Altitude Correction factors

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kjhansen

Member
Joined
May 26, 2001
I got the altitude correction factors from the GNTTYPE board and ran my numbers through them. Per the G-Tech Pro, which has been pretty accurate for me in the past, I ran a 12.68 as 111.3 mph here in Colorado Springs at 6100 feet, more or less. According to these numbers my corrected ET and MPH are 11.71 and 120.37mph. This seems pretty damn fast for my mods. The table only goes to 5500 feet, so I figured out how much to add and subtract to the ET Factor and MPH Factor to carry it out to 6100 feet (-.0013 and +.0014 respectively). Anybody know how accurate this table is, especially above 5500 feet?
Thanks,
Keith

Mods:
Engine: 144k miles, stock with new valve springs at 125k miles
Exhaust: Custom single-shot, 3" THDP, test pipe with dump, electric cut-out (open for run)
Fuel: Walbro FP with hotwire, Mark Martone FPR, FP gauge, 100 octane homebrew, homemade alcohol injection system with .026 jet at 90psi
Air: K&N behind headlight, big neck intercooler, Cheetah Stage III turbo, 22psi
Cooling system: Aluminum radiator, coolant lines to throttle body blocked, hi speed fan switch
Trans: J&M performance trans, modified D5 torque convertor by Century Performance, StageRight Transbrake, aftermarket transcooler, TCC lock-up switch
Suspension: Coil spring air bags (7r, 5l for street), 4" pinion snubber, boxed lower control arms
Tires: Nitto 275-50-15 DR's
 
I'm a little leery of those correction factors myself. For some comparason, a club member ran an 11.40 at Bandimere (5800ft) and an 11.20 at Pueblo (4800ft). I heard he ran a 10.6 - 10.7 at Bowling green before breaking his motor.
 
Ah... The altitude at BG is pretty much sea-level-480 feet. Did he make any changes to the car between Colorado and BG? The numbers he should have run were pretty close to what he did run according to the correction chart. It puts him in the high 10.5 range, so that's pretty close depending on his 60 foot times. What was his mph?
Keith
my times below were in San Antonio (700 feet) and before the THDP and RJC power plate...
 
Yep, those are the same numbers as on the GNTType web site. I had to extrapolate the numbers for 6100 feet since these only go to 5500.
Keith
 
I don't think people really realize what a difference altitude makes. My best timeslip for my stock Typhoon (custom chip and C16) is 13.2 from the local track (~2400'). Converted to sea level its 12.7. So in fairness do I have a 12 second ride or a 13 second ride? Personally I think everyone should correct their ETs to sea level so we are all on the same page so to speak. But that's just me, and people seem hung up on timeslips.
 
altitude correction is only there because NHRA needed a way to level the playing field for their "record times"

no one disputes the effect altitude has on performance, but you ran what you ran and until you try it at sea level, you'll never know

just because your time "corrects" to something better doesn't mean you did it

BTW, most NHRA records are set at air conditions that are below sea level...witness Boise last year and Englishtown recently
 
Originally posted by azgn
no one disputes the effect altitude has on performance, but you ran what you ran and until you try it at sea level, you'll never know
Click to expand...

That's all fine and dandy if you don't live 20 hours from a track at sea level. :rolleyes: ;) Anyways, its not a discussion I really want to get into. I only suggest that it may be useful if everyone's posted times were corrected to sea level to compare fairly. Just as posting your build is important when asking for help, I think if someone wants to post a best time in their signature they should also post the conditions under which it was run. You sound like your 10.93 was run at sea level. What if you ran it up where Keith does and it was only a 12.00 car? Would you post it at all? Or would it say 12.00 @ 6100'? ;) Just a thought.
 
