Do you REALLY have Torque, or you have been told you do?
06-06-2007, 08:48 PM
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Jean,
Unfortunately, my friend....your post is filled with many, many errors.
1. First off, BMEP is simply an engineering calculation to estimate what the mean pressure in the cylinder would have to be to create the measured torque......it is a calculation and not actual reality.
2. BMEP of turbo and/or supercharged engines can not be adjusted to the BMEP of a naturally aspirated engine by simply dividing by the boost ratio.....period.
3. BMEP is an easy and quick way to estimate if intake/head/cam/chamber/piston/rod/crank/ignition/exhaust changes provided a benefit vs. another setup in a naturally aspirated engine.......
In a turbo and/or supercharged engine, it would be BMEP/boost, but once again, you can not assume that calculating boost to atmospheric = a naturally aspirated engine. It is a comparison ratio, not an absolute.....and that is the key point here. It is a comparison ratio between two similar engines, not an absolute that can be translated back and forth from boosted to naturally aspirated.
4. It does give an estimate of a maximum value for a naturally aspirated engine's output when using optimum engine design (about 235 psi).
5. There are so many variables when talking turbocharged engines that it depends on A/R, trim, housing, wheel, intercooler, efficiency island, turbine rpm, PR etc. etc. that you have to weigh response and boost vs. output or BMEP to get a useful answer.
If you look at your numbers, you see the turbocharged cars at the bottom. That's because you can't simply divide the torque output by the boost ratio to get the naturally aspirated equivalent BMEP. All of those cars, if you ran them at 0 boost, (which you may not be able to do since many might still produce boost even with the wastegates locked open) would have higher BMEP's than listed when naturally aspirated (prob. around 175-190). There is a long, drawn-out calculation that can estimate what the output of a turbo and/or supercharged engine would be if naturally aspirated, but you need to know the air temperature, humidity, absolute and relative pressure of the intake air and we don't have that.
Also, when you use the correct naturally aspirated BMEP for a turbo and/or supercharged engine, you'll still be off when you correct it for boost because of the density change of the intake charge. All your the BMEP discussion is good for is to estimate how some naturally aspirated engines compare to each other in terms of peak torque/displacement.
You could also use it to compare two turbo or supercharged engines at say both at 1.0 bar, then at 1.2 bar, 1.4 bar etc. etc. even though you have considerable variables to compare when boosted. The argument of saying a TT has 420 ft.lb of torque which is some equivalent naturally aspirated number (167 in this case) which then limits it's boosted max is completely flawed.
There are a couple useful ways to use BMEP for the layman: If someone claims a naturally aspirated engine has a BMEP of 200+, it better have been built by someone good or it's probably BS.....but once again, how often do you use that?Especially considering that those 150-230psi BMEP numbers mean nothing with turbo or supercharged cars!
Also, peak anything (HP, torque) is pretty much a bragging number and not what really matters. Area under the curves is what matters and anyone who states otherwise must be operating their car at a single RPM number.
A little more info for you to chew on and to show how useless this number can be. F1 engines (naturally aspirated) produce around 230psi BMEP numbers. Top technology right? Consider Winston Cup engines. Naturally aspirated, overhead valve, big displacement, V-8, flat tappet lifters (yes, no rollers), pushrods, four barrel carburetors and no electronic ignition. Are you sitting down? 230 psi BMEP. I can see the F1 fanboys crying in their champagne right now....LOLOL....so how can this be?? Is F1 really a joke?
No, but BMEP isn't all is cracked up to be. Why? Because the trick is to produce 230+psi naturally aspirated and spin up to 20,000 rpm......now that's impressive. But so is an American V-8 which can produce 230+psi naturally aspirated and spin to 10,000 rpm (which they can do)......so why all the hoopla with F1 and their technology? Because you remember the HP = (torque x rpm)/5252 right? This means that for performance considerations, it's the area under the power curve, not the torque curve that matters.
