# 420lbft at 6700rpm say Middlehurst



## R33_GTS-t (Apr 27, 2005)

I just received a brochure from Middlehurst stating the above. Whilst at first glance it looks to be inaccurate, is there any truth in it? This would equate to 530bhp.


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## Nocturnal (Nov 5, 2004)

Does it rev any higher? there are still power to be made if it continue reving.

But I think the new GTR have a big flat torque cruve, so it wouldn't sound too far off the mark.


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## Chuck_H (Jul 28, 2006)




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## R33_GTS-t (Apr 27, 2005)

^^^That's a hypothetical graph. No curve is really that flat in reality.


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## Ultimategtr (May 29, 2007)

you know i was thinking the same thing... im sure it delivers more peak power..
to compare something.. the new 911 turbo has about i think 460ftlbs and 480hp, its only a 3.6l tho, so im sure it pumps out at least 480-500ftlbs.

also, iv heard that the new GTR runs 10.2psi only?? is that true?

EDIT- im sure the power output is lower then what it really is, as NISSAN have done so in the past, as we all know it.


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## Wink (May 29, 2007)

R33_GTS-t, "^^^That's a hypothetical graph. No curve is really that flat in reality." - ha, ha, ha, you boys.......!!! Nissan are NOT allowed to make up a hypothetical graph, there are laws against that. It is certainly real data taken on a steady state dyamometer. As the engine management is now torque structure based, effectively when there is more than sufficient boost to achieve the target torque then it (and cam timing, spark timing, fuelling etc) will be controlled to control the torque to the target. Obviously, in the vehicle, during transient driving then the engine may not achieve this torque curve, but it has to be homologated steady state at least!!


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## Wink (May 29, 2007)

Oh yes, and your maths is wrong, sorry....

490Nm (ish) @ 6800 rpm = 470 Bhp!

P (kW) = 2*pi*r (rev/sec) * T(Nm) * 10-3


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## canman (Jul 7, 2001)

Yep Wink is on the money with his maths.

Will be interesting to get it on a Dynapack and see how efficient that new gearbox is and to find out what really comes out at the hubs.......

If the torque curve is even close to that shown in Nissans pictures it'll be a hoot to drive......


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> R33_GTS-t, "^^^That's a hypothetical graph. No curve is really that flat in reality." - ha, ha, ha, you boys.......!!! Nissan are NOT allowed to make up a hypothetical graph, there are laws against that. It is certainly real data taken on a steady state dyamometer. As the engine management is now torque structure based, effectively when there is more than sufficient boost to achieve the target torque then it (and cam timing, spark timing, fuelling etc) will be controlled to control the torque to the target. Obviously, in the vehicle, during transient driving then the engine may not achieve this torque curve, but it has to be homologated steady state at least!!


I've seen plenty of flat torque curves claimed before and subsequent dyno and in-gear acceleration tests have proved them to be wrong.

E.g. The Audi 1.8T - 155lbft 1750rpm-4600rpm? Nope.

Powertrain Performance Graph for Audi A3 1.8T -97 (110 kW)

If the graph has no bearing on the real world, then, as far as I'm concerned, it is hypothetical.


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Oh yes, and your maths is wrong, sorry....
> 
> 490Nm (ish) @ 6800 rpm = 470 Bhp!
> 
> P (kW) = 2*pi*r (rev/sec) * T(Nm) * 10-3


Since when did 420lbft equal 490Nm???? We're talking about what Middlehurst have written here, not the spirit level graph.


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## R33_GTS-t (Apr 27, 2005)

canman said:


> Will be interesting to get it on a Dynapack and see how efficient that new gearbox is and to find out what really comes out at the hubs.......


If a dynapack yields a curve that flat, I will buy a new GTR and eat it.


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## Wink (May 29, 2007)

"I've seen plenty of flat torque curves claimed before and subsequent dyno and in-gear acceleration tests have proved them to be wrong".

Exactly....these are transient, not steady state. The performance curve is quoted based on steady state performance. 

"If the graph has no bearing on the real world, then, as far as I'm concerned, it is hypothetical."

Hypothetical.....do you know what this means? The REALITY is you are probably right when the rate of change of engine speed is high, although to counter this the transient exhaust back pressure is lower. When the rate of change of engine speed is lower (i.e. in higher gears) then the torque will be similar to the steady state torque curve. 

With regards to the torque, Pk torque is just over 420 lbs ft, not the torque at Pk power, which is 365 Nm!


