davegtt

Id like to ask why people find the need to have their cars remapped just because they have changed their turbos for a bigger 1??? surely this is pointless? u could have a T2 turbo running 20psi and change it to a T3 turbo and run 20psi, there shouldnt be no difference in the fueling aspect of the car. the only difference I personally see is the fact that the boost will come in at a different rpm, say 1.5k revs later on the T3 ??? no?

Im becoming slightly intreged by how the impreza ECU works.

what boost does the std car run? 1 bar? lets say u up the boost using a dawes device (fancy bleed valve as far as im concerned) to 17psi, does the ECU automatically adjust the fueling for this to compensate for the extra air flow? or will the car be running lean????

there seems to be a big "grey" area over all this, I see some members posting comment that I would agree with then I'll see another post by some1 mentioning its vital for a remap otherwise bang goes the engine...

is this all down to "tuners" hyping all this up for extra business maybe? certainly that is how the renault 5 tuning world has been brought down. 5 years ago nobody would dream of touching a reno 5 without the tuners advice or products only to find now most people DIY it and know that alot of the stuff we've been fed over the years is rubbish.

replies eagerly awaited. should be an interesting discussion as Im still trying to learn how the scooby tuning world works

Dave

john banks

If using an airflow sensor then the fuelling usually is OK until you saturate the injectors or airflow sensor - up to the load/airflow calibration limits of the sensor in the ECU it will attempt to run the last available AFR on the map.

Ignition is a little trickier - the OEM ECUs run relatively low boost and lots of timing at high RPM. A big turbo may need far less advance at high RPM where the ECU doesn't listen for knock because of the background noise level. This could easily damage the engine.

There are ways to get around things to some degree with correct monitoring, but you can optimise gains from a bigger turbo with a remap.

davegtt

stil not sure if I actually follow that, surely there is no difference when running say 1 bar of boost on a small turbo to a large turbo if the boost is the same when "on boost" at 5k rpm I dont follow why there may be differences in timing etc? only possible difference that I see personally would be the intake temp being lower on the larger turbo no?

so why do we need to remap?

CustomScoobyIOM

Igntion timing NEEDS to be adjusted with more boost due to detonation threats. With a bigger turbo, it causes the engine to go quicker, thus moving the pistons up and down quicker. If the ignition isnt adjusted then the spark is produced at the wrong time within the engine and can cause the engine to blow apart over period of time.

If the spark is produced as the piston is coming up to the top of the block (Well side!) then the spark too early is going to cause the piston to be pushed back down again or at least try too putting excessive strain on the piston, the rod and ultimately the crank.

Well thats a crap way of explaining it but John Banks and the rest will explain it better! Just getting in on the discussion!

davegtt

But this is what Im trying to say, a bigger turbo doesnt have to mean bigger boost levels you could have a T2 turbo run 10psi a T3 turbo run 10psi a T4 turbo run 10psi, it doesnt matter.

thats why Im asking cause on the TSL thread, the guy wanted a bigger turbo fitting and TSL refusing cause of a car leaving un mapped with these mods. well as far as Im concerned unless the boost is adjusted there is no mod. just the turbo will be more efficient in the sence of less heat generated... be no difference to fitting a bigger IC (intercooler) for example...

is no 1 following what Im trying to say?

thanks for the rest of your post though, very informative thanks

ozzy

I'm following what you're saying and it does make sense. I'm not sure it's as simple as that though. With an IC there's a big difference between a TMIC and switching to a FMIC, but that's affecting the air into the engine and will muck up fuelling.

Turbo is a different matter, but I'm sure someone can explain it.

Jolley

But the bigger turbo would surely give you more boost by the nature of the way it works, unless you take measures to reduce the boost it gives (i.e. remap)?

greasemonkey

Yes it does. Different turbos require different levels of wastegate modulation, and bigger turbos will tend to flow more air at higher engine speeds as well as heating it less, which leads to denser intake charge, which leads to greater risk of detonation, as the ECU fuels on MAF, and many of them don't know what the charge temp is, let alone know when it's dropped.

