Motec M150 Linearizing throttle response via Throttle Translation

Hello all,

This is probably a hair brain idea, I am new to tuning. In my normal world (PLCs) which is what I know, you can linearize flow characteristics of say, a water valve, by "inverting" the flow characteristic of the valve, and applying this inverse curve to the output ... so my proposition is this, in M1 tune the Throttle Body Area % characteristic is mapped in 2D table vs servo position. So essentially that would be the approximate flow characteristic of the TB?

*If* this is the case, if you inversed this curve and applied to throttle translation map, I'm thinking this would basically give linear flow characteristic of the throttle body (as butterfly's are non-linear)

I just played around in Excel inversing the curve, so you can see what I mean.

Your confusion is the way a Throttle Request is treated -- basically it looks up the Y axis value, and set's the servo to the X axis value (always seemed inverted to me). I think you will find that the default curve is already doing what you want to do. But try it for yourself and see.

For circuit cars I generally set up the throttle target on the dyno so that torque is proportional to pedal position - so for example 50% pedal travel will give 50% torque approx etc. Most drivers seem to like it like that.

The curve definitely doesnt always end up looking like the graph above. GM LS throttles for example have some sort of odd linearisation curve already built into the TPS output. For road cars its normally nicer to have the torque increase slower at small throttle openings to prevent the "bunny hop" effect etc.

Thanks for the feedback! David raises a good point, I wonder if the M150 uses the TB area % curve to essentially automatically linearize the throttle demand some what, and then the throttle target can be adjusted from there for the desired throttle responsiveness . Otherwise 75% of the throttle would be in the first 45% of the throttle demand (logarithmic curve)

I like Adams suggestion to calibrate via engine torque , I'm guessing if you checked the engine torque at multiple throttle positions (10, 20, 30, 50, 75, 100) you could interpret a curve from there. I'm going to be using a Bosch 82mm DBW

Application is actually for an Outboard engine on a boat (4.6L V8) so getting good control at low throttle demand (between say 0-30%) will make the boat a lot easier to drive at slower speeds, super fine control up top is probably not as important

Hi James,

You may find that the 82mm throttle body is a size too large for that engine, especially if it is Naturally Aspirated. This can lead to difficulties in getting a nice throttle response down low as the air mass vs. throttle plate angle changes rapidly.

The larger GM throttle bodies deal with this by having a scalloped pocket on one side of the throttle body that the blade travels in for the first ~25% of its travel, reducing the amount of air mass into the engine at low throttle openings and giving a more progressive response at low throttle demands.

Thanks Stephen,

The 200hp model comes with 60mm TB, (limited to 50% TPS) , the 300hp model is mechanically identical but comes with 80mm TB (and a different tune) we are targeting just over 300hp once tuned with the M150 so I feel like there must be a reason the manufacturer needed 80mm on the higher HP model, I guess we will see! There's a large difference in surface area of the two TBs. I'm guessing that's what that little plate on the 60mm is for

I agree, David, should be pedal on the "x" axis as it's the input, and "y" for the TB, as it's the output.

James, it's not uncommon for the highest torque at lower rpm to be reached at less than full throttle opening, just something to watch for when mapping the values as some ECUs also allow tailoring for RPM as well as pedal position.

For a MoTeC M1 firmware that does not use Throttle Mass Flow calculations (Torque Modelled Firmware), the best method to achieve the desired throttle behaviour can be achieved in many different ways and I recommend to people to choose the method that works best with the way they are mentally wired to process the throttle position, and I will try to cover some specific comments on this. This gets further complicated by Throttle Pedal Translation which I will also cover as it has been mentioned above.

The purpose of the throttle area table is to represent the the ratio of the effective throttle area. Now there is a calculated throttle area for a given position. A gas flow area can be measured to populate an effective throttle area, but again can be incorrect dependant on an engines air demand (which is dependant on factors such as displacement, camshaft, induction etc). As no Throttle Mass Flow calculation is taking place, the end result of the Throttle Area table is to define the relationship between the Throttle Servo Position and the Throttle Position channel.

This is where the first point of how your brain is wired comes into it, as in the M1, requests for certain control subsystems reference the Throttle Position for Throttle Aim targets. So as examples, the Idle Control has a Idle Actuator Throttle Aim Maximum (that the % of Idle mass flow is calculated off), Anti Lag has a Throttle Aim, gear shift blipping will have a Throttle Aim etc.

