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159 - Diesel Tuning Fundementals - Questions

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Ask questions about webinar lessons here. To see the Previous Webinars for a complete list of archives tuning webinars. 

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I am extremely excited about the Diesel Webinar and future courses coming up!! I dare say I'm more interested in Diesel engines probably more than Andre himself ;)

I'm sorry for the delay in asking these questions but i was not able to attend the webinar while live. There are several questions i would like to get answered if you can.

1) Are the courses or information you provide in your training going to be related to performance with or without emissions?

2) Do you have a video on calibrating the MAF sensor in another course or is this different with turbo charged common rail diesels?

3) Was mentioned that 1.1 Lambda is the richest smoke free but what lambda would be most power?

4) What Lambda sensor was used in the video? I have been told they are not reliable with diesel .

5) @ 20:52 you mentioned the combustion rate is much quicker than a petrol engine. What is the velocity rate of the combustion? I believe petrol is around 60 feet per second.

6) @ 24:00 The Injection Pulse width is being discussed. Increasing the pulse width increases the power output to the rear wheels but moves the 50% burn rate further into After TDC. Does the 50% rate need to be moved by advancing the timing or would it be better to opt for a larger injector to keep the timing about the same and keeping the 50% burn closer to TDC?

7) @ 25:00 Fuel pressure is capable of delivering the same fuel mass for a given pulse width but is there some sort of calculation for this to know what fuel pressure you would need to achieve such a goal?

8) @ 26:42 You mentioned a Optimal point for the 50% burn rate. Is that a degree of rotation or an amount after the injection pulse?

9) @ 30:00 The practical demonstration on the pulse width increased the power output with an increased pulse width but in the throttle percentages less than 100% you would want to tune these cells for "feel" while driving, correct? As in you don't need to maximize the torque for each throttle % rather you would adjust for a smooth transition between throttle positions ranging from least to most power with more throttle press.

10) @ 32:06 EGT temps being dangerous to the engine. What would you consider a maximum point for being dangerous/critical? Say for example for a daily driven vehicle / Street performance / Competition Racing?

11) @ 33:00 The practical demonstration on the effects of timing is very helpful but my question is could you do like your petrol courses where you show increasing the timing by a degree or so and seeing the effects on the graph and when the torque starts to fall stop before causing damage to the pistons as you mentioned?

12) @ 36:42 You mentioned the Fuel Mass main limit. What determines that number? I would think the limit would pertain to the pulse width limit.. As in you dont want to inject fuel for a long period of time for the RPM the engine is rotating at. Maybe I dont understand what this means?

13) @ 38:45 The Engine Load is being mentioned and was wondering what determines this %? I always thought it was just the throttle position or least what I've been told.

14) @ 41:47 You mentioned just increasing the injector pulse width would not be ideal for torque but would that mean it would still increase horsepower? Still assuming that the delayed 50% burn rate is a bad thing?

15) @ 43:45 Replacing the injector nozzles with larger ones would be a better option in some cases but how large is too large? Would that be based on the injector solenoid capability of opening reliably for such short pulse duration at idle RPM?

Thank you for your time and Very happy to see Diesel stuff coming out now :)

Also looking forward to the Pilot Injection timing and pulse width webinar! Many tuners here in the US just disable it because of not knowing how to tune it.

Hey Dwayne, thanks for your questions. We are very excited about the upcoming diesel course and I'm sure it's going to be hugely beneficial to many out there. I'll try to answer your questions here but please bare in mind that we are also constantly learning in the diesel performance world too.

1. Primarily we will be dealing with performance based engines that don't require emissions compliance. We have however just ordered a 5 gas analyser and opacity meter for our Mainline dyno and will be doing some work around emissions compliance for both petrol and diesel in the near future.

2. We discuss the concept of MAF scaling in the Practical Reflash Tuning course. The concept is similar on a diesel engine however we would be looking at lambda estimate vs measured lambda as opposed to fuel trims. The trouble is that scaling the MAF requires accurate injector data which at least in the aftermarket may not be the reality.

3. As with any application, max power can be found by testing. It's going to vary based on the application but will be richer than the smoke limit. You also need to watch EGT as this will rise sharply as you add fuel.

4. We are using a MoTeC LTC with a the Bosch LSU4.9 sensor. So far I've had no trouble and we have been running the sensor for close to 12 months

5. I don't have a specific combustion speed. This again will vary depending on the exact operating conditions. If you do want more information around this then I'd recommend looking up some SAE papers on the subject.

6. You can gain power by simply increasing the pulse width however the 50% burn moves later in the cycle which is potentially a disadvantage. You're likely to gain power by then advancing the injection timing however care needs to be taken doing so as explained in the webinar.

7. Generally the rule of thumb is that more fuel pressure is better when operating at high load. The limit of course will be the fuel pump and spill valve. Experimentation on the dyno will show you the effect of fuel pressure vs pulse width.

8. The point mentioned is a number of degrees after TDC. Unless we can see in cylinder pressure however, this is unlikely to be too critical since we don't know where it's occurring. Just like tuning ignition timing in a petrol engine, we're just using the dyno to let us know when the burn is optimal.

9. Correct, we could achieve maximum torque at minimal throttle but this isn't desirable. We want to tune the table to deliver a reasonable relationship between torque and throttle position.

10. It's always hard to put an exact number on EGT as there are so many aspects that can influence the reading, particularly including injection timing and pulse width which may have fuel still burning very late in the engine cycle, or alternatively exposing the piston and cylinder head to higher peak temperatures than what is signalled by an EGT sensor. As a general rule of thumb I'd suggest trying to stay under about 700-800 deg C for performance road use including towing and for all out competition use you could get away with 900-1000 deg C but this is going to hurt parts if the temperature is sustained for any time.