Yes, the area under the torque curve matters for feel and drivability, but the power curve area is king for performance. So if F1 can turn 230psi BMEP at twice the RPM as the WC V-8's, they can either produce twice the power, or equal power with half the displacement all while being naturally aspirated. This allows F1 to build engines which are significantly lighter than other designs which then allows the cars to have higher corner entry and exit speeds, which is what determines road course races.
So you see, saying a "adjusted for atmospheric" BMEP of 167psi on a 996TT limits its boosted output to some maximum number is a totally flawed and incorrect argument....
Output is governed by one thing assuming the engine can handle the physical loads........mass of air-fuel burned....period. A greater mass of air-fuel burned, a greater output noted. That mass of air is limited by atmospheric pressure in a naturally aspirated engine so therefore you can have baseline BMEP numbers for that specific situation.
That's all I have to say about this topic. Take it or leave it.
Cheers,
Scott (Owner of a Porsche with a true 1,000 ft lbs of torque at the crank at only 1.5 BAR.)
Unfortunately, my friend....your post is filled with many, many errors.
1. First off, BMEP is simply an engineering calculation to estimate what the mean pressure in the cylinder would have to be to create the measured torque......it is a calculation and not actual reality.
2. BMEP of turbo and/or supercharged engines can not be adjusted to the BMEP of a naturally aspirated engine by simply dividing by the boost ratio.....period.
3. BMEP is an easy and quick way to estimate if intake/head/cam/chamber/piston/rod/crank/ignition/exhaust changes provided a benefit vs. another setup in a naturally aspirated engine.......
In a turbo and/or supercharged engine, it would be BMEP/boost, but once again, you can not assume that calculating boost to atmospheric = a naturally aspirated engine. It is a comparison ratio, not an absolute.....and that is the key point here. It is a comparison ratio between two similar engines, not an absolute that can be translated back and forth from boosted to naturally aspirated.
4. It does give an estimate of a maximum value for a naturally aspirated engine's output when using optimum engine design (about 235 psi).
5. There are so many variables when talking turbocharged engines that it depends on A/R, trim, housing, wheel, intercooler, efficiency island, turbine rpm, PR etc. etc. that you have to weigh response and boost vs. output or BMEP to get a useful answer.
If you look at your numbers, you see the turbocharged cars at the bottom. That's because you can't simply divide the torque output by the boost ratio to get the naturally aspirated equivalent BMEP. All of those cars, if you ran them at 0 boost, (which you may not be able to do since many might still produce boost even with the wastegates locked open) would have higher BMEP's than listed when naturally aspirated (prob. around 175-190). There is a long, drawn-out calculation that can estimate what the output of a turbo and/or supercharged engine would be if naturally aspirated, but you need to know the air temperature, humidity, absolute and relative pressure of the intake air and we don't have that.
Also, when you use the correct naturally aspirated BMEP for a turbo and/or supercharged engine, you'll still be off when you correct it for boost because of the density change of the intake charge. All your the BMEP discussion is good for is to estimate how some naturally aspirated engines compare to each other in terms of peak torque/displacement.
You could also use it to compare two turbo or supercharged engines at say both at 1.0 bar, then at 1.2 bar, 1.4 bar etc. etc. even though you have considerable variables to compare when boosted. The argument of saying a TT has 420 ft.lb of torque which is some equivalent naturally aspirated number (167 in this case) which then limits it's boosted max is completely flawed.
There are a couple useful ways to use BMEP for the layman: If someone claims a naturally aspirated engine has a BMEP of 200+, it better have been built by someone good or it's probably BS.....but once again, how often do you use that?Especially considering that those 150-230psi BMEP numbers mean nothing with turbo or supercharged cars!
Also, peak anything (HP, torque) is pretty much a bragging number and not what really matters. Area under the curves is what matters and anyone who states otherwise must be operating their car at a single RPM number.
