What Airflow Rate Do You Guys Hit At WOT?

[DramaFoYoMama]

I am just curious what g/s you hit airwise when at WOT. This is really just for my amusement. I was tuning a friend's car Friday night and noticed that he only hits .64g/s with a cam and headers (I think he is losing compression - car has over 120,000 on the clock). :( On the other hand, I hit .96g/s. Granted I have 72 more cubes than him, but this is on the stock 2002 LS1 cam. :shock: (Don't ask why I still have the stock cam. :lol: ) Anyway, where are you guys at?

[Blacky]

Those figures sound more like a grams per cylinder value, grams per second should be up around 300.

The maximum grams per cylinder under perfect conditions on a perfect engine can be be calculated using the following formula:

m = PVM/RT

m = mass in grams
M = 28.96 grams/mole (molar mass of air)
P = (use atmosphere: 101.3kPa)
V = 0.708 (5.7/8) liters per cylinder
R = 8.314 constant
T = IAT (Use standard temp: 21degC = 273.15+21=294.15degK)

m = (101.3*0.708*28.96)/(8.314*294.15) = 0.8493 grams/cylinder

The closer you are to that figure (normally aspirated) the better your engine is working.

Regards
Paul

[redhardsupra]

few questions:
1. would it be reasonable to use the result of this calculation to compare it with MAF or to DynamicAirflow, to see if the VE/MAF is dialed in?
2. what is the 8.314 constant coming from?
3. this formula works for me (as in the values are comparable to MAF/DynAir) only if I skip the whole molar mass of air. am i missing something?

[MCG]

few questions:
1. would it be reasonable to use the result of this calculation to compare it with MAF or to DynamicAirflow, to see if the VE/MAF is dialed in?
2. what is the 8.314 constant coming from?
3. this formula works for me (as in the values are comparable to MAF/DynAir) only if I skip the whole molar mass of air. am i missing something?

The R is the universal gas constant used in Ideal Gas Law PVM/RT.

R = kNa where k is Boltzmann's constant and Na is Avogadro's Number.

Boltzmann constant is in ergs K. It basically is the amount of kinetic energy in each molecule of gas at absolute temperature for an ideal gas

Avogadro's Number is the number of molecules required to make up the same mass as the molecular mass in grams.

[deezel]

Also consider:
The airflow values reported by the scan tool may be incorrect if the MAF and/or VE calibration is off. I could make my MAF read 400 g/s, but that doesn't mean that its really flowing that much air.

[redhardsupra]

I've seen ~40-41lb/min@6000rpm on my stockish z06 cam powered LS1, and up to 44lb/min on more typical 'cam only' setups. once you slap on the FAST90/90 setup, i've seen 52lb/min of airflow on stock cubes. 382-383 strokers i've seen flow over 63lb/min@6000rpm and still flowing more at higher rpm. this is data from cars i've either extensively tuned myself, or from the few ppl that i know are as compulsive-obsesive about tuning as i am. You know who you are ;)

[Blacky]

The R is the universal gas constant used in Ideal Gas Law PVM/RT.

R = kNa where k is Boltzmann's constant and Na is Avogadro's Number.

Boltzmann constant is in ergs K. It basically is the amount of kinetic energy in each molecule of gas at absolute temperature for an ideal gas

Avogadro's Number is the number of molecules required to make up the same mass as the molecular mass in grams.

Aaaarrgghhhhh!!! my chemistry teacher has come back to haunt me :shock: :shock: :shock:
Who realised back in high school when this stuff was being taught that we would actually use it in real life? I certainly did not.
Paul

[MCG]

I finally get to use my math and physics minors! Its just that I've been out of school since '87, so I have to rely on school books and internet searches to remember all the little details. The concepts stick, but the details are far gone :)

[DramaFoYoMama]

I've taken Physics and understand the concepts, but I did some calculations that don't really seem logical. I used an atmospheric pressure of 103 kPa as measured by EFILive. I then used 21C (was the average temp reported by EFILive - intake temp and velocity are inversely proportional) and came up with 1.052g/cylinder. If I'm hitting .92g/cylinder now, that means the stock cam is a bad mofo, which we know it isn't. What's the case here? I have a Ram Air II hood on my 02 Z/28 with the FIPK II. It's just an open system and isn't sealed. Isn't the whole "ram air" effect nonsense on our cars? For reference, the motor is a 422, stage 3 6.0 heads that flow 320 CFM (have to find the flow sheet to find what it hits on the stock cam lift), and an unported 90/90. There's no way the stock cam can keep up with that. Anyone have an explanation?

[joecar]

Isn't the whole "ram air" effect nonsense on our cars?
Well, yes, no and maybe [not]...

It does get cold air (from outside engine compartment).
The ram air effect may possibly be effective above 170 MPH.
The scoops increase drag.
The neighbourhood kids say "Dooooode... it's the Batmobile...".
:)

[jfpilla]

Those figures sound more like a grams per cylinder value, grams per second should be up around 300.

The maximum grams per cylinder under perfect conditions on a perfect engine can be be calculated using the following formula:

m = PVM/RT

m = mass in grams
M = 28.96 grams/mole (molar mass of air)
P = (use atmosphere: 101.3kPa)
V = 0.708 (5.7/8) liters per cylinder
R = 8.314 constant
T = IAT (Use standard temp: 21degC = 273.15+21=294.15degK)

m = (101.3*0.708*28.96)/(8.314*294.15) = 0.8493 grams/cylinder

The closer you are to that figure (normally aspirated) the better your engine is working.

Regards
Paul

Paul,
Going above the calculated number is good?
I just looked at 2 dyno runs and 2 track runs. My number with a 6.0 liter and 22* is .88512. IAT at 2 different tracks a weekend apart was 22*. In both cases my best times were identical. The cylair in both cases was .96 1st gear, .91 2nd and 1.01 3rd. One dyno was done on the AM of one track run. It produced 7 more HP and 19 more ft lbs(and best times) than a dyno run a month earlier, which only produced .81 gms/cyl. Does this all make sense?
What could have produced the lower gms/cyl and lower power on the first dyno?
Regards
Joe

[Blacky]

The cylair number is calculated by the PCM based on MAF (or MAP/RPM/VE table in SD mode). Did you change anything in the tune between now and then?

Different ambient air pressure (altitude) or temp would cause a difference.

The value I calculated is the mass of air that will fit into a cylinder at STP (standard temperature and pressure). If either of those change then the mass of air will also change.

Paul

[DramaFoYoMama]

I didn't know it used the VE table to calculate that. I'm running lean across the board, which means it should actually be hitting higher, correct? If so that brings me even closer to my max theoretical flow. This makes me beg the question more, what the heck?

[jfpilla]

Paul,
I changed MAF values based on Dynair. It lowered some.
Regards
Joe