Stock Intake Box vs. Aftermarket Air Intake

[TopGun8818]

Alright guys, I went to the junk yard last week and picked up a stock air intake box unit (only $20 and came with a K&N filter in it). My car (2gb gsx) already came with an aftermarket Stillen intake when I bought it. The reason I'm asking for a comparison is because my underhood temperature gets extremely hot when the weather starts to get warm. I figure with this issue it might be a good idea to put the stock box back in as it is enclosed and draws in cooler air from the outside by the fender (yes, I'm aware the outside plastic part outside by the fender is positioned very bad and plan to detach it - I'll leave the rest of the air box assembly intact though). I'm aware of the custom CAI threads that are out there but I don't want to go that direction just yet. I plan to do the RRE hood vent mod in the coming months to draw the hot air out and help alleviate the underhood temperatures. Anyone seen a difference in terms of performance by doing this? I already researched the threads with no luck so I figured I start this new thread.

 

[my dreamt dsm]

Humm! I never notice a down fall when I replaced my stock box, kn filter with my kn fipk kit. Just gains imo.

 

[91stocker]

Do you have a tubular header? If you still have the stock exhaust mani, are you running the oem heat shields?

 

[TopGun8818]

I'm running a FP manifold with no heat shields. I'm sure in a car that's not running a front mount intercooler the open front bumper allows for better cooling to the radiator and so fourth. I noticed a big change in underhood temps once I installed the front mount in my vehicle. It seriously gets so hot that I have come to believe that the intake breathes really hot air which in turn decreases the effectiveness of running the aftermarket intake in comparison to the stock air box. There are plenty of threads where people have built a custom air box, CAI, and block off plate to keep the hot air away from the intake. As per their logs they have noticed cooler engine temps. I figure I could stick the stock air box to achieve the same goal - obviously there might be a HP difference as the stock box is more restrictive but at this point I just want to be able to run the car in the summer without worrying about overheating issues. Check my mods list, I have already upgraded numerous things to make the car run cooler including rewiring the mishimoto fans to come on at the same time along with a lower temp thermostat and aluminum mishimoto radiator.

 

[Pipnorcali]

I made a lil air box for mine dropped 10-15 degrees
This was my first one made with a old underhood shield n duct tape , I have a diff alum in there now but no pics.

A guy makes a blanket for the fp manifold

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[Melbowski]

IMHO I'd say to rock the stock box and reap the benefits: Cool air from the fender, heat-shielding from under-hood temps, less heat transfer from materials, bolt-on convenience, proper air-flow over the MAF, and more accurate data in the MAF Smoothing table within the ROM if you want to get hardcore. There really is no downside to using the stock box unless you're making a metric shit-ton of power, but lets break it down anyway.

Intake Temps: A primary problem with aftermarket intakes is that (as you noted) they sit right in the piping-hot engine bay with no shielding, pulling 200* air from the engine bay through the MAF. Also of note is that most are made of nice shiny metal, which are very nice to look at, but also very good at heat transfer... So not only are you pulling hotter air in, but the pipe itself is transferring more heat into your incoming air than the stock system would. Every 100* air rises, it loses about 5% of its density; basic thermodynamics tells us that aftermarket intakes are likely worse than stock just by placement and materials. That is what I would call a "downgrade." A true cold air intake is about the only option worth your time.

Restriction: Some will talk about air flow restriction, but honestly on a turbo-charged vehicle that's negligible since the turbo is actively pulling air into the motor. You're not going to hit real power-raping restriction on a turbocharged motor until either your filter is so full of gunk that it can't flow, or the intake tube is blatantly too small, i.e. the speed of the air coming through the intake is approaching the speed of sound and therefore cannot move any faster through the intake. Lets also not forget that this rate of air-flow is determined primarily by the turbo's inlet port, which your intake tube has to shrink down to fit. You could run a 5 gallon bucket as your intake pipe and it's still just going through a tiny hole at the bottom where it connects to the turbo inlet port.

Turbulence is still a problem though, and is probably the only area I feel aftermarket intakes take the cake. The "ribbed for her pleasure" design of the stock intake is primarily for assembly convenience and sound deadening, not for performance. Even in that case, the only intakes that win out are the pricey ones that are polished nice and smooth inside; anything cheap off ebay looks like they're sandblasted on the inside, and are far from smooth. The cheap units may still be better turbulence-wise over the stock tube, but likely only marginally so.

MAF Flow: The stock MAF is literally calibrated to be used with the stock box. Any changes to the intake (box/inlet tube/inter-cooler piping/etc) will skew the air-flow data. You can see this data on the MAF Smoothing Table within the stock ROM. For reference look at a 3/S smoothing table; even with the same MAF, table values are quite different simply because the intake systems are very different. Luckily the ECU uses the O2 sensor at idle and while cruising to make adjustments to this error so your fueling remains consistent (note this does not adjust the smoothing table, it merely adds/removes fuel based on a linear trim adjustment percentage). However at WOT these trims are almost completely ignored, and leads to fueling that is not consistent with the values in the fueling table. The difference is not extreme, but it's definitely there.

Also a note on oil-coated filter elements; I'd suggest sticking with a dry-flow design. Though our cars don't use a hot-wire style MAF like GM cars, the Karmen Vortex style sensor is not immune to oil contamination. Luckily for us it doesn't stop it from working, but it can reduce its ability to properly calculate air-flow. If you're like most DSMers, you want that MAF as precise as possible to keep your baby running as smooth as possible.

There's still more to it, but I'm calling it good with the novel I have here. Long story short: use the stock intake box setup. Unless you're rocking a true cold air intake you're just wasting your time. Even if there is an improvement from using an aftermarket intake it would likely be a couple whp at most, so unless your car is a dyno-queen you're not going to see any benefits. Seeing as your mods put you at a mild street-build and I don't see any tuning hardware/software, I don't see the intake being anything you should worry about. Also get a heat shield for that FP manifold; the more heat you keep in the exhaust, the less you let get into the engine bay. Just my two cents.

 

[TopGun8818]

Melbowski, this is the exact feedback I was looking for. Thank you for the write up.