A little more info for you to chew on and to show how useless this number can be. F1 engines (naturally aspirated) produce around 230psi BMEP numbers. Top technology right? Consider Winston Cup engines. Naturally aspirated, overhead valve, big displacement, V-8, flat tappet lifters (yes, no rollers), pushrods, four barrel carburetors and no electronic ignition. Are you sitting down? 230 psi BMEP. I can see the F1 fanboys crying in their champagne right now....LOLOL....so how can this be?? Is F1 really a joke?
No, but BMEP isn't all is cracked up to be. Why? Because the trick is to produce 230+psi naturally aspirated and spin up to 20,000 rpm......now that's impressive. But so is an American V-8 which can produce 230+psi naturally aspirated and spin to 10,000 rpm (which they can do)......so why all the hoopla with F1 and their technology? Because you remember the HP = (torque x rpm)/5252 right? This means that for performance considerations, it's the area under the power curve, not the torque curve that matters.
Yes, the area under the torque curve matters for feel and drivability, but the power curve area is king for performance. So if F1 can turn 230psi BMEP at twice the RPM as the WC V-8's, they can either produce twice the power, or equal power with half the displacement all while being naturally aspirated. This allows F1 to build engines which are significantly lighter than other designs which then allows the cars to have higher corner entry and exit speeds, which is what determines road course races.
So you see, saying a "adjusted for atmospheric" BMEP of 167psi on a 996TT limits its boosted output to some maximum number is a totally flawed and incorrect argument....
Output is governed by one thing assuming the engine can handle the physical loads........mass of air-fuel burned....period. A greater mass of air-fuel burned, a greater output noted. That mass of air is limited by atmospheric pressure in a naturally aspirated engine so therefore you can have baseline BMEP numbers for that specific situation.
That's all I have to say about this topic. Take it or leave it.
Cheers,
Scott (Owner of a Porsche with a true 1,000 ft lbs of torque at the crank at only 1.5 BAR.)
Last edited by M-Phibian; 06-06-2007 at 09:48 PM.
06-06-2007, 09:53 PM
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True 1,000 ft lbs is almost 10% more torque than the "Mission 400 plus" project car.
Its RS-Tuning 3.8 ltr. engine also runs at 1.5 bar.
Around 1050 hp @ 7700rpm.
That would be around 50% above the maximum real torque numbers from the chart above.
Its RS-Tuning 3.8 ltr. engine also runs at 1.5 bar.
Around 1050 hp @ 7700rpm.
That would be around 50% above the maximum real torque numbers from the chart above.
06-07-2007, 12:28 AM
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Jean,
The first thing that leaps out is that the higher the compression the better the BMEP. A 997 RSR has over 13:1 compression and btw they are 3.8 ltr and the lowly 993 turbo has 8:1 and will pull more torque than any of the NA engines even with the world class BMEP. The turbo will not have the linear cylinder pressure that a NA has, but will be variable due to boost and timing charactoristics of a the dme. So it seems to me you can't compare the two.
Secondly, in the real world elevation drasticly effects performance of NA engines. I know at 3000 ft elevation NA cars performance is off at least 10% where turbo engines are uneffected. So the BMEP is dependant on a constant most likely sea level. If the turbo is unaffected by elevation changes (up to a point) there is an inherent contridiction in the formula or it doesn't apply equally to turbo engines.
The first thing that leaps out is that the higher the compression the better the BMEP. A 997 RSR has over 13:1 compression and btw they are 3.8 ltr and the lowly 993 turbo has 8:1 and will pull more torque than any of the NA engines even with the world class BMEP. The turbo will not have the linear cylinder pressure that a NA has, but will be variable due to boost and timing charactoristics of a the dme. So it seems to me you can't compare the two.
Secondly, in the real world elevation drasticly effects performance of NA engines. I know at 3000 ft elevation NA cars performance is off at least 10% where turbo engines are uneffected. So the BMEP is dependant on a constant most likely sea level. If the turbo is unaffected by elevation changes (up to a point) there is an inherent contridiction in the formula or it doesn't apply equally to turbo engines.
06-07-2007, 12:55 AM
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Originally Posted by M-Phibian
That's all I have to say about this topic. Take it or leave it.
