5800 ft Elev= Bring it on

[TurboTnZ06]

I just moved to Denver from Dallas. Well, expecting to be slow at altitude given the same boost, as per discussion on this board, I went to Bandimere raceway last night. The boost did start out low (baselined with my Dallas setup = 13.2 @ 107 on about 10-12 boost), so finally I got about 15 psi boost and ran 12.1 @ 112 on a bad launch. They closed the track early so I didn't get to tighten the wastegate rod anymore, but I'm sure once I get it back to 17 psi where it should be I should be able to run my good usual ol' high 11's at 114-115 mph. I have no cage so I can't go much faster than the occasional 11.9x or I get kicked out. Everyone said I would run slower, but it felt strong on the 112 mph run at 15 psi.

I saw some discussion on that it would take X boost at 5000 ft to equal N boost at sea level. I'm confused. If the oxygen and nitrogen % (given different densities at altitude) is the same at sealevel as it is at 5000 ft, then why would compressing it to the same density make my car slower?

 

[1badTTA]

Great topic. I have often wondered what the difference ACTUALLY would be. I know in an NA car there will be a difference but why would there be a difference in a turbo car with an adj. wastegate? Maybe you can be the posterchild for this since you have a car with plenty of runs at low altitude and now live at high altitude.

Anybody know what the standard correction for altitude is going from 5800 to sealevel on a 12.1@112 run

Maybe you really have a 10 sec car

 

[Nick Micale]

Am far from an expert on atmosphere and conditions but do know the critical factor is density altitude [DA]. This really determines what the actual make-up is of the air going into the motor.

A track at 3000' can have conditions where it is the same as at sea level, or it could the same as 7000' on another day.

NHRA uses correction factors for high altitude tracks. Not sure what they use at Denver, but at 3500' tracks it is 0.9669. Using that factor, your 12.1 ET would be 11.6!

This is a reason that many guys wonder why their car is so slow compared to other similar cars. If one is at sea level, or below, on a cool day, and the other at altitude, there will be a big difference. Here in the desert, our "normal" race conditions are 3-4000' DA, even though we are not that high in elevation.

 

[TurboTnZ06]

If you go up to the top of Mt. Evans (14,000 feet) and trap some air in a bottle, bring it down to sealevel, wouldn't the % of oxygen and nitrogen be the same as sealevel at the same density once the air in the bottle is compressed so that the density is the same, but less volume compared to a bottle of air captured at sea level? Wouldn't this mean that me running 17 psi in Dallas would yield the same mph +- 1 at 17 psi boost in Denver? Everything in my car is exactly the same as it was in Dallas, even the static FP setting. IIRC my indicated FP was a little higher in Dallas, but I may be getting light headed at this frickin altitude...

I hear the DA at Bandimere can be upwards of 8000 ft!!!

 

[JDEstill]

Ah, but 17 psig boost at elevation is not the same as 17 psig boost at sea level. Boost is measured as gauge pressure, or the difference between the reading and the local atm pressure. But air density is dependant on the actual absolute pressure. Your 17 psig boost at altitude might give the same air density as 15 psig boost at sea level, because the local air pressure up there might be 2 psi less than sea level air pressure.

John

 

[JDEstill]

Also, when under boost, even taking into account the elevation you'll see less of a power drop than a n/a car. A 2 psi drop in atmospheric pressure is a much bigger percentage of the manifold pressure of a n/a car than it is of a boosted car.

Example, going from 14.7 psia local air pressure to 12.7 psia local air pressure, a n/a car might see the air density in his intake drop by 14% (and presumably power would drop by ~14% as well), while a turbo car running 17 psi boost would only see a 6% drop in manifold air density.

John

 

[TurboTnZ06]

Ah, but 17 psig boost at elevation is not the same as 17 psig boost at sea level. Boost is measured as gauge pressure, or the difference between the reading and the local atm pressure. But air density is dependant on the actual absolute pressure. Your 17 psig boost at altitude might give the same air density as 15 psig boost at sea level, because the local air pressure up there might be 2 psi less than sea level air pressure.

But my boost/vac gauge (VDO) reads about 2-3 in HG vacuum when the engine is off, keep in mind it was zeroed out in Dallas with the engine off. My indicated boost is theoretically going to be the same, right?