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## Wink (May 29, 2007)

Opps, torque at pk power is 365 lbs.ft = 490 Nm ish!!


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Exactly....these are transient, not steady state. The performance curve is quoted based on steady state performance.


If you look at the bottom of the graph on the rri.se site I linked to, it says "mode - steady state". Like I said, the graph's pure fantasy in real world terms.



Wink said:


> Hypothetical.....do you know what this means? The REALITY is you are probably right when the rate of change of engine speed is high, although to counter this the transient exhaust back pressure is lower. When the rate of change of engine speed is lower (i.e. in higher gears) then the torque will be similar to the steady state torque curve.


Hypothetical - 'Supposed to be, but not necessarily so.' An adequate description of the graph posted.



Wink said:


> With regards to the torque, Pk torque is just over 420 lbs ft, not the torque at Pk power, which is 365 Nm!


You mean 365lbft at peak power. If you read the full thread, you'd realise that the figure and rpm I quoted came on a brochure from Middlehurst.


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## mattb (Feb 12, 2002)

Wink, don't bother arguing with the R33, he's not here to find out the answer to his question just argue with anyone and everyone. He will most likely come up with a conspiracy theory as to how all motor manufacturers are working together to defraud the general public  

Just let him get on with it, even if you are right he won't accept it.


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## R33_GTS-t (Apr 27, 2005)

mattb said:


> Wink, don't bother arguing with the R33, he's not here to find out the answer to his question just argue with anyone and everyone. He will most likely come up with a conspiracy theory as to how all motor manufacturers are working together to defraud the general public
> 
> Just let him get on with it, even if you are right he won't accept it.


Now there’s a dumb contribution. I’ve clearly explained my reasoning above. There’s no conspiracy theory as such, it’s just that the curves are tweaked to fit after the test. The mechanical parts with their tolerances, accurate as they may be, do not unit to produce a perfectly horizontal line. It may be close but the graph above never came directly off a dyno print like that without various algorithms being applied to it.

As regards the original question, this topic is nothing to do with it. The original question focuses on a quote from a brochure. Either it is a misprint, or individual testing has shown it to be true. Why you have to butt in and try and turn this into a retarded argument is beyond me.


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Opps, torque at pk power is 365 lbs.ft = 490 Nm ish!!


Peak power rpm is 6400. 365lbft at 6400rpm is not 480ps (473bhp) anyway, it’s 440bhp. I don’t know where you’re getting that from.


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## canman (Jul 7, 2001)

R33_GTS-t said:


> it’s just that the curves are tweaked to fit after the test. The mechanical parts with their tolerances, accurate as they may be, do not unit to produce a perfectly horizontal line. It may be close but the graph above never came directly off a dyno print like that without various algorithms being applied to it.


I don't think anyone was suggesting it'll look "exactly" like that curve on a dyno, I think it's fairly obvious to most that real dyno plots don't look like that, but what most people are saying is that if it's anywhere close to that it'll be awesome, none of us knows if it will or won't be like on a dyno so for now I'll just wait and see.


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## Wink (May 29, 2007)

"it’s just that the curves are tweaked to fit after the test".

This engine EMS for this is a TORQUE STRUCTURE! I bet you don't know what that is do you R33.....I know, tell us with a series of large technical words randomly stiched together in to a sentence. Anyway, as it is a torque structure, the flat torque curve (within 2 - 5 Nm) can be achieved throughout the speed range with no external "tweaks"

"The mechanical parts with their tolerances, accurate as they may be, do not unit to produce a perfectly horizontal line. It may be close but the graph above never came directly off a dyno print like that without various algorithms being applied to it" - amateurs comment!

"Peak power rpm is 6400. 365lbft at 6400rpm is not 480ps (473bhp) anyway, it’s 440bhp. I don’t know where you’re getting that from"

I was talking about the 6700 rpm engine speed....you know, the engine speed you mentioned at the top of this thread :chuckle:


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## Wink (May 29, 2007)

If you notice from the graph is actually looks like pk power is at 6000 rpm. 

Anyway, R33, you are an amateur......no worries though, you are sort of right without realising!!!! There is no doubt that this graph has been constructed from achieved steady state points, and plotted in excel; the answer is simple as to why it is the shape it is...they have the "smooth line" enabled, which slightly skews the curve through points you can make out on the picture (hence Pk power appearing at 6000 rpm instead of the claimed 6400 rpm). Strictly speaking an engineer should only use straight lines between decrete points to prevent it what has happened with this curve. 

