Howdy all!
BACKGROUND
I've just spent the last few days reading a kabillion threads, articles, and papers on Air Intakes (AI): CAIs, WAIs, Ram Air Intakes (RAI), superchargers, turbochargers, and the like. Several of those were here from ecomodder.
What I found was a miasma of special cases where one type of intake would give better HP / FE in one regime, but could have the opposite effect in another. So I tried to distill down the things we can definitively say:
1) Reducing pumping loss through the engine improves fuel economy. Viewing the engine as a big air pump, that has the immediate corollary
2) Increasing AI pressure
could improve fuel economy under certain conditions, such as WOT on a fuel injected vehicle, vehicles with carburetors, turbos, etc. But under low load with fuel injection, the higher pressure is wasted, because the throttle just restricts to keep stoichiometric.
The essential problem is that, while a crapton of modifications make the oxygen at the AI more dense (cold, pressure), that delivers more
power, not necessarily better fuel economy. It helps pulse and gliders, but does little for someone like me who sets the cruise control.
I'm currently designing the front to Champrius 4.0 and a big part of that is how to properly route the radiator outlet flow. The stock design is to dump a huge portion right under the engine, and about 40 sq in through the cat channel. I'm going to enclose the entire engine bay as best I can, but am still concerned about air near the top of the radiator having to take several twists and turns to exit through a rough compartment.
My bright? idea was to put an (Warm Ram Air Intake) WRAI
behind the radiator near the top and connect it to the stock air box. Even if this does nothing for the engine itself, I believe it will give me minor gains just providing suction near the top of the radiator. More specifically, it will make the radiator more efficient enabling a smaller air inlet, and it will reduce outlet flow across a rough engine bay. This is maybe 0.5% stuff, but it's low hanging fruit since I'll be modding that whole area anyway.
Champrius is a 2009 Toyota Prius with normal coolant temperatures 185-190F and stock air intake around 5-10F above ambient. The inlet duct is located on the passenger side above the wheel, which goes through a resonator, then a hose, and into the air box. I've already done tests where using engine bay air directly makes FE
worse by around 2%, even though the temp was +5F higher. The only explanation I had at the time was that the higher air pressure near the front of the wheel was significant (I didn't know about RAIs back then), or that my margin of error was larger on those runs for some reason.
QUESTIONS
Would the WRAI described above (behind the radiator) be better than the stock intake for FE at 65 mph cruise control? That question really boils down to:
Does anyone know the difference in pressures at the wheel well top vs. behind the radiator? (Julian Edgar, where are you when we need you?
I know the MAF measures mass air flow and temperature, so this could be the same as...
Does the car measure AI pressure? If so, I could just mock up what I'm thinking and measure all the stats directly.
Can anyone think of issues with doing the WRAI? Right off the bat, it seems to me that we'd be trapping heat in a loop, which should help with cold starts / weather BUT might be dangerous in a heavy load / hot day scenario. Subtleties like ignition timing etc. need to change with the air characteristics, but I'm assuming the fuel injected ECU magically takes care of all that.
And for the bonus question: has anyone already built and measured such a device? I came across a ton of DIY mods for CRAIs (Cold Ram Air Intakes) but couldn't find any WRAIs.
Apologies in advance for ye readers that have already seen variants of AI questions a dozen times. If this is a standard question that I simply haven't found yet, please direct me to the appropriate sources and I'll do more research myself.
Thanks!
