Dyno Runs / Correction Factors
10-28-2009, 07:18 PM
#16
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Interesting stuff. I just got back from the track Friday here in Houston. I was trapping 107 with a t50 from turbonetics set at 16 psi, fpr at 3 bar, wastegate, 3" no cat exhaust. Stock injectors and AFM.
First gear I pretty much rolled out as I didn't want to break into 13's since I didn't have a helmet with me (yep 14's at over 107 heh)
The thing is though, once I hit second gear I would spin madly and not get traction until third gear since I have no LSD.
I was wondering, if I had gained traction in second, would I have trapped higher or lower.
Also, it seems to me that at 14-15 psi you would make a bit more than 250 whp. I know the altitude effects that, but I wasn't aware that it'd be that much.
First gear I pretty much rolled out as I didn't want to break into 13's since I didn't have a helmet with me (yep 14's at over 107 heh)
The thing is though, once I hit second gear I would spin madly and not get traction until third gear since I have no LSD.
I was wondering, if I had gained traction in second, would I have trapped higher or lower.
Also, it seems to me that at 14-15 psi you would make a bit more than 250 whp. I know the altitude effects that, but I wasn't aware that it'd be that much.
10-28-2009, 07:33 PM
#17
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Where i really noticed the difference at low latitude (when i lived in Houston with the car) was the off-boost performance. Much better off-boost at low altitude.
-Dana
-Dana
10-28-2009, 07:45 PM
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Shoot, not mine. It's a complete dog until around almost 4000 rpm. I have a bad exhaust leak at the y pipe and I'm pretty sure it's running too rich at lower rpms.
10-28-2009, 07:49 PM
#19
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Interesting stuff. I just got back from the track Friday here in Houston. I was trapping 107 with a t50 from turbonetics set at 16 psi, fpr at 3 bar, wastegate, 3" no cat exhaust. Stock injectors and AFM.
First gear I pretty much rolled out as I didn't want to break into 13's since I didn't have a helmet with me (yep 14's at over 107 heh)
The thing is though, once I hit second gear I would spin madly and not get traction until third gear since I have no LSD.
I was wondering, if I had gained traction in second, would I have trapped higher or lower.
Also, it seems to me that at 14-15 psi you would make a bit more than 250 whp. I know the altitude effects that, but I wasn't aware that it'd be that much.
First gear I pretty much rolled out as I didn't want to break into 13's since I didn't have a helmet with me (yep 14's at over 107 heh)
The thing is though, once I hit second gear I would spin madly and not get traction until third gear since I have no LSD.
I was wondering, if I had gained traction in second, would I have trapped higher or lower.
Also, it seems to me that at 14-15 psi you would make a bit more than 250 whp. I know the altitude effects that, but I wasn't aware that it'd be that much.
probably would be a little higher trap. Not much though. And I have you beat with 14's at 115
10-28-2009, 08:39 PM
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Sid.. this is where we completely dis-agree.. And I hate that.
I don't care what your altitude is.. If you're boosting 15psi. You're seeing the EXACT same amount of air in the cylinders as you are at sea level.. The difference you would correct for is the pressure differential that the turbo has to make up for. So if your turbo is 80%efficient at 15psi. but has to "Push" about 18psi to get 15 at the manifold.. The turbo is going to be Less efficient and use more exhaust pressure etc to make up the difference.. SOOOOO many ifs... if the turbo is close it it's efficiency at 15, and has to go to 18.. I can guess at a 5% loss. This STILL not being equal to a 5%adjustment. too much to explain, and Im sure this is not making any sense to anyone becuase Im actually too lazy to explain all the hooptyjew, but in the end.. If you're boosting and you're putting a correction factor above 6% just for altitude, you're blowin smoke up your own skirt. EDIT.. Ha! dana said all that already.. lol - I always rant on on this subject.. apologies.. Dana covered this in first post and kinda admitted to "feeling" the 255whp.