Oh yes, teh original development engines did make Pk power at 6800 rpm, but obviously Nissan have been able to reduce this speed slightly!


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> This engine EMS for this is a TORQUE STRUCTURE! I bet you don't know what that is do you R33.....I know, tell us with a series of large technical words randomly stiched together in to a sentence. Anyway, as it is a torque structure, the flat torque curve (within 2 - 5 Nm) can be achieved throughout the speed range with no external "tweaks"


Within 2-5Nm now?* So that's not flat is it?:chuckle: Does the graph posted show these 5Nm variations? No. The prosecution rests.

*I'm going to place a bet on 12-15Nm.

I'll be honest. I've not heard the term 'Torque Structure' but I'll guess it's another term for something that's already been done. It probably means that the EMS tries to yield the torque curve shown, hence why it can vary boost between 0.7 and 0.8bar depending on ambient conditions and any other measureable transient conditions fed back to it. However, even with closed loop control over the actual torque itself, assuming it can measure this without being hooked up to a dyno, it could still never achieve a flat curve - like that shown - due to unpredictabilities in airflow, ambient conditions and the combustion process itself. Implementation of a Kalman filter would probably converge on the exact curve but would never exactly duplicate it.

Now perhaps you'd like to clarify for us whether the EMS does measure the torque being developed and maintain closed loop control over it. 

Manufacturer's manuals are full of torque curves resembling the Norfolk Broads but it never happens.:chuckle: 



Wink said:


> amateurs comment!


Good come back.



Wink said:


> I was talking about the 6700 rpm engine speed....you know, the engine speed you mentioned at the top of this thread :chuckle:


Ha ha, that's rich. You've switched between the original topic and the secondary graph constantly. You quoted, "peak power engine speed," which is 6400rpm.

Incidentally, do you actually know what steady state means? What are you going to do? Ask the air to be good?


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> If you notice from the graph is actually looks like pk power is at 6000 rpm.
> 
> Anyway, R33, you are an amateur


Actually I work as an engineer for a living, so that makes me a professional. Just a minor semantic issue.



Wink said:


> ......no worries though, you are sort of right without realising!!!! There is no doubt that this graph has been constructed from achieved steady state points, and plotted in excel; the answer is simple as to why it is the shape it is...they have the "smooth line" enabled, which slightly skews the curve through points you can make out on the picture (hence Pk power appearing at 6000 rpm instead of the claimed 6400 rpm). Strictly speaking an engineer should only use straight lines between decrete points to prevent it what has happened with this curve.


It wouldn't look any less realistic if they had. In fact I could probably reproduce that graph in Excel.



Wink said:


> Oh yes, *teh* original development engines did make Pk power at 6800 rpm, but obviously Nissan have been able to reduce this speed slightly!


Nissan for t3h win.


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## R33_GTS-t (Apr 27, 2005)

canman said:


> I don't think anyone was suggesting it'll look "exactly" like that curve on a dyno, I think it's fairly obvious to most that real dyno plots don't look like that, but what most people are saying is that if it's anywhere close to that it'll be awesome, none of us knows if it will or won't be like on a dyno so for now I'll just wait and see.


Nobody's saying it won't be a great engine and look moderately similar to that but we've seen graphs like this before, from Audi, BMW and even for the Rover 200 Turbo. Unfortunately, there are too many external influences for them to remain true in reality. That was my only point and I wasn't the one who tried make a war of words out of this.


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## Wink (May 29, 2007)

R33 blah, you are all over the place man:chuckle: 

I'll try and answer you questions...

"Within 2-5Nm now?* So that's not flat is it? Does the graph posted show these 5Nm variations? No. The prosecution rests."

It's flat to within 0.3 - 0.85%...in my book that is pretty damn flat!

Torque structure - this is a recent concept that has been enabled through more powerful processors. Essentially, the air path and manifold is modelled under all conditions (well, nearly), and all the engine maps effectively input into defining the engine brake torque irrespective of temp, altitude, humidity, etc, etc. Your comments about "unpredictabilities in airflow, ambient conditions and the combustion process itself" are not true in the time domain which effects engine torque. The variability is in hardware effects through production tolerances that effect mean airflow, resulting in slight inaccuracies in predicted torque - that said, I suspect the engine would make considerably more torque than the target torque curve under normal conditions in the UK - this is due to the density of the air, which is the key thing rather boost pressure...people often associate boost with airflow, which is only half the story!!

