2004 stock turbo, E85, road dyno at 5500'
Sep 8, 2010, 07:40 PM
#16
No. That's bogus. 29.50 is a made up number. 24.01 is the actual atmospheric pressure. There's no point is using a "corrected" baro reading to do a "correction".
Really, the un-corrected value is the only one that matters. That's why I posted it first. The only reason I presented a corrected one is because most dynojet plots you see up there (or in colorado, or utah, or whataver-mountain-country) are corrected. As per my first post the corrected one is very close to what an actual dynojet read on my car a few months ago. The very fact that is it "corrected" means that it is only a multiple of power delivered.
To me, it doesn't matter one way or the other. I brag about lap times, not dyno sheets
cheers
d
Really, the un-corrected value is the only one that matters. That's why I posted it first. The only reason I presented a corrected one is because most dynojet plots you see up there (or in colorado, or utah, or whataver-mountain-country) are corrected. As per my first post the corrected one is very close to what an actual dynojet read on my car a few months ago. The very fact that is it "corrected" means that it is only a multiple of power delivered.
To me, it doesn't matter one way or the other. I brag about lap times, not dyno sheets
cheers
d
Next, dont worry about what they post. All the high elevation people that use & post charts with ridiculous CFs are using the CF incorrectly, per the SAE standards on the CF.
Or you can just both (corrected & UNcorrected) again like you originally did
And yeah, lap times have better bragging rights.
Dec 2, 2010, 08:06 AM
#17
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Jay if you look at the logged baro in all of the logs I sent you and convert kPa to inHg, you'll see that the baro really is 24.xx at this altitude. Almost every weather station here corrects actual barometer readings to sea level, that way people have a reference to relative humidity, and not absolute humidity.
Here's the thing about correction factors though...the data and multiplier is calculated based on a NA motor. Turbo's, by their very nature, normalize for altitude since they are mass flow. The turbo doesn't care that local atmospheric pressure is 12.0psi, it's still going to push 35.0psia into the motor when you request 23psig (35.0psia - 12.0psia = 23.0psig).
So the turbo normalized for altitude, so no correction right? Well not so fast, since the ambient pressure is lower, and therefore, mass flow under vacuum is less, it takes more flow to spool the turbo. Also, since the turbo must achieve higher turbine shaft speeds to reach the same boost pressure as it would at sea level, the efficiency chart is shifted, meaning that for the same boost level as sea level, the turbo is working harder and therefore adding more heat.
So here's the thing, the uncorrected dyno is wrong. And the corrected dyno is not right. If you were to take our high altitude cars to sea level and re-dyno, you would see that the torque curve is shifted to the left since the turbo spools sooner. And you would also see a slight increase in torque across the rev range as the turbo is pumping more efficiently and not creating as much heat.
Does this matter from a tuning standpoint? Not really, as long as you understand that the turbo is working harder and creating more heat to get to the same (psig) boost level as one would at sea level and that it will take more WGDC and rpms to achieve the same boost, the rest is about the same. I'll leave out the discussion on fuel octane, and how the lower octane is fine for NA cars at altitude, but hinders forced induction cars.
But as far as tuning, the only thing that matters is the Delta hp/tq. So long as you use either uncorrected or corrected for both before and after, your gains will still be quantified.
As far as references go, I do pump sizing and flow calculations for very high volumetric pumps all over the rockies at different elevations. Think V-16 quad turbo cummins making 2000hp and burning 90gals of diesel per hour, pumping for days on end. Engineering mistakes not accounting for altitude can have huge time and cost impacts on projects of the scale I deal with.
Here's the thing about correction factors though...the data and multiplier is calculated based on a NA motor. Turbo's, by their very nature, normalize for altitude since they are mass flow. The turbo doesn't care that local atmospheric pressure is 12.0psi, it's still going to push 35.0psia into the motor when you request 23psig (35.0psia - 12.0psia = 23.0psig).
So the turbo normalized for altitude, so no correction right? Well not so fast, since the ambient pressure is lower, and therefore, mass flow under vacuum is less, it takes more flow to spool the turbo. Also, since the turbo must achieve higher turbine shaft speeds to reach the same boost pressure as it would at sea level, the efficiency chart is shifted, meaning that for the same boost level as sea level, the turbo is working harder and therefore adding more heat.
So here's the thing, the uncorrected dyno is wrong. And the corrected dyno is not right. If you were to take our high altitude cars to sea level and re-dyno, you would see that the torque curve is shifted to the left since the turbo spools sooner. And you would also see a slight increase in torque across the rev range as the turbo is pumping more efficiently and not creating as much heat.
Does this matter from a tuning standpoint? Not really, as long as you understand that the turbo is working harder and creating more heat to get to the same (psig) boost level as one would at sea level and that it will take more WGDC and rpms to achieve the same boost, the rest is about the same. I'll leave out the discussion on fuel octane, and how the lower octane is fine for NA cars at altitude, but hinders forced induction cars.
But as far as tuning, the only thing that matters is the Delta hp/tq. So long as you use either uncorrected or corrected for both before and after, your gains will still be quantified.
As far as references go, I do pump sizing and flow calculations for very high volumetric pumps all over the rockies at different elevations. Think V-16 quad turbo cummins making 2000hp and burning 90gals of diesel per hour, pumping for days on end. Engineering mistakes not accounting for altitude can have huge time and cost impacts on projects of the scale I deal with.
Dec 2, 2010, 08:42 AM
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Oh, and Chuck, we need to get together the next time you're in Farmington for the Solo events here. I've lived here 2.5 years and not made it to a single one as I've been working out of town for every single weekend they come here. I'd love to get my car out on the course at Sunray, as it looks pretty fast.
For reference, here's my car on VD in Farmington, 91pump, uncorrected and corrected, respectively. Baro and temp for correction are logged values for the pull. Car is basic bolt-ons running a TME turbo with 10.5 hotside. Jay did the tuning, as I'm never home enough to remember where I left off. Altitude of the road I was using is 5600'.
Over the winter I'm going to start amassing parts to hang in the spring. On my list of to do is:
-Degree S2 cams, then play with cam timing
-FIC 1100 high Z injectors
-HKS turbo
-FID/Toxicfab manifold, haven't decided which yet
-E85 (I'll probably have to make a run to ABQ and 55 gal drum it)
And probably by then my stock clutch will give up the ghost, and while I'm at it I'll probably have Jack's rebuild the tranny.
For reference, here's my car on VD in Farmington, 91pump, uncorrected and corrected, respectively. Baro and temp for correction are logged values for the pull. Car is basic bolt-ons running a TME turbo with 10.5 hotside. Jay did the tuning, as I'm never home enough to remember where I left off. Altitude of the road I was using is 5600'.
Over the winter I'm going to start amassing parts to hang in the spring. On my list of to do is:
-Degree S2 cams, then play with cam timing
-FIC 1100 high Z injectors
-HKS turbo
-FID/Toxicfab manifold, haven't decided which yet
-E85 (I'll probably have to make a run to ABQ and 55 gal drum it)
And probably by then my stock clutch will give up the ghost, and while I'm at it I'll probably have Jack's rebuild the tranny.
Last edited by dude; Dec 2, 2010 at 09:03 AM. Reason: linked img files to post.
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