Another MAF vs Speed Density question - changing altitudes
#1
Another MAF vs Speed Density question - changing altitudes
Hey guys, I'm swapping a LQ9 with rectangle port top end into my 1996 Bronco. I'm getting mixed input on if I should run MAF or speed density. The truck will spend a lot of time split between being at sea level and then going through the mountains. Its an adventure vehicle.
How does speed density react to altitude changes compared to a MAF? What should I run known it will semifrequently go up the mountains in the PNW and surraounding national parks?
How does speed density react to altitude changes compared to a MAF? What should I run known it will semifrequently go up the mountains in the PNW and surraounding national parks?
#2
TECH Apprentice
Ask your tuner
Speed density generally does not do well with altitude change if you do not have an additional map sensor going to atmosphere to reference air density
At least this is what my tuner told me
I will not have altitude changes but may still run an additional map this way to not make the correction do the work if I wind up going on a long road trip
Speed density generally does not do well with altitude change if you do not have an additional map sensor going to atmosphere to reference air density
At least this is what my tuner told me
I will not have altitude changes but may still run an additional map this way to not make the correction do the work if I wind up going on a long road trip
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Woodylyf767 (06-19-2024)
#5
TECH Apprentice
02 Tahoe, 2 Bar SD tune: No MAF.
Magnuson pushes 11 pounds manifold pressure.
I tuned it in Alaska, at 50 degrees Fahreneit ( summer) at SEA Level.
Drove it through Canada, Montana, Wyoming, Colorado to Texas, Ran great at 105 degrees in Texas.
SanteFe New Mexico, 7000 feet and 80 degrees F: No problem, full boost, smooth idle.
Ran up to south rim of Grand Canyon ( 9200 feet) ran great the whole way, no problems.
We put 11,000 miles on in 3 weeks, 3 canadian provinces and 11 states without issue. Rotated tires once, changed oil once. Other than that, never turned a wrench.
Back in Alaska now. It's been 8 years, that little 4.8 Liter has ZERO oil consumption, and has had NO issues..
.
Short story: Speed Density will run anywhere, at any temperature or elevation, with out issue.
It's ALL about SPEED x Density, with a little help from your IAT
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Woodylyf767 (06-19-2024)
#6
TECH Veteran
iTrader: (1)
Altitude affects density, which is calculated based on MAP and temperature. No need to separately take baro readings or any other such nonsense. Tuners that tell you it won't work are either stupid or lazy (or both).
edit-- Millions of factory vehicles were SD only and the manufacturers used the same tune selling them in Denver as the ones sold in Daytona.
edit-- Millions of factory vehicles were SD only and the manufacturers used the same tune selling them in Denver as the ones sold in Daytona.
Last edited by gametech; 06-19-2024 at 01:21 AM.
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#8
If you go to a higher elevation, yes the air pressure goes down.... But the entire point of speed-density is to determine how much air gets into the combustion chamber with each intake stroke, based on the density of the air in the manifold and the speed the engine is running at. So it's constantly measuring the air pressure in the manifold, and it doesn't know or care whether that pressure is low because the throttle isn't all the way open, or if it's low because the car is at high altitude.
In theory the atmospheric pressure makes a difference in exhaust backpressure, which in turn could affect cylinder filling. If your cam doesn't have overlap (which I'm guessing is the case for a Bronco) then I'd be shocked if that made a measurable difference in VE. I do kinda wonder how much if matters (or if it matters at all) for cams with a lot of overlap though.
In theory the atmospheric pressure makes a difference in exhaust backpressure, which in turn could affect cylinder filling. If your cam doesn't have overlap (which I'm guessing is the case for a Bronco) then I'd be shocked if that made a measurable difference in VE. I do kinda wonder how much if matters (or if it matters at all) for cams with a lot of overlap though.
#9
TECH Senior Member
MAP (manifold absolute pressure) sensor handles barometric pressure variations.