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Nick Mann
28-04-2009, 04:44 PM
Please note - his thread has been severely edited to keep it on track. Only the relevant information has been kept. The original thread, which became a discussion on the use/usefulness of the search function is now here:

http://www.clubvr4.com/forum/showthread.php?t=39753

Dom B
05-05-2009, 11:51 AM
Does anyone know off hand and from testing what the maximum boost the stock turbos can deliver at max rpm air flow rate. I have heard that they struggle when the air flow gets high at the higher end of the rpm scale. Mine certainly has little top end.

Wodjno
05-05-2009, 11:55 AM
Search is your friend /yes

Dom B
05-05-2009, 02:20 PM
search is only as good as the phrase you enter and unless you know exactly what the thread was then you don't stand a hope in hell of finding it.

All you searchers please point me to the Compressor flow maps of the turbonetics turbo chargers we have in the wheel trim we have.

Wodjno
05-05-2009, 02:29 PM
there is NO specific exact Max boost level figures..
And this is quite clear in the Gazzilion threads and posts of the forums about the said subject.
Some have managed to maintain 1 bar to the redline, but very few. 0.85-0.9 bar seems the average. But every car is different..
Wear and tear on a multitude of engine elements determine that.
Also dependant on how individuals are boosting there car and any supporting mods also.. Wear and tear on the Tub's themselves i would say is the largest factor.
So 1 bar for me and a few.. 0.9 for most others..
But like i said.. It has been posted and talked about many times and you will find that the information is conclusively inconclusive..

And i still say Search is your friend.. As any info given in this thread is by members that have contributed to other threads in discussion about the same subject..

PS.. And if we removed all the Treads that have been posted cos no bugger used the search long enough to find the info they required ! Then the database would be 1/5th the size.. And i would say that is more fact than conjecture for removing search posts..

Nick Mann
05-05-2009, 02:30 PM
No idea!

I have had over 1.0 bar at 6800 rpm, but I can't tell you how efficient that is. When wiring a boost solenoid incorrectly I have recorded 1.6 bar in 4th on hitting the loud pedal.

Dom B
05-05-2009, 02:59 PM
/ignores previous 5 posts....

No idea!

I have had over 1.0 bar at 6800 rpm, but I can't tell you how efficient that is. When wiring a boost solenoid incorrectly I have recorded 1.6 bar in 4th on hitting the loud pedal.

Ahh some numbers, now we are talking, that is an answer to my question. thanks nick, have some rep.

It rather strikes me that these small but efficient turbos are quite capable of a lot of power. Some people say they are maxed out at 350bhp and others have recorded 400bhp+ on standard turbos.

Regardless of the pipe work, the actual turbo unit itself should be good for some serious flow rates. Sorting the restrictions in the pipework is the technical challenge that we can enjoy.

If we can hit basically 1 bar (14.7psi) then we should be able to extrach a decent ammount of power. I also get the impression that the fuel cut is the biggest problem getting more than 1bar and not the turbos themselves.

Did i read right that the guy with the very powerful FTO was using only 18psi of boost? That is not far off. 1.25 bar or so.

Wodjno
05-05-2009, 03:04 PM
Ahh some numbers, now we are talking, that is an answer to my question. thanks nick, have some rep.



So my figures didn't show up in your search of this thread :inquisiti

Dom B
05-05-2009, 03:40 PM
Well i did find a few references to 1 bar but they always talked about fuel cut being the stop point meaning that the figure was hidden. what i want to really know is what they are capable of maybe from a standalone aftermarket ecu test mule.

I am up for doing some decent testing. I have some dyno facilities so can get some half useful figures out, its not great but is a good comparitive test. Unfortunately i have decided against a megasquirt ecu at the moment due to the complicated interaction of the ecu with all the other systems like abs, ayc, air con, dash panel etc. I have to do more research on how i can leave the original ecu in place with some dummy loads but it not get thrown by the megasquirt ecu changing things, and the two units fighting each other.

Wodjno
05-05-2009, 03:47 PM
I held 1 Bar to the redline "Just" With no fuel cut..

So Fuel cut is not the underlying factor in not being able to hold anymore..

I was running an uprated pump, E-manage Ultimate, Larger FMIC, some hardpipes and a Greddy profec E-01..

lots and lots of ON ROAD testing done..