Cheers,
Scott (Owner of a Porsche with a true 1,000 ft lbs of torque at the crank at only 1.5 BAR.)
Cheers,
Scott (Owner of a Porsche with a true 1,000 ft lbs of torque at the crank at only 1.5 BAR.)
Thank you for your perspective, I think I have done all this reading on the net before, read a few books and had quite a few discussions with engine builders, I even tried to read the definition of BMEP before posting
I can obviously write back and comment on every line that you have typed , but since you have given me the choice, I will choose not to take it, but to leave it.
You seem to be one of the persons who are happy and comfortable with their chassis dyno numbers, therefore this thread is irrelevant to you.
You can have your 1000 lb.ft of torque and I am happy for you, but just have them at a boost that is possible.
BTW, Todd K. and I have had multiple discussions over this topic and all this BMEP data has been shared with him long time back and we are in agreement over it, just like the max. HP flow of a stock K16
Nice video vs. the M6 BTW!
Best
Jean
06-07-2007, 01:18 AM
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Originally Posted by JJayB
Jean,
The first thing that leaps out is that the higher the compression the better the BMEP. A 997 RSR has over 13:1 compression and btw they are 3.8 ltr and the lowly 993 turbo has 8:1 and will pull more torque than any of the NA engines even with the world class BMEP. The turbo will not have the linear cylinder pressure that a NA has, but will be variable due to boost and timing charactoristics of a the dme. So it seems to me you can't compare the two.
Secondly, in the real world elevation drasticly effects performance of NA engines. I know at 3000 ft elevation NA cars performance is off at least 10% where turbo engines are uneffected. So the BMEP is dependant on a constant most likely sea level. If the turbo is unaffected by elevation changes (up to a point) there is an inherent contridiction in the formula or it doesn't apply equally to turbo engines.
The first thing that leaps out is that the higher the compression the better the BMEP. A 997 RSR has over 13:1 compression and btw they are 3.8 ltr and the lowly 993 turbo has 8:1 and will pull more torque than any of the NA engines even with the world class BMEP. The turbo will not have the linear cylinder pressure that a NA has, but will be variable due to boost and timing charactoristics of a the dme. So it seems to me you can't compare the two.
Secondly, in the real world elevation drasticly effects performance of NA engines. I know at 3000 ft elevation NA cars performance is off at least 10% where turbo engines are uneffected. So the BMEP is dependant on a constant most likely sea level. If the turbo is unaffected by elevation changes (up to a point) there is an inherent contridiction in the formula or it doesn't apply equally to turbo engines.
The 997RSR has much higher compression as you said. It has a BMEP of 209, run two turbos through it and you can get mind boggling numbers, it will blow in your face too.
This is why the fastest Porsche turbocharged engines are the ones running GT3 engines, or cams, heads, intakes etc..While looking at the data, one needs to think why an engine is more efficient than another, the RSR is indeed more efficienct as a result of its compression, but this is how the engine was built, therefore the BMEP belongs to the engine.
Finally of course conditions vary, but Porsche data is based on DIN standards, anything that varies from it, will create different numbers, then again, any dyno reading, uncorrected to DIN or SAE is pretty worthless do you agree? Therefore data is comparable as long as standards are being respected.
If I have an engine showing the same BMEP than a 997GT3 at atmospheric conditions, I know what to think!!
I would look at Porsche factory or tuner turbo engines, but engines that have been dyno'ed on reputable engine or chassis dynos, and try to check the validity of the data by comparing it to this, when you see a 10% + difference, you will find that the engine uses different turbos, twin plug, higher compression, no exhaust, maybe MAP instead of MAF, N/A intake, etc..
Cheers
Last edited by Jean; 06-07-2007 at 06:44 AM.
06-08-2007, 06:15 AM
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Data from me
I get 538 lb ft (729NM) at peak torque which I am reliably informed will be at a boost of ~ 1.25 bar on the RS engine dyno.
