blown 944

Not to mention the extra heat generated by further compressing the air to get the same pressure as sea level.

there is a loss turbo and definately no turbo.

dand86951

OOPs, my typo, I meant AFM not MAF, I agree most of the early EFI systems used non mass air flow meters and thus needed altitude compensation.

nize

my MAP setup takes a temperature reading after the throttle body, so it's reading the temperature of the already-compressed air. no need to compensate in this case.

good point when applied to a MAF or AFM system, though, assuming they don't take a secondary 'correct' temperature reading after the TB.

TurboTim

Map sensors cannot read temperature. IAT or MAT sensors read temperature. There is proably one of those in your MAP system.



Tim

nize

you are right tim. as i have mentioned, i have a temperature sensor after the TB in addition to a MAP sensor.

dand86951

Tim, in thinking about this, would it be possible to use an auxillary MAP sensor not connected to actual manifold pressure to feed a voltage to the TEC to use as a fuel correction factor?

Might be more trouble than it is worth but a thought.

nize

for that amount of trouble, why not go all map with a temperature sensor in the manifold?

dand86951

The temperature sensor in the manifold is already in the system and the ECU does correct for the effects on density caused by inlet air temperature and also by coolant temp. The ambient barometric pressure is to some extent accounted for by the MAP system but if you are up at altitude and correspondingly low pressure then the oxygen content in the air will not be the same so a correction table could be possible. I don't know that it is needed for sure, so I was just thinking that since the fuel curve is modified by coolant temp and air temp in the ECU and if altitude is a factor then why not use a second MAP sensor and modify the fuel and/or ignition curve based on altitude.

George D

MAP.

Rogue_Ant

A car with a MAP sensor (Speed Density) does not need a second MAP sensor for barometric pressure. Rather a Speed Density system utilizes absolute pressure, so 'altitude' is part of the equation to begin with.


-Rogue

dand86951

Rogue, I agree that the MAP sensor automatically takes into account the altitude as it is based on Absolute Pressure, however as George's car seems to illustrate even though it may be operating in a cell with a given Absolute pressure say 180 Kpa, when the car is at 8500ft altitude then that 180 Kpa of pressure doesn't have as much oxygen in it as the same 180kpa which occurred at sea level??

I haven't had mine up to a high enough altitude to verify nor have I been able to dig out any hard facts but it does seem to me there may be some effects which could modified by having a correction table based on ambient absolute pressure. On the other hand maybe the physics says it should all be taken into account by the absolute pressure.

I do know that in my airplane it will only make 100% rated power up to a given altitude. Above that the Turbo doesn't have enough flow to make up for the lower density so it will only make x % of max rated power which decreases as I climb even higher.

Rogue_Ant

Assuming the same temperature and humidity, then absolute 180kpa is 180kpa regardless of altitude, the density is the same. Where most people get confused is the lower atmospheric pressure at altitude, and think that gauge pressure is the same as absolute.


-Rogue

95ONE

Soooooooo.................... 1/4 mile numbers yet?

David Floyd

Or timed 100 to 200 kph sprint, several have posted in the past to compare to.

95ONE

This post was pushed back 4 pages already.
George, have you made it to the track yet?
Even if you don't do a bad *** run, it should still be fast. please post so we can get our cars rep up.