aspec gt3540r
05-30-09, 09:34 PM
#51
BDC Motorsports
I agree with Ernie on this one. Also, with regards to corrections at high altitude, I don't believe it should be applied on a boosted setup as the manifold pressure that the MAP sensor itself is reading is accurate (the same as) to what it would be at lower altitude.
Btw, nice setup.
B
Btw, nice setup.
B
Last edited by BDC; 05-30-09 at 09:34 PM. Reason: Adding 'nice setup'
05-31-09, 01:43 PM
#53
Racing Rotary Since 1983
iTrader: (6)
i post this w no agenda other than to get things right on the board...
23%? correction factor?
Altitude
For example, let's consider a dynamometer located at 5000 feet above sea level. At such elevation, most cars suffer terribly due to the lack of air density. As a result, their power outputs fall noticeably compared to identical cars that operate at or near sea level. For this reason, just about every dynamometer applies a hefty altitude correction in the magnitude of 20% (SAE correction, in this case). This means that a car that put down an actual 100 wheel hp is "corrected" up to 120 wheel hp. While this correction amount is reasonably accurate in some cases, it is notoriously optimistic in the case of turbocharged engines. In such engines, power output rarely falls as dramatically in response to air density reduction. This is due to their turbo control systems that combat air density reductions by allowing for higher boost pressures. These increased boost pressures can almost completely offset the ambient pressure reduction and make the "altitude correction" almost completely unnecessary. However, I have yet to see a high-altitude tuner come forth and not apply the positive correction factor when displaying their grossly optimistic dyno results.
credit Shiv Patek.
http://www.modularfords.com/forums/s...ad.php?t=54099
Introduction
Most everyone is familiar with the usual SAE (or STD) dyno correction factor, which are used to scale the measured power and torque to what would be measured at some reference set of ambient (weather) conditions. (For SAE J1349, these are: absolute ambient air pressure of Pref = 990 mb, ambient temp of Tf = 77 °F, and RH = 0%.) These correction factors were developed for naturally-aspired engines wherein the intake manifold pressure goes in direct proportion to the ambient pressure. (See link to the derivation given above.) Therefore, the scaling factor (αp) for indicated power with pressure has the inverse relationship and goes simply as
αp = Pref/Pdry
where Pdry is the dry-air partial pressure at the time of the measurement and Pref is the reference air pressure. Since it can be shown that the boost pressure (and hence the total intake manifold pressure) for an engine with a P-D supercharger is also directly proportional to ambient pressure, these correction factors still apply for these cases as well, at least to first order. (It will not correct for changes in the parasitic drive power of the SC as air density goes up and down, for example.)
For a turbocharged engine, however, this is not the case. Since these setups typically employ boost controllers that are designed to keep boost pressure constant, the total intake manifold pressure is less affected by changes in ambient pressure. (It is still affected since the intake manifold pressure is the sum of ambient plus boost pressure, but to a lesser amount.) As a result, turbocharged engines don’t gain or lose much power as the atmospheric pressure changes up or down. Therefore, the standard SAE J1349 type correction factors are wholly inappropriate for turbocharged applications. Below is a description of how pressure would scale for a typical turbocharged engine with boost controls to keep boost constant.
Turbo correction factor
Skipping all the math, (if someone really wants to see it let me know), for a turbocharged engine with a constant boost pressure, (after the turbos are fully spooled), it can be shown that the indicated power and torque would scale with pressure as
αp = (Pref + Pb)/[Pdry(1 + Pb/Patm)]
where Pref is the reference dry-air absolute pressure (29.235 in-Hg for SAE), Pb is the boost pressure also in in-Hg (= 2.036*PSI), Pdry is the absolute dry-air partial pressure at the time of the measurement, and Patm is the total absolute air pressure at the time of the measurement. To get the brake power scaling, clearly the mechanical efficiency needs to be factored in here as well. (See that other thread).
