Is it possible to have an intercooler that is to big for your turbo?
for instance
do you think this intercooler is to big for a stock turbo
yes
:word:
Power Gain of IC & Pipes: HP rise = Density Change + 1 - ((Atmos Psia + Comp Psig) / (Atmos Psia + Manifold Psig))
Density Change: ((Turbo Outlet Temp + 460)/(IAT+460))-1
IIRC
so what exactly makes an intercooler to big for a turbo
and what disadvantages are there from this
its too big when pressure drop becomes an issue. then your just making your turbo do all that work for nothing lol
i started working on an intercooler write up a while back. i will finish it this weekend/early next week.
take a look at boostangs post. i assume he didnt just make that up, but i dont have the time to compare them to my notes. perhaps a couple of us can put together a write up.
oh, found it in my docs… here is what i had, but it still needs to be cleaned up. there isnt anything in there about pressure drop yet.
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).
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.
Pressure drop
Another aspect of intercoolers to be considered is pressure drop. The pressure read by a boost gauge is the pressure in the intake manifold. It is not the same as the pressure that the turbocharger itself puts out. To get a fluid, such as air, to flow there must be a difference in pressure from one end to the other. Consider a straw that is sitting on the table. It doesn’t having anything moving through it until you pick it up, stick it in your mouth, and change the pressure at one end (either by blowing or sucking). In the same way the turbo outlet pressure is higher than the intake manifold pressure, and will always be higher than the intake pressure, because there must be a pressure difference for the air to move.
The difference in pressure required for a given amount of air to move from turbo to intake manifold is an indication of the hydraulic restriction of the intercooler, the up pipe, and the throttle body. Let’s say you are trying to move 255 gram/sec of air through a stock intercooler, up pipe, and throttle body and there is a 4 psi difference that is pushing it along (I’m just making up numbers here). If your boost gauge reads 15 psi, that means the turbo is actually putting up 19 psi. Now you buy a PT-70 and slap on some Champion heads. Now you are moving 450 gm/sec of air. At 15 psi boost in the intake manifold the turbo now has to put up 23 psi, because the pressure drop required to get the higher air flow is now 8 psi instead of the 4 that we had before. More flow with the same equipment means higher pressure drop. So we put on a new front mount intercooler. It has a lower pressure drop, pressure drop is now 4 psi, so the turbo is putting up 19 psi again. Now we add the 65 mm throttle body and the pressure drop is now 3 psi. Then we add the 2.5" up pipe, and it drops to 2.5 psi. Now to make 15 psi boost the turbo only has to put up 17.5 psi. The difference in turbo outlet temperature between 23 psi and 17.5 psi is about 40 deg (assuming a constant efficiency)! So you can see how just by reducing the pressure drop we can lower the temperatures while still running the same amount of boost.
I have seen some misunderstandings regarding intercooler pressure drop and how it relates to heat transfer. For example, one vendor’s catalog implies that if you had little or no pressure drop then you would have no heat transfer. This is incorrect. Pressure drop and heat transfer are relatively independent, you can have good heat transfer in an intercooler that has a small pressure drop if it is designed correctly. It is easier to have good heat transfer when there is a larger pressure drop because the fluid’s turbulence helps the heat transfer coefficient (U), but I have seen industrial coolers that are designed to have less than 0.2 psi of drop while flowing a heck of a lot more air, so it is certainly feasible.
Pressure drop is important because the higher the turbo discharge pressure is the higher the temperature of the turbo air. When we drop the turbo discharge pressure we also drop the temperature of the air coming out of the turbo. When we do that we also drop the intercooler outlet temperature, although not as much, but hey, every little bit helps. This lower pressure drop is part of the benefit offered by new, bigger front mount intercoolers; by the Duttweiler neck modification to stock location intercoolers; by bigger up pipes; and by bigger throttle bodies. You can also make the turbo work less hard by improving the inlet side to it. K&N air filters, free flowing MAF pipes, removing a screen from the MAF, removing the MAF itself when switching to an aftermarket fuel injection system, the upcoming 3" and 3.5" MAFs from Modern Muscle, these all reduce the pressure drop in the turbo inlet system which makes the compressor work less to produce the same boost which will reduce the turbo discharge temperature (among other, and probably greater, benefits).
hope this helps
:tup: thats pretty much what I have in MS Excel too.