11. The problem with injection timing is that depending on your pulse width you may continue to see gains in torque as you advance the timing, simultaneously causing damage to your pistons. You need to tread incredibly carefully when altering injection timing as it's a very easy way to destroy an engine.

12. Fuel Mass Limit is simply the way MoTeC deal with the fuel delivery. We can define this to be whatever we want. Generally we would choose this value to keep the lambda under control and provide smoke free operation at WOT.

13. Again the engine load in the MoTeC ECU may be different to how it is defined by an OE ECU.

14. If we increase power then at the exact same point we must by definition see more torque - The two are linked together. The problem with increasing pulse width is the effect on the 50% burn point so we may see a gain in power/torque but it may not be as significant as it would be if we could deliver the same fuel mass in a shorter pulse width.

15. Right now I can't answer that question. We are going to be fitting some larger nozzles to our 1KD injectors in time and will report back.

The pilot pulse is difficult to tune optimally without in cylinder pressure sensing but I've also found it easy enough to get a very noticeable reduction in noise without much trouble using a single pilot pulse.

Thank you for the timely response!

I'm excited to be learning along side you all. Your answers were exactly what i had expected. Looking forward to seeing/ hearing the results of the pilot injection!

Keep up the great work Andre and team! Make sure you keep Taz Man busy lol

Just curious on why you stopped at 15 degrees on the webinar when you went from 0 to 5 to 10 then 15. Would you have seen more power at 16-20? If so did you stop from fear of the injection on the piston edge?

One can assume that the timing would need to be advanced with higher rpm. I read a study done by some college here in the states on ignition delay and it varied with rpm, humidity, temperature and even quantity of fuel. I will try to find the study and link it here.

The only reason I stopped at 15 degrees is because we didn't see any further gain as we moved from 10 to 15 degrees. Yes, as the rpm increases the general trend is to advance the injection timing.

Hi Andre, I have a question, some big diesel engines like big trucks they have multibole injection on the same injection stroke, to get a better (smooth) burn of the fule and reduse noise. Is that something that i possibole to do on the motec ecu?

I assume you're talking here about multiple injection events during the engine cycle? If so then this is a technique that's common on most current common rail diesel engines and the MoTeC can replicate this. Often there are one or two pilot pulses that occur prior to the main fuel injection event, and a post pulse that happens later in the engine cycle. We will be running a webinar shortly on pilot pulse tuning and its effect.

Yes. Thanks.


You used a rule of thumb of no richer than Lambda 1.1 for preventing visible smoke. Do you have a rule of thumb for how early you can advance the start of injection timing main event before damage occurs? When you say piston damage, is there any kind of warning sign for it (kind of like how you can hear knocking on a petrol engine) or are you just humming along and without warning you hear a loud noise and have just cracked a piston?

Thanks. Good webinar.

Hey Raymond, I'll be honest, at this stage I can't offer a rule of thumb for injection timing. It's made harder because we can't just say 'never advance the injection event more than XX degrees' for example because a safe injection timing event will vary from engine to engine, vary with engine rpm, and also vary with the specific injector. With this in mind it's always best to start with an OE timing map and I'd probably be cautious of advancing the injection by more than perhaps 5-10 degrees from this point. My preference is to start by leaving the injection timing at the OE point and instead focus on increasing the fuel mass via pulse width and more fuel pressure. For example with our 1KD Toyota engine I've managed gains of approximately 60% in terms of peak power without adjusting the injection timing.

When the pistons fail in my very limited experience you don't get any warning. We had one fail (not due to injection timing I should say) and we had a little rattling noise that persisted at light throttle - almost a bit like a bearing rattle. Following from that within the space of a couple of minutes there was a loud crack and it was game over. For some background though there are 4 generations of the 1KD piston. 3 are known to be problematic with cracking and this can be irrespective of power level or modifications. W'eve now built a short block with the latest generation pistons and had no trouble.

Thanks for the response.

Hey team, the Diesel Tuning Fundamentals course is out now. Long time in the making, but it's here now.

hello, I just finished my training diesel engine is I encounter difficulties after this training, I understood all your videos and this has increased my knowledge. But I can not know exactly how to modify an engine ecu. I encounter difficulties at the time and injection time because your test does not sound on ecu manufacturer and bench power. Example: when a fuel demand of 40 mg your calculator corrects the ti during the modification of the moment of injection while the ecu constuctor no. I still do not know how to really change my turbo pressure (take into account the exhaust manifold pressures exhaust, the maximum allowable pressure of the turbo and the intake temperature), as well as how to reliably change my rail pressure and my limiter. couple I hope you can help me.

Hi Maxime, the specifics of making tuning changes will depend on the ECU you're tuning but yes, it is likely to look different to the MoTeC ECU that we used for some of our practical demonstrations. The fundamentals that we cover in the course however don't change.

What you will need to do with a factory ECU is consider the way you are increasing the fuel mass and what that will do to your required timing. For example if you increase the fuel pressure it's possible to maintain the same injection pulse width and still deliver more fuel mass. Since the pulse width hasn't changed, you don't specifically need to alter the factory injection timing maps. Usually your modifications will involve increasing the fuel pressure AND the pulse width and this will generally require the injection timing to be advanced.

We will be filming our Practical Diesel Tuning course early this year and this will have specific worked examples on some common diesel engines. It's likely we will start by offering a worked example on the GM Duramax using HP Tuners but we aim to also cover Ford Powerstroke and Cummins as time allows.

We usually reply within 12hrs (often sooner)

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