Below is a table showing how the two correction factors might differ for a turbocharged engine measured at a mile high with everything else at SAE J1349 conditions; Pref = 29.235 in-Hg, RH=0%, etc. There are other assumptions that I'll not get into here. Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures. It should also be pointed out that the difference between the two will change as the other conditions change. For example, as the absolute ambient pressure approaches the reference pressure, the difference is reduced.
For the above conditions, the SAE J1349 correction factor is: CFsae = 1.254
First column = boost pressure in psi
Second column = boost pressin in in-Hg
Third column = dyno CF appropriate for a turbocharged engine (CFturbo)
The 4th column shows how much the SAE J1349 CF overcorrects the results (relatively speaking), i.e., 100%(CFsae/CFturbo - 1)
Code:
Pb Pb
(psi) (in-Hg) CFturbo sae/trbo-1
5.0 10.18 1.178 6.40%
7.5 15.27 1.155 8.53%
10.0 20.36 1.137 10.22%
12.5 25.45 1.123 11.61%
15.0 30.54 1.112 12.76%
17.5 35.63 1.102 13.74%
20.0 40.72 1.094 14.57%
22.5 45.81 1.087 15.30%
25.0 50.9 1.081 15.93%
27.5 55.99 1.076 16.49%
30.0 61.08 1.072 16.98%
howard coleman
23%? correction factor?
Altitude
For example, let's consider a dynamometer located at 5000 feet above sea level. At such elevation, most cars suffer terribly due to the lack of air density. As a result, their power outputs fall noticeably compared to identical cars that operate at or near sea level. For this reason, just about every dynamometer applies a hefty altitude correction in the magnitude of 20% (SAE correction, in this case). This means that a car that put down an actual 100 wheel hp is "corrected" up to 120 wheel hp. While this correction amount is reasonably accurate in some cases, it is notoriously optimistic in the case of turbocharged engines. In such engines, power output rarely falls as dramatically in response to air density reduction. This is due to their turbo control systems that combat air density reductions by allowing for higher boost pressures. These increased boost pressures can almost completely offset the ambient pressure reduction and make the "altitude correction" almost completely unnecessary. However, I have yet to see a high-altitude tuner come forth and not apply the positive correction factor when displaying their grossly optimistic dyno results.
credit Shiv Patek.
http://www.modularfords.com/forums/s...ad.php?t=54099
Introduction
Most everyone is familiar with the usual SAE (or STD) dyno correction factor, which are used to scale the measured power and torque to what would be measured at some reference set of ambient (weather) conditions. (For SAE J1349, these are: absolute ambient air pressure of Pref = 990 mb, ambient temp of Tf = 77 °F, and RH = 0%.) These correction factors were developed for naturally-aspired engines wherein the intake manifold pressure goes in direct proportion to the ambient pressure. (See link to the derivation given above.) Therefore, the scaling factor (αp) for indicated power with pressure has the inverse relationship and goes simply as
αp = Pref/Pdry
where Pdry is the dry-air partial pressure at the time of the measurement and Pref is the reference air pressure. Since it can be shown that the boost pressure (and hence the total intake manifold pressure) for an engine with a P-D supercharger is also directly proportional to ambient pressure, these correction factors still apply for these cases as well, at least to first order. (It will not correct for changes in the parasitic drive power of the SC as air density goes up and down, for example.)
For a turbocharged engine, however, this is not the case. Since these setups typically employ boost controllers that are designed to keep boost pressure constant, the total intake manifold pressure is less affected by changes in ambient pressure. (It is still affected since the intake manifold pressure is the sum of ambient plus boost pressure, but to a lesser amount.) As a result, turbocharged engines don’t gain or lose much power as the atmospheric pressure changes up or down. Therefore, the standard SAE J1349 type correction factors are wholly inappropriate for turbocharged applications. Below is a description of how pressure would scale for a typical turbocharged engine with boost controls to keep boost constant.