 

[azgn]

if our cars had manifold pressure gauges like turbo airplanes, you can see what is happening.....the higher you go, the less manifold pressure you have, even though the uncorrected boost stays the same....to raise the manifold pressure back up, you need more throttle (and ultimately, boost)...

so 17 lbs in Dallas is 17 lbs in Denver, but if you correct the manifold pressure to the altitude, you have less power in Denver because the air is less dense

btw, the correction for 5500' is .9315 so your 12.1 corrects to 11.27! Maybe something else changed or your car really likes Denver......you could have been running lean in Dallas, 'cause you'll sure be richer in Denver if you don't adjust your fuel

(also those correction factors are for na cars.........we can obviously turn up the boost to compensate)

 

[GN138]

TurboTnZ06: Where in Colorado do you live?

BTW...we have a local racing/ street racing/ car board:

www.cosr.com (I go by DarkLord on that board)

Please join us, as there are only 3-4 of us Turbo Buick guys and a great mix of domestic and import muscle.

Thanks

 

[badboy86gn2]

ITs just like the guys said you must of done something or the car likes denver i know for a fact that you will run slower going higher ive seen many go to texas to run and yes they run faster alot now as for the tables

na=about one second
turbo=7tenths

that is why when we dyno here they give that number and corrected

like i said we have z06 corvettes run at best 13.7-13.9

Johnny

whats your combo and are you running nitrous

 

[badboy86gn2]

also do you have the heads done and rebuilt motor???? those times are very impressive for that boost

 

[TurboTnZ06]

I'm in Superior somewhere, I get lost in Interlocken trying to get home everyday.

Well, I was a little lean in Dallas at the top of 3rd gear, but made good power and no knock problems on 116 race gas.

NO NOS!! nor alky(yet). Boost controller is on its way hopefully and I weighed 3575 #'s last night with me, 5 gallons of 116 in the tank and a spare T wheel with 225 60 Zr 15 yokoham spare tire. I lef the spare in the car accidentally when I raced- (doh)

My mods: Yes, it is a built up 109 block that should handle 10.80's unless I go to a better than stock crank.

TE44.63, CAS V4, very well ported heads (Competition machine of Plano did the head work and all the valves are speced out to be like within a few thousandths as this is a non adjustable valvetrain (0.008" is the biggest margin on one of the valves installed height I think- yes I'm crazy sometimes, being an engineer and all), 210/210 billet roller cam, precision upper plenum, wiesco pistons .035 over, billet mains, thdp, atr dual 3 SS, 50's, Jay Carter chips, Bruce's 9/11 converter @ 3000 stall, hotwired 340, a bunch of other stuff which costs $, FP static at 42#'s. 275 50 DR's which suck. I pulled a 1.89 60 foot:-( TurboLink 4.0.
The engine was align honed and balanced and polished rods (I think I told Billy Dukes to polish them- well, it's been a while). Billy put the engine to gether and it is bad ass. Took it to 6400 rpm on the dyno and was was still well over 300 hp and tq with an old unlocked D5 converter.

 

[Donald McMullin]

Air Density @ Standard Temperature:

Sea Level = 0.0750 lb/ft3
6000 ft el. = 0.0599 lb/ft3

Lower air density (lbs) because less O2, etc.

To flow the same pounds of air in Denver that you did in Dallas, you must have more ft3 of air (at Denver air density) flowing into turbo.

Yes you will have less HP at same boost, but remember you have less air resistance for the "Flying Brick".

Deep Enough
Donald McMullin

 

[GN138]

I live just south/ east of you in Broomfield.

You don't by any chance drive a White T, do you?

That's the only other T I've seen in the area. All the rest are black GN's and 1 grey/ silver T.

 

[TurboTnZ06]

I'll be on the lookout in Broomfield where my office is. I drive a chromed out Turbo T with grey faded paint. I am planning on going W02 with it next week and then paint the body to look like new.

I'm still sceptical that pressurizing Denver air is different than pressurizing Dallas air. What is in the air that replacwes the 02 content by percentage????? I know too much to accept this on faith. Please explain the reason why molecules of 02, by percentage to nitrogen+ other air gases, is lower at the same pressure in Denver than the same pressure in Dallas.