I think those are normally aspirated correction factors, also. They don't take into account someone cranking up the boost at altitude, but not being able to run that same level of boost at sea level. There is no reason a turbocharged at 5500 ft car can't be tuned to within 5% of the hp of a turbocharged car at sea level (vs. 15% hp loss for a normally aspirated car)
 
Good point I never thought of that. I do know of a guy running a Syclone that ran .5 seconds faster at Mission (track at sea level) compared to our own track. He is one of the better SyTy tuners too so I think there is some merit to the altitude argument with turbocharged vehicles. But you make a very good point also.
 
actually, if I corrected my times, they would be in the 10.80's and times in Las Vegas would be 10.70's.....doesn't really serve any useful purpose because you are where you are!

if you run 11.1's in Denver, you know you are well into the 10's anywhere else (I grew up in Colo and did a lot of racing at the old Castle Rock track so I very well understand the situation with altitude!)

a whole lot of other variables come into play, like density altitude....running at 5200' in Colo and 45* is the same as running at 1500' and 95* in Phoenix (that may not be exactly accurate, but you get my drift)

the good bracket racers all have their little weather stations & computers with 'em and can tell ya exactly what the air is like.....most of the time here in the desert, at our 1400' track, the air looks like 3-4000' because of temp & humidity (lack thereof)
 
I think turbocharged cars can overcome some of the altitude affect with more boost but...
The president of our local club graphed the amount of boost it took to push his car to 120mph at 3 different tracks and elevations. The result was a fairly linear graph. It took 18# of boost at sea level and 28# of boost at 5880ft . :eek: Although one can turn up the boost, you're just pushing more "stuff" into the motor and not necessarily more O2. Last Wednesday the barometer at the track was 23.3" and the temp was 80* - not ideal conditions.
I invite all flatlanders to our annual muscle car shootout at Pueblo in September to see the altitude affect for for themselves. :)
 
Hey Royal,
You guys ever go to Pueblo on other days besides in September? I'd like to go down there sometime and see how I run at low altitude (only 4800 compared to 6100 or more here in the Springs)! In their literature they say you can rent the track. Hmmm.
Keith
 
The only time I have been is with with the club's Muscle Car Shootout. We rent the track and have a Buick only Bracket then open the brackets up to anyone in the afternoon.
It's worth it to go. I think every member ran a personal best last year at the low altitude. I'm not positive what they're doing this year, but they used to run test and tunes on some Saturdays.
Most club members run at Bandimere on test and tune Wednesday (ricer) nights and on Club Clash Fridays.
 
I think this is mixing apples and oranges a bit.

Atmospherics plays a bigger part in forced induction motors than they do in normally aspirated cars, true enough. HP and torque are made from either one. You can make 500 hp in a turbo or normally aspirated.

Just for the sake of argument though I can tell you that when we go to Palmdale ( 3500 feet ) I have to take out 15% fuel out of the fuel map. Thinner air.

Now at Pomona ( 500 feet ) I have to put 15% back in, sometimes more.

I think the altitude corrections are pretty accurate. The numbers you get for corrections should be pretty close to what you would run at sea level. Come to think of it, if you have sea level runs to compare the mph and et should be about the same.
 
Well, I have seen it bear out very closely when running at sea level. But the argument than you just turn up the boost seems to make sense too. Oh well. Just have to make the 14 hour journey to make one pass and get the timeslip. Then file it in a safety deposit box at my bank. :rolleyes: ;) :p
 
Well, I don't think you can just "turn up the boost" either. For one thing, I made my runs in San Antonio (700 feet) at 24psi of boost on my stock engine. I was getting some knock retard even with 116 octane leaded AND alky injection. If I "turn up the boost" here in Colorado Springs I'll probably "blow up the engine." I've read about guys running 28-30psi, but I'll bet they're not on stock 144K-mile engines, heads have never been off.
Keith
 
i could be totally off, but when i read that people turn up the boost in colorado vs new jersey....i figured they were talking they turned thier boost back up....when i drove from fl to nebr to colo, i saw a 5 lbs difference by the time i was at 8000 ft...so i just thought with the right gas, i could just turn the boost back up to 18 psi and go along my may....however i didnt have the 93 octane avail to me in colo so i didnt do it....

dan
 
"turning up the boost" at altitude may compensate somewhat for the lesser air density and lower oxygen, but it certainly won't blow the engine up because the higher you get, the richer your air/fuel ratio gets.....in other words, you add boost to try and lean it back out......the best bet would be to lower fuel pressure and add boost.....you willl still never achieve the power available at sea level......cars run slower when there is less oxygen...period
 
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