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As pretty much everyone knows, the factory air filter housing is a freaking joke.
It's amazing these cars run as well as they do with this abomination attached to the MAF inlet.
I can't imagine how some engineer thought it was a good idea to design it like they did.
And, on top of that is the fact that the grill openings in the bumper are blocked off blanks, only opening in them is for the fog lights, no appreciable airflow at all.
At the very least, opening the grills would allow air to enter and get to the air filter housing, where it would bounce off of it since it is hardly capable of taking in all that extra air.
So, looking at the slim pickings for a good C5 CAI, I am going to engineer my own.
In the interim while waiting for parts to get here and get started fabbing things, I took the cover off the stock filter housing and zip tied the filter to it, but am not flipping it and cutting a hole in the air shroud to the radiator.
It is just temporary, and my car is not driven in the rain, so am not worried about water getting in the filter.
It does whistle a tune now, it is happy to be breathing a little more freely!
It was funny, one of the grommets from the air intake bridge was missing when I was removing the filter housing and all, when I took the air filter housing apart, the grommet fell out on the floor!
Unless you do a baseline dyno run how will you know what you're engineering will actually make a difference? If you really go thru with it it'd be interesting to see what each system you install dyno's at, both good and bad. Like an Engine Masters experiment.
Unless you have access to cool ambient airfrom outside the hood area you are just making a noisier air cleaner. the engine heat from the closed hood gives you air intake temps of 150-170F degrees gong into the TB. a good scan tool will show you what the temps are while going down the road. In the early days of the C5, engineers were always looking to increase the amount of oxygen entering into the TB with various different air intakes. The first was developed by a few GM engineers/programmers and was called the Icebox, then a few more followed such as Calloway, etc. and they all opened the radiator shroud and sealed the air intake to it. Also the VeraRam developed the fresh air intake from the front driving light opening. These all lowered the air entering the TB to a few degrees above ambient temps. After that the list of so called CAI came on the market thinking the original GM design was restrictive. Unless you were modifying the engine they did nothing, Many of the GM SCCA racer engineers used the Black Wing air cleaner because it was a superior filter during that time. In a stock engine HP/TQ depend on the amount of air entering thru the TB and the speed and temperature is measured at the MAF and the calculations are determined by the PCM (of which only 17% is programmable. The dual snorkel air cleaner actually lost 5hp because to much air was entering the MAF that is slowed the speed of air going three and the PCM adjusted downward its engine management adjustment. So while we commend your effort to create another air cleaner, it does not become a cold air intake unless you draw outside ambient air into the MAF. Cooler air is more dense and contains more oxygen per cc. HTH
Unless you do a baseline dyno run how will you know what you're engineering will actually make a difference? If you really go thru with it it'd be interesting to see what each system you install dyno's at, both good and bad. Like an Engine Masters experiment.
Unless you have access to cool ambient airfrom outside the hood area you are just making a noisier air cleaner. the engine heat from the closed hood gives you air intake temps of 150-170F degrees gong into the TB. a good scan tool will show you what the temps are while going down the road. In the early days of the C5, engineers were always looking to increase the amount of oxygen entering into the TB with various different air intakes. The first was developed by a few GM engineers/programmers and was called the Icebox, then a few more followed such as Calloway, etc. and they all opened the radiator shroud and sealed the air intake to it. Also the VeraRam developed the fresh air intake from the front driving light opening. These all lowered the air entering the TB to a few degrees above ambient temps. After that the list of so called CAI came on the market thinking the original GM design was restrictive. Unless you were modifying the engine they did nothing, Many of the GM SCCA racer engineers used the Black Wing air cleaner because it was a superior filter during that time. In a stock engine HP/TQ depend on the amount of air entering thru the TB and the speed and temperature is measured at the MAF and the calculations are determined by the PCM (of which only 17% is programmable. The dual snorkel air cleaner actually lost 5hp because to much air was entering the MAF that is slowed the speed of air going three and the PCM adjusted downward its engine management adjustment. So while we commend your effort to create another air cleaner, it does not become a cold air intake unless you draw outside ambient air into the MAF. Cooler air is more dense and contains more oxygen per cc. HTH
Uh-huh, tell me something I don't know...
