Jeff K

He's just trying to figure out what to buy with all the money you are sending him

D.Wiggs

ROFLMAO!!!!!

Jeff K

I know he can't afford anything big with the money I sent him...all I got was a steering dampener and the crossover steering kit

Big Blue24

XLR is exactly right and this exhaust turbine BS has some effect but not nearly as much as temp of boosted air. The equation for pressure is PV=NRT where P is pressure, V is volume, N is number of air molecules, R is a constant, and T is temperature in Kelvins. Kelvins are the same as Celsius plus about 100*. What all this stuff means is that 60 psi of air at 100* is the same as 30 psi of air at 50*. Since P is in atmospheres and T is in Kelvins, in standard units this is more like 60psi at 100*F = 54psi at 50*F.

All that talk about a compressor's efficiency range means something too. When the stocker is "off the map" it is pushing 50psi at nearly 500*F. Yuck. That equals 34psi at 200*F.

Now what is not clear? A larger wheel makes cooler boost which equates to more pounds in weight of air at the same boost psi.

At peak efficiency, a turbo is nearly 70 % efficient. When you ask a stocker to make 50 psi boost, it is 20-25% efficent, meaning that it is not compressing more pounds of air,"more mass", more weight, more molecules of air, it is super heating the air because it is only 25 % efficient at compressing 0 psi to 50 psi.

A stock charger at 40 psi is moving= compressing nearly the same amount of air that it does at 50 psi. It is simply adding heat to get that higher pressure not more air molecules.

XLR8R

Well said!!!

THURENfab.

Gotcha... So can you tell me the difference between the 40psi charge temp of the stock turbo, vs the same 40psi of a better aftermarket turbo? I'm still curious if anyone has "the numbers"...


So if I am getting what you are saying, cutting the charge temp in half adds 11% more air? If thats the case, a better turbo must be cutting the intake charge down 75% or so? That seems like a TON!


I see.... Is that a realistic #? A stock turbo at 50psi is pumping air at 500 degrees?

Big Blue24

Yes, that is a realistic number. When you get that far off the map, efficiency drops off to like 10%. That means that ten percent of the pressure rise is due to air molecules N and 90 % is due to temperature increase.

Now I personally don't know a ton about stock turbos on newer trucks, but on my 99' with an HX 35, 45 psi is like 400-500* depending on the ambient air temp. Also remember that 35 psi is considered the max usable boost from this turbo.

CamperAndy

Might as well give the correct numbers here. Kelvin is the "Absolute" scale of Celsius. Kelvin ZERO degrees = -273.15 degrees Celsius. Using Kelvin in your formula allows you to use temperatures below freezing to calculate flows and volumes ( can't do that using negative numbers for temp).

If you want to use Fahrenheit then you use the Rankin absolute scale and the reference of Rankin ZERO = -459.67 degrees Fahrenheit.

XLR8R

Realistic?
Probably not...

The stock Holset on the '05 heats the charge air to ~350*F max (as sampled in the pre-CAC pipe w/digital pyro) at 48psi boost (as measured in intake airhorn). The factory CAC does a great job of cooling this hot air down to within 25*F of ambient; naturally, the differential varies with OAT & load on the engine - 10*F diff is the norm for most driving.

We also have the pre-CAC pipe pressure-tapped, and the airhorn wired for digital pyro - this gives useful data for calculating volume on both sides of the "intercooler", which helps in the pursuit of quality boost.

drewblood

thanks xlr8r Ive been told I was nuts when I say my intake air temp is 10 to 15* on average above ambient except when its above 90* then 25 to 30* haven't been able to understand this but I guess its reaching the CAC efficiency

Big Blue24

Now CamperAndy, I was using Kelvin and then converting to Fahrenheit with my TI 86 grapher. If I was using Kelvin, you're right 100 kelvin is like -279.67 fahrenheit. But if I were using Kelvin the difference between 100 and 50* would be the same as 50 and 25 psi boost at those respective non real world numbers. XLR does have more ways than the average joe like me to monitor boosted air temp. Theoretically though, an HX 35, not your new fandangled variable vane or whatever it is, is way off the map at 50 psi and if it could be done without blowing up the turbo, I'll bet 400 to 500*F is where it would rest at 50 psi, ambient air temp playing a big role in those numbers. Now just as XLR stated, airhorn temps would be much lower but if you take 50 psi of 400* air and take it down to 200* it will have dropped down to 34.3693 psi that actually reaches the cylinders. Hence why NOS is so effective, it gives not only 37 % O2, but chemical intercooling that drops charge air temp dramatically and allows the motor to swallow more air.

XLR8R

OK - you guys with calculators - if a given mass of air is 100*F at 45psig, what is it's pressure at 350*F?

Mr Bee

Also, one thing not mentioned, compressed air is hotter and thinner than static air. If the larger turbo can move the same air with less pressure then it is creating less heat and you are getting a more dense air charge into the motor.

CamperAndy

The formula is for a fixed volume and for this it is

P2=(T2K/T1K)*P1

Where

P1 = starting pressure (psig)
T1K = starting temperature in Kelvin (Degree C + 273.15 = Kelvin)
T2K = ending temperature in Kelvin (Degree C + 273.15 = Kelvin)
P2 = ending pressure (psig)

So P2 = (449.8167/310.9278)*45

results P2 = 65.10 psig

Sorry for taking so long to get this back to you but I have been working and did not know this thread was still going

abc4yew

Man, I need an O5 turbo...on My truck 40psi of boost on the filter side of the CAC is 300 degrees Celcius, and on the intake side it is at least 150 degrees C. I wouldn't spray water if it wasn't 150 degree C. Water boils at 100 degree C. My CAC must be crap too as I'm only dropping 150degrees C. If I'm only doing runs. IF I'm towing forever and everything gets heat sunk with temperatures the CAC only takes 100 degrees C or less out of the air.

Drive your truck hard for awhile at 25psi boost then see how long you can hold your hand on top of the intake horn...

The engine needs the charge air heated to at least 100 degrees C to operate efficiently I was told.... If you spray too much water the burn is not as good as the intake air is too cold. Way too much water and you quench out.

We all should have a boost gauge and pyro on the intake and exhaust manifold to really see what is going on. KS

Kelvin being 273 degrees C affects you gozintas alot

PV=NRT

P1V1/NRT1= P2V2/NRT2

If T1 =50Celcius
and
T2=100Celcius
then it PV would be double...

But it is T1=323 Kelvin
and
T2 =373 Kelvin

So the difference between P1V1 and P2V2 is 15%

KS