Software Simulation of C7 LT1 HP/Torque
02-16-2013, 11:34 AM
#1
Melting Slicks
Thread Starter
Software Simulation of C7 LT1 HP/Torque
With all of this debate over the C7 LT1 Horsepower/Torque ratings, I took a stab at loading the preliminary LT1 specs from the Corvette Action Center posting into the Virtual Engine Dyno Software. I make no claim as to the accuracy of the predicted results, however the numbers are interesting. I used SAE correction since it yields lower numbers.
Here are the specs entered into the software (I tweaked the cam timing to get 450 lb/ft torque on 87 Octane):
I ran two simulated tests, the first at 87 Octane:
The second at 96 Octane (a conservative estimate for E85):
In my first try the software said this combination is achieved a volumetric efficiency of 101% all the way to 6500 RPM which does not make sense. I used the calibration feature to force the VE and torque peak down to about 4250-4500 RPM and it now looks more like the GM curves. I am speculating the cam specs of 200/206 degree duration with the .551/.524" lift and 116.5 degree lobe separation is fooling the software because there was nothing like that in the old days. The specs must be unique to the VVT cam, and this 2005 version software just doesn't know what to do with it.
Let the speculation continue…
Here are the specs entered into the software (I tweaked the cam timing to get 450 lb/ft torque on 87 Octane):
I ran two simulated tests, the first at 87 Octane:
The second at 96 Octane (a conservative estimate for E85):
In my first try the software said this combination is achieved a volumetric efficiency of 101% all the way to 6500 RPM which does not make sense. I used the calibration feature to force the VE and torque peak down to about 4250-4500 RPM and it now looks more like the GM curves. I am speculating the cam specs of 200/206 degree duration with the .551/.524" lift and 116.5 degree lobe separation is fooling the software because there was nothing like that in the old days. The specs must be unique to the VVT cam, and this 2005 version software just doesn't know what to do with it.
Let the speculation continue…
Last edited by adamsocb; 02-16-2013 at 04:41 PM. Reason: Revised the Simulation, Changed Rocker Arm Ratio to 1.8
02-16-2013, 11:42 AM
#2
Le Mans Master
OK, I am not a real gearhead, so I am not going to say what you have is inaccurate, but GM has said all along that the LT1 generates is max torque up through the lower RPM range to 4000 RPM will the graph show the peak well above that range.
As far as the HP, I think it will be above the estimated 450, but I doubt in the base model that will be available in 2014 MY it will come close what you have on the graph.
As far as the HP, I think it will be above the estimated 450, but I doubt in the base model that will be available in 2014 MY it will come close what you have on the graph.
02-16-2013, 11:49 AM
#3
Melting Slicks
Thread Starter
OK, I am not a real gearhead, so I am not going to say what you have is inaccurate, but GM has said all along that the LT1 generates is max torque up through the lower RPM range to 4000 RPM will the graph show the peak well above that range.
As far as the HP, I think it will be above the estimated 450, but I doubt in the base model that will be available in 2014 MY it will come close what you have on the graph.
As far as the HP, I think it will be above the estimated 450, but I doubt in the base model that will be available in 2014 MY it will come close what you have on the graph.
02-16-2013, 01:05 PM
#4
Team Owner
crap in- crap out. you can't even get the rocker arm ratio correct.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
This the official GM Hp/torque dyno graph....
Notice that the torque has dropped to 365 at 6500 RPM and the horsepower is also falling, down to 445 at 6500.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
This the official GM Hp/torque dyno graph....
Notice that the torque has dropped to 365 at 6500 RPM and the horsepower is also falling, down to 445 at 6500.
02-16-2013, 03:10 PM
#6
Burning Brakes
crap in- crap out. you can't even get the rocker arm ratio correct.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
"Interesting first attempt at a simulation. I noticed a few places where your parameters seemed inaccurate. You might want to try adjusting these items and running it again to see what happens."
02-16-2013, 03:24 PM
#7
Melting Slicks
Thread Starter
crap in- crap out. you can't even get the rocker arm ratio correct.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
This the official GM Hp/torque dyno graph....
Notice that the torque has dropped to 365 at 6500 RPM and the horsepower is also falling, down to 445 at 6500.
Your simulation shows the engine making HP and torque at 7250 RPM, when the LT1 won't turn more then 6500 RPM and it makes it's max HP at 5900 according to GM.
