forgot i wrote this up… i don’t think i ever posted it up.
it wasn’t totally finished, but i have become old and lazy.
so enjoy
For this to be of any real use you are going to have to know what the efficiency rating is for you intercooler. I am sure some digging on the internet, or a call to the people who made it will give you the answer you need.
What’s that big shiny hunk of aluminum do? Its a heat exchanger just like your radiator. It pulls the heat out of the air passing through it thereby lowering your intake temps and giving you more dense/cooler air. It will actually lower boost?!?!!?!? oh no’ssss
Yes, that’s right. The colder more dense air will actually be at a lower boost pressure. (that’s a good thing)
Here is a quick example…
If we take some cylinder (size is no matter) and fill it with air, and then cap it off, it will be at 14.7psi. Now if we were to heat that cylinder up 100*C it would raise about 5psi (give or take). :shock:
So figure the air coming out of the turbo to be the hot air, and the air from the intercooler to be the cooler air. That’s the pressure drop.
Ok back on track.
Lets say its a 60F day, and your turbo is pumping out 10psi at a blistering 260F. That’s a temperature rise of
260 - 60 = 200F (that’s hot)
and lets say that your intercooler is 60% efficient. That means it will remove 60% of the temp change.
200 x .60 = 120
This leaves you with an intake temp of
200 - 120 + 60 = 140*
That’s cool and all, but what we are concerned with is the change in density.
Change in density can be calculated with this formula
Dc = [ (Dt + 460) / (It + 460) ] - 1
Where
Dc = Density change
Dt = Compressor outlet temp
It = Intercooler outlet temp
So in our example we would have
Dc = [ ( 260 + 460) / (140 + 460) ] - 1
Dc = ( 720 / 600 ) - 1
Dc = .20
In theory that means we will have a 20% increase in density, and a 20% increase in power…but that’s not going to be the case. The intercooler is a restriction, as well as the rest of the charge pipe. There is also the inherent pressure drop from the air being cooler after the intercooler. If your piping and intercooler aren’t total crap you shouldn’t see more than 10-15% pressure drop from the turbo to the manifold.
How much power am I going to make with this hunk of aluminum?
HPr = Dc + 1 – [ (Ap + Bc) / (Ap + Bm) ]
Where
HPr = Rise in HP
Dc = density change from the intercooler
Ap = Ambient Pressure
Bm = Boost pressure at the manifold
Bc = Boost pressure at the compressor
Lets look at this with the data we have been looking at. We are getting a 20% (Dc) increase in density, Ap is 14.7 (we are at sea level), pressure in the manifold (Bm) is the boost pressure minus the 15% loss thought the pipes; so that gives us 8.5psi, and pressure at the compressor (Bc) is 10psi. lets fill in the equation.
HPr = .20 + 1 - [ ( 14.7 + 10 ) / ( 14.7 + 8.5 ) ]
HPr = 1.20 - ( 24.7 / 23.2 )
HPr = .14
That’s a 14% increase in power.
That’s pretty good for a big hunk of aluminum. Just imagine what would happen if you shelled out cash and bought a real intercooler… Something that had say… 80% efficiency.