Look at the flow map of a TD04L and you'll see it's fundamentally different to an '05, a VF34 or whatever. While you can in some cases get away without the remap, there are equally many cases where you'll put the engine at extreme risk by changing the turbo and driving flat out without taking any other steps.

Best leave the whys and wherefores of that to the other thread.

Nope. Changing the turbo is a fundamental modification.

Yes, we're following what you are trying to say, the problem is that you're not looking at the full picture. You're correct to say that changing to a bigger turbo has some of the same effects as changing to a bigger I/C. However, you're wrong to think that this doesn't have any effect. In some cases changing to a bigger intercooler can also need a remap, as it drops charge temps to an extent where det becomes a danger.

ozzy

The Turbo could compress more air (raise boost) under certain load (rpm's) and the ECU may not adjust the fuelling accordingly, causing it to run lean ?

You can't therefore control what boost a large turbo gives if you put the engine under load and increase the flow rate of the Turbo.

That's why you need to drive around off-boost? no?

Stefan

john banks

If you run the new turbo at the same boost at the same RPM as the old one then it generally is OK, but people don't fit new turbos for this to happen.... the factory turbos drop boost abruptly at the top and the OEM ECU map for the boost curve runs them in their highly efficient areas resulting in a reliable, cool, octane sparing motor that takes lots of timing.

However, a lot of people adding a bigger turbo are already using boost control, the small turbo they already had will drop off at the top if they run any decent midrange because the exhaust manifold pressure at high RPM will blow open the wastegate. Fit the bigger turbo and it may well hold the old boost level to the red line. Get to 6000 RPM and run your 18 PSI and the ECU may well try to run 30 degrees of timing there because that is the last value on the map.

Running off the factory solenoid and ECU map doesn't also guarantee that the boost curve will be anything like the same.

A larger turbo running at the same boost though has a number of factors that influence the ignition timing:

- lower charge temperature tends to reduce the chance of detonation
- less exhaust manifold pressure reduces end gas pollution of the fresh charge also reducing the chance of detonation

So you end up with more airflow at the same boost level and it is very engine friendly, hopefully the airflow sensor will see this correctly and fuel correctly assuming the ECU and mechanical limits of the fuel system are not exceeded.

There is a flip side though... the cooler charge whilst allowing advance also implies greater cylinder pressure = more torque, this requires less ignition advance.

I have only touched on a few of the dynamics going on, some factors allow more, some less advance, difficult to predict and better to monitor detonation live and adjust to what the engine needs to stay detonation free and make torque.

By adjusting the octane used, as well as the actuator/boost controller balance as well as fuel pressure and retard features on Delta Dash, you can make a reasonable job of running a bigger turbo. But it is not quite fit and forget and run the same boost as you did before.

I always advised people to run on wastegate pressure (8 PSI) or better still part throttle with no boost at all until mapped.

nom

Stop looking at boost. It means nothing in 'real' terms. What makes the difference is the amount of air which is fed into the engine. I think you'll agree that it's quite possible - with a good breath - to create 1 bar of pressure with your own lungs - but it's not going to do much for an engine! It's all flow rate...

A bigger turbo will (should!) flow a greater mass of air for the same boost, therefore more fuel needs to be added for the same boost. That's the fuelling, & will be sorted by the MAF to some extent (as John has already pointed out) which measures the mass of air going into the engine, and so will 'automatically' compensate. However, a MAP based fuelling system won't compensate at all, as it only looks at differential pressure, not air flow...

Timing: think that one's done?

Boost control: the standard ECU is 'set' to its original turbo. It knows that it needs to keep to, say, 1 bar, but a small turbo will spin up quick & have very little 'momentum'. A larger turbo will spin up slower, but then fly past the 1 bar & the ECU will not be able to react well to it - it's quite possible to get up to 1.5bar+ without trying (& slam into fuel cut ). This can obviously be avoided by fitment of e.g a Dawes & setting it to the required 1 bar. Fine, except that at higher rpm it's likely that the larger turbo would be able to merrily continue producing 1 bar (where the smaller one would have reduced boost), and ignoring the advance which there would be far too much of, it's quite possible that even if the MAF sensor wasn't saturated, the injectors would be, so follows underfuelling, excessive heat, knock, then bang

So, at best, not getting a remap means that you're not making the best of the kit on the car, and at worst, you end up with a broken engine

nom

Oops - was writing that just as John was explaining further too

Bob Rawle

However you can have the same amount of air from different combinations, it is possible to [pick the same map point at different boost levels dependant on throttle so one turbo might achieve it at say 0.8 bar and another might need b1.4 bar to get the same air flow.

