neevosh

I'm using the RX-7Fashion kit with the Apex core. Today I was bored so I measured my pressure loss from the intercooler. With boost controlled by the wastegate spring, I measured .62 out of the compressor and .45 at the manifold. That's a differnence of .17kg/cm3, or about 2.4psi. I don't know if that's all intercooler or if the throttle body had a small part to play in it. My significant mods are DP and Apex GT CB.

Pressurized

Typical pressure drop for an intercooler is arounf 1psi...

maxcooper

Neevosh, good for you for actually measuring this.

I have heard reports that the RX-7 Fashion A'PEXi core intercooler has somewhat high pressure drop. Your measurements confirm this. My guess is that the average IC has about 2 psi of pressure drop. Only the very best (by this measurement) have something down near 1 psi. Lower pressure drop is always better, but it is not the only factor to consider.

Pressure drop depends on a lot of things, so the same IC on two different cars could have different maximum pressure drop. The pressure drop increases with the amount of flow, so the highest measurements will be found at high RPM under full boost. Different cars flow different amounts of air, so there will be variation from car to car.

You will make more power at the same boost level if you had an IC with less pressure drop that cooled the intake temps to the same level.

-Max

SleepR1

Max,

I'm confused again with pressure drop from an aftermarket IC.

I thought with a pressure drop (from a large IC), you get less exhaust restriction, and thus the turbos can "suck" in more air, and thus more boost. I thought this was the reason for upgrading the ECU if I decide to go with an M2 Large IC?

In fact you'd make more power with higher pressure drops from a larger IC, so do I have a** backwards again (ay, Dio, mio!).

maxcooper

You have to hold manifold (after the IC) boost pressure constant to consider the effects of IC pressure drop. One common misconception about pressure drop is that it is a "pressure drop" in your boost -- it isn't. It is just the difference in pressure before and after the IC.

Exhaust restriction increases with pressure drop, which means power goes down as pressure drop goes up. Why? Because the turbos have to make your manifold boost pressure plus the pressure drop. When the pressure drop is high, your turbos have to do more work to make up that pressure (to maintain the same boost in the manifold) and thus offer more exhaust restriction. Of course, more exhaust restriction means less flow, which lowers the pressure drop that you will be able to measure. All this stuff is related, but it is very clear that pressure drop is universally bad. The lower the pressure drop the better.

But, pressure drop is not the only thing to consider, so you have to weigh the effects of pressure drop against other factors (like IC cooling efficiency) when making IC purchase decisions.

Big ICs tend to have lower pressure drop, because their cross sectional area is bigger, giving more room for the intake charge to flow through. It is ICs with small cross sectional area, or convoluted piping, or crappy end tanks, or a core that doesn't flow well for its size that have high pressure drop. Few ICs are good in all of these areas, but the least offensive units have the best (lowest) pressure drop. I don't have any first-hand experience with the IC this post was about, but it seems that this unit has piping and end tank problems. The core might be bad, too, but that seems unlikely considering the other applications it is used for.

-Max

SleepR1

Thanks for clearing me up again, Max! Wade Lanham had explained this to me before, but everytime I see the words, "pressure drop", I get it all ***-backwards again

So basically high IC pressure drop is bad, low IC pressure drop is good, but everything's relative to everything else...yeah, I think I get it...

I'm going back to the supsension/wheels/tires/brakes forum now...I get that stuff