Dom B
05-05-2009, 04:07 PM
I have been doing some rough calculations. It seems that for 7000rpm for example that a 2500cc (i know it's just under this) and pushing 2.1bar of boost Absolute (so 1.1bar relative) needs 549.5cfm of air or 38.5Lb/min. This should relate to 366bhp at 1.1bar boost.

Do those figures sound somewhere in the ball park from known cars out there?????

WodJNo does this sound somewhere around what your car gives?

I am still searching for the compressor maps of the 03 turbos that we have, i can only find td04 maps so far.

Wodjno
05-05-2009, 04:10 PM
Never did get a good run on the rollers.. As the extra loading of the rollers induced fuel cut :(
So i think the Max was around 320ish..

Dom B
05-05-2009, 04:18 PM
So the figures are not far off taking into account that i uses 1.1bar to be just over.

Nutter_John
05-05-2009, 04:31 PM
cavemans runs at 1.2 bar and produces 345 bhp

brads runs 1.1 bar and produces 375 bhp

Anything above 1 bar the and amount of heat being pushed out of the turbos is huge therefore you lose power due to running higher temps

Turbo_Steve
05-05-2009, 09:36 PM
There are compressor maps for them somewhere (dare I say to search for TD03 and compressor map!?) and it shows them to be progressively less and less efficient beyond 400cfm (IIRC). Btw, I agree the search function is poo.

Generally, it appears the bearing setup in our turbos can't hack it.....brads power tails off past 5000rpms.

bradc
05-05-2009, 09:45 PM
My max power is at 5300rpm, and the car is above 200kw at the wheels from about 4300rpm to 6800rpm or thereabouts. It peaks at 1.1 bar and spends most of the graph at about 1bar. My 228kw ATW is the highest I've seen at the wheels for any car with stock turbos.

Wodjno
05-05-2009, 09:47 PM
My 228kw ATW is the highest I've seen at the wheels for any car with stock turbos.
/Hmmm

Turbo_Steve
05-05-2009, 11:28 PM
But it must be remembered that brad has a nice big intercooler, and (more importantly) an entirely custom map, presumably with plenty of timing and perfect fuelling to make the most of it.

Also, whilst pressure is important, it's actually flow, and not pressure, that the Fuel Cut will operate on. So a more restrictive inlet, or throttle body, or whatever, will push up the pressure for equivalent flow.

bigoxo
06-05-2009, 05:40 AM
have seen 20psi on mine but not for long as i crapped my pants - i set the MBC up wrong, i now run at around 12psi.

Ryan
06-05-2009, 06:55 AM
I've seen mine spike at 17psi on a cold evening.

pitslayer
06-05-2009, 11:11 AM
Sure I read on a previous thread that in the uk fuel cut is much more prominent than in NZ, something along those lines, sure Brad posted it up something about temp difference, I cant really remember, but I am sure I have read a few times that 18psi is the max, efficent, but 20psi can be seen

As for search, yeah I gotta agree though that the search function here is utter poo, and you end up spending half hour trying different phrasing, what really needs to happen is getting this thread updated and making it much more easier to see
http://clubvr4.com/forum/showthread.php?t=18493

Turbo_Steve
06-05-2009, 11:28 AM
The difference in fuel cut will be down to air density: the MASS of the air is the significant factor, so at a different altitude (what height are you above sea level?) air temperature and perhaps more significantly in the case of NZ, humidity level, you will potentially require more air to reach the same pressure.

Let's not lose sight of the target here: boost pressure has very little to do with the turbo, and has everything to do with the trying to force a given amount of air through a specific restriction (an engine).

AlanDITD
06-05-2009, 06:26 PM
Are you forgetting the pissing compressor outlet we have, i would say thats another huge restriction.

I cant understand that at all when the rest is 2. 2.5 and 3" its just a bit barmy.

Turbo_Steve
06-05-2009, 09:10 PM
LOL...but that is done for a reason!
That turbo outlet is still rated to the maximum flow, and is part of the shape of the compressor map. Opening it out MAY improve top end efficiency, however it can also cost you lower down as you're changing the compression profile of the scroll: the whole principal of the compressor is building up resistance to actually achieve compression: hence why the pipework should progressively get larger from the turbo to the inlet to maintain good flow, and why really good intercooler design is so goddamn complicated!

Dom B
07-05-2009, 12:30 AM
I have been looking furiously for td03 maps but i can only find td04 and bigger maps.

Talking about the bearings not hacking it i saw some excellent tests with ball bearings against oil film bearings and it showed that the ball bearing had 50%+ less friction at low boost but the higher it got the smaller the gap was and on full boost the ball and oil bearings were almost identical.

