Just wondering, I wonder how much power I am
loosing just by living above 5000 Ft. I know
are folks in the same boat as me on this board. I'm sure I'll have some fun next time I go back to Austin though. (The truck and 6th street).

G



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2000 F-150 Supercab Shortbed 3.55LS
5.4L

MODS
4WD valence W/hooks
K&N air filter
Hellwig rear sway bar
Raven muffler
Superchip
Cervini ram air hood being painted/installed

'67 Honda CL77 305 scrambler
'67 Honda CL160 scrambler
12 string Ovation
Mid-mo mandolin
Ovation mandolin

 

A Relative Air Density chart in an old tuning book I've got indicates 17-18% power loss between 5,000 sf and sea level, IF you can adjust the fuel/air ratio to be optimum for both locations. This also assumes both are at the same air temp. Since conditions can vary a lot and it is hard to say how well your computer adjusts the air/fuel ratio for changing condtions, I'll guess 15% - 25%.

If you assume that the 5,000 sf location is cooler, than the power loss is slightly less. A 20 degree F loss in temp increases the realtive air density by about 2.5%.

BTW, barometric pressure is the big factor in how weather effects performance, and lower elevations have higher pressure.

[This message has been edited by dirt bike dave (edited 02-18-2001).]

 

Hi Geeky,

The basic formula for determining power loss due to altitude in normally-aspirated gasoline engines is a 3% loss in power for each 1000 ft. increase in altitude above sea level, all else being equal. So at 5000 ft., figure that you've lost roughly about 15% of the power you would make a sea level.

This is *not* to dispute in any way the information in "dirtbikedave's" post, by the way, as there are about as many "formulas" for determining power loss due to altitude as there are vehicles above sea level!

Some of these formula's are for older non-computer controlled fuel-injected engines. Today, with computer controled fuel injection systems, we have much more precise control over optimum A/F ratios & spark advance, etc., thanks to decent load measurment capability & constant monitoring of oxygen content in the spent exhaust stream. In modern vehicles, from our experience, it seems that the 3% "rule of thumb" seems to hold up pretty well.

So in this case, your 260-hp (bone-stock power at sea level, so we're not taking your mods into consideration here for the purposes of this "exercise") 5.4 would be reduced to a power ouput of about 221 hp at 5000 ft, and of course this is an approximate figure, but close enough for modern computer-controlled fuel-injected engines.

And, NOLA's comment about forced induction (supercharging) being the one of the best solutions for the actual problem caused by altitude, which is a lack of oxygen content, is right on the money of course; supercharging is perfect for putting more atmosphere into the motor's cylinders, & high-altitude is a natural application for forced induction. In WWII fighter aircraft, nitrous oxide was first used for this same purpose (being used as an oxygen-releasing agent), to provide more power at higher altitudes, if memory serves, I think the Germans did this first.

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer

[This message has been edited by Superchips_Distributor (edited 02-18-2001).]

 

If you factor in a temperature drop of 4 degrees Farenheit for every 1,000 feet of elevation, the RAD chart I have matches Mike's estimate of a 3% loss per 1,000 feet of elevation. That sounds like an excellent figure for a 'ballpark' estimate.

 

Mike

Are you saying that a supercharged vehicle like the Lightning will have less than 15% drop in power at 5000 feet? In other words will a stock supercharged vehicle suffer less at altitude than a na motor. If so what would be the equation for a supercharged vehicle?
Thanks

 

Well, with the lightning, I would suspect that it would depend on where you bought it, and was it set up for "high altitude principle use". I would suspect that there would still be a power loss due to the altitude being a factor, as the blower would be less efficient as the air thinned out. However, I would almost say that the 3% rule would have to be ammended to take into account the differences in the efficiency of the blower. Also, does anyone know if the lightning's computer setup pushes the spark advance as close to detonation as possible? If it did, then, the computer could take advantage of the reduced boost pressure by advancing the timing a bit, thus gaining power (though, not quite as much as it would have with full boost).

However, I would have to say that, given the performance improvement that the superchips lightning application gives, this is definitely not the case. If it is, then it doesn't push hard enough. So, given this, I would almost be willing to say that the power drop off may be more pronounced as altitude increases, though, this may not actually hold entirely true until you hit something closer to 10K feet, since there is a curve to how the pressure drops off after 7500ft (well, there always was a curve, but, between sea and 7.5K, its almost straight).

In other words, I have no idea what the final effect would be. I would suspect that, all things being equal, the lightning would still have ample power to melt the tires down to the wheels and beat any stock chevy truck of equal or earlier vintage at almost any usable altitude.

