Originally Posted by Inygknok
well, i was organizing all the parts in boxes the other day to clean up the mess i did in one of the rooms.... my mother finally got my gf to bitch at me about it.
so anyhow.... i was staring at the intercooler and thinking on it...... true, if u have a too big of an intercooler, with piping (from turbo to IC to intake manifold), there will be a pressure drop, which means that working the turbo at higher pressure levels would become pointless.... at least in a street car.
so.... in order to avoid as much pressure drop as possible... how would i go about finding out just how big i could go on an I/C and piping without having that high of an effect on the pressure?
im very concerned since i wanted to order up a custom intake manifold from a guy in some supra forums. he does a very kick ass job, and not that i dont mind, but the manifold turns out to be 4 inches thick (a lot more than stock). ill ask him and some of his other clients how the manifold has affected them, but i would like to know if someone here is capable of doing the whole math and help me figure out the answer.
You need to understand a few things here. Generally a larger intercooler will have less impedence to flow than a smaller one. The coil is made up of two headers with parallel heat exchange tubes. So the larger the IC the less pressure drop .
A large IC will have more volume, so you can expect a delayed pressure at the plenum as the turbo spools up. This is where you have to balance lag with performance.
When the car is stationary the exhaust heat is localised around the exhaust piping. On a FWD it generally means that a front mount will be exposed to exhaust manifold heat. This leads to heat soak, which raises the charge temp initially. So a large IC will take longer to cool under driving conditions.
If you are running an IC with say 2 psi drop, you need to look at your wastegate setup and install a compensating boost controller. You will also need to check your turbine and compressor performance to make sure there is satsifactory boost at desirable rpm. You may find the tendancy for stall increases, although if are reducing the drop it may actually improve things.
I would be pursuing an IC with static regain headers. You can identify these by looking for tapered plenums. This promotes even flow through the matrix tubes.
Although fairly uncommon, have your guy weld a threaded nipple (or boss) to the low point of the headers. You can then fit pet cocks to drain any oil accumulation that may occur over time.
Don't be too over the top with mandrel this and mandrel that. When some oracle tells you it provides laminar flow, be assured that the reynolds number is so high there isn't a chance in hell it will ever approach laminar conditions. Just go for radius bends with least obstructions to reduce turbulance and flow seperation.
In so far as working out pressure drop, you need to establish your index performance. For example if you want to work around 6000 rpm you can approximate the flow by using litres disp x rpm x VE/120. e.g. a 1.8 litre engine will have a swept volume of 1.8 x 6000 x 0.85/120 = 76.5 l/s (162cfm). You find the density ratio you work out by applying the ratio of the ambient temperature to the adiabatically adjusted boost temperature. The next step is to simply apply the flow, density and temperature figures to the capacity index value of the IC and square it to find the drop.