Guess we'll see what I can come up with.
Anything will be better than the stock filter housing.
Yes, makes a noticeable difference above 3,000 rpm.
Frankly, until you have a cam, etc., you’re not going to net much with cool-er air in summer.
IMHO, get yourself a Z06 airbox ($150-ish) fill it with a Wix filter. Then start looking at cams and headers. Maybe a set of 243 heads. Just a cam, even a mild midrange, and tune will make a huge difference.The stock cams are really small…
So, the filter I ordered came in over the weekend.
It is a S&B and is actually the filter that came with their CAI, which was discontinued since demand has fallen off after 22 years...
This thing is really big, you can look at dimension numbers online, but until you have it in your hands it is hard to really tell, it is so fat it doesn't let the pins fit right in the bridge, guess the S&B bridge was shaped differently.
Going to have to do some re-thinking of my plans for the shroud, but I'll figure something out.
One good thing about this filter is since it was intended for the C5, it already has a hole for the A.I.R. tube to pop right in and since the filter housing is rubber or urethane, no grommet is needed, the hose elbow just fits directly in the hole.
Anyway, more supplies to fab the shroud should be here this afternoon, not sure when I will get to finish it, too freaking hot to work much on it.
Looks like what it needs is a big scoop in the front of the hood!
Well, braved the skeeters and heat, couldn't sit with these parts calling me to come out and play.
Anyone need a front hood seal? You can buy pre-cut pieces for $12 to $18, or do what I did and buy a bulk pack with 33 feet for only $15, so I have enough leftover to do about 10 more cars...
And, I drilled the openings in the grill blanks to let more air in.
Okay, finally got this thing fabbed and installed.
I may make some refinements and small changes later on, going to run it for a while and see how it does.
I made this out of a sheet of .125 thick ABS plastic, textured on one side.
This stuff cuts fairly easily, bends well when heated to about 300* to 350* using a heat gun.
Joined the seams with Gorilla Ultimate Epoxy.
First made a prototype/pattern in cardboard, flattened that out and traced onto the ABS sheet, cut that out, heated and folded it, then sealed the seams.
The first design I made was wider than the final version, but once made up in the plastic, it would not work.
I guess the cardboard was flexible enough that it allowed the hood to close, but once in the plastic form, the hood would not close.
Turned out the hood hinge buttresses were hitting it when the hood was closing, so I narrowed it up about 2.5" per side and it finally cleared.
A also ended up having to shorten the overall height by about .5" to get more hood clearance.
It is held in place with a velcro strap around the inlet hose behind the MAF, and more velcro up front.
Final configuration
Last edited by Ltngdrvr; Jul 27, 2025 at 09:31 PM.
I work in the performance aftermarket and the truth is the factory intake is not really bad. The K&N intake is only 11 HP improvement. We make a lot of money on these low HP items. Note too they are not cumulative with other parts most times. You can’t add a CAI on top if a programmer etc. you will see gains but not at the full rating of the parts.
Most CAI are very little gain and often open to water damage.
Spend the money on a Cam and heads if you really wants eat of the pants gains.
I work in the performance aftermarket and the truth is the factory intake is not really bad. The K&N intake is only 11 HP improvement. We make a lot of money on these low HP items. Note too they are not cumulative with other parts most times. You can’t add a CAI on top if a programmer etc. you will see gains but not at the full rating of the parts.
Most CAI are very little gain and often open to water damage.
Spend the money on a Cam and heads if you really wants eat of the pants gains.
Stock C5 air intake is total garbage, has almost zero outside air going to it, and a pitiful air box and crappy little panel filter.
Mine is at least going to get more available airflow, and cooler than just underhood air, especially at speed.
And, I only have just a little over $100 out of pocket invested.
