Hey John, the intake charge is heated when it hits the turbo, which is why the UICP is typically called the "hot pipe" and this is cooled back down after the intercooler, which is why the LICP is typically the "cold pipe."
That being said, doesn't the MAP sensor account/compensate for the difference in density from the compressed, charged air entering the intake manifold, versus the air that would pass through a MAF sensor situated just after the air filter?
ok, don't want to beat this maf vs speed density thing to death, especially since it seems jumbo decided to go speed density anyway, but to answer frank on this....
I do know about the hot & cold side of the fmic, the turbo is not heating the air just because the turbo itself is hot, it is heating the air because it is compressing it & just the act of compressing the air itself raises it's temperature alot, just one of the laws of gasses in general. but realize that even the "cold" side, after the intercooler can be & most times is still hotter than the air originally entering the turbo, sometimes much hotter. there will be a difference in density. the air pretty much changes properties to the point that is is not the same measured air that entered the air filter before the turbo. now, the maf sensor is no longer acurately telling the ecu exactly what is entering the engine at all, the maf sensor is now almost performing like a load sensor instead of a true maf sensor. a blow through setup, while admitedly having the problem of turbulence & non laminar airflow, it is at least actually exposed to the actual density of the mass of air that is entering the motor.
contrary to what some may believe, a map sensor & speed density setups in general are not nearly as good as acurately measuring the mass air flow into the engine. that's right, from a fuel calculating standpoint MAF is definately superior to speed density. the main reason most will go to speed density is because a MAF sensor is usually a restriction, combined with the problems were talking about of both draw thru & blow thru complications that will render the maf that much less effective to begin with of acurately measuring the mass air into the engine, once the maf info is no longer acurate it looses it's big advantage...
speed density is guessing at the actual amount of air that it must match fuel too, it does not see the actual air at all. no, instead it just sees the rpm of the engine, the load(map) of the engine & the inlet air temperature, & from this information it must refer to tables to try & guess how much air is entering the engine. this is a tuners job, to modify the tables so that when the engine is operating in a certain perameter & at each & every different perameter the tables will show it how much fuel to add, all the while never actually "seeing" the air itself.
maf actually sees the air. if the ecu actually sees the air it can be easy to know how much fuel to add. that is why a maf car can have things done to it that can change the VE of the engine quite a bit & for the most part the MAF will still allow the ecu to do a good job of matching fuel to air. add headers, an exhaust & an intake & even a cam & it will still run pretty well as far as A/F ratio. the maf sensor sees more air, it adds fuel to compensate. on the other hand with a speed density setup the same changes that would alter the VE of the engine can really make it run like crap & will require retuning, the ecu running speed density is blind to the additional air entering the engine & can sometimes be even more misled by stuff like cam changes for example, it will see the decreased vacuum as add'l load & start to dump more fuel where more is not needed & will not know there is more air entering the engine at higher rpms either, the tables it refers to that tell it how much fuel to add will need to be altered accordingly....
in the end think of a maf setup as having eyes where a speed density setup is blind. speed density is only switched to when maf is at the point of being restrictive or no longer acurate, which is often the case when FI is thrown into the mix, a properly tuned speed density setup though can only hope to rival a properly set up maf setup if the maf can really stay acurate & not be restrictive...
---------- Post added at 02:06 AM ---------- Previous post was at 01:51 AM ----------
He also mentioned placing the BOV "as close to the turbo as possible" though I remember John mentioning at least 12 inches from the turbo, I think...
not I... I'd agree & say close as practical to prevent surge... although anywhere between the turbo & the intercooler will still do the job well really I think. it will still intercept & vent the reverse wave from the closed throttle body