Turbo correction factor
Skipping all the math, (if someone really wants to see it let me know), for a turbocharged engine with a constant boost pressure, (after the turbos are fully spooled), it can be shown that the indicated power and torque would scale with pressure as
αp = (Pref + Pb)/[Pdry(1 + Pb/Patm)]
where Pref is the reference dry-air absolute pressure (29.235 in-Hg for SAE), Pb is the boost pressure also in in-Hg (= 2.036*PSI), Pdry is the absolute dry-air partial pressure at the time of the measurement, and Patm is the total absolute air pressure at the time of the measurement. To get the brake power scaling, clearly the mechanical efficiency needs to be factored in here as well. (See that other thread).
Below is a table showing how the two correction factors might differ for a turbocharged engine measured at a mile high with everything else at SAE J1349 conditions; Pref = 29.235 in-Hg, RH=0%, etc. There are other assumptions that I'll not get into here. Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures. It should also be pointed out that the difference between the two will change as the other conditions change. For example, as the absolute ambient pressure approaches the reference pressure, the difference is reduced.
For the above conditions, the SAE J1349 correction factor is: CFsae = 1.254
First column = boost pressure in psi
Second column = boost pressin in in-Hg
Third column = dyno CF appropriate for a turbocharged engine (CFturbo)
The 4th column shows how much the SAE J1349 CF overcorrects the results (relatively speaking), i.e., 100%(CFsae/CFturbo - 1)
Code:
Pb Pb
(psi) (in-Hg) CFturbo sae/trbo-1
5.0 10.18 1.178 6.40%
7.5 15.27 1.155 8.53%
10.0 20.36 1.137 10.22%
12.5 25.45 1.123 11.61%
15.0 30.54 1.112 12.76%
17.5 35.63 1.102 13.74%
20.0 40.72 1.094 14.57%
22.5 45.81 1.087 15.30%
25.0 50.9 1.081 15.93%
27.5 55.99 1.076 16.49%
30.0 61.08 1.072 16.98%
howard coleman
06-01-09, 01:35 AM
#55
BDC Motorsports
There's alot I could say on this subject: one of those things being folks w/ PowerFC's up at high altitude should *Not* re-calibrate the offset on their MAP sensors to read at or near 0.00"Hg when the engine is off at 0"!!!
B
B
06-01-09, 02:47 AM
#56
Full Member
Join Date: Mar 2009
Location: Iowa
Posts: 92
Likes: 0
Received 0 Likes
on
0 Posts
From what I understand the only difference for different elevations is how fast the turbo spins. This would have an effect on compressor efficiency which in turn would affect your power. How much would depend on your setup and tune.
Also, if you tune the turbo for all its worth at low elevation and drive at a higher elevation (say tuned in miami but live and drive in denver) you will likely over spin the turbo and kill it in short order.
Is there anything wrong with this line of thought?
Also, if you tune the turbo for all its worth at low elevation and drive at a higher elevation (say tuned in miami but live and drive in denver) you will likely over spin the turbo and kill it in short order.
Is there anything wrong with this line of thought?
06-01-09, 10:10 AM
#57
covered in dust
Thread Starter
iTrader: (1)
Join Date: Apr 2005
Location: new mexico
Posts: 451
Likes: 0
Received 0 Likes
on
0 Posts
Im really not too concerned with what is realistically correct as far as correction vs not on a turbo car. I am at 5600ft and everyone here, and it seems like most people online, use their corrected #'s to compare. All that really matters to me is the butt-ometer, and yup, it feels fast to me.
06-01-09, 01:59 PM
#59
BDC Motorsports
Im really not too concerned with what is realistically correct as far as correction vs not on a turbo car. I am at 5600ft and everyone here, and it seems like most people online, use their corrected #'s to compare. All that really matters to me is the butt-ometer, and yup, it feels fast to me.