I do know that the higher boost levels affect our thrust bearings first. I have seen 360degree replacements that have a 10-20% more load bearing capacity. The higher boost levels push the compressor back and the thrust bearing hits metal as the oil film cannot support it against the shock boost loads.

Brads car is obviously more volumetrically efficient. He must have a lot of larger hard pipes, perhaps a bigger intercooler and maybe a bigger airbos and throttle body too???

Perhaps cavemans set up is more stock but with a higher boost?????

Is this correct at all?

Kenneth
07-05-2009, 12:46 AM
Brads car is obviously more volumetrically efficient. He must have a lot of larger hard pipes, perhaps a bigger intercooler and maybe a bigger airbos and throttle body too???

Perhaps cavemans set up is more stock but with a higher boost?????

Is this correct at all?

Brad has a 600x300x100 intercooler.
I believe all his pipe work is 2.5" aluminium, custom made and he has a standard throttle body.

Brad runs separate intake pipes to each turbo, each with its own pod filter. These reside in a shielded box where the battery would usually be.

He also has 2.5" down pipes into 3" main pipe which leads to a duel exit exhaust.

Dom B
07-05-2009, 12:52 AM
Brad has a 600x300x100 intercooler.
I believe all his pipe work is 2.5" aluminium, custom made and he has a standard throttle body.

Brad runs separate intake pipes to each turbo, each with its own pod filter. These reside in a shielded box where the battery would usually be.

He also has 2.5" down pipes into 3" main pipe which leads to a duel exit exhaust.


Has brad also deleted the MAF??? Or does he put it at the entry to the airbox?

Kenneth
07-05-2009, 12:58 AM
Has brad also deleted the MAF??? Or does he put it at the entry to the airbox?

Brad runs an Autronic SM4 fully standalone ECU and has no MAF.

His car was also tuned and setup by a respected tuner who IIRC does a lot of work on competition cars.

hi flyer
07-05-2009, 08:04 AM
I've seen 28psi or tad under 2 bar on our td03s, but they were hi-flowed. It had a few other mods. Very quick car.

bradc
07-05-2009, 08:42 AM
Back on topic about my car, click on my name then go to see my car. You'll see the engine bay piping and so on. I do have the larger 64mm throttle body, some VR-4's came with 60mm ones.

Caveman has put up external pictures of his car but nothing showing the enginebay. What I do know is that whatever power his car recorded at the wheels - I think around 205kw sounds familiar, he has an auto so will lose about 7% extra over me, so he would be at about 220kw ATW with a manual

Turbo_Steve
07-05-2009, 08:50 AM
I'm no sure I agree with the use of the term VE in this instance, but yes, brads setup does not incur many parasitic breathing losses: the worst is most likely the pressure drop across his intercooler.

As Ryan points out, I would be interested to know what difference porting the turbos would make on a car like brads: I suspect it would be a lot of effort for minimal gains.

I'm sure we posted up the compressor maps for our turbos somewhere....I'll do some searching.

The brearings themselves actually don't seem to be the problem: do a quick search on TD03 Hybrid, and the first thread you see goes into great detail.
We've been looking into hybrids and all sorts, but by the time you've bored enough meat out of the exhaust housing, you may as well have simply fitted a TD04 compatible turbo and made up some downpipes.

Don't get me started on ECUs :D :D :D :D

Kelly&Ben
09-05-2009, 08:42 AM
surely the simple answer is you can run whatecer boost you like max on standard turbo's 3 bar if u like... they wont last 2 seconds tho so about 1.2bar is max i believe b4 they just become heat guns and all small turbo's loose boost top end. i used to have a blit k24 on my old car. even that at 1.3 bar would tail off to 0.9 up top of revs

Dom B
09-05-2009, 12:49 PM
surely the simple answer is you can run whatecer boost you like max on standard turbo's 3 bar if u like... they wont last 2 seconds tho so about 1.2bar is max i believe b4 they just become heat guns and all small turbo's loose boost top end. i used to have a blit k24 on my old car. even that at 1.3 bar would tail off to 0.9 up top of revs

It's not quite that easy. At the flow rates we are discussing the td03 cannot supply enough air. My question was aimed at just how much air mass can the stanrd turbo supply before it hits this point when at max revs. You can certainly spike the boost to a very high level at lower rpm where the engines air consumption is within the flow rate of the compressor and of the exhaust flow rate of the very small turbine, after this the turbine starts causing surge against the compressor flow which is multiplying cubically with speed increase. Really a turbo is only very efficient at one speed and flow, but the manufacturers work with this limitation. Its a bit like car engines are only really designed for 1 speed but they have ways of getting a wider spread of power to make a car usable.