I guess it is the lower wind resistance in conjunction with the chip liking the thinner air up here? All I did was crank the waste gate rod to get more boost. Maybe the guage is inaccurate at this altitude and I'm pushing more molecules of 02 than I did in Dallas? I don't have the boost sensor for the TurboLink 4.0 to cross check.

 

[BLACKBADGER]

Density

Ran across a .density altitude chart. The density at 5200 ft with the temp 100 degrees is just over 9000ft. Sea level same temp. density would be like 2500ft. Even at 0 centigrade/32 degrees,freezing the density altitude at 5200 is equivelent to being at 7000ft. The only time density equals pressure altitude at 5200 ft is when the Temp is Zero . They Love that Cold air. Refrigerated IC would help up here to compensate for the density.

I'm new to these cars and I've always heard people talk about getting chips burnt/made for their said combo and "altitude", Most get it set ,and I maybe wrong for Pressure altitude(actual ft/altitude above sea level), and not Density maybe chips should be burnt for the mean yearly density altitude according to temps at any given altitude/standard temp.

 

[TurboTnZ06]

I found an NHRA correction chart and it says .9702 for turbo/super cas in a 1/2 table compared to NA cars which use the .9405 at Bandimere 5800 ft. If NHRA does it, then I must be wrong and my high school teacher for advanced placement chem 2 class is gonna be upset if he ever knew. Of course I only got a 2 out of 5 on my AP test to test out of chemistry college credits in HS...I'll stick to software engineering I guess.

So for the 1/2 NHRA correction factor at Bandimere:

12.12 * 0.9702 = 11.76 sec

112.2 * 1.0281 = 115.35 mph

The mph is about right, though the ET is better than my best and I had a bad launch. I've run high 11.90's at 112.x mph before with good launches at Ennis, Tx.

 

[TurboTnZ06]

After thinking about it, I didn't seem to find the answer to my question. The manifold absolute pressure hint was what I needed to understand this. Here's my version:

A turbo buick will make less power at 5800 ft evelation versus sea level (at the same indicated boost level at the throttle body) because the engine is basically an air pump which is not able to move the same amount of air when it is less dense. On the down stroke, pistons create a low air pressure area in the cylinders and then the air is forced in by the higher air pressure in the manifold. However, the air that is unmeasured in the intake manifold and heads on its way to the engine is operating under a lower pressure because the exhaust side of the engine is feeding to a lower airpressure. So, the air compressed to 17 psi in the V4 intercooler is the same at 5800 ft as sea level, but once that air gets into the engine it is not able to flow the same. Basically, the pressure drop from turbo boost to exhaust tips is greater at altitude than sea level. It has a hard time making the same power because the air tries to get out of the engine as the higher airpressure always moves to the lower air pressure.

I've read that there is about a 3psi drop for turbo engines at altitude. So at my indicated 15 psi boost, reading a few inches HG vacuum off, I'm really flowing closer to 16 or 17 psi actual boost over atmospheric pressure. Because of this, the turbo works harder to get to the same boost level as sea level, and the air gets hotter than usual adding to the HP loss?

I dunno, 12.1 @112 at 15 psi indicated boost isn't too much to be sad about. I'll go back to the track once I get my new TV cable in the mail. Bandi isn't open for like 2 weeks anyway cuz of the top fuel races next weekend. Definitely more times to come...

I only saw one GN out there last time and he was near stock I think running 14's.

 

[Lee_Burough]

I suspect that the temperature (in the 60's at Bandimere that night) and humididty (prolly in the 30-40% range that night) and barometric pressure (prolly over 30.00 that night) combined in your favor with a positive affect on your performance.

I don't think you'll have the same experience during a hot day at Bandimere

 

[TurboTnZ06]

You're right, it did feel nice out that night (my Z06 said 60'ish when I drove the vette to get some fast food after I got home later) and it was my last run of 4 that night before they shut it down.

My runs in order, of course I hot lapped it and no ice and way too little boost on the first run.
13.2, 12.6, 12.5, 12.1
I haven't run 13's in the Buick since I did a john force burnout on my launch once at Ennis back, prolly cuz a turbo accord ricer oiled up the track for me...

I didn't see a TTA, but then again, I wasn't looking too hard. I talked to a Mil Yellow '03 Z06 guy and was checkin out the little blonde driving her red C5 coupe too...way cool.