Question

I was wondering why a manufacturer would detune an engine. An example -- there are many others -- is the Mercedes-Benz OM612 engine. Same engine, lower (peak) power output in the Sprinter than in the E-class. The same hardware (and thus the same cost), yet they 'artificially' lower the power output and thus the specs they can use to sell the product.

Does it have to do with using the same engine for different purposes? With a van you probably want a different power and torque curve than with a sedan. In the example I gave, that seems to be the case, with the van reaching top power and top torque at a lower rpm than the sedan.

Or are there other reasons (fiscal, strategic,...) that lead to these decisions? Using the same example, in Belgium the engine was detuned whereas in other countries it was not (both for the same cars), as can be seen in the Wikipedia page. I live in Belgium but I have no idea why they would have done this for Belgium specifically. In this case, the only difference is the peak power output, the rpm at which this occurs and the max torque is still the same.

If non-design reasons are involved, would it (sometimes) make sense to tune these again to their 'normal' specifications?

Answer 1

I'd be tempted to restate the question as "How do vehicle manufacturers decide what to tune for?" For the question as asked, there are a lot of possible reasons, and probably no way to know in a specific case unless somebody involved speaks up, but in general:

• To match the engine to a specific use case (as you suggested here).
• To find a balance between performance, durability, and marketing needs (detune in Sprinter to improve reliability, tune in E-class for marketing/performance).
• To fit into a particular regulatory class (in the US, for example regulations change with the load capacity of a vehicle).
• To meet insurance requirements (horsepower limits for example).
• To balance "fleet" requirements (another example from the US, makers are rewarded/penalized on maker's overall averages for fuel consumption and maybe for emissions as well, so tuning may get tweaked to manage this).
• Maintaining or adjusting a product "line" – a maker may want to have a "logical" progression of features or performance and so adjust numbers to make this happen, or may be trying to move customers for strategic or economic reasons.

For an operator of the vehicle it would seem that, after evaluating the "good" reasons for the tuning decisions, there would be no reason not to adjust the tuning to suit the operator's needs.

Answer 2

Great answers, but there is also one more reason for manufacturers to detune engines:

• can the vehicle take the torque?

A van isn't built like a sedan, and it's frame is built to handle weight (downward force). The extra torque from the engine could twist the frame. This was a reason for detuning engines for the T-top version of some American muscle cars back in the day.

Also, we are only talking about the engine: torque is applied to the entire driveline. Can the transmission handle it?

Answer 3

Emissions concerns. In order to comply with the emissions laws in one place, they tune the engine differently. Laws are often different between commercial vehicles (vans) and cars. They may also detune to protect a brand. For example, the corvette / camaro have very similar engines, but the camaro one is usually slightly less powerful to protect the corvette brand.

Answer 4

One reason is to have a common engine between products with high and low sales volumes.

Some numbers pulled from Wikipedia:

Sprinter vans - total sales in Europe and the USA about 130,000 per year.

W210 cars - harder to get the actual number and there are many minor variants, but it looks like fewer than 10,000 per year in total.

Sources: https://en.wikipedia.org/wiki/Mercedes-Benz_Sprinter https://en.wikipedia.org/wiki/Mercedes-Benz_E-Class_(W210)

More likely, they raised the power of the car engines, possibly trading off lower reliability and higher servicing costs, as a cheaper option rather than supplying a purpose-designed engine.

The same philosophy also applies to aircraft jet engines - there may be almost zero mechanical difference between variants of the same engine type with 30% difference in maximum thrust. The only change is the electronic engine management system. Since airlines now tend to buy "power" (i.e. a complete package including fixed price maintenance, etc) rather than just "engines"), the lower power variants are cheaper to operate because of lower maintenance requirements, better guaranteed fuel consumption, etc. Not to mention the reduced cost of engine certification, flight testing, etc, - all of which is eventually paid for by the customers one way or another.

Answer 5

Many reasons.

In a car, it's a small light vehicle and customers buy them based on HP numbers / 0-60 times / handling etc.

In a van, it's got to slog away carrying a heavy load, withstand operator abuse, and be economical and reliable for the warranty period regardless of that abuse / poor treatment.

De-tuning does not necessarily mean what you think - HP is based on torque X RPM, but for a heavy vehicle you need low down torque and a good spread (flexibility), not a sports-car "peaky" shove-in-the-back-and-then-shift kinda behaviour. A truck with a racing-car cam in it would be awful to drive.

You're comparing a work horse with a race horse. One can't run fast, but the other can't pull a plough.

