Truth on Cold Air Intakes

[Willie 66]

Hey all,

I would really like to start a "scientific" thread sharing real benefits and drawbacks of cold air intakes. Giving real data from dynos would be a great treat, especially if there are before and after runs. If you decide to share, please give good details on your particular application to help out the guys and gals who may be considering purchasing a CAI.

Here's my vehicle:
I have a 2002 GMC Sierra 1500, Extended Cab, 2WD with the 5.3L. Approximately 160,000 miles. Rear end gears are 3.73's. I have 18" aftermarket rims with ever-so-slightly oversize tires. The only performance parts I put on prior to the CAI was a true-dual cat-back exhaust setup: Flowmaster 40's, no crossover, dumped under the truck. I've owned the truck since October 2010 and have never once touched 17 mpg, even on the highway (I got 16.9 once on a straight run down the interstate). I live in southeast Texas to give y'all an idea of climate.

Here's my experience:
I purchased the CAI hoping to make good on the promise of horsepower and mileage gains. I figured out that with 1.5 mpg gains, I could financially "break even" within a year, given how many miles I put on the truck annually, how much the CAI cost, and the price of gas. As far as power goes, I was hoping for a cost-effective gain in torque for towing and highway passing power.

I purchased the AEM Brute Force intake mostly because I like the look over other options. The dry filter was also a plus. I figured all the CAI's on the market are pretty much the same anyway: same size tubes, shapes, materials, cone filters. I could have got all crazy with it and did the ram air tube down to the air dam and wrapped the tube with insulation, but there was no way I could justify the extra cost.

I waited about a tank or two of gas to really test the truck since I knew the computer would need to do some adjusting. Being the car nut that I am, I really pay attention to the way my truck acts and reacts to my inputs. Since I installed the CAI about 3 months ago, I felt a noticeable drop in torque particularly between 2000-3000 RPM. This sucks, because this is both highway cruising speed and a happy spot for towing; however, once the engine revs above 3000 RPM, it has a noticeable gain in power. The CAI made the engine really punchy when downshifting to 2nd at about 60 mph. Both of these situations (bad low end, good high end) are reflected in the handy-dandy dyno sheet which came in the box with the intake. The dyno sheet showed the torque and power curves of a GM 6.0L before and after the CAI - There was a drop in power in the low range, and a rise in power in the high range. Not the same engine as mine, but comparable enough.

There has been absolutely no gain in mileage. No change in driving style. Perhaps we can attribute this to the low gears and the fact that yes, this is a pickup with a really high drag coefficient... Still, I expected to see mileage increase to at least 17.

Here's the TL;DR summary: CAI was bad for low end torque, good for high RPM horsepower, and yielded no gain in mileage. Side note: the added rumble is BOSS. Truck sounds great.

Like stated above, if anyone has real before and after data that could add to the discussion, that would be fantastic.

[ironroad9c1]

Flowmasters are the worst exhaust you can install, contrary to the name(great marketing ,poor product) they do not flow.

[Keith Seymore]

Well...since I designed the system in question (the GMT800 engine air induction system; most of which is still in use today) I might be able to share some insights -

The system was capacitized for the "big engines" of the day: the L18 8.1L large block and the 6.2L diesel.

Flow restriction specification (from GM Powertrain) was a ridiculous 1" Hg restriction at "max flow", from the ambient air inlet to the intake valve. Since that was essentially unachievable, and since we (the vehicle side) cannot control what goes on inside the engine, we negotiated that back to "from ambient air inlet to the throttle body inlet", which was more in line with what we could control. Max flow was established as 272 g/s.

Since the system was designed around the biggest engines, that means it was over achieving for all the smaller engines (4.3L, 4.8L @ 212 g/s, 5.3L @ 230 g/s and 6.0L @ 242 g/s). So, from a restriction standpoint, you shound not see any improvement in going to an aftermarket air induction system.

From a cold air standpoint - the gains from air inlet temperature reduction are enough to offset any increase in flow restriction, but we also had stringent air inlet temperature increase requirements that were met. The fender inlet shields the intake from hot underhood air, while also preventing water ingestion (those two requirements are typically at odds with one another).

Lastly, the tuning devices that you see: quarter wave tuners and helmholz resonators, are not in the flow stream and do not affect restriction. They are tuned to attentuate specfic targeted frequencies, and absorb the energy pulses as they radiate backwards out of the throttle body.

Bottom line - the production system was designed by a "hot rodder" and was consciously packaged and components chosen to minimize flow restriction; an aftermarket intake is incrementally directionally correct in some aspects, but probably not measureable.

K

[ironroad9c1]

Yep I have never understood why people don't understand all the money