You show the intake CFM at 750, where did you get that figure? You show the exhaust from a mid year with long tubes and aftermarket mufflers with a 3" intake/exit.
This the official GM Hp/torque dyno graph....
Notice that the torque has dropped to 365 at 6500 RPM and the horsepower is also falling, down to 445 at 6500.
How do you know the rocker arm ratio is incorrect? I did not see a ratio in the specs. The LS3 ratio was 1.7 but in the pictures of the LT1 head the rockers look shorter. In any event I don't think it makes much difference since the lift (intake .551" and exhaust .524") are at the valve not the cam.
Even though the 87mm TB can flow up to 1300CFM I didn't change it since the motor didn't need more than about 750 CFM anyway. I adjusted it to 1300 and the simulated graph did not change.
I still cannot figure out why the software is placing peak torque at 6000 RPM with a 200 degree cam duration. It may just be wrong. I used the
"Calibration" feature to force the peak VE and torque down where it is on the GM graph and the HP follows accordingly.
So much for out of date (2005) engine simulation software.
02-16-2013, 03:43 PM
#8
Team Owner
One point at a time:
How do you know the rocker arm ratio is incorrect? I did not see a ratio in the specs. The LS3 ratio was 1.7 but in the pictures of the LT1 head the rockers look shorter. In any event I don't think it makes much difference since the lift (intake .551" and exhaust .524") are at the valve not the cam.
Even though the 87mm TB can flow up to 1300CFM I didn't change it since the motor didn't need more than about 750 CFM anyway. I adjusted it to 1300 and the simulated graph did not change.
I still cannot figure out why the software is placing peak torque at 6000 RPM with a 200 degree cam duration. It may just be wrong. I used the
"Calibration" feature to force the peak VE and torque down where it is on the GM graph and the HP follows accordingly.
So much for out of date (2005) engine simulation software.
How do you know the rocker arm ratio is incorrect? I did not see a ratio in the specs. The LS3 ratio was 1.7 but in the pictures of the LT1 head the rockers look shorter. In any event I don't think it makes much difference since the lift (intake .551" and exhaust .524") are at the valve not the cam.
Even though the 87mm TB can flow up to 1300CFM I didn't change it since the motor didn't need more than about 750 CFM anyway. I adjusted it to 1300 and the simulated graph did not change.
I still cannot figure out why the software is placing peak torque at 6000 RPM with a 200 degree cam duration. It may just be wrong. I used the
"Calibration" feature to force the peak VE and torque down where it is on the GM graph and the HP follows accordingly.
So much for out of date (2005) engine simulation software.
GM has spent tens of millions of dollars over the past 5 years designing the LT1 and then GM shows us a dyno graph of the LT1, and everyone on this forum calls it BS. Why????
Then people say GM doesn't know what they are doing, and try and discredit GM's numbers, by pretending that they are more informed about designing engines then GM. Why???
02-16-2013, 05:08 PM
#11
Melting Slicks
Thread Starter
I found the article in GM High-Tech Performance where the rocker arm ratio is listed at 1.8 and made the change. I was previously estimating the ratio based on the picture of the LT1 head.
And BTW, I am neither defending what this software comes up with or disputing GM's engineers. The LT1 engine with DGI and VVT is a new paradigm and GM can tune it to do whatever they want. It does seem odd to me the VE would fall off as fast the GM curve given what might be possible. The truth will be known soon enough, and all of this is just idle speculation on a Saturday afternoon.
And BTW, I am neither defending what this software comes up with or disputing GM's engineers. The LT1 engine with DGI and VVT is a new paradigm and GM can tune it to do whatever they want. It does seem odd to me the VE would fall off as fast the GM curve given what might be possible. The truth will be known soon enough, and all of this is just idle speculation on a Saturday afternoon.
02-16-2013, 05:57 PM
#14
Race Director
02-16-2013, 06:08 PM
#15
Melting Slicks
Thread Starter
My understanding of torque is that it is a product of displacement, dynamic compression ratio, and volumetric efficiency (VE). In a naturally aspirated engine VE can only get to 100% or maybe 101% with good intake and exhaust tuning. The dynamic compression ratio is always less than the static compression ratio due to valve timing overlap. In traditional racing engines the cam duration is made longer to increase VE at high RPM which causes more valve overlap and lower dynamic compression ratio. The causes the torque peak to move up the RPM scale and produce more horsepower at higher RPM. I am thinking the VVT is able to optimize overlap for higher compression at low RPM and combined with the DGI make for a very strong flat torque curve starting at low RPM. There may be some penalty in VE at high RPM which causes the torque to drop off more than when the cam is optimized for high RPM. Of course more duration and overlap also hurt fuel economy with conventional injection since some of the unburnt charge goes out the exhaust. DGI should be able to help that as well.
