[NISFAN]

With all the threads on 'which tuning box?' 're-map vs. tuning box' 'Tuner A offering 335hp', etc. I thought I would post a thread to look at the Diesel engine in general, power output and mapping.

First of all, lets mention mapping. I think its fair to say, most people have an idea about mapping that originates from the spark ignition engine....i.e. Petrol engine. An easy assumption as petrol 'mapping' or 'tuning' has been with us private motorists for many decades, and although we may not all know the ins and out of Petrol tuning, we have some idea about the complexity. Tuners are Gods.

The thing is, there is a massive difference in the way a Diesel works in comparison to a Petrol. In Petrol mapping, the tuner dances on a tight rope between boost pressure (In turbo/ supercharged applications), ignition advance, AFR (Air Fuel Ratios) and Detonation (an extremely undesirable condition), whilst keeping an eye on EGT's and other things. All these parameters are tightly linked, and a change to one very often affects the others. To make matters worse, a petrol engine is throttled.... it does not take a full charge in every rotation of the engine, and the AFR needs to be within a very tight tolerance window. This gives another dimension (fuel metering) altogether that does not affect Diesels.

Summary: It takes much skill to arrive at the most (reliable) power for a given application when mapping a Petrol engine. Get it wrong and the engine could expire in a matter of seconds. FACT!!!

A diesel on the other hand is a much more simple beast. For starters it self ignites, more about that another time, but relevant to bear in mind.

A Diesel can also be described as a variable AFR device. To explain, a Diesel has no need for a throttle valve, it generally takes in a full un-throttled breath of air with each rotation at any engine speed. The amount of power it makes is solely down to how much Diesel is injected. So on low engine loads (idling for example) a Diesel can be running at over 100:1 AFR (air to fuel ratio in weight).......a clue to why they can be so economical . They inject just the right amount of fuel to maintain engine speed in these situations.
On full load the power is increased by injecting more diesel...this can be done until you get close to the stoichiometric rate of Diesel around 14.5:1. In fact at Stoich(or any richer) the engine starts producing a massive amount of smoke. Making it richer much beyond Stoichiometric and power starts to drop off. So a very easy indication of where the limit is and less parameters to adjust in the first place.

So we can see a clear difference between mapping a Spark ignition engine and a Diesel. For SI, the mapper has to balance many parameters to get the engine to run correctly and produce power (and not explode in seconds). For the Diesel you only really control fuel quantity and boost pressures, almost everything else is a function of engine design....mechanical.

You can immediately see that the skills threshold to become a 'Diesel mapper' is very low. Actually it is not. What I am saying is although any muppet could alter a map on a Diesel, it takes much skill to do it right from an engine efficiency and longevity point of view. So yes you still need to consider who to trust.

On to how Diesels are set up....The Turbo Diesel.

As Diesels are un-throttled, a naturally aspirated Diesel could run maximum torque at idle as it could at any other point in the rev range (within a small margin), they have a naturally very flat torque curve...or at least capable of. Turbo's upset this a little as maximum torque would be a function of boost pressure as well as fuel metering. Turbo's also have a flow diagram where they are most efficient at certain flow rates, it also needs to be running at a given speed in order to produce flow (turbo lag, boost threshold, etc). This of course impacts the Diesel engine torque values. But one of the main reasons we have an arching (D shape on its back) torque curve typically from a modern TD, is that it is not good for the engine to produce very high torque at low revs (roughly,1st 1/4 of rev range), and the same again at high revs (last 1/4 of rev range). So the OEM mapper puts in a torque limit map. This is a restriction of fuel flow regardless of what is going on in general, and is typically this D shape. What it means is a typical engine of a set displacement and design will be less restricted (map wise) in the middle part of the rev range, more restricted either side. The low end doesn't really feature for anything other than perhaps 'driveability', but the top end does control the horsepower figure. Horsepower being a simplistic function of torque x revs.
In essence, there is little scope to increase torque in the middle part of the rev range on a well set up engine. Where gains can be made is in the upper part between the onset of the torque limit map and the demise of boost pressure.

How?

Well this can be achieved a few ways. The tuning box method will report lower fuel rail pressure to the ECU, tricking it to increase fuel. It can also misreport boost pressure, thereby getting the engines ECU to increase the boost pressure value. By altering the ECU inputs, it fools the ECU into changing it's outputs to a different set. More boost, more fuel = more power.