"Incidentally, do you actually know what steady state means?" In this case I'm talking about engine speed, obviously, which is held there by the dyno +/- 1 - 2 rpm. 

"Actually I work as an engineer for a living, so that makes me a professional" - Ok, just not an automotive engineer then! The graph can from an excel spreadsheet as Nissan do not have any other plotting tools for engine data.

Nissan probably reduced the speed to save on cost ultimately....or allow for an engine uprate in the future. The 6800 rpm Pk power was accompanied by a max continuous engine speed of 7600rpm, a max intermittent engine speed of 7800rpm, and a valve bounce speed of 8100 rpm....so Titanium valves were used to get the valvetrain mass down lower (inlet valve mass down from 65 grams to 33 grams by going Ti)! Lowering the engine speed would enable conventional valves to be used, and the performance could always be achieved at a lower speed (6400 rpm) anyway!


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## Wink (May 29, 2007)

Oh yes, just read your notes again....

yep, you are right, there is no feedback on torque, so is all predictive, but will be flat for each engine from its baseline if that makes sense!


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## R33_GTS-t (Apr 27, 2005)

You obviously know a fair bit about this, so I'm not knocking you. However, cutting a long story short, you seem to be suggesting that the map contains lists, that back in the day would have been called look-up tables. These tables contain various combinations of ambient conditions, that are measured(?) versus rpm and gear. Against each combination there is a corresponding AFR, igntion timing, valve timing, and boost pressure, with the aim of creating the same flat torque curve. The other alternative is that, given the speed of the processor, it simply reads in the measured values and calculates the appropriate AFR, igntion timing, valve timing, and boost pressure to implement.

This will yield a very nearly flat torque curve but not one as flat as the one shown shown. Even using laboratory conditions to manage the ambient conditions, the actual engine itself will produce heat, which will affect combustion and torque. Different harmonics at different engine speeds and different temperatures will also affect airflow. Different mixing dynamics at different piston speeds will even play a part. 

Having designed, built and programmed a digital controller from top down and bottom up, and done an MSC** in UAV control, I can guarantee you, that, in anything remotely resembling a complex system, you can't hope to control any variable exactly without having a closed loop. Even with a closed loop, mother nature will do her best to screw you up, but at least your control loop can fight back. The more complex the system and the faster the changes, the faster you need to sample (with a digital system). The faster you sample, the more bits you need in the word lengths being used to store your variables and the less time you will have to manipulate these variables, before sending the control outputs back into the system. At 6000rpm, you have 0.01s between samples. In order not to produce anomalies due to a delayed response, you will have to make the gap between sample and output a hundreth of this, i.e. 0.0001s. The level of the programming being applied will also have an impact here. Higher level languages will make your ECU retarded. Given that you're manipulating continuous variables, the rate and magnitude of change on things like boost, valve operation etc. will also introduce transient affects into the airflow. One way around the speed issue is to use FPGAs but that restricts you in terms of the algorithms you are able to implement and still leaves you with the transient affects.

**It was supposed to be a PhD, but I did all the required work in 1 year so funding was cut before the minimum length was reached.


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## bonzelite (May 14, 2006)

Do you guys mean bhp to indicate "brake horse?" 

The factory lit on the VR38DETT is in net hp, not brake horse. IIRC, brake horse is without any accessories attached, net is full accessories with losses due to friction. 

Anyone?


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## Wink (May 29, 2007)

Brake horse power and net horse power are the same thing....the brake is the engine dyno mounted off the flywheel so all engine friction and accessories losses (although the accessory load is small) are included.

"However, cutting a long story short, you seem to be suggesting that the map contains lists, that back in the day would have been called look-up tables. These tables contain various combinations of ambient conditions, that are measured(?) versus rpm and gear."...mmmm, sort of! A torque based EMS is essentially a model based controller, so whilst there are still look-up tables as such, there response on the output are "filtered" through the models....it does make it a pain in the @rse to run on the test bed often when you simply want to change spark and fuel! 