B
06-15-09, 03:39 PM
#60
35r 13b first gen
iTrader: (3)
Join Date: Apr 2002
Location: Richland Center WI
Posts: 1,290
Likes: 0
Received 0 Likes
on
0 Posts
im glas im at 470 some ft altitude haha. I have a streetport 12a with 47 OER sidedraft carb.. going blowthrough. getting a gt35r from turblown.net with 1.00 ar what kinda numbers you think i can put down with that?
06-29-09, 03:13 PM
#61
From what I understand the only difference for different elevations is how fast the turbo spins. This would have an effect on compressor efficiency which in turn would affect your power. How much would depend on your setup and tune.
Also, if you tune the turbo for all its worth at low elevation and drive at a higher elevation (say tuned in miami but live and drive in denver) you will likely over spin the turbo and kill it in short order.
Is there anything wrong with this line of thought?
Also, if you tune the turbo for all its worth at low elevation and drive at a higher elevation (say tuned in miami but live and drive in denver) you will likely over spin the turbo and kill it in short order.
Is there anything wrong with this line of thought?
06-29-09, 06:38 PM
#62
Original Gangster/Rotary!
iTrader: (213)
I have the A-spec 500r 1.06 w/3inch DP. Steve K street tunned my car very conservativly and it made 415WHP on a mustang dyno at 17 psi. I can tell you that i have had a few Turbo cars and driving from Las Vegas to California coast they seem to pick up one pound of boost on the same setting once i hit the good green O2 air in Cali
06-29-09, 07:57 PM
#63
I have not been able to drive the car much lately thats why its up 4 sale but I believe 3rd&4th gear pulls hit 17Psi by 3800 to 4Grand. This set up has a great powerband and The bigger wheel along with the 1.06 hotside should keep making power up to 28 Psi. I think this turbo is just starting to get into its Ef. range around 18 and will continue to make great gains with added boost.
12-06-09, 04:31 PM
#64
Rotary Enthusiast
Join Date: Mar 2001
Location: Edwards, CA
Posts: 1,023
Likes: 0
Received 0 Likes
on
0 Posts
i post this w no agenda other than to get things right on the board...
23%? correction factor?
Altitude
For example, let's consider a dynamometer located at 5000 feet above sea level. At such elevation, most cars suffer terribly due to the lack of air density. As a result, their power outputs fall noticeably compared to identical cars that operate at or near sea level. For this reason, just about every dynamometer applies a hefty altitude correction in the magnitude of 20% (SAE correction, in this case). This means that a car that put down an actual 100 wheel hp is "corrected" up to 120 wheel hp. While this correction amount is reasonably accurate in some cases, it is notoriously optimistic in the case of turbocharged engines. In such engines, power output rarely falls as dramatically in response to air density reduction. This is due to their turbo control systems that combat air density reductions by allowing for higher boost pressures. These increased boost pressures can almost completely offset the ambient pressure reduction and make the "altitude correction" almost completely unnecessary. However, I have yet to see a high-altitude tuner come forth and not apply the positive correction factor when displaying their grossly optimistic dyno results.
credit Shiv Patek.
http://www.modularfords.com/forums/s...ad.php?t=54099
Introduction
Most everyone is familiar with the usual SAE (or STD) dyno correction factor, which are used to scale the measured power and torque to what would be measured at some reference set of ambient (weather) conditions. (For SAE J1349, these are: absolute ambient air pressure of Pref = 990 mb, ambient temp of Tf = 77 °F, and RH = 0%.) These correction factors were developed for naturally-aspired engines wherein the intake manifold pressure goes in direct proportion to the ambient pressure. (See link to the derivation given above.) Therefore, the scaling factor (αp) for indicated power with pressure has the inverse relationship and goes simply as
αp = Pref/Pdry
where Pdry is the dry-air partial pressure at the time of the measurement and Pref is the reference air pressure. Since it can be shown that the boost pressure (and hence the total intake manifold pressure) for an engine with a P-D supercharger is also directly proportional to ambient pressure, these correction factors still apply for these cases as well, at least to first order. (It will not correct for changes in the parasitic drive power of the SC as air density goes up and down, for example.)