Excellent point about the heat though, after the efficiency limits of the compressor are reached most of the energy goes into heating the air and then the thermal barrier of what the intercooler can deal with is reached.

The problem i have at present is that i can only find td04 compressor maps and am still searching for td03 ones. Someone mentioned that there were some on here a while ago but so far i haven't managed to find them.

Ryan
09-05-2009, 09:26 PM
So dom are you ever going to tell us what you actually do then :D

I have to say though, whenever i use the search function it pops up most of the answers i need. But then im looking for fixes or basic questions rather than the more technical information like this thread was started for.

I think the search is very good for that, and all the info re fixes and tech info is already in the members resource area.

Well anyway an interesting thread,

whats the max flow rate of td03's anyway ;)

Not sure if this answers your question Alan:

Urghhh - stupid upload crap doesn't work properly.

Try here: http://img99.imageshack.us/img99/5783/turbospecs.gif

^ originally uploaded by Kieran but can't find it!

Mark 4
09-05-2009, 10:22 PM
http://www.clubvr4.com/forum/showthread.php?t=35321&highlight=td03+map


Simple search - "TD03 map" /pan /pan /pan

AlanDITD
10-05-2009, 12:48 AM
Cold night up here tonight peaking 15psi holding 14psi most of the way then a small drop to 12psi in the last few revs.

Fuel cut alot easier though, had a scary moment powering into a corner a quick boost spike and the car cut power AYC does nothing then it seems.

Anyway cheers for the links, what is it you have planned dom?

Steve just to go back to the point earlier about building in restrictions, i.e the skimpy compressor outlets we have, Can you explain a bit more? Is there any benefit then to porting the compressor outlet, the compressor inlet etc etc.

Turbo_Steve
10-05-2009, 11:43 AM
To be truthful: I don't know. My understanding is that there needs to be sufficient restriction within the turbo for it to actually achieve compression, though I would have thought this could be achieved against the resistance of the valves themselves.

AlanDITD
10-05-2009, 12:15 PM
Hmmmm i always thought the more free flowing from the turbo the better. Simply because most bigger powered cars tend to run either 2.5" or 3" all the way round to stop any restrictions. That was a 400p cossie and the mental 488hp corsa.

But yeah i thought all the restriction would have started intake runners where the air slows down and splits.

Also dumpvales are there to stop the turbo stalling when backed up air from the throttle body closing. In theory is it not kinda the same? any restricion causes air to back up onto the turbo either causing it to stall or in this case get very very hot.

Thats all just an educated guess though, i know nothing about turbos and efficiencys

psbarham
10-05-2009, 12:50 PM
To be truthful: I don't know. My understanding is that there needs to be sufficient restriction within the turbo for it to actually achieve compression, though I would have thought this could be achieved against the resistance of the valves themselves.

yeh as above a pressure is only achieved with a restriction, for example get a pressure washer and take the lance off the hose and the water just runs out, put the lance and nozzle on it and the water coming out will come out at what engineers call a "fair old lick" :inquisiti

AlanDITD
10-05-2009, 12:52 PM
yeh as above a pressure is only achieved with a restriction, for example get a pressure washer and take the lance off the hose and the water just runs out, put the lance and nozzle on it and the water coming out will come out at what engineers call a "fair old lick" :inquisiti


So it will increase spool time, not overall pressure over an RPM range?

Dom B
11-05-2009, 12:48 AM
http://www.clubvr4.com/forum/showthread.php?t=35321&highlight=td03+map


Simple search - "TD03 map" /pan /pan /pan

Not quite.

If you look at the post of that thread even kieren agrees that there is loads of td04 info available and very little or almost no td03 info available. That is exactly what i was meaning when i said i haven't been able to find any specific td03 compressor maps.

The things kieren posted are useful to some extent but they are not a real compressor maps which are needed to plot rpm and load figures across it. The plot shown is more a comparative chart to help select a turbo on some approx data. It is helpful though.

I am sure they are out there they will be found eventually.


The chat about the piping diameter, restrictions etc is very interesting, right along the lines of the sort of info that makes a real difference in turbo applications.

