introuble

At higher altitudes wouldnt I need more fuel running the same boost pressure than I would at a lower elevation? I am in UT and we are about 4800 Ft. Answers?

sawood12

At the same boost pressure you'd need the same fuel irrespective of altitude. However because the air is less dense at higher altitudes the turbo needs to spin faster to achive the same boost pressures so max boost might not come on until higher up the rev range. I.e. to achieve the same level of performance you need to drive the car harder.

dand86951

If you are still running the factory DME and KLR the cars have a barometer (or altitude) correction feature. This adjusts the fuel flow according to the altitude you are at. I may be wrong but I believe this still comes into play even if you are running aftermarket chips, but that you would need to discuss with your chip supplier.

special tool

If you are asking a general question about altitude related AFR, you always use LESS fuel at higher altitude.
This is because there is LESS oxygen available.

I change the slow and main jet on my (psycho) 2 stroke when I go up even 1,500 feet.

sawood12

15psi is still 15psi whatever altitude you are at therefore you are getting the same amount of air. 15psi at 0 degrees is more dense therefore needs more fuel to maintian AFR, whereas 15psi at 20 degrees is less dense and needs less fuel to maintain AFR.

N/A cars will use less fuel as they will not be drawing as much air into the engines due to the lower surrounding pressure.

Is your question aimed at how does the stock motronic system account for altitude? or the theoretical aspects of fuelling at altitude? At higher altitude and therefore less pressure the barn door of the AFM will not open as wide due to the lower mass of the air passing through it so your fuelling will be automatically adjusted.

Rogue_Ant

Only if your using an absolute. I.E. not gauge. My gauge reads nearly 3psi less [absolute] up here then at sea-level.


Rogue

TurboTommy

15 psi boost will be less absolute pressure at higher elevations than 15 psi boost at sea level. The absolute pressure determines fuel requirements.

dand86951

Great quote about the 2 stroke, when it comes to altitude most of them that are carbuerated very definitely are. I remember a very memorable ride up Pikes Peak on a 2 stroke Kawasaki triple. It was definitely Psycho on that trip. It would not run unless wide open and then it would go from 0 hp to 60 hp in the blink of an eye, lots of fun on that gravel road.