So now you do need greatly differing timing to cope with the difference in cylinder temps and pressure.

But depending on what is in the map if you get the ecu looking at a different point then it could well have incorrect values in it.

After all a map is two axis and a set of numbers (third), whats in them is the picked by an algorythm of some sorts dependant on a variety of inputs, the ecu can't calculate afr and the pick a point, it works on assumptions ie turbo size, fuel pressure, intake resistance, boost and rate of spool amongst others (like battery voltage)

some further thoughts

bob

davegtt

2 contradicting posts there. I would fully agree with John as he has take the time to explain what Im trying to learn, I am trying to look at the big picture and thats why Im asking the question, Im not arguing with people, I know what Ive learnt from turbo'd motors in the last 4 years and moving to this car and forum I see different things being said which I dont believe/understand. Thus Im asking

thanks for your patience in explaining, I am aware of the amount of FLOW is increased with a bigger turbo but didnt think that would play a part in the fueling aspect of the car. not too worry I like Johns explanation of the ingnitions advance etc. I'll finish reading the thread now

davegtt

OK getting confused again, so Ive understood that fueling needs to be adjusted for the mass that the bigger turbo is producing, OK so I now know that. yet now Im being told the MAF will compensate for this. and the MAP only looks at pressure, therefore my original comments were near enought right if I was running the same boost ont he smaller turbo to the bigger turbo the MAP doesnt need to be changed???

and before jumping on my back.....

Yes I know it does because of timing and top end fueling etc etc.... yes? but that would have been the answer I was looking for, some1 basically pointing out in theory Im right. (go on tell me Im wrong ) yet Ive not considered timing and top end fueling.

I think I should just stick to carburettors...lmao

again thanks for your input guys

john banks

Cooler charge goes hand in hand with higher combustion pressures which generally need less timing advance. Which effect is more significant is found out when you map a particular setup. So the apparently conflicting statements by GM and myself are generalisations trying to tie down the effect of an individual variable, but the variables tend to interact with each other, neither of us are stating an absolute rule, circumstances vary etc.

nom

Erm, right, ok...
Using relative numbers - say a small turbo at 1 bar is providing 1 'unit' of oxygen for the cylinder to burn - this one unit is at the temperature that the turbo/intercooler provides it to the cylinder.
Now assume a larger turbo - more efficient. This is also set to produce air at 1 bar; however, it is more efficient, and produces a cooler charge & greater flow, meaning that the 1 bar actually produces 1.5 units of oxygen.

Hope that makes sense so far I'm not convinced!

So we have two turbos, both producing 1 bar of pressure, but one providing 1 unit of oxygen, the other producing 1.5 units. The fuelling depends on the number of units of oxygen... the MAF sensor measures that 1.5 units of oxygen have passed into the engine; the MAP sensor measures that the boost pressure is at 1 bar. So the MAF will compensate for the increase in flow from the larger turbo, the MAP sensor will not, and hence will dramatically underfuel.

davegtt

where you got to hope that makes sence so far well yes it did I do understand this...

now the bottom half...

u say the MAF will compensate for the extra flow, well what is it compensating????

maybe I should start at what does the MAF do and what does the MAP do? I understood the Map supplies the fueling side of things, no idea what this MAF is? when u originally said the MAF will compensate I presumed u meant that it would supply the extra fuel so there should be no need for the MAP to compesate????

cheers again, were getting their slowly

nom

Ah, that might help

MAF: Mass Air Flow (meter), or words to that meaning, anyway . Basically, a little hot wire that manages to measure the amount (by mass) of air passing it.

MAP: Manifold Absolute Pressure. I think... Anyway, the level of boost as measured at the manifold (so just before it goes into the cylinders).