Tuning boxes can be a simple box of resistors intercepting one or two sensors (although these don't work on modern self calibrating engines so well), to a fully programmable box that carries out it's own secondary level of 'mapping' (probably ACS, Steinbauer, Brabus, et al) and takes info from a large array of parameters.

Re-mapping - The other method is to crack the ECU and reprogram it's mapping tables. Technically a more 'complete' solution, as the ECU has a continuous and infinite amount of adjustment and calibration going on to it's main map due to outside influences....ambient pressure, coolant temperature, engine modes, AC ON, gearbox torque limits, DPF restriction, etc. So correcting the inner base map keeps all these other corrections 'in order'. Something a 'tuning box' is not likely to be able to achieve.

Cracking the ECU also gets you access to things like the throttle pedal map, speed limiter, etc. added bonus.

Summary: Both methods are capable of giving more power, one is more of an outside influence, the other integrated into the heart of the ECU.

So which is safer?

This is where it becomes tricky.....both if done on a professional level can be safe. This is to give marginal power increases and to keep within the component manufacturer's limits. Turbo, fuel pumps, DPF, EGT's, etc.

The danger is, many 'tuning companies' are a guy with a laptop and a bit of kit used to access either of the two above. In fact any one of us reading this could go out and buy all the gear needed to become a 'tuner'. Would you trust yourself tuning your own engine?......exactly!!! There are no standards.

The other thing is, tuners, to get over another with the same bit of kit, are under pressure to up the ante. We've all seen the company x says 315hp company Y is now at 325hp type scenario. Okay, many buy a map and cut and paste (Cut n paste tuners), and they might only resort to exaggerating the figures. Others might start to dabble where they really shouldn't. Fact is, outside of some very big names, you can almost be certain this is going on.

Trust them and their claims at your peril.

Technically, if your car is still under warranty, a tuning box is least intrusive, and can be removed which pretty much leaves things absolutely unaffected. For the BMW ECU, to re-map you have to use the ECS tuning tool, which means opening up the ECU.....This alone breaks the seal on it rendering the ECU warrantee less. Then the data in the ECU is changed. The tuners might tell you the checksums still compute, etc, but it would be quite simple for BMW to verify the version of code and see they don't match up. It is just software and by changes lines of code it differentiates it from the standard code, simples! At the end of the day, it depends on the failure and how far the repairing BMW dealer is willing to delve into it. Having said that, BMW diagnostics are linked back to Germany, so they (BMW Gmbh) could interrogate an ECU before passing off a warranty claim.

So it all depends on how far you are willing to push the engine, if you prefer the effects to be reversible, how much you trust Mr. Tuner guy and his laptop and bought in software, what value you place on a warranty.

Hope it has been somewhat informative.

PS: Sorry for being long winded....yes you'll not get those 10 minutes of your life back.

PART 2

OK so after a few questions and interest I thought I would talk about the fundamental differences between a diesel and a petrol engine....surely they are the same, both 4 stroke, just different fuel?

....well not quite.

Lets talk about the Petrol engine first as most are familiar with this.

During the intake stroke, a petrol engine takes in both air and fuel. Remember that strict AFR thing? Yep, a petrol engine needs a very homogenous mix of air and fuel in a very tight ratio to burn at all. Too rich or lean and no bang happens. So the fuel and air need to be mixed and swirled for a good even mix. This is achieved by mixing them during the intake stroke.

Once the cylinder is charged with air/fuel, the next stroke is compression. Here we are limited on a petrol engine, because air heats up as it is compressed. The 'air' in the case of a petrol engine is full of correctly metered fuel, so is highly combustible. Therefore, the compression can't be so high that the air/fuel mix gets to the ignition temperature, otherwise we would experience pre-ignition. Typical petrol compression ratios are around 10:1, slightly lower for Turbo/SuperCharged engines.

In an ideal world, the spark would fire at TDC on a petrol engine, however, this is not the case. Contrary to the ideas some people have, the bang is not a sudden event. It actually takes time for the flame front (started by the spark plug) to travel through the air fuel mixture. Because of this 'delay' in reaching peak pressure, the spark is actually fired slightly before TDC. The aim is to reach peak pressure at around 12 degrees after TDC crank rotation. From there in cylinder pressure drops as the piston moves downwards creating a larger 'can' to burn in, and most of the fuel air already is burned by this stage.