"The faster you sample, the more bits you need in the word lengths being used to store your variables and the less time you will have to manipulate these variables, before sending the control outputs back into the system. At 6000rpm, you have 0.01s between samples. In order not to produce anomalies due to a delayed response, you will have to make the gap between sample and output a hundreth of this, i.e. 0.0001s. The level of the programming being applied will also have an impact here. Higher level languages will make your ECU retarded"....... Modern ECU's obviously have different rasters for different parameters to get around this problem....obviously there is a speed synchronous loop for the key variables - as you say, this has to be the fastest in the time domain, probably 5X faster than the max engine speed multiplied by the number of timing teeth to get the right resolution. There are then several time synchronous loops, may be at 10 ms and 50 ms for the time dependant variables (although the sampling rate will be at least 5X this). If you work the sampling rate out in kHz though, your figure does't look too bad "i.e. 0.0001s" is only 10kHz...it's just there are a lot of 10 kHz eating into the MHz processor!


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> mmmm, sort of! A torque based EMS is essentially a model based controller, so whilst there are still look-up tables as such, there response on the output are "filtered" through the models....it does make it a pain in the @rse to run on the test bed often when you simply want to change spark and fuel!


I don't think you've grasped what I'm saying. The AFR and ignition are changed dynamically, so they should be adjusting during the run to maintain the target torque, as per model curve.




Wink said:


> Modern ECU's obviously have different rasters for different parameters to get around this problem....


By 'raster', I'm assuming you just mean a matrix, which is nothing new.



Wink said:


> obviously there is a speed synchronous loop for the key variables - as you say, this has to be the fastest in the time domain, probably 5X faster than the max engine speed multiplied by the number of timing teeth to get the right resolution. There are then several time synchronous loops, may be at 10 ms and 50 ms for the time dependant variables (although the sampling rate will be at least 5X this). If you work the sampling rate out in kHz though, your figure does't look too bad "i.e. 0.0001s" is only 10kHz...it's just there are a lot of 10 kHz eating into the MHz processor!


Indeed, and there are a lot of calculations that need to be done within that 0.0001s period. I would also like to suggest that the ECU should be sampling at least 10-20 times the rate of the item under control, i.e. 20 X 7000 x timing teeth. Also, bear in mind that the calculation time should be a twentieth (or less) of the sampling time to produce an accurate response. However, I believe this can be done with a modern GHz processor, _providing it's not operating Windows_.

The problems still lie with the unpredictabilities mentioned in the previous post and the lack of closed loop control. Measuring the ambient variables is one thing, but the system has no method of actually correcting the torque, should it stray (for the reasons mentioned in previous post or other) away from the required curve.

Having said all this, whether that curve was realised exactly like that under laboratory conditions or not, has no real validity in real life. Nobody will see that curve on a tuner dyno, or feel it exactly like that on the road, as we've agreed. Just as well really. If it was exactly flat, it wouldn't be a curve.:chuckle: That said, I'm sure it will still be fantastic and flatter than other torque curves. Good work.


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## R33_GTS-t (Apr 27, 2005)

bonzelite said:


> Do you guys mean bhp to indicate "brake horse?"
> 
> The factory lit on the VR38DETT is in net hp, not brake horse. IIRC, brake horse is without any accessories attached, net is full accessories with losses due to friction.
> 
> Anyone?


When you say 'net hp', do you mean, at flywheel excluding internal losses, or at the hubs excluding most drivetrain losses, or at the wheels excluding all losses (that which actually accelerates you)?


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## Wink (May 29, 2007)

"I don't think you've grasped what I'm saying. The AFR and ignition are changed dynamically, so they should be adjusting during the run to maintain the target torque, as per model curve."

Obviously instantaneous AFR changes, but averaged over even a small time domain these are essentially very steady as far as fueling quantity and spark is concerned (at a fixed engine speed and load). These days, in order to achieve the extremely challenging emissions targets, AFR distribution has to be minimised and combustion stability is extremely good (Standard Deviation of IMEP's of <0.1, COV IMEP <2%). As I'm sure you know already, when operating closed loop (of AFR) at part load the stratergy is too deliberately switch the AFR between just rich and lean of stoichimoetric at around 0.5 - 1Hz as this enables (cheaper) switching HEGO to be used rather than more expensive linear HEGO's. 

"By 'raster', I'm assuming you just mean a matrix, which is nothing new."

Raster means layers (I think), but they are essentially different sampling rates used for different variables dependant on how critical they are.

"If it was exactly flat, it wouldn't be a curve. That said, I'm sure it will still be fantastic and flatter than other torque curves. Good work." 

- As I said, the transient torque curve will be different to that quoted, which is measured steady state. There are some +ve aspects during a transient (lower exhaust back pressure), but -ve too...i.e. LAG! 