So - neither actually 'supply' the fuelling side of things, but either (or sometimes both) are used by the ECU, along with other inputs such as rpm, throttle position/movement, inlet temperatures, etc. so that it can calculate the correct amount of fuel to be injected, amongst other things.

Some ECUs use MAF/rpm as the main information for fuelling, others use MAP/rpm. The standard Subaru ECUs use the MAF, which is why the ECU is typically able to take quite a few modifications & still fuel correctly - at least, fuel correctly to a point... It also explains why they are so susceptable to a failing MAF!

I think that gets us another step further along?

davegtt

no you lost me now lol only playing.

right I understand now, apart from the fact that u say the MAP doesnt supply the fueling the ECU does (sort off) yet I thought the MAP was basically the ECU....lol

ohhh its all good fun

no seriously though I sort of follow what youve been trying to explain and its a little clearer now. thanks for that.

dowser

The Subaru ECU's use the MAF, TPS and MAP sensor inputs (in unknown quantities quite frankly...by me, anyway, but *mostly* MAF ) to decide which point on the load scale of the maps to reference against revs and take a value when making fuelling and timing decisions.

Richard

davegtt

aha, a very clear explanation of that then, thank you very much

AvalancheS8

In this thread, Map or MAP had been used both as an acronym for Manifold absolute pressure and as a word refering to the "maps" which the ECU uses to decide on fueling etc. The first - MAP is a sensor, or sensor output, as is the MAF. The second is a chart stored in the memory of the ECU with values for fueling, or advance or whatever (depending on which map - the ECU uses several to decide on what to do with all the things it controls). It's the second kind of map that gives rise to the word "re-map" i.e changing the values in the ECUs charts so that it delivers the appropriate amount of fuel etc.

In a std Subaru ECU it is mainly the input from the MAF (sensor) not the MAP (sensor) that determines the fueling - it is a MAF based system. If you replaced your ECU with a Link system, the MAF sensor is removed and the ECU relies mainly on the MAP (sensor) to decide the fueling. In each case the ECU uses it's maps to decide how much fuel is needed.

Clear now ?!!

davegtt

fekking ell right so everything I though Id just learnt has gone outta the window, so there are 2 Map/MAP's yes? map being the programming of the ECU (which I thought it was all along) and MAP is a sensor??? great

so going back to what originally was said if the MAF changes the fueling on the ECU for a greater flow rate on a bigger turbo then the only reason the ECU needs remapping is to make sure ingnition timing etc are all in accordance with its new characteristics???

is that right???

this threa is starting to get confusing now..lol

AvalancheS8

Bingo.

davegtt

thank funk for that, were getting there

cheers for all the help guys

btw, surely you'd know if the timing was out on the car it'd drive like a sack of **** no?

john banks

Ish, the fuelling may benefit from tweaking, but the engine should not go pop from being lean assuming the electronic and mechanical limits for fuelling aren't hit/exceeded.

The vast majority of load is MAF based, I can't see any effect from MAP as I ran 1.8 bar with a MAP sensor reading atmospheric and it made no real difference. I think the main TPS effects are for transients, but a MAF based system is quicker to respond to transients than MAP so doesn't need as much TPS input to load.

The car may run quite well whilst detting. Some report that it was fantastically fast the minute before it popped

The VAG ECUs (Bosch) are so good at detecting and controlling det that usually they just run rough and jerkily as the ignition is unevenly retarded due to det. Subarus just blow up

davegtt

I know a car can run fine and unnoticed if the fueling is out yet I was always under the impression if the timing was out it'd be lump or weak etc etc.

as far as Im aware running lean will damage the engine quite alot, be so easy to split a liner or pop the head gasket in ALOT of case from my experience.

john banks

If the timing is too advanced it will det. You will only hear severe det in the cabin without aids. Moderate detonation shock waves that you can't hear can do damage to the big end bearings and ring lands in particular.

dowser

John - latest version of Flash'02 reveals various transient TPS related enrichment maps...would be very nice to get the same for the classics, but very unlikely too I guess

Richard