Robert is correct to an extent, piping doesn't affect spool time, although it might take slightly longer for the pressure (boost) to completely pressurize the piping, which can sometimes add just a tad bit of "lag"... although in many cases, this is negated by an intercooler core with a lower pressure drop. I've datalogged boost pressures on WRX's with stock TMIC's vs FMIC's and have seen peak boost pressures come in at the exact same RPM on both setups, it really depends on the setup, and the efficiency of the FMIC core you're using.
You also shouldn't make less power either... think about it, if your stock TMIC has let's say a 3psi pressure drop, meaning, that during the heat exchange process, you lose 3 PSI of boost by the time it gets to the manifold... so if you're seeing 15psi at the manifold (most people with Mazdaspeeds tap the factory BPV connected to the manifold for boost pressure), your turbo is actually pushing 18psi, it's just losing 3psi going through the intercooler. Now, if you're running a FMIC that has a lower pressure drop, let's say 1psi, if your turbo is still pushing the same 18psi, at the manifold, you should now be seeing 17psi as opposed to the 15psi you were with the stock manifold... in theory there should be no power loss, and, on top of that, if you adjust the boost to see the same pressure at the manifold as you did with the TMIC, so we'll say 15psi, now because of the lower pressure drop, your turbo will only have to push 16psi in order to see 15psi at the manifold... meaning, your turbo wouldn't have to work as hard, and in the process, since your turbo would be spinning at a lower RPM, you should also see lower IAT's, which could not only result in more power (although probably minimal gains if any) but the lower IAT's will more importantly make the car more resistant to detonation. More resistant to detonation would mean less likely you are to get knock counts... less knock counts means a happier ECU... happier ECU means it's less likely to pull timing, which would have decreased overall power. This is a good thing.
Now, if you are seeing a loss in power, it's most likely for one of the following reasons:
1. You have a boost leak. With a FMIC, you have a lot more piping, more couplings to tighten, hoses to connect, ect, it's very easy to have a boost leak if you don't know what you're doing and don't clamp everything down properly.
2. Your factory BCS (boost control solenoid) is allowing the wastegate to bleed more boost. This is also common among certain cars, and also the reason why some people bolt on an intercooler with a lower pressure drop, and at first the car feels faster, but this effect slowly dwindles over time. Your car has a MAP (manifold absolute pressure) sensor, that often times works in conjunction with your BCS. When the MAP sensor sees 17psi, yet, something in your ECU's algorithm says you should only be seeing 15psi, it can allow the BCS to not bleed off as much pressure coming from the compressor housing, which would cause your wastegate to open at a lower boost level, bleeding off more boost pressure, resulting in the same (or sometimes lower) boost pressure at the manifold as you were seeing before swapping to a more efficient intercooler.
The only way to combat your factory BCS bleeding off boost... engine management. Or of course a boost controller, which essentially takes your factory BCS out of the loop somewhat, and allows you to set you boost to the level of your liking. The problem with a boost controller without any other form of EM, is that you obviously wouldn't be tuned for it, and could run lean in some areas, which could lead to motor damage depending on how lean you're running that car... that combined with the fact that if you take your ECU's boost control out of the loop, that's another safety parameter you no longer have, as the ECU will now have no way to bleed boost off in the case of a run lean condition, or overboost.
Boost controllers can be wonderful tools IMO, but only when paired with a good source of engine management. Their ability to control boost can in some cars helps make and hold boost where the OEM BCS would have trouble, but in order to be on the safe side, you must run some form of EM and tune for it. Most people (like myself), just prefer to tune with the factory BCS if possible, mostly just for simplicities sake, as for most applications, the OEM BCS is more than adequate. Especially in the case of the Mazdaspeed 3/6, as I've heard they have very advanced BCS' from the factory.
Now, with that said, in order to actually make more power out of a FMIC setup, in most cases, you're going to have to make sure you have no leaks, and of course... tune for it.
I would recommend a FMIC for non-horsepower reasons though. Do you know why Mazda used a TMIC for the Speed3/6? Cost cutting and ease of packaging. It's an inferior design (to a FMIC) that is more prone to heat soak. I would recommend a FMIC to anyone just for it's increased ability to cut down on heat soak... when the TMIC gets hot, not only does your pressure density go down (colder air is denser) which brings down power, the higher IAT's (intake air temperatures) go up, and higher IAT's are more likely to detonate... so not only do you lose power when your car is heat soaked, it's more likely to det.... if it dets, even just a couple of minor knock counts that probably won't hurt the motor (probably won't, doesn't mean they can't), your car is equipped with a knock sensor from the factory, which, it's signal is transferred to the ECU... when the ECU sees a knock count, what do you think it does? Likely it pulls timing, in an attempt to make the car run safer... what happens when you retard timing? You lose power.
Which is why in short, I recommend a FMIC to anyone who is serious about eliminating heat soak.... even on a stock turbo.
Side note: Just to let you know, not sure what you meant about a "larger turbo like a Subie", as yes, the STI's VF39/43 is larger than the Speed's K04, but not all Subies run a VF-series turbo, the 02-07 WRX's ran a TD04-13T, which in fact is actually smaller than the Speed's K04. So, not all Subies have "larger turbos". Just an FYI.
Has anyone seen this?
Good explanation though, and I agree 100% cost:benefit is better with the FMIC vs. ricer hood.-
TJditallo
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