This engine has been designed for minimum lag, and the EMS stratergy will be to achieve the desired torque, so the wastegates will be held shut under some transients when under steady state conditions they may be opened up a bit. The hardest thing to evaluate during engine development is the transient performance due to the response of the dyno (fixed acceleration rate) and how you control the wastegates. The run-up curve (as it's known) is often tested with the wastegates wired shut, but any control issues with the test bed or engine control during the development phase can result in a massive boost spike....we often saw 800Nm out of the engine for a small period of time as it came on boost, often followed by some kind of engine failure (it was our fault for not controlling the engine properly). 

I guess the final point is that a very flat torque curve can feel flat in the car.....it is the rate of change of acceleration (known as jerk) that makes the car feel fast!!


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Obviously instantaneous AFR changes, but averaged over even a small time domain these are essentially very steady as far as fueling quantity and spark is concerned (at a fixed engine speed and load). These days, in order to achieve the extremely challenging emissions targets, AFR distribution has to be minimised and combustion stability is extremely good (Standard Deviation of IMEP's of <0.1, COV IMEP <2%). As I'm sure you know already, when operating closed loop (of AFR) at part load the stratergy is too deliberately switch the AFR between just rich and lean of stoichimoetric at around 0.5 - 1Hz as this enables (cheaper) switching HEGO to be used rather than more expensive linear HEGO's.


Is the AFR technically a closed loop, as you don't actually measure the AFR, you only measure the amount of air coming in and inject fuel accordingly? Anyway, I don't doubt the ability of an ECU to control AFR, I was only responding to your earlier remark, which confused me a little at the time, but we appear to be talking the same language. If the AFR needs to be fettled at a given rpm and load, does this not mean that the airflow is also changing?



Wink said:


> Raster means layers (I think), but they are essentially different sampling rates used for different variables dependant on how critical they are.


The different sampling rates will be down to the maximum frequency that the different variables change at. I.e. ambient pressure and temperature will remain fairly steady, but airflow rate will likely change fairly fast. So a higher sampling rate will be used for the airflow rate measurements. If you don't sample any given variable fast enough, you can't accurately re-construct, in the digital world, the waveform that represents its change in the analogue (real) world.



Wink said:


> - As I said, the transient torque curve will be different to that quoted, which is measured steady state. There are some +ve aspects during a transient (lower exhaust back pressure), but -ve too...i.e. LAG!


This is why turbos come on boost faster up hills and/or in higher gears. The steady state dyno effectively makes it a steep hill and a high gear (with the brakes on too).



Wink said:


> This engine has been designed for minimum lag, and the EMS stratergy will be to achieve the desired torque, so the wastegates will be held shut under some transients when under steady state conditions they may be opened up a bit. The hardest thing to evaluate during engine development is the transient performance due to the response of the dyno (fixed acceleration rate) and how you control the wastegates. The run-up curve (as it's known) is often tested with the wastegates wired shut, but any control issues with the test bed or engine control during the development phase can result in a massive boost spike....we often saw 800Nm out of the engine for a small period of time as it came on boost, often followed by some kind of engine failure (it was our fault for not controlling the engine properly).


This is known as an insufficiently damped response. You'll find that the root locus of the all-up system (when this happened) had a phase angle of around -Pi radians and a damping coefficient approaching 0. Ideally you want a phase angle of -1 radian and a damping ratio of 0.707 (root 2/2).



Wink said:


> I guess the final point is that a very flat torque curve can feel flat in the car.....it is the rate of change of acceleration (known as jerk) that makes the car feel fast!!


I know. I hope this thing doesn't feel as flat as a turbo Audi under acceleration. Effective but boring.:chuckle:


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## bonzelite (May 14, 2006)

Wink said:


> Brake horse power and net horse power are the same thing....the brake is the engine dyno mounted off the flywheel so all engine friction and accessories losses (although the accessory load is small) are included.


thanks, my bad, I meant "gross horsepower." I used the wrong terms. Gross HP is without any accessories attached, right?


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## Wink (May 29, 2007)

Gross horse power....depends which standard it is measured using.....gross can mean no accessories attached, but SAE DIN gross is measured with no inlet and exhaust backpressure too. As a rule for a NA engine, 1 kPa reduction in inlet loss increases power by 1 - 1.5%, and and 1 kPa reduction in exhaust back pressure increases BMEP by approx 1.5 kPa! 