It is very true that without a restriction there is no measurable pressure at the exit of the turbo. However the compressor wheel and the diffuser (the circular part of the snail shell before it becomes the turbo outlet pipe) still serve to increase the pressure of the air as it passes across the centrifugal compressor. It is impossible for the air not to increase in pressure ratio from inlet to outlet (P1/P2) across the wheel itself. The airs own inertia is its own restriction. If you could measure the very edge of the compressor wheel in a totally open unconnected turbo, you would still be able to measure the pressure. However this would only be for the few mm around the edge of the wheel. The problem with measuring it any further without a restriction to build pressure against, is that the compressed flow will be diffusing back to atmospheric as it exits so by the outlet there will be no relative pressure measurable by the time it gets there.

Strangely if you uncase the compressor completely and run the turbo with no front housing at all, the pressure at the edge of the wheel will actually be less than atmospheric due to the acceleration of the air lowering the pressure on account of the bernoulli effect.

When you design a hard pipe system the temptation is to go bigger and bigger. Bigger does promote better flow and at high rpm high bhp that's great. However every part of a system introduces a pressure drop. The intercooler is a prime example. You drop several psi across a poorly designed intercooler and every intercooler will drop some amount. In a low pressure turbo application of say 3psi (perhaps an aftermarket kit for a standard compression normally aspirated engine) you are better off without an intercooler at all. At these pressures there is so little heating that there is almost nothing to intercool. Whats more the presure drop across it cancels out any pressure gain. Net result the car is not any faster then before. The 1.8t vw engine has many BHP levels and the 150bhp ones don't even have an intercooler, they have a bit of squashed pipe just to lose some heat without the pressure drop.

Big Hardpipes with a big volume and also big intercoolers with a big volume mean that there is a large mass or air to move. The bigger the space then the slower the air moves for the same pressure. So huge system at low rpm means mega lag while you wait to get the compressor to squash up that mass of air which acts like a massive spring then to get it moving as that much air has serious inertia and is at a virtual standstill at low rpm. That's why big turbo cars have big lag in a lot of cases.

There is an optimum trade off of big for flow vs small for air speed and low air mass inertia. The trade off size allows enough flow for high power but sufficient air speed for fast response. In our case peoples testing seems to show that 2.5" seems to work very well and allow sufficient scope for high BHP without trading too much drivability.

There is an interesting thing about peoples boost gauges. When air expands into a bigger space for the same flow rate either the airspeed or the pressure will change. In the real world both will change. (in fact temperature does too, this is how a refrigerator works). So if you tee your boost gauge off the snail shell you will have a different reading than if you tee off the manifold plenum volume for the same car. So comparing boost pressures depends on where you measure it. Ideally you would measure it right in the port but that is very tricky. To compare OE pressure you need to tap off as close to the OE sensor as possible, i think it is on the plenum on these cars, perhaps someone can jump in to confirm that or not.

People say why make the hard pipes bigger if the compressor outlet is so small. Well The compressor outlet is small but it is well matched to the compressor itself. You have a fixed restriction of the turbo outlet. It is generally not a good idea to mess with this size as it is carefully matched to slowly expand the air up to the larger pipe size at a rate that wont cause stagnation or flow separation which in turn would cause turbulence and choke the outlet. Polishing does help as it lowers the Reynolds number meaning that turbulence wouldn't happen until a higher speed or a more aggressive angle or the diffuser expansion. So the turbo outlet can be considered fixed and therefore so is its restriction and pressure drop.

However you still have to get the air to the point of combustion. With our intercooler too that is a long and torturous path. You get pressure drop from a length of pipe as with any part of the system and it is per unit length. i.e. the longer the pipe the higher the pressure drop. The smaller the diameter then also the higher the pressure drop.

Imagine trying to blow through a straw 1 mile long and a pipe 2" in diameter and 12" long, which would be easier?

So the engineers need to expand up the tube size to minimise the pressure drop on it's journey otherwise the engine would be choked not being able to get enough air through thin piping.

I better have a rest before i type any more

Stevo
11-05-2009, 06:03 AM
impressive, sombody passed physics with a nice high score unlike me /GJ

Turbo_Steve
11-05-2009, 09:46 AM
Dom.....good explanation....especially as we were having a similar discussion around intercoolers the other day! LOL :D

I take (very mild) issue with the term "lag" being used on the inlet side...unless we're talking 5" turbo piping, on a road car lag remains relatively confined to the exhaust side...inlet side issues are generally percieved as "throttle response" rather than lag. If you have a turbo which will flow 450cfm, then even spoolin we're talking in terms of 50-100cfm flow rate. That means it's take a minute to fill 100cubic feet of intercooler and associated pipework. As these typically have a total volume of about 3cubic feet.......we're not talking a huge amount of time. That said, it IS perceptible, esepcially on fast road / small circuit cars, but usually as "hesitation" rather than lag.