And since we're guestimating, 107mph is around 280-290@the wheels full weight.
I don't care what your altitude is.. If you're boosting 15psi. You're seeing the EXACT same amount of air in the cylinders as you are at sea level.. The difference you would correct for is the pressure differential that the turbo has to make up for. So if your turbo is 80%efficient at 15psi. but has to "Push" about 18psi to get 15 at the manifold.. The turbo is going to be Less efficient and use more exhaust pressure etc to make up the difference.. SOOOOO many ifs... if the turbo is close it it's efficiency at 15, and has to go to 18.. I can guess at a 5% loss. This STILL not being equal to a 5%adjustment. too much to explain, and Im sure this is not making any sense to anyone becuase Im actually too lazy to explain all the hooptyjew, but in the end.. If you're boosting and you're putting a correction factor above 6% just for altitude, you're blowin smoke up your own skirt. EDIT.. Ha! dana said all that already.. lol - I always rant on on this subject.. apologies.. Dana covered this in first post and kinda admitted to "feeling" the 255whp.
And since we're guestimating, 107mph is around 280-290@the wheels full weight.
Last edited by 95ONE; 10-28-2009 at 08:58 PM.
10-28-2009, 09:09 PM
#21
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Sid.. this is where we completely dis-agree.. And I hate that.
I don't care what your altitude is.. If you're boosting 15psi. You're seeing the EXACT same amount of air in the cylinders as you are at sea level.. The difference you would correct for is the pressure differential that the turbo has to make up for. So if your turbo is 80%efficient at 15psi. but has to "Push" about 18psi to get 15 at the manifold.. The turbo is going to be Less efficient and use more exhaust pressure etc to make up the difference.. SOOOOO many ifs... if the turbo is close it it's efficiency at 15, and has to go to 18.. I can guess at a 5% loss. This STILL not being equal to a 5%adjustment. too much to explain, and Im sure this is not making any sense to anyone becuase Im actually too lazy to explain all the hooptyjew, but in the end.. If you're boosting and you're putting a correction factor above 6% just for altitude, you're blowin smoke up your own skirt. I always rant on on this subject.. apologies.. Dana covered this in first post and kinda admitted to "feeling" the 255whp.
And since we're guestimating, 107mph is around 280-290@the wheels full weight.
I don't care what your altitude is.. If you're boosting 15psi. You're seeing the EXACT same amount of air in the cylinders as you are at sea level.. The difference you would correct for is the pressure differential that the turbo has to make up for. So if your turbo is 80%efficient at 15psi. but has to "Push" about 18psi to get 15 at the manifold.. The turbo is going to be Less efficient and use more exhaust pressure etc to make up the difference.. SOOOOO many ifs... if the turbo is close it it's efficiency at 15, and has to go to 18.. I can guess at a 5% loss. This STILL not being equal to a 5%adjustment. too much to explain, and Im sure this is not making any sense to anyone becuase Im actually too lazy to explain all the hooptyjew, but in the end.. If you're boosting and you're putting a correction factor above 6% just for altitude, you're blowin smoke up your own skirt. I always rant on on this subject.. apologies.. Dana covered this in first post and kinda admitted to "feeling" the 255whp.
And since we're guestimating, 107mph is around 280-290@the wheels full weight.
The mbc only opens the wastegate at your setting of 15 psi or 29.7 psi absolute pressure, no matter what altitude you're at.
There's no way for the system to know the atmospheric pressure in our cars, so it will always try to build whatever you have it set to and doesn't take it into account. So 29.7 psi absolute is what your manifold should always see if your boost gauge is reading 15 psi.
After the turbo it doesn't matter at all what altitude you're at. All that matters from that point is the amount of air in the intake tract (a fixed volume obviously), the pressure (29.7 psi @ 15 psi indicated), and temperature (here's where the difference comes in since your turbo will possibly be further out of it's efficiency range.)
