1/4 Mile Run at Bandimere (Colorado)
08-19-2011, 02:37 PM
#32
Three Wheelin'
Density altitude is a comparison of how dense the air is on a particular day and elevation compared to a standard day. The factors are altitude, temperature and, to a lesser degree, humidity. So, in this case the track is at ~5,800 feet of elevation but the temperature was mid-90's (I think) and presumably the humidity was fairly high, at least for Denver. Crunch all those numbers together and you end up with air density that is equivalent to the air density at 9,000 feet of elevation on a standard day.
All that mumbo jumbo just means that there was less air for Joshua's and Sid's turbos to fiendishly ingest air, which means slower spool up and the turbo having to spin faster to produce full boost (and potentially be outside the optimal range on the turbo's boost curve.) For us it means slower cars, for pilots it can mean the difference between getting off the ground and not!
Here's how it's calculated: (Cut & paste from Wikipedia)
Density altitude can be calculated from atmospheric pressure and temperature (assuming dry air).
where
DA = density altitude in feet
P = atmospheric (static) pressure
PSL = standard sea level atmospheric pressure (1013.25 hPa ISA or 29.92126 US))
T = true (static) air temperature in kelvins (K) [add 273.15 to the Celsius (°C)] figure
TSL = ISA standard sea level air temperature in kelvins (K) (288.15 K)
b = 0.234969
All that mumbo jumbo just means that there was less air for Joshua's and Sid's turbos to fiendishly ingest air, which means slower spool up and the turbo having to spin faster to produce full boost (and potentially be outside the optimal range on the turbo's boost curve.) For us it means slower cars, for pilots it can mean the difference between getting off the ground and not!
Here's how it's calculated: (Cut & paste from Wikipedia)
Density altitude can be calculated from atmospheric pressure and temperature (assuming dry air).
where
DA = density altitude in feet
P = atmospheric (static) pressure
PSL = standard sea level atmospheric pressure (1013.25 hPa ISA or 29.92126 US))
T = true (static) air temperature in kelvins (K) [add 273.15 to the Celsius (°C)] figure
TSL = ISA standard sea level air temperature in kelvins (K) (288.15 K)
b = 0.234969
But along these lines I'm at 4300 ft (Carson City NV) with my MBC sit to 17 here I drove down to San Jose Ca sea level and forgot to reset the MBC. I blew off the TB to inter cooler hose on my virgin drive, had to jury rig it back on and limped to San Jose. Got it fixed the next morning. Jumped on the freeway and let her rip, it was now at 21lbs on pump gas! Car did not seem to care but my friend screamed and turned the boost down! It was fast at that boost!
Point being if your driving from altitude to sea level and you don't have an EBC,you need to keep an eye on your boost levels!
08-19-2011, 03:40 PM
#33
Race Car
Talking to a few of the turbo guys who have traveled around it sounds like it is about a 5-7tenth difference depending on the car. Im pretty sure our cars are at a pretty big disadvantage considering where the turbo is located.
I have watched other 951's have trouble breaking into the 14's up here, even at higher than stock boost levels.
Personally, I'm pretty happy as this is the first time I have taken one of these cars up and stayed in the same second et. Usually I have ran as much as 3 seconds difference.
A couple notes regarding air. I logged all of my runs and to give an idea of the difference that high elevation makes; I tried earlier to run 25 psi (what I usually run) and the MAF only registered 4.18v, down here it registers 4.5 most any time. The difference is about 80-90 hp iirc.
Also, if you take a look at some other recent runs people have done, their mph is higher than mine or Josh's at lower boost than what we were both running up here.
So IMO, from experience and looking at the evidence, it does make a bit of difference, even with a turbocharger.
Doesnt reallyatter though bc I couldn't use any more power at the drag strip in the cats current state.
I have watched other 951's have trouble breaking into the 14's up here, even at higher than stock boost levels.
Personally, I'm pretty happy as this is the first time I have taken one of these cars up and stayed in the same second et. Usually I have ran as much as 3 seconds difference.
A couple notes regarding air. I logged all of my runs and to give an idea of the difference that high elevation makes; I tried earlier to run 25 psi (what I usually run) and the MAF only registered 4.18v, down here it registers 4.5 most any time. The difference is about 80-90 hp iirc.
Also, if you take a look at some other recent runs people have done, their mph is higher than mine or Josh's at lower boost than what we were both running up here.
So IMO, from experience and looking at the evidence, it does make a bit of difference, even with a turbocharger.
Doesnt reallyatter though bc I couldn't use any more power at the drag strip in the cats current state.
08-19-2011, 04:18 PM
#34
Race Director
Sid and myself decided to go for some runs at Bandimere here in Denver. We lined up this run, and IIRC it was the best run for both of us.
Both cars are on E85. Sid's car is using a GT30r sized turbo, at 16psi, and C-Tune (clutch-limited, starting to slip). My car is using a K27/8, 20psi, and M-Tune.
The popping/backfire is due to the 2-step, which holds RPM at ~4000 to help build boost at the line, and allows flat-foot-shifting.
Finally, I attached a screen-shot of the weather data right after our runs. The effective altitude was 9000ft! Typically vehicles run at least a full second slower here then they do at sea-level. For reference, stockish LS1/LS6 Camaros/Corvettes tend to run mid 14seconds.
And yes, Sid got a hole-shot on me
Both cars are on E85. Sid's car is using a GT30r sized turbo, at 16psi, and C-Tune (clutch-limited, starting to slip). My car is using a K27/8, 20psi, and M-Tune.