Just for an example, if you look at the LS7 HP/Torque graph the torque peaks at 470 lb-ft just above 5000 RPM and stays above 450 out to about 6500RPM.
It is interesting the LT1 is expected to make 450 lb-ft max torque but drop to 360 lb-ft by 6500 RPM. If the LT1 could make 400 lb-ft out to 6500 RPM the HP would be 495. The tuning we are seeing could be for fuel economy, drivability, or any other of a number of reasons.
This engine will have great possiblities and GM may be holding much in reserve for the first year or two.
02-16-2013, 06:13 PM
#16
Melting Slicks
Thread Starter
02-17-2013, 02:20 PM
#17
Practically yes since other forms of fuel delivery are less precise and may not be able to deliver and time the perfect air/fuel ratio at a given RPM. I don't know how my software calculates air/fuel precision and that may be part of the problem, but I don't think it explains why the torque and VE were so far up the RPM scale in my uncalibrated simulation.
My understanding of torque is that it is a product of displacement, dynamic compression ratio, and volumetric efficiency (VE). In a naturally aspirated engine VE can only get to 100% or maybe 101% with good intake and exhaust tuning. The dynamic compression ratio is always less than the static compression ratio due to valve timing overlap. In traditional racing engines the cam duration is made longer to increase VE at high RPM which causes more valve overlap and lower dynamic compression ratio. The causes the torque peak to move up the RPM scale and produce more horsepower at higher RPM. I am thinking the VVT is able to optimize overlap for higher compression at low RPM and combined with the DGI make for a very strong flat torque curve starting at low RPM. There may be some penalty in VE at high RPM which causes the torque to drop off more than when the cam is optimized for high RPM. Of course more duration and overlap also hurt fuel economy with conventional injection since some of the unburnt charge goes out the exhaust. DGI should be able to help that as well.
Just for an example, if you look at the LS7 HP/Torque graph the torque peaks at 470 lb-ft just above 5000 RPM and stays above 450 out to about 6500RPM.
It is interesting the LT1 is expected to make 450 lb-ft max torque but drop to 360 lb-ft by 6500 RPM. If the LT1 could make 400 lb-ft out to 6500 RPM the HP would be 495. The tuning we are seeing could be for fuel economy, drivability, or any other of a number of reasons.
This engine will have great possiblities and GM may be holding much in reserve for the first year or two.
My understanding of torque is that it is a product of displacement, dynamic compression ratio, and volumetric efficiency (VE). In a naturally aspirated engine VE can only get to 100% or maybe 101% with good intake and exhaust tuning. The dynamic compression ratio is always less than the static compression ratio due to valve timing overlap. In traditional racing engines the cam duration is made longer to increase VE at high RPM which causes more valve overlap and lower dynamic compression ratio. The causes the torque peak to move up the RPM scale and produce more horsepower at higher RPM. I am thinking the VVT is able to optimize overlap for higher compression at low RPM and combined with the DGI make for a very strong flat torque curve starting at low RPM. There may be some penalty in VE at high RPM which causes the torque to drop off more than when the cam is optimized for high RPM. Of course more duration and overlap also hurt fuel economy with conventional injection since some of the unburnt charge goes out the exhaust. DGI should be able to help that as well.
Just for an example, if you look at the LS7 HP/Torque graph the torque peaks at 470 lb-ft just above 5000 RPM and stays above 450 out to about 6500RPM.
It is interesting the LT1 is expected to make 450 lb-ft max torque but drop to 360 lb-ft by 6500 RPM. If the LT1 could make 400 lb-ft out to 6500 RPM the HP would be 495. The tuning we are seeing could be for fuel economy, drivability, or any other of a number of reasons.
This engine will have great possiblities and GM may be holding much in reserve for the first year or two.
02-17-2013, 04:46 PM
#18
VETERAN
Good guess work Adam
Hey man, nice try, for a Saturday afternoon effort and we don't yet know all the engine numbers, this was very interesting to look at. We can only hope that the C7 actually has more HP and Torque than what GM has released thus far. I believe it will.
Cheers,
Cheers,