Now for instance, If you have a linear Throttle Area table, then Throttle Position = Throttle Servo Position. This is easier for some people to tune as anywhere a Throttle Aim is in the package, they can directly corelate it to how much they want the throttle to open. In most cases with straight bore Throttle Bodies, 90% of people are able to tune a car quicker and achieve a better result doing this. Where it becomes a bit tricky to navigate is when a throttle with a scalloped bore is used (like what is found on many more modern Chevrolet and Ford applications) where 30% of the throttle position accounts for 10% of the area (which is done for idle and low throttle driveability) however the 10 or so percent of servo position after that can be 30% of the torque delivery.

If you have a Throttle Area table that represents the Area/Flow/Torque, then in these sub systems where you are inputting a Throttle Aim, you need to think of it more in a Airflow request through the engine (I say Airflow instead of Torque, as for a given Airflow the amount of Torque output will be relative to the optimisation of ignition timing, which in Anti Lag Strategies for instance your flowing air through the engine to drive an exhaust turbine to keep a turbo producing boost, you don't want to be generating a bunch of torque, as this will make the car push). This method also becomes beneficial in instances where there are very non linear relationships between the position and area (oversized throttle/multi throttles on an engine, or throttles with non linear behaviour such as scalloped bores and barrel throttles)

Once you have decided on how you want, or which relationship best suits you and your application, you can then influence the behaviour with the Throttle Translation.

The Throttle Pedal translation converts the relationship between the measured pedal position and the pedal request. Pedal Request = Throttle Aim. This allows you to adjust the driver feel between the Throttle Pedal/Lever and the Throttle Servo Position when the Throttle Aim is sourced from the pedal. In the case of the M1 GP firmware, you can build a table for the relationship between the Pedal Position and the Engine Speed, and then have 10 different profiles attached to a driver switch so the user can choose the profile that best suits their driving preference or type of driving they are doing at the time, for instance in your application you might have a map for driving around, and a fidelity map for getting the boat back on the trailer/mooring/picking up a skiier. This also can improve drivability of cars with small, aggressive clutches to minimise the pedal input to bring and hold the engine speed up to a level that won't stall whilst letting the clutch out. at lower engine speeds, but still having a linear relationship up top. See attached map for one application where to make the engine feel more 'peppy' and responsive down low, there is a a more aggressive translation and as the engine speed increases, the behaviour is closer to linear.

It's important to define these two distinctions, as the pedal translation defines the interaction between the driver and the throttle aim, whereas the area defines the relationship between the Throttle Servo Position and the Throttle Aim ( regardless of where it is requested from)

Do you only run your application in fresh water, or do you run the boat in open (salt) water as well? My hesitation with the Bosch throttle would be that they aren't sealed the best, and the body of the unit is raw alloy, whereas the Mercury 250/300/450R throttle that is the same size is built for Marine use, has a coated body and is the same size. The air guide shown on the 60mm is also on the 250/350R 80mm throttle as well, I believe it is Mercury's attempt to encourage even flow towards each bank at low throttle openings, as it is not on the 450R.

Your application will have the added complexity that your output has a constant and non linear slip to contend with, which can vary based on prop.

I have tuned half a dozen or so 4.6L V8 outboard engines on MoTeC M1's and in my case found that I achieved best behaviour with a linear Throttle Lever/Pedal translation, and due to the air guide on throttle blade has a non linear throttle area table.

Thanks Nathan!! A lot of information to unpack , I will have to read that a few times to fully digest. I am not personally doing the tune , I'm going through a reputable MoTeC dealer (interstate). Cut-over is not done yet , but pretty much locked and loaded. I'm working through the M1 training for fun and also so I can have a better understanding of how it works and what to ask , hopefully I'll have half an idea if I need help/support later!

The only thing not so sure on is the CANbus (smartcraft) from helm/binnacle to engine for DTS controls but that is a work in progress. Have you happened to look at this previously by chance? I know MoTeC offer a smartcraft firmware option (which I have requested) but that is more to read engine data on NMEA2000 bus as far as I know. The "mechanical" versions are technically still DTS, they just use a Pot sensor on the cable throttle and convert that to throttle demand. Would be a lot easier. I Have access to an outboard dyno here in Darwin so should be able to get some before and after numbers for power. Hoping for a safe 350 but probably wouldn't push it much past that, it's not a 300R. especially if it needs crazy timing to do it.

The 4.2L (V6) Yamaha can be tuned to 320 safely so should be interesting.

Good point on the alloy body, originally I was actually just going to upgrade to the genuine Merc 80mm but the lead time & cost was too extreme, around $800 all up for the intake system. Going bosch was less than half the cost of the mercury parts. I built my own adapter plate , I don't have the tools to do accurate metal work but I am a composites specialist so I made one from compression molded fiberglass, I'll either make make my own cold air intake, or modify the stock one to suit. I find Lanox spray works pretty well to protect from corrosion so I will just have to make it as part of my regular maintenance to keep an eye on the TB.