The next stroke is exhaust, and they are identical in the diesel, so no comparison needed.

Now the diesel....

On the intake stroke, only air is drawn in, no fuel at all just yet.

Due to this fuel less charge, we can take advantage of a more efficient pump and increase the compression ratio to more like 20:1, no detonation can take place, and we also want the air to be above the spontaneous ignition temperature.....big difference.

So compression done we move onto the power stroke.....here the injector squirts diesel into this superheated compressed air, causing the diesel stream to ignite immediately as it enters the cylinder. The burn process in a diesel is much slower, not because diesel burns slower, but because the diesel is not all present up front like a petrol, it takes time for the injector to squirt the fuel in. As a consequence, the pressure in the diesel doesn't peak quite as high, but is more sustained for longer portion of the stroke. This gives a clue as to why diesels are generally more torquey. They potentially have a higher cylinder pressure at a larger crank angle than on the petrol engine, giving great mechanical advantage on the crank.

This difference also gives a clue to why a diesel is not a high revver.....the combustion process is slower, so no point speeding up the process, as it will result in unburnt fuel at BDC, which is a waste. Also the engine components on a diesel are much stouter and therefore heavier than those required in a low compression engine, and heavy masses do not like being flung about at high speed.

Hope that gives a little more insight into the derv burner.

[teaston]

Holy 'wall of text' Batman!!

[Nick the Greek]

Reminds me of when we used to "tune" our two stroke motorcycles.

Flat out with one hand always covering the clutch........

[Tengocity]

Thanks Gordon- I found it interesting, factual and balanced.

I didn't know some of the engine technicalities, but your thoughts on the pros and cons mirror where I got to in evaluating the various options before I remapped.

From what my dad has said (BMW tech) the moment a car is hooked up to a diagnostics machine then BMW in Germany can see the data and know of something is amiss.

Now what I don't know is whether it is at the 'first level' of interrogation that the better tubers try to deal with.

The other day Mark mentioned that a BMW engineer said that DMS were able to cover their tracks, however I accept that it can only be to some extent.

I really don't think anyone should go down the tuning route on the belief that it won't be uncovered.

I haven't myself, and would classify myself as having taken an informed risk.

[dopper99]

Very comprehensive Nisfan. This thread should be a Sticky so we can point the people to it that keep asking about tuning (on a near daily basis).

[magic77]

Exellent post and so true. GOing back to my VAG days had a Leon TDI 115bhp. First Tuning box I bought was a in-line plug into the fuel rail and a small potentiometer you would twist. Thought I try it and within a week car was on rollers and getting a Revo map was brilliant after that. Similar with my e46 that went to Paramount Performance and got a full proper map best choice for a 320D and E90 in end ended up with a Power Pack update. Boxes work and give good results but IMO nothing beats a proper map. Though I think it will be a long time before I dabble with the 335i still trying to find space to use all the power I have righ tnow

[NISFAN]

Originally Posted by teaston

Holy 'wall of text' Batman!!

I'm sorry, I did warn......at the end

Originally Posted by Nick the Greek

Reminds me of when we used to "tune" our two stroke motorcycles.

Flat out with one hand always covering the clutch........

Ha, I made a mountain of holed pistons in my attempt to be the fastest when I was a lad.

[NISFAN]

Originally Posted by Tengocity

Thanks Gordon- I found it interesting, factual and balanced.

Thanks Terry, I guess the often asked question to any kind of tuning companies are always the same. I find some tend to be very misleading on the common answers.

We know that ECU companies go out of their way to stop re-mapping by putting in software locks, encrypted files, etc. They do this because they know it is rife, and a potential warranty nightmare...so only logical that they have ways to monitor any kind of tampering. I'm sure they would be able to tell if an ECU has been re-mapped. You do have to break the seal on the ECU case for the mapping plug to be attached on the BMW ECU. That is a simple physical check. Whether they will check for a blown turbo? Who knows?

[NISFAN]

Originally Posted by dopper99

Very comprehensive Nisfan. This thread should be a Sticky so we can point the people to it that keep asking about tuning (on a near daily basis).

No, I'm waiting for the shady tuner types to pay me to take it off....it could be bad for business.