As for "Is the AFR technically a closed loop, as you don't actually measure the AFR, you only measure the amount of air coming in and inject fuel accordingly?". Air can be measured using a HFM, or assumed from pressure and engine speed, and fuel is estimated, but AFR is accurately measured in the exhaust using a lamda sensor....this measurement is used to validate and trim the fuelling.


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> As for "Is the AFR technically a closed loop, as you don't actually measure the AFR, you only measure the amount of air coming in and inject fuel accordingly?". Air can be measured using a HFM, or assumed from pressure and engine speed, and fuel is estimated, but AFR is accurately measured in the exhaust using a lamda sensor....this measurement is used to validate and trim the fuelling.


The Lambda sensor is only providing an estimate of AFR at inlet, which is all it can do, being in the exhaust.


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## Wink (May 29, 2007)

"The Lambda sensor is only providing an estimate of AFR at inlet, which is all it can do, being in the exhaust." 

Errr, not sure what I understand what you are saying?! Obviously the lamda sensor measures the exhaust AFR, which is a combination of the air mass flow measured with the HFM and the fuel flow which is estimated in the strategy (injector pulse width and fuel pressure is known). I guess I was trying to say is in terms of accuracy, the HEGO (+/- 1 - 2%) is more accurate than the HFM (+/- 5% typically), and injector flow (+/- 5% build tolerance), and hence the HEGO will be used to trim the fuelling quantity (and adaptive elements in the stratergy) to maintain stoich AFR. The airflow is obviously less significant (even in a torque structure) than the AFR as the high conversion efficiency window for a Three Way Cat is pretty small in AFR terms.


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Errr, not sure what I understand what you are saying?! Obviously the lamda sensor measures the exhaust AFR, which is a combination of the air mass flow measured with the HFM and the fuel flow which is estimated in the strategy (injector pulse width and fuel pressure is known). I guess I was trying to say is in terms of accuracy, the HEGO (+/- 1 - 2%) is more accurate than the HFM (+/- 5% typically), and injector flow (+/- 5% build tolerance), and hence the HEGO will be used to trim the fuelling quantity (and adaptive elements in the stratergy) to maintain stoich AFR. The airflow is obviously less significant (even in a torque structure) than the AFR as the high conversion efficiency window for a Three Way Cat is pretty small in AFR terms.


I'll try explain. The AFR entering the cylinder is what is actually burned in the mix - this is the manipulated value. Unless you are measuring that directly, there is no closed loop control. A tertiary parameter is being used to estimate the value being controlled in this case. It's not quite closed loop because the measured value is separate from the manipulated value in time and space.

Is the new GTR really running a stoichiometric (14.7:1) AFR!? Or did you just mean that it was close to stoichiometric?


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## Wink (May 29, 2007)

"The AFR entering the cylinder is what is actually burned in the mix - this is the manipulated value. Unless you are measuring that directly, there is no closed loop control....blah"

At part load the engine has to run closed loop on AFR at stoich in order to achieve the extremely stringent emissions legislation....the switching range is less than +/- 0.02 lambda. It runs rich and openloop during light-off, and the engine uses secondary air too (the air rail is incorporated into the cylinder head). 

At full load the engine obviously over-fuels to control the turbine in temp to 950 degC.


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> At part load the engine has to run closed loop on AFR at stoich in order to achieve the extremely stringent emissions legislation....the switching range is less than +/- 0.02 lambda. It runs rich and openloop during light-off, and the engine uses secondary air too (the air rail is incorporated into the cylinder head).
> 
> At full load the engine obviously over-fuels to control the turbine in temp to 950 degC.


Appreciated, but your version of 'closed loop' isn't actually 'closed loop', as I've mentioned. The measuring point is distinctly separate to the control point and there is a process between the two that you have little control over. The relationship between the lambda sensor and the AFR at inlet is also dependent on the combustion process, which is never exactly consistent. Therefore the measured value is separate to the controlled value in time and effectivity and there is no consistent, direct link between the two.

A little surprised to hear it's running stoichiometric, but if I remember rightly it's using direct injection, which helps make this possible.


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## Wink (May 29, 2007)

Typical figures of Standard Deviation of Indicated Mean Effective Pressure (SDIMEP) and Covariance of IMEP (CoV IMEP) for this engine would be 0.08 and less than 2% under all warm engine speeds/load - this means the combustion is pretty damn consistant dont you think?