I believe this is using the ideal gas law where pressure, volume, and temperature are all functions of one another.
10-28-2009, 09:47 PM
#23
10-28-2009, 09:59 PM
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10-28-2009, 10:33 PM
#25
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The mbc only opens the wastegate at your setting of 15 psi or 29.7 psi absolute pressure, no matter what altitude you're at.
There's no way for the system to know the atmospheric pressure in our cars, so it will always try to build whatever you have it set to and doesn't take it into account. So 29.7 psi absolute is what your manifold should always see if your boost gauge is reading 15 psi.
There's no way for the system to know the atmospheric pressure in our cars, so it will always try to build whatever you have it set to and doesn't take it into account. So 29.7 psi absolute is what your manifold should always see if your boost gauge is reading 15 psi.
So my manual boost controller is set to basically 16psi (that's what my boost gauge shows) minus the difference in atmpsheric pressure between high altitude and low (so about 3psi) and then minus whatever error the gauge has (its not a calibrated gauge). Assuming zero error, I am only boosting to 13psi.
At one point I actually just cranked up boost to 19psi to compensate. Just not sure if the fuel map could handle this so I backed off.
Also, something that is a limit at high altitude is that in the infinite cheapness of gas companies, since we have less compression, they sell us nice fuel. Fuel is generally 85, 87 and 91 Octane. So two points lower limits boost even if we can crank it up and compensate.
-Dana
10-28-2009, 11:01 PM
#26
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Bruce,
I don't think we are dis-agreeing. I am fully in tune with you regarding 15psi at 0 ft elevation is 15 psi at 5800ft regarding how much air is being made into HP. The difference IMO is the amount of energy required to get to 15 psi (turbo efficiency,or out of) and the lag that comes with the lack of air before boost.
Please re-read my first post in this thread and I think you will see we agree. I don't think that a correction factor of 1.23 means **** actually. I am just using what (dyno) the local guys have been using for comparison. The only HP figure I will use from this point forward is the track MPH and yes it is ~ 315 hp at 107 if your car has the benefit of the off boost response that you have at sea level. However, we do not have that here at all, actually the lag is very pronounced as you are compressing thinner air which obviously takes more energy ie: long spool /transient time. There is something to be said about inertia or lack therof.
Regardless... just so we are on the same page..and please feel free to point out where we may dis agree. When I went 107, IMO it was making ~ 300+hp at the end of the track (upper rpms). The turbo just could not keep up. If you looked at my first dyno graph you'll notice the nose dive in HP and tq .
Then, when I went high 116 it was keeping up but had clutch issues. This would translate to ~ 400 rwhp. Now the dyno showed higher, but I have never claimed anything more than just over 400rwhp. Again though, this particular run had a really crappy 1/8 mile mph soo..IMO it would have went somewhat faster if the clutch wasn't being such a POS.
I don't know where we are dis agreeing??
Now when someone throws out a 1.26 correction factor at sea level hmmm... That's something to really wonder about IMO.
and FYI the only reason I will continue to go to the same dyno is to use the comparison. The numbers mean nothing really.
I will know exactly what it is this next year b/c I will make a point of getting up there. This year just slipped away way to fast
I don't think we are dis-agreeing. I am fully in tune with you regarding 15psi at 0 ft elevation is 15 psi at 5800ft regarding how much air is being made into HP. The difference IMO is the amount of energy required to get to 15 psi (turbo efficiency,or out of) and the lag that comes with the lack of air before boost.
Please re-read my first post in this thread and I think you will see we agree. I don't think that a correction factor of 1.23 means **** actually. I am just using what (dyno) the local guys have been using for comparison. The only HP figure I will use from this point forward is the track MPH and yes it is ~ 315 hp at 107 if your car has the benefit of the off boost response that you have at sea level. However, we do not have that here at all, actually the lag is very pronounced as you are compressing thinner air which obviously takes more energy ie: long spool /transient time. There is something to be said about inertia or lack therof.