For a turbocharged engine, however, this is not the case. Since these setups typically employ boost controllers that are designed to keep boost pressure constant, the total intake manifold pressure is less affected by changes in ambient pressure. (It is still affected since the intake manifold pressure is the sum of ambient plus boost pressure, but to a lesser amount.) As a result, turbocharged engines don’t gain or lose much power as the atmospheric pressure changes up or down. Therefore, the standard SAE J1349 type correction factors are wholly inappropriate for turbocharged applications. Below is a description of how pressure would scale for a typical turbocharged engine with boost controls to keep boost constant.
Turbo correction factor
Skipping all the math, (if someone really wants to see it let me know), for a turbocharged engine with a constant boost pressure, (after the turbos are fully spooled), it can be shown that the indicated power and torque would scale with pressure as
αp = (Pref + Pb)/[Pdry(1 + Pb/Patm)]
where Pref is the reference dry-air absolute pressure (29.235 in-Hg for SAE), Pb is the boost pressure also in in-Hg (= 2.036*PSI), Pdry is the absolute dry-air partial pressure at the time of the measurement, and Patm is the total absolute air pressure at the time of the measurement. To get the brake power scaling, clearly the mechanical efficiency needs to be factored in here as well. (See that other thread).
Below is a table showing how the two correction factors might differ for a turbocharged engine measured at a mile high with everything else at SAE J1349 conditions; Pref = 29.235 in-Hg, RH=0%, etc. There are other assumptions that I'll not get into here. Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures. It should also be pointed out that the difference between the two will change as the other conditions change. For example, as the absolute ambient pressure approaches the reference pressure, the difference is reduced.
For the above conditions, the SAE J1349 correction factor is: CFsae = 1.254
First column = boost pressure in psi
Second column = boost pressin in in-Hg
Third column = dyno CF appropriate for a turbocharged engine (CFturbo)
The 4th column shows how much the SAE J1349 CF overcorrects the results (relatively speaking), i.e., 100%(CFsae/CFturbo - 1)
Code:
Pb Pb
(psi) (in-Hg) CFturbo sae/trbo-1
5.0 10.18 1.178 6.40%
7.5 15.27 1.155 8.53%
10.0 20.36 1.137 10.22%
12.5 25.45 1.123 11.61%
15.0 30.54 1.112 12.76%
17.5 35.63 1.102 13.74%
20.0 40.72 1.094 14.57%
22.5 45.81 1.087 15.30%
25.0 50.9 1.081 15.93%
27.5 55.99 1.076 16.49%
30.0 61.08 1.072 16.98%
howard coleman
23%? correction factor?
Altitude
For example, let's consider a dynamometer located at 5000 feet above sea level. At such elevation, most cars suffer terribly due to the lack of air density. As a result, their power outputs fall noticeably compared to identical cars that operate at or near sea level. For this reason, just about every dynamometer applies a hefty altitude correction in the magnitude of 20% (SAE correction, in this case). This means that a car that put down an actual 100 wheel hp is "corrected" up to 120 wheel hp. While this correction amount is reasonably accurate in some cases, it is notoriously optimistic in the case of turbocharged engines. In such engines, power output rarely falls as dramatically in response to air density reduction. This is due to their turbo control systems that combat air density reductions by allowing for higher boost pressures. These increased boost pressures can almost completely offset the ambient pressure reduction and make the "altitude correction" almost completely unnecessary. However, I have yet to see a high-altitude tuner come forth and not apply the positive correction factor when displaying their grossly optimistic dyno results.
credit Shiv Patek.