I'm currently working on 135Bhp/litre (yes, that's pretty high) naturally aspirated engine and that runs CoV's of up to 15% at low engine speeds and loads - you can hear this instability but can't feel it until it goes above 20%. At full load CoV IMEP is also <2%y, so no problems there. 

The cold SDIMEP for the GTR engine was supposed to be less than <0.18, but we tried hard to convince them that they should let this increase to 0.25 to 0.3 during cold start up to enable lots of spark retard - typically VW and Ford would allow these high levels of SDIMEP for 10 - 20 seconds after cold start but you can hear and feel it in the vehicle....but it is needed to light the catalyst off. 

The engine is Manifold Port Injected and therefore not direct injection. As I said, it runs stoich at part loads, as all but a handful of cars do. Those that don't run stoich run lean through charge stratification, but Direct Injection is needed for this and some kind of de-NOx trap...which are expensive, increase exhaust backpressure, and have big temperature problems. 

At full load it runs rich, again as 98% of cars also do - those that can run stoich throughout the entire speed range have either gay outputs, or are Direct Injection and utilise materials that allow very high exhaust gas temperatures to be used. 

The GTR engine is limited by the turbine-in temperature of 950 deg C. We tried to get MHI turbos for this application with Titanium Aluminium turbine wheels....these are ok to turbine-in temps of 1050 deg C which is benefitial from a performance point of view (as excessive over-fuelling to control exhaust temperatures actually reduces power), but with no luck. That said, running 1050 deg C turbine-in temps would push the exhaust valve closer to the 800 deg C limit, and the valves are already sodium filled!!


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## R33_GTS-t (Apr 27, 2005)

Wink said:


> Typical figures of Standard Deviation of Indicated Mean Effective Pressure (SDIMEP) and Covariance of IMEP (CoV IMEP) for this engine would be 0.08 and less than 2% under all warm engine speeds/load - this means the combustion is pretty damn consistant dont you think?


For the purpose of semantics, it doesn't really matter how consistent the process in between is. The bottom line is that it's there and it affects the value you're trying to control before you measure it, hence breaking the loop.



Wink said:


> The engine is Manifold Port Injected and therefore not direct injection. As I said, it runs stoich at part loads, as all but a handful of cars do. Those that don't run stoich run lean through charge stratification, but Direct Injection is needed for this and some kind of de-NOx trap...which are expensive, increase exhaust backpressure, and have big temperature problems.


Must have got my wires crossed. During development, I heard rumours of direct injection. Maybe this will be saved for the 2009 V-Spec, now that Porsche have gone DI with their mid-life update.



Wink said:


> At full load it runs rich, again as 98% of cars also do - those that can run stoich throughout the entire speed range have either gay outputs, or are Direct Injection and utilise materials that allow very high exhaust gas temperatures to be used.


I think I'm having trouble due to the fact that my ECU won't go rich early enough rpm-wise. When I use heavy throttle around 2000-2500rpm, the ECU tends to resort to safe-mode and limits to 0.6bar until reset. After fitting a de-cat, the boost builds quicker and I think that the ECU is failing to allow for it.



Wink said:


> The GTR engine is limited by the turbine-in temperature of 950 deg C. We tried to get MHI turbos for this application with Titanium Aluminium turbine wheels....these are ok to turbine-in temps of 1050 deg C which is benefitial from a performance point of view (as excessive over-fuelling to control exhaust temperatures actually reduces power), but with no luck. That said, running 1050 deg C turbine-in temps would push the exhaust valve closer to the 800 deg C limit, and the valves are already sodium filled!!


Something for the V-Spec? 

Did the GTR go with VNT and electric-assist in the end?


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## Trev (Nov 1, 2003)

Really, in all honesty....who gives a f**k?

It's fast, looks great and I want one.


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## mindlessoath (Nov 30, 2007)

nvrmindl


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## mindlessoath (Nov 30, 2007)

ok... so whats the real wheel hp figures for this car? is this estimated to be wheel hp, or flywheel hp?

i know opinion magazine had aftermarket "amuse" exuast dynoed on the dyno jet - which i hate that method, but its a dyno regardless. 

in any case they estimated at 500hp or something like that, is there dyno jet describing what it would be at the flywheel? argggggggggg someone do more dyno's for the gtr for real world wheel hp!


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## AJFleming (Feb 25, 2003)

Hasnt one already been strapped to a dynapack and made more like 550bhp? Sure I read that somewhere?


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## R33_GTS-t (Apr 27, 2005)

[email protected] and [email protected] have been measured on 2 different, standard R35s.


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