Silly me, How could I have missed that! But of course it adds 25 hp, They couldn't say it if wasn't true could they.....Ha ha. We don't need no dyno when all we have to do is read the box.
Stock C5 air intake is total garbage, has almost zero outside air going to it, and a pitiful air box and crappy little panel filter.
Mine is at least going to get more available airflow, and cooler than just underhood air, especially at speed.
And, I only have just a little over $100 out of pocket invested.
We love factory intake systems
Factory intakes in general are designed to produce specific temp and pressures within the intake tract while also providing protection against debris and water, and its also nice if they are easy to service.
The target pressure drop as measured on the crankcase exit areas at wide open throttle with a OEM paper filter thats been 'broken in' for a couple weeks (1,000miles of driving or around 5 to 8% of filter lifespan) is approx 1.2"Hg to 1.8"Hg for majority of vehicle manufacturers. Some may adequate 0.5 to 0.7"Hg with low mileage filters at factory output.
As output increases, pressure drop increases, e.g. 1.8"Hg becomes 2.5"Hg and so on, due to friction creating addl pressure gradient at higher intake air velocity.
The target temperature somewhere around the temperature of plastic insulating manifolds on the running engine, I think 112*F to 118*F? became available. Thus air just over 88*F seems traditional at low flow speeds, consider that air temp can be 112*F when engine is off and flow stops, and also 88 to 95*F while at idle in traffic, and ambient during the moments just after a full clear such as wide open throttle.
We can calculate the time required for a full clear by comparing engine bay volume with engine breathing rate volume as,
With 10cubic feet as underhood volume,
An engine producing 500bhp (~430rwhp?) consumes approx XCFM * .069(115*F iirc) = 50lb/min, X is 730CFM with warm air
730CFM is 730/60 = 12 cubic feet per second
12 cubic feet per second of flow through a 10 cubic foot engine bay - we do math
At 500hp less than 1 second to bring intake air down from 90*F or whatever to ambient, no matter where the filter is placed or how hot it gets the air coming in.
The warm air's purposes is help vaporize fuel and improve economy. All power plants in the world run the highest feasible temperature for efficiency = economy. The incoming heat energy of air is useful to help do work during combustion.
The heat is problematic when compression increases so anytime combustion engines switch from economy mode to power mode, they need to start clearing out that intake air heat so it doesn't upset the fuel and overheat the engine internal parts like the piston which can butt ring ends and over-expand while develop internal cracking at high temperatures. Oil and air cooling the pistons are important in racing and must grow with hp/displacement ratio.
The goal of the factory intake seems ultimately for those two things:
-conserve heat energy of the engine as part of incoming air. (and just like also it may utilize exhaust heat/velocity component energy to help clear a cylinder and does 'work' to bring in fresh air against friction so the piston doesn't have to do that work instead)
-clean the oil by producing a pressure drop during WOT transitions as fast as possible by using the smallest volume and direct attachment with no restrictions to the crankcase from the air filter tract
Plus it also provides protection from debris and water (usually)
We can summarize even better,
-economy (conservation of energy)
-cleanliness (high mileage potential)
When we mess with that factory good intentions we had better know what we are doing, such as during forced induction,
-We should measure and set the crankcase depression to around 1.0 to 2.0"Hg at wide open throttle with a sufficient response time
-Ensure filter tract and crankcase is air tight by performing pressure test(1psi only) and/or other testing as available
-Ensure filtering is being done down near OEM or better particulate ranges, 1 to 2uM is a kind of minimum requirement for engines that you really really care about. If the engine cost is very high then I would be double or triple filtering down to 0.1uM or whatever I could get because it beats finding another engine.
Air debris is a serious insult to an engine
Summary:
Mimic factory intake pressure / temp for ideal economy and oil cleaning effects
It takes about a second to clear out the hot air at 500bhp
Addl notes recommendation etc...
If you want power use forced induction to double or triple output, leave mostly stock for reliability and quality(untouched original is its own kind of quality)
C5 Cold Air Intake