I'm nit picking here, I will admit, as good overall pipework design will offset this massively (the organ pipe design, again).

666damned
25-05-2009, 08:57 PM
i'm no expert on turbo's,but have worked with compressor's(bear with me....lol...)....increase in pressure+increse in temperature ........ my cousins kwak zxzzr turbo monster record attempting bike is producing around 540 bhp at the wheel !!!!........and he uses a water/methanol internal cooling spray of the charge air....reduces temp of chagre air and therefore can increses pressure/density....he's also running a relatively small intercooler in comparison to the power the thing is producing,i'd say 300mm square..!!..............i've seen people at the shows doing 1/4 strips and 0-60 runs and they heve all been spraying the outside of the intercooler with co2 extuinghuishers to cool them down........to me its a waste of time(unless its also got a mist spray externally as well) and theres much more gain to be had when done internally.............

Turbo_Steve
25-05-2009, 11:22 PM
Hardly a waste of time: If you can freeze the surface of the intercooler, it becomes a "heat sink" for the duration of the quarter mile. In theory, anything you inject into the charge means less space in the cylinder for fuel\air mix, which means less power.

Water injection allows you to run more boost or more advance, however it does so at a fractional reduction in VE.

666damned
25-05-2009, 11:29 PM
Hardly a waste of time: If you can freeze the surface of the intercooler, it becomes a "heat sink" for the duration of the quarter mile. In theory, anything you inject into the charge means less space in the cylinder for fuel\air mix, which means less power.

Water injection allows you to run more boost or more advance, however it does so at a fractional reduction in VE.

does the methanol add to the charge plus a bit more power to the mix than the reduction of the fuel/air mix steve?.......also forgot to mention that he's also running quite a monster of a fuel rail under about 40psi ........

Turbo_Steve
26-05-2009, 08:15 PM
adding anything to the fuel is a risky proposition at best: methanol will change the calorific value of the fuel whilst not neccesarily changing it's octane rating.
Often, aromatics will effectively surpress detonation, whilst compromising the calorific value of the fuel: this means that you'll run more advance, but get the same effective power output. Pure water seems to be the best compromise. If you're going to start changing the fuel composition, I'd consult a really good petro-chemist first. There are more benefits to be had by simply switching to C10 and a dedicated map.

666damned
27-05-2009, 11:03 AM
adding anything to the fuel is a risky proposition at best: methanol will change the calorific value of the fuel whilst not neccesarily changing it's octane rating.
Often, aromatics will effectively surpress detonation, whilst compromising the calorific value of the fuel: this means that you'll run more advance, but get the same effective power output. Pure water seems to be the best compromise. If you're going to start changing the fuel composition, I'd consult a really good petro-chemist first. There are more benefits to be had by simply switching to C10 and a dedicated map.


you got me now Steve...............:laugh: :laugh: :laugh:

Turbo_Steve
27-05-2009, 04:09 PM
Just to add, this does rather depend where you're injecting: I am working on the assumption that you're planning to tap the inlet manifold, or just before the throttle body (which, notably, has a bloody heater in it!).

If you're injecting prior to, or into the intercooler, then the methanol will evapourate prior to reaching the cylinder. This severely negates it's impact on the combustion process...though it still displaces a little air/fuel mix.

Davezj
27-05-2009, 08:39 PM
What would happen if you used a second set of injectors to spray a little more fuel in to the inlet manifold to cool the air and compensate for fuel cut. well it is not really fuel cut it is fuel starvation and the ecu cuts the ignition to stop lean burning doesn't.

Turbo_Steve
27-05-2009, 11:21 PM
er.....unless you change the ECU software, the ECU doesn't know about the extra fuel, so still fuel cuts.
Essentially, the ECU cuts fuel cos it doesn't know what to do with an airflow number that big.

Davezj
27-05-2009, 11:49 PM
In closed loop running at a constant speed, doesn't the O2 sesor read the fuel mix and relay that back to the ECU which backs off the primary injectors beacuse it is running rich with the added fuel from the second injector, i didn't think the ECU used maps when running closed loop mode only when in open loop, when at WOT.

i don't know this just thinking about it.