Reading Jean's chart I should see around 515 lb ft at this boost, I guess the extra over ~ 4.5% can be attributed to my mods.
Brilliant thread Jean
I get 538 lb ft (729NM) at peak torque which I am reliably informed will be at a boost of ~ 1.25 bar on the RS engine dyno.
Reading Jean's chart I should see around 515 lb ft at this boost, I guess the extra over ~ 4.5% can be attributed to my mods.
Brilliant thread Jean
06-08-2007, 06:20 AM
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MOD,
Thanks, I hope it is useful .
That falls in the ballpark number indeed. You have a Secan and some great turbos among others. Your overboost might take you beyond 1.25 Bar? I am sure this is where max. torque is as well. Give and take a few % points, no big deal in the larger scheme of things.
Thanks, I hope it is useful .
That falls in the ballpark number indeed. You have a Secan and some great turbos among others. Your overboost might take you beyond 1.25 Bar? I am sure this is where max. torque is as well. Give and take a few % points, no big deal in the larger scheme of things.
06-08-2007, 06:26 AM
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Get over boost to around 1.3 / 1.35 bar in the higher gears for a short time.
Highest sustained boost I have seen on the road is 1.2 bar in 6th, from 100mph ish up to around 160 where it eases back to 1.1 bar. Guess the Secan is helping matters here
Highest sustained boost I have seen on the road is 1.2 bar in 6th, from 100mph ish up to around 160 where it eases back to 1.1 bar. Guess the Secan is helping matters here
06-08-2007, 08:14 AM
#25
Yes the car has Torque. I was told by a Sachs clutch and pressure plate rated at 800fwtq. It started slipping on the Protomotive dyno at 660rwtq. Now theres a 1000ft-lb 'monster' clutch in there and the practically new Sachs from Kevin at UMW is for sale.
06-08-2007, 10:30 AM
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Originally Posted by Acropora
Yes the car has Torque. I was told by a Sachs clutch and pressure plate rated at 800fwtq. It started slipping on the Protomotive dyno at 660rwtq. Now theres a 1000ft-lb 'monster' clutch in there and the practically new Sachs from Kevin at UMW is for sale.
This possibly has as much to do with the shape of the torque curve as to the peak number.....
A 500lb/ft max tt which puts on 200lb/ft in 500 rpm (say between 4000 and 4500rpm) will "light up" a clutch whereas a 600lb/ft tt with a much gentler curve (and bigger area under) may well work fine with the same clutch.
06-08-2007, 04:10 PM
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Jean,
I am interested in your calculations.
Where did the BMEP #'s come from (ex; 167 for a 996TT motor).
It seems that the 996TT motor is much more efficient in reality than its air cooled brethrens'
similar BMEP #'s would indicate. I also have discussed with Todd the potential of my car
and seems like my motor maxed out with stock cams and internals somewhere just south (less)
than 700. Now with MAJOR changes such as heads, cams, more efficient turbos (like Garret
BB's) is it not conceivable that this "jump' in efficiency is more than the 5% or so you claim
is the max???
It does seem logical that ultimately it is how much air and fuel you can get thru a motor.
What is Torque of RUF RT12 Motor?? Which I believe runs 11 flat quarter mile approx.
What would be the torque (of a car that weighs the same as the RT12 and runs 1 second
quicker thru the quarter??
It does appear that when comparing turbo charged motors to N/A motors that
the results do not compare "apples to apples".
Also many advances have been made to the modification methods of the 996TT
and if you believe 60-130 mph #'s, we have seen some real big torque numbers.
food for thought,
Regards,
Marty
I am interested in your calculations.
Where did the BMEP #'s come from (ex; 167 for a 996TT motor).
It seems that the 996TT motor is much more efficient in reality than its air cooled brethrens'
similar BMEP #'s would indicate. I also have discussed with Todd the potential of my car
and seems like my motor maxed out with stock cams and internals somewhere just south (less)
than 700. Now with MAJOR changes such as heads, cams, more efficient turbos (like Garret
BB's) is it not conceivable that this "jump' in efficiency is more than the 5% or so you claim
is the max???