They may also limit emissions for similar reasons, if memory serves Skoda did a 1.9TDi that was identical in two vehicles - one was the "sports" which went like stink but emitted lots of CO2 (so higher tax class in Europe) and used more fuel, and one was the "eco" tune which sipped fuel & got you zero-tax and low insurance. I know which one fleet buyers would be going for. Same engine in a VW Transporter I'd wager they drop the HP numbers but up the torque.

Also they electronically limit the torque based on gear as they make gearboxes smaller & lighter (and make 5th/6th out of plastic for cheapness/noise reduction) so you can't have full torque trying to race your fully-laden van off the traffic lights (saves many clutch & gearbox rebuilds under warranty).

My last van (GM/Renault/Nissan Vivaro) shared the GM 1.9TDi with the Vectra et al but hit a brick-wall rev limit at 4krpm, pretty sure none of their cars did that.

Land Rover used to de-tune Defender engines for all these and more: Bad fuel in remote locations, static running (powering PTO units etc.) for long periods in hot places, and to avoid over exuberant driving by employees / squaddies. Often they had 30% less peak-HP than the same engine in a Range Rover.

Some industrial engines (based on car or truck engines) are tuned specifically to work at ONE fixed RPM - 1500 or 3000 for generators, with carefully tuned cam profiles etc. to suit. They can make much better power at that ONE RPM than the other variants but, again, would utterly suck in a vehicle.

I saw a guy who built a 4x4 (SJ410) with a ridiculous race-tuned car engine he found, it utterly sucked - it was all-or-nothing power delivery (zero below 5000rpm, then a million HP), very hard to drive, easy to stall, poor control, it stressed the drivetrain with all the jerking / clutch slipping, and overheated when working hard at low speeds. People in identical vehicles with bone stock engines were able to drive circles round him. Sure he had lots of HP at 5000RPM, very useful for bragging down the pub.

Edit to add: Top Gear demonstrated one example of tradeoffs for larger HP numbers when they reviewed one of the Mitsubishi Evo's. The top of the line most powerful one (400HP?) was awful to drive as all the power was at one point, the lower spec one (~300HP?) actually drove better as it had a broader spread of torque, meaning you didn't have to change gear as much. They raced the 400HP one against their camera car people-carrier (Fiat Multipla?) off the line from tickover and the minivan out-dragged it for a long time until the turbos spun up & everything came into the zone. You could probably find it on YouTube if you're interested.

Answer 6

A coworker once told me about his job at International Harvester. They could sell more power engines as an upgrade that was triggered by a software key.

So yes, for some industrial and farm engines, they sell the same hardware but hold back the performance in software alone, to produce different priced products.

Answer 7

I'm not sure if my example fits the phenomenon you are describing, plus this is more like an extended comment. But VW detuned (as in willingly limited) the power of the engine in the Golf III 2.0 16V.

1. German Wikipedia describes this and gives a reason:

   The strongest VW engine competing [with the VR6] has been the ... 2.0 16V with the engine code "ABF" that performed at 110kW (150HP). ... The 16V received power limitations by the ECU via software, because in tests it often spreaded over 115kW.

   (Sloppy translation & emphasis mine.)

   So besides differentiating it from far more expensive models with roughly the same power specifications (i.e. the VR6), inconsistent power output of the manufactured engine may be a possible reason. That may be one answer to your question about the reasons for detuning an engine.

2. Considering your last question about the retuning and its worth:

   Specifically in this example there has been a very active community of chip tuners that "fixed" the software in the ECU. (Most people in Germany interested in the ABF engine will have heard the name Garlock at some point.) It's quite hard to say where retuning to the normal engine potential ends and where actual chip tuning to get the last bit of power out starts. However - sticking to the example - testers of the so-called Garlock chip report very pleasant results in the respective forum thread (German - but you might be interested in the pictures).

Apologies for the German sources.

Answer 8

I've Seen some answers like " engine twisting the body frame", which is highly unlikely as the engine is separated from body by rubber mounts which totally absorbs any form of torque which in turn is directed to the drive.

The main reason for de-tuning an engine is strictly for economical reasons, making the vehicle suitable for the road, whereas uptuning would prepare the vehicle for racing.

In both situations, the engine has running limitations for it to start and continue.

Looking for other reasons is unnecessary. Engines are tested separately from the rest of the vehicle before being introduced to them. That place is called a "heat lab" which is an area where the unit can be tested to destruction. The main contribution to an engines destruction are over loosened parts and over tightened. No water and oil. It is possible to over oil an engine. Water systems are normally sealed.