Eurospec
28-05-2009, 12:22 AM
All the O2 feed back does is move a trim. The trim has 18% iirc range +/- outside this the ecu cannot compensate.

So the ecu is using the 2 fuel maps in cruise and uses the trims to adjust the pulse width outputs do the injectors based upon O2 volt.

In Open loop, the trims are not used.

cheers,

Ben.

Davezj
28-05-2009, 01:22 PM
excellent info thanks for putting me right on that.

this obviously would work in the real world, and very simple theory, i know there is a lot more to consider but at a basic level am i thinking along the right lines.
So in theory i could add 18% more fuel with a second injector (an a bit of electronic gadgetry) and this would fool the standard ECU into using the max negative trim on the fuel map to decrease the primary injector pulse, all the way up to the point when normal fuel cut is reached. However the ECU still has that -18% trim set. so the ecu can still happily add the extra +18% fuel trim to utilise some extra boost. asuming it has been turn up.

but that would only be closed loop operation, but when you want the extra fuel to stop fuel cut and use the extra boost, it will be at WOT so the ecu will delivery a fixed amount of fuel anyway.

is that about right.

Turbo_Steve
28-05-2009, 02:32 PM
No: fuel cut is an absoloute: The ECU looks at the number coming from the MAF and cuts the fuel: it's that simple. Sorry: I really like your thinking, but one of the reasons fuel cut is so hard to defeat is that it's fairly primitive in it's operation: It takes one of the primary sensor signals that the ECU requires to be accurate (that you don't want to mess with) and then uses it to stop thefun :D

I'm generally of the belief that manufacturers know what they are doing with fuel cut: it's pretty much chosen at the point where the factory injectors can't be guaranteed to do the job. You MAY get more (most will) without any problems if you subvert the ECU. But 1 in 1000 (or whatever) will not.

I generally take the view that if you're up against fuel cut, it's time to be looking at mapping anyway.

Nutter_John
28-05-2009, 02:43 PM
I have been beefing up on the Evo 8 maps and if you look at those you can see where and when the fuel cut will be hit

there is a table that is rpm based and as a load cell value

so for instance if the engine is at 4000 rpm and in the 230 load cell you have a fuel cut match so it will cut fuel

Now I would iamgine there will be a similar table in the vr4 maps

Turbo_Steve
28-05-2009, 04:07 PM
That's interesting: I didn't know that it was RPM dependant: figured it was just the limit of the normal map table.

Nutter_John
28-05-2009, 05:19 PM
here is the table from a evo 8

Eurospec
28-05-2009, 05:36 PM
Yeah, thats exactly how it works. Its a load vs rpm dependant cut.

see there on the evo how the cut is higher in the assesed load scale right in the spool range? thats beacuse they know thats the most likely place that the turbo will overshoot.

In Vr4's its always around 4 to 4.5k. Whilst this is outside the spool area for a stock car it may be that they were more concerned with limiting peak torque there for some reason.

Cheers,

Ben.

Eurospec
28-05-2009, 05:37 PM
PS, nutter, that must be a 260 table right? 230 is pretty damn low.

Cheers,

Ben.

Nutter_John
28-05-2009, 05:48 PM
Yep your right ben it is from the standard uk spec 260 map , withdrawn via my new openport 2.0 thingmabob

Turbo_Steve
28-05-2009, 06:18 PM
Have to confess, I've never really taken much interest in fuel cut.....usually at that point the ECU is going in the bin...it's only recently with factory flashing that this becomes a LOT more interesting.

AderC
28-05-2009, 08:44 PM
PS, nutter, that must be a 260 table right? 230 is pretty damn low.

Cheers,

Ben.

If you thought that was low check out the VR-4's equivalent....

uploaded/1988/1243539747.jpg

aDe

Davezj
28-05-2009, 08:45 PM
yeh interesting stuff.

it is a shame that i can't add a second set of injectors to deliver more fuel. i could do a water injection system as i came across a really good install and write up with all the stuff required to do it. but it was on a 5.0L V8.

Davezj
28-05-2009, 08:48 PM
is the load a changable peramiters in the Mh7202 ECU

Nutter_John
28-05-2009, 08:57 PM
If it is in a table and has been defined in the XML then there is no reason why you should not be able to offset the load to a higher zone , but this would need to be test on a dyno so you can move the load cell around and make sure you are still very safe

They have left it low for a good reason that we don't know

miller
28-05-2009, 09:17 PM
Whos brave enough to push those 100% figures into the 200's!!!!