It does seem logical that ultimately it is how much air and fuel you can get thru a motor.
What is Torque of RUF RT12 Motor?? Which I believe runs 11 flat quarter mile approx.
What would be the torque (of a car that weighs the same as the RT12 and runs 1 second
quicker thru the quarter??
It does appear that when comparing turbo charged motors to N/A motors that
the results do not compare "apples to apples".
Also many advances have been made to the modification methods of the 996TT
and if you believe 60-130 mph #'s, we have seen some real big torque numbers.
food for thought,
Regards,
Marty
06-08-2007, 05:29 PM
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Originally Posted by Woodster
Where did the BMEP #'s come from (ex; 167 for a 996TT motor).
It seems that the 996TT motor is much more efficient in reality than its air cooled brethrens'
It seems that the 996TT motor is much more efficient in reality than its air cooled brethrens'
Originally Posted by Woodster
similar BMEP #'s would indicate. I also have discussed with Todd the potential of my car
and seems like my motor maxed out with stock cams and internals somewhere just south (less)
than 700. Now with MAJOR changes such as heads, cams, more efficient turbos (like Garret
BB's) is it not conceivable that this "jump' in efficiency is more than the 5% or so you claim
is the max???
and seems like my motor maxed out with stock cams and internals somewhere just south (less)
than 700. Now with MAJOR changes such as heads, cams, more efficient turbos (like Garret
BB's) is it not conceivable that this "jump' in efficiency is more than the 5% or so you claim
is the max???
Originally Posted by Woodster
It does seem logical that ultimately it is how much air and fuel you can get thru a motor.
As you modifiy the engine, you improve its efficiency, with displacement, static compression, turbos, cooling, air flow etc, and you reach a higher BMEP, the point being made is that this new BMEP, at 0 boost levels, increases by a limited percentage depending on what was done.
Originally Posted by Woodster
What is Torque of RUF RT12 Motor?? Which I believe runs 11 flat quarter mile approx..
Originally Posted by Woodster
What would be the torque (of a car that weighs the same as the RT12 and runs 1 second
quicker thru the quarter??..
quicker thru the quarter??..
this is not a 60-130mph test Marty, it cannot be used to predict quartermile times.
Originally Posted by Woodster
It does appear that when comparing turbo charged motors to N/A motors that
the results do not compare "apples to apples".
Also many advances have been made to the modification methods of the 996TT
and if you believe 60-130 mph #'s, we have seen some real big torque numbers.
the results do not compare "apples to apples".
Also many advances have been made to the modification methods of the 996TT
and if you believe 60-130 mph #'s, we have seen some real big torque numbers.
I have much more data to support my findings but I will do it at my own pace, or maybe not
Last edited by Jean; 06-09-2007 at 11:58 AM.
06-08-2007, 05:48 PM
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Originally Posted by Stummel
True 1,000 ft lbs is almost 10% more torque than the "Mission 400 plus" project car.
Its RS-Tuning 3.8 ltr. engine also runs at 1.5 bar.
Around 1050 hp @ 7700rpm.
That would be around 50% above the maximum real torque numbers from the chart above.
Its RS-Tuning 3.8 ltr. engine also runs at 1.5 bar.
Around 1050 hp @ 7700rpm.
That would be around 50% above the maximum real torque numbers from the chart above.
Mission 400 has a BMEP of 198, and according to my information, the engine has been completely redesigned from scratch, the heads have further been modified with special combustion chamber shapes etc.. Beyond $200k of engine work alone.
06-09-2007, 09:41 AM
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Thanks Jean,
this is great info as my car is sitting on Todd's dyno as we speak
(and he is on vacation of course).
Cheers,
ps: I will see Lat in a few hours and will say hi for you.
Marty
this is great info as my car is sitting on Todd's dyno as we speak
(and he is on vacation of course).
Cheers,
ps: I will see Lat in a few hours and will say hi for you.
Marty