The popping/backfire is due to the 2-step, which holds RPM at ~4000 to help build boost at the line, and allows flat-foot-shifting.
Finally, I attached a screen-shot of the weather data right after our runs. The effective altitude was 9000ft! Typically vehicles run at least a full second slower here then they do at sea-level. For reference, stockish LS1/LS6 Camaros/Corvettes tend to run mid 14seconds.
And yes, Sid got a hole-shot on me
08-19-2011, 04:18 PM
#35
Three Wheelin'
The turbo cars can kinda compensate for the altitude though correct? But the NA cars are just screwed? What if you had a NA nitrous car 100 hp shot at sea level what happens at altitude in that case?
08-19-2011, 04:43 PM
#36
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Very cool - and damn impressive. Low 13s @110 at altitude on a 26/8 with only a 2.2 60'? Put some stickier tires back there and get yourself down into the 2.0 60' range and there's your 12.9.
You may have posted this before Josh, but what's all done to your car aside from the turbo @ 20psi and the M-Tune?
You may have posted this before Josh, but what's all done to your car aside from the turbo @ 20psi and the M-Tune?
K27/8
M-Tune w/ 80# injectors @ 3bar FP
3" Exhaust (stock downpipe)
50mm HKS wastegate
Modded factory Intercooler
EBC
HV Fuel pump
I do have the 968 transmission, so the gears are a little shorter (I was a good way into 4th gear by the traps). I just filled the trans mount with urethane.
I had a 2.1 60' earlier, but on the run against Sid, I came out at ~10psi of boost - a bit too much I guess. Tires are fairly sticky: 275 Toyo Proxe 4s.
I've got an HY35 turbo here looking at me (GT30r equivalent), so soon as I get it in, I will be hunting for 12s
08-19-2011, 04:47 PM
#37
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Lol - yep 
I launched at ~10psi of boost... guess it was a bit too much
Turbo cars do help compensate for altitude, but not totally - especially if you are running it at the limits. At 9000' there is over 4psi less air pressure. So that means your turbo has to make 4psi more pressure to achieve the same absolute pressure. For smaller turbos, they simply can't make up the extra pressure, and larger turbos have to work a lot harder to do it, lowering engine VE and thus HP.
I launched at ~10psi of boost... guess it was a bit too much
Turbo cars do help compensate for altitude, but not totally - especially if you are running it at the limits. At 9000' there is over 4psi less air pressure. So that means your turbo has to make 4psi more pressure to achieve the same absolute pressure. For smaller turbos, they simply can't make up the extra pressure, and larger turbos have to work a lot harder to do it, lowering engine VE and thus HP.
08-19-2011, 05:13 PM
#38
Three Wheelin'
9000 ft! Man I'm at 4300 and I thought that was high! I remember driving up here in my little toy truck 22r with carb! Now that was screwed! Then I made the trip in my Merkur XR4TI (back in the day) now that was fun! Pre internet forums and wide band and MBC stuff so I don't know what it was boosting? Less I know but still better than a carb car!
08-19-2011, 05:39 PM
#39
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9000 ft! Man I'm at 4300 and I thought that was high! I remember driving up here in my little toy truck 22r with carb! Now that was screwed! Then I made the trip in my Merkur XR4TI (back in the day) now that was fun! Pre internet forums and wide band and MBC stuff so I don't know what it was boosting? Less I know but still better than a carb car!
08-19-2011, 05:42 PM
#40
Three Wheelin'
Yep, kids today have no clue! But what about NA car and nitrous at the strip at altitude? Anybody?
08-19-2011, 06:01 PM
#41
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08-19-2011, 06:35 PM
#45
Race Car
With nitrous it is not as bad. Ultimately, the strength of components is more of a factor. Nitrous is not as efficient so more needs to be used to get the same power as you would at lower elevations. This brings the engine that much closer to destruction.
For example; take a 2.5 Na and run it up here it will probably run an 18 second quarter. Now add a 50 shot and you may break 16's. At sea level, the same car would run 17's and a 50shot would put it in the high 15's most likely. Now take the same car and add a 200 shot up here and most likely you'd be lucky to run 15's and would probably blow it up. At sea level you could up the nitrous slightly 100 shot and most likely run 14's or there abouts. 200 hp would probably still kill it. The point is, you would just need too much to make it work up here and would blow it up.
When I raced my nova up here I had to run quite a bit more and it was always on the edge. It ran mid to high 8's up here, I ran much less in phoenix and it ran mid to low 8's with ease. NA, was even better, due to the cars build. It ran low to mid tens up here and low 9's with ease in az.
For example; take a 2.5 Na and run it up here it will probably run an 18 second quarter. Now add a 50 shot and you may break 16's. At sea level, the same car would run 17's and a 50shot would put it in the high 15's most likely. Now take the same car and add a 200 shot up here and most likely you'd be lucky to run 15's and would probably blow it up. At sea level you could up the nitrous slightly 100 shot and most likely run 14's or there abouts. 200 hp would probably still kill it. The point is, you would just need too much to make it work up here and would blow it up.
When I raced my nova up here I had to run quite a bit more and it was always on the edge. It ran mid to high 8's up here, I ran much less in phoenix and it ran mid to low 8's with ease. NA, was even better, due to the cars build. It ran low to mid tens up here and low 9's with ease in az.