Nutter_John
28-05-2009, 09:19 PM
will not need to got that far mike , high 100's may be enough for stock

shame i don't own a vr4 anymore as i would have done it by now :D

Kenneth
28-05-2009, 10:00 PM
once I sort out the high knock count my Galant is already showing, then ill give it a go. I even have a MH7202 ECU here which has those re-written, as well as some mods to the high octane fuel maps.

IIRC the VR-4 load scale is only mapped up to 200, so that will be max. I think I set it to 190

Nutter_John
28-05-2009, 10:16 PM
Yeah Ken your right it is only mapped to 200 load ( which is roughly 1 bar ) so to increase beyond 1 bar we need to rescale all the maps to 230/240 ish

but pushing the load cell area to 190 will be around 0.9 bar ish

miller
29-05-2009, 12:02 AM
Im gonna whip my ECU out and check the numbers..if it can be flashed im thinking a Eurospec visit may be in order!!

Eurospec
29-05-2009, 10:48 AM
The boost cut table is interesting.

100 load very roughly equates to 100kpa- ie atmospheric and therefore 0 psi boost.

Most fuel cut heuristics also have a time dimension. I know not if this is in the code or if its in a definable table.

For example, when you configure cut in a standalone you do so by setting a peak load and an ammount of time that this can be exceded for before the cut.

I would suspect that the same occurs in a stock ecu.

The interesting point is that the heuristic must recalculate on each rpm zone. So lets say the cut time is 2 secs and the table looks like this:-

3000 120
4000 120
5000 150

Even if load exceeds 120 at 4000rpm if it stays in there for less than 2 secs then it wont cut. So you could run say 150 load accelerate like hell through 4000 rpm in less than 2 secs and then stay in 5000 for as long as you like at 150.

This theory would explain why we see some cars that boost cut on the dyno (where the acceleration rate is controlled) but yet dont do it on the street, and also visa versa where you set up a car in 3rd on the dyno and get no cut, yet in 4th or 5th where the acceleration rate on the road is much slower you do get cut at the same boost and rpm.

Cheers,

Ben.

Nutter_John
29-05-2009, 01:06 PM
on the Evo it is defined as 1000ms , so if we can find that zone in the vr4 table you can adjust the time offset

Mark 4
29-05-2009, 09:44 PM
That is a brilliant explanation Ben, thank you very much.

bradc
29-05-2009, 11:58 PM
Which is one second in case people can't multiply and divide.

Being over 1 bar for a second doesn't happen often in a VR-4 in the lower gears which is why boost cut only really happens in 3rd and above. You could just add an extra 0 in there and make it 10 seconds ;)

Nutter_John
30-05-2009, 08:54 AM
Your a numpty Brad

The values are absolute so 100 kpa is normal atmosphreric pressure , 200 would be 1 bar

bradc
30-05-2009, 10:44 AM
'You're a....'

Wodjno
30-05-2009, 11:01 AM
The boost cut table is interesting.

100 load very roughly equates to 100kpa- ie atmospheric and therefore 0 psi boost.

Most fuel cut heuristics also have a time dimension. I know not if this is in the code or if its in a definable table.

For example, when you configure cut in a standalone you do so by setting a peak load and an ammount of time that this can be exceded for before the cut.

I would suspect that the same occurs in a stock ecu.

The interesting point is that the heuristic must recalculate on each rpm zone. So lets say the cut time is 2 secs and the table looks like this:-

3000 120
4000 120
5000 150

Even if load exceeds 120 at 4000rpm if it stays in there for less than 2 secs then it wont cut. So you could run say 150 load accelerate like hell through 4000 rpm in less than 2 secs and then stay in 5000 for as long as you like at 150.

This theory would explain why we see some cars that boost cut on the dyno (where the acceleration rate is controlled) but yet dont do it on the street, and also visa versa where you set up a car in 3rd on the dyno and get no cut, yet in 4th or 5th where the acceleration rate on the road is much slower you do get cut at the same boost and rpm.

Cheers,

Ben.

That explains why i always got fuel cut on rolling road days /yes

I had to decrease my boost level to around .8 bar, until RPM was over approx 5000rpm then the boost could be raised as the time the car was in each RPM range above 5000rpm, must have been lower than that set in the table..

BAh !! Rolling roads :inquisiti You gotta love em amd you gotta hate em :D