Regardless... just so we are on the same page..and please feel free to point out where we may dis agree. When I went 107, IMO it was making ~ 300+hp at the end of the track (upper rpms). The turbo just could not keep up. If you looked at my first dyno graph you'll notice the nose dive in HP and tq .
Then, when I went high 116 it was keeping up but had clutch issues. This would translate to ~ 400 rwhp. Now the dyno showed higher, but I have never claimed anything more than just over 400rwhp. Again though, this particular run had a really crappy 1/8 mile mph soo..IMO it would have went somewhat faster if the clutch wasn't being such a POS.
I don't know where we are dis agreeing??
Now when someone throws out a 1.26 correction factor at sea level hmmm... That's something to really wonder about IMO.
and FYI the only reason I will continue to go to the same dyno is to use the comparison. The numbers mean nothing really.
I will know exactly what it is this next year b/c I will make a point of getting up there. This year just slipped away way to fast
10-28-2009, 11:03 PM
#27
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isn't the wastegate a differential diaphram?
so the amb P is lower, the wastegate opens at lower manifold P
???
and isn't our boost gauge differential also?
if not wouldn't it read to 2 bar (atm + boost)
if I park my car in the mountains it appears that the gauge reads slightly less than 0 (needle widths maybe), and it reads exactly 0 at my house, 1100 feet lower...0= atm P
so the amb P is lower, the wastegate opens at lower manifold P
???
and isn't our boost gauge differential also?
if not wouldn't it read to 2 bar (atm + boost)
if I park my car in the mountains it appears that the gauge reads slightly less than 0 (needle widths maybe), and it reads exactly 0 at my house, 1100 feet lower...0= atm P
10-28-2009, 11:20 PM
#28
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Turbo correction factor
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)]
Pref = reference dry-air absolute pressure (29.235 in-Hg for SAE)
Pb = boost pressure also in in-Hg (= 2.036*PSI)
Pdry = absolute dry-air partial pressure at the time of the measurement
Patm = total absolute air pressure at the time of the measurement.
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%, T=77F
Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures.
For the above conditions, the standard 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)
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%
so at 15 psi boost the cf is ~11% (0% RH, std atm P and 77F)
adjusting for temp, humid and atm P 8 to 10% is a good guesstimate...
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)]
Pref = reference dry-air absolute pressure (29.235 in-Hg for SAE)
Pb = boost pressure also in in-Hg (= 2.036*PSI)
Pdry = absolute dry-air partial pressure at the time of the measurement
Patm = total absolute air pressure at the time of the measurement.
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%, T=77F
Note how the “typical” correction factor overestimates the results and gets increasingly worse at higher boost pressures.
For the above conditions, the standard 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)
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%
so at 15 psi boost the cf is ~11% (0% RH, std atm P and 77F)
adjusting for temp, humid and atm P 8 to 10% is a good guesstimate...
10-28-2009, 11:34 PM
#29
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Just one other thing to throw out here since Arthur is doing some math... :-). Weather stations at the track up here are regularly registering 8-10,000 of air. The track is actually in the foothills
So when looking at the trap speeds up here compared to dyno correction factors this should be considered IMO.
It has always been that I have had to lean the cars down from where I live to the track which is only a 1/2 hr away.
So when looking at the trap speeds up here compared to dyno correction factors this should be considered IMO.
It has always been that I have had to lean the cars down from where I live to the track which is only a 1/2 hr away.
10-28-2009, 11:39 PM
#30
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Your post was quite good. Where did you find that formula? SAE probably has it already figured out.
Using you numbers my "corrected" HP would be about 280-290hp. That is pretty close to where a K27/6 should be in poor tune. I think Tony G made 330ish RWHP with a K27/6.
-Dana
Using you numbers my "corrected" HP would be about 280-290hp. That is pretty close to where a K27/6 should be in poor tune. I think Tony G made 330ish RWHP with a K27/6.
-Dana