Oh, and Mike, I think you are right, I believe it was the Germans who did it first with NOS in fighters. However, I think it didn't last particularly long as most countries realized the advantages of forced induction via mechanical impellors was the way to go. Granted, jets came out right after the war, so, while the piston engine was reaching the pinacle of its development, it was quickly eclipsed by turbine engines in their infancy due to their higher power to weight ratio and their greater reliability. My dad has so much first hand knowledge on this from being in the airforce during their transition from propellor driven aircraft to jets, and, from his 30+ years with Delta Airlines Maintnance division. The stories I could tell...

 

Another way of looking at this is that it is an excelent reason/excuse to buy that supercharger package. IIRC, forced induction seems to overcome all those problems with reduced air-pressure. That's why they used superchargers on the large radial engines on the old propellor driven airliners. They needed to get to a high altitude for economy reasons, and, those radials need lots of air to run right. They put blowers on them (actually, geared blowers so they could run low boost/blower rpms at low altitude and high boost/blower rpm at high altitude).

Now, you have to realize that a blower setup that produces 6 lbs of boost at sea-level will not put out 6 lbs at 5000ft. However, the difference will likely only be a pund or so. You might investigate a slightly smaller pully (I would say, around 2 lbs more rating) to get matching performance.

Granted, a blower is a bit unrealistic, but, it is the best equalizer you've got to deal with the altitude difference.

 

Hi Hilander,

No, I'm not saying that, *any* internal combustion engine is going to lose power due to less oxygen at higher altitudes; supercharging won't *stop* that effect, it simply helps by packing more atmosphere into the combustion chambers, thus getting more oxygen into the motor. I don't know what the figure (the % of power drop per 1K ft. increase in altitude above sea level) is for supercharged engines, but I suspect that figure could be even a bit higher than the 3% number for normally-aspirated engines, as NOLA speculated in his post.

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer

 

Hi NOLA,

I'll bet with that wealth of background you could tell us some stories!

Feel free, we're all ears around here, & thanks for your post!

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer

 

I agree, a s/c would be cool at any altitude. I guess the days of them just being for extreme performance guys are long gone. Seems like through the 60's and 70's my impression of a s/c engine was for drag purposes mostly. You know, little duece coupe with big blower sticking up way above the hood. I am thinking that the modern s/c systems seen around here are a little easier on the mill. Either that or folks are more willing to take a chance with a new vehicle. I plan on upgrading to the functional ram air as soon as the kit is available. I am sure that will help some.

Wow, so when I do get back to Austin my truck should be a real hotrod with that kind of increase. I can see me now at the roadside park in Lampasas with my neg. cable off.

G

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2000 XLT
5.4L, 3.55ls
Toreador Red
Supercab, Short bed
Custom cloth seat covers-front
K&N air filter
Raven Z33 muffler
Hellwig rear sway bar
Front valence from 4WD W/cutouts for tow hooks
Superchip
Cervini's ram air hood being pained/installed
Future upgrades???
Functional on ram air
Better tires/wheels
Front Hellwig
5.4L bittet fender badges

 

Thanks Mike & Nola,
I feel better now. Now I can work out what my L will do at sea level. By the way I have a G-Tech and tested my warmed over Jeep Grand Cherokee for 0-60 both here and at sea level. The Temps were similar, not sure about other weather conditions. The results. 5000 feet 0-60 8.15
0050 feet 0-60 6.95
Approx 15%. Very accurate guys.

 

Hi geeky,

You make an excellent point, and many of us probably thought about superchargers that same way for many years. It's only been recently, in the past decade or so, that the aftermarket manufacturers have done enough R&D, and with the advent of computer controls as well, the sum total of all that technology is that we now have basically bolt-on supercharger kits that almost anyone can install over a weekend and have a good reliable long-lived vehicle.

Back for most of the 80's and before, a blower was a major undertaking, and you have to basically do all the engineering yourself to make everything work reliably on the street. Now we have great kits available, so the normal logic many of us grew up with has changed in this regard, lucky for all of us!

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer

 

Hi Hilander,

Very intersting post, that's a 14.72% change, very close to the rough estimate of 15%, assuming an exact altitude of 5000 ft.

Thanks for your numbers!

------------------
Mike Troyer
Performance Products, Inc.
National Distributor of Superchips
(540) 862-9515
Email: mtroyer@compuserve.com
Performance Products F150Online Superchip ordering system: F150Online Superchip Ordering System
First National F-150 Online Rally Event Organizer