http://www.modularfords.com/forums/s...ad.php?t=54099
Introduction
Most everyone is familiar with the usual SAE (or STD) dyno correction factor, which are used to scale the measured power and torque to what would be measured at some reference set of ambient (weather) conditions. (For SAE J1349, these are: absolute ambient air pressure of Pref = 990 mb, ambient temp of Tf = 77 °F, and RH = 0%.) These correction factors were developed for naturally-aspired engines wherein the intake manifold pressure goes in direct proportion to the ambient pressure. (See link to the derivation given above.) Therefore, the scaling factor (αp) for indicated power with pressure has the inverse relationship and goes simply as
αp = Pref/Pdry
where Pdry is the dry-air partial pressure at the time of the measurement and Pref is the reference air pressure. Since it can be shown that the boost pressure (and hence the total intake manifold pressure) for an engine with a P-D supercharger is also directly proportional to ambient pressure, these correction factors still apply for these cases as well, at least to first order. (It will not correct for changes in the parasitic drive power of the SC as air density goes up and down, for example.)
For a turbocharged engine, however, this is not the case. Since these setups typically employ boost controllers that are designed to keep boost pressure constant, the total intake manifold pressure is less affected by changes in ambient pressure. (It is still affected since the intake manifold pressure is the sum of ambient plus boost pressure, but to a lesser amount.) As a result, turbocharged engines don’t gain or lose much power as the atmospheric pressure changes up or down. Therefore, the standard SAE J1349 type correction factors are wholly inappropriate for turbocharged applications. Below is a description of how pressure would scale for a typical turbocharged engine with boost controls to keep boost constant.
Turbo correction factor
Skipping all the math, (if someone really wants to see it let me know), for a turbocharged engine with a constant boost pressure, (after the turbos are fully spooled), it can be shown that the indicated power and torque would scale with pressure as
αp = (Pref + Pb)/[Pdry(1 + Pb/Patm)]
where Pref is the reference dry-air absolute pressure (29.235 in-Hg for SAE), Pb is the boost pressure also in in-Hg (= 2.036*PSI), Pdry is the absolute dry-air partial pressure at the time of the measurement, and Patm is the total absolute air pressure at the time of the measurement. To get the brake power scaling, clearly the mechanical efficiency needs to be factored in here as well. (See that other thread).
Below is a table showing how the two correction factors might differ for a turbocharged engine measured at a mile high with everything else at SAE J1349 conditions; Pref = 29.235 in-Hg, RH=0%, etc. There are other assumptions that I'll not get into here. Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures. It should also be pointed out that the difference between the two will change as the other conditions change. For example, as the absolute ambient pressure approaches the reference pressure, the difference is reduced.
For the above conditions, the SAE J1349 correction factor is: CFsae = 1.254
First column = boost pressure in psi
Second column = boost pressin in in-Hg
Third column = dyno CF appropriate for a turbocharged engine (CFturbo)
The 4th column shows how much the SAE J1349 CF overcorrects the results (relatively speaking), i.e., 100%(CFsae/CFturbo - 1)
Code:
Pb Pb
(psi) (in-Hg) CFturbo sae/trbo-1
5.0 10.18 1.178 6.40%
7.5 15.27 1.155 8.53%
10.0 20.36 1.137 10.22%
12.5 25.45 1.123 11.61%
15.0 30.54 1.112 12.76%
17.5 35.63 1.102 13.74%
20.0 40.72 1.094 14.57%
22.5 45.81 1.087 15.30%
25.0 50.9 1.081 15.93%
27.5 55.99 1.076 16.49%
30.0 61.08 1.072 16.98%
howard coleman
Had to dig this one up....BRILLIANT post Howard. I cringe everytime someone posts SAE #s on a turbocharged car at 6000+ft of density altitude. Having just moved to ABQ, I laughed at all the ooh and aahs when my stock 996TT layed down 450awhp (SAE of course) and then went on to trap 114mph. Thanks to you and Steve for caveating this.
Thread
Thread Starter
Forum
Replies
Last Post