On a serious note, I believe the top power for a 330d is up to 330hp.....a bit longer and it will reach 400 Not at all bad for a 315hp limit Turbo.

[Nick the Greek]

It always worries me when a fella posts....

"Back in my VAG days...."

Pre op?

[Tengocity]

Originally Posted by NISFAN

No, I'm waiting for the shady tuner types to pay me to take it off....it could be bad for business.

On a serious note, I believe the top power for a 330d is up to 330hp.....a bit longer and it will reach 400 Not at all bad for a 315hp limit Turbo.

Any views on the theoretical max for the 335d?

[....,,,,..,,..]

Excellent write up and very informative

My tuning side of things goes back to carbs, webers etc and stripping engines down for more sporty cams n stuff, none of this new dangled electronics

[Lorcan]

Excellent post Gordon

[NISFAN]

Originally Posted by Tengocity

Any views on the theoretical max for the 335d?

No, I haven't looked into what spec turbo is fitted on a 335d. From memory, the Twin is a small feeding a large in series, so just knowing the max flow on the large turbo will give you the answer. I will have a look when I get a chance.

[F30Andy]

Excellent job Nisfan.

I have been pondering this for some time now and after all the posts about tuning was on the verge of making a choice I may have regretted.

I think I'm gonna follow your advice and stick with the big boys. Superchips will be getting a call from me this side of Christmas.

[FSE23]

Thanks for the excellent post. I have never done any engine tuning but I was thinking of sth. However even before reading your text I decided not to do anything at all. i'm too scary . But your post has broadened my knowledge

[pdk42]

Thank you. Very interesting and informative post!

[Nick the Greek]

I'd moderate the praise chaps....

NISFAN will be asking for donations next!

[PurpleTT]

Originally Posted by pdk42

Thank you. Very interesting and informative post!

What he (and plenty of others) said.

Thanks for that, Professor. I may be boring the young 'uns at work with some of that knowledge soon.

[HighlandPete]

Interesting topic Gordon, well put together.

Particularly note your comment on the torque curve and not ramping up the torque to high levels at low rpm. Many don't realise that the torque pulse can have detrimental effects on the engine and drivetrain.

I'm aware of some 'tuners' pushing too far and causing drivetrain vibrations on BMW models. Then of course we have issues with DMF and torque converter wear if we push the limits too hard at low rpm.

Interesting the 335d has been raised and what the limits are. I read that the wastegate will come into play above 4,200rpm to control turbine speed. I've no data on what the criteria is, but imagine there has to be a very considered implementation of adding boost at the top end to retain reliability and longevity of the turbo. Saying that we don't hear too much about failed turbos on the sequential turbo setups, even on tuned examples.

HighlandPete

[Proftinkerpot]

Originally Posted by NISFAN

No, I haven't looked into what spec turbo is fitted on a 335d. From memory, the Twin is a small feeding a large in series, so just knowing the max flow on the large turbo will give you the answer. I will have a look when I get a chance.

Excellent initial thread Nisfan. Loads of detailed explanation. On the above thread, I am not sure of the max output of the turbo but I think I read the 8 speed ZF autobox was limited to 400bhp. It may even have been less.
I think it was mentioned on a thread about the Alpine tuned 335d. I have also read a few articles now saying that manufacturers leave a lot less headroom in components such as euros nowadays. This is to reduce production costs although they will argue smaller turbo spools quicker therefore has less lag. The result is less tune-ability without changing a costly turbo.

[Tengocity]

Originally Posted by Proftinkerpot

Excellent initial thread Nisfan. Loads of detailed explanation. On the above thread, I am not sure of the max output of the turbo but I think I read the 8 speed ZF autobox was limited to 400bhp. It may even have been less.
I think it was mentioned on a thread about the Alpine tuned 335d. I have also read a few articles now saying that manufacturers leave a lot less headroom in components such as euros nowadays. This is to reduce production costs although they will argue smaller turbo spools quicker therefore has less lag. The result is less tune-ability without changing a costly turbo.

The ZF8 box in the 335d has a torque limit of 700NM, which is 516lb/ft. Not sure if there is a bhp limit. The steinbauer ECU goes above this, but Alpina, ACS and Hartge stop at this when they up the engine output so I asked DMS to stick to it too.
I know there is likely to be no major risk going a little above it, but I plan on having the car to a high mileage so felt sticking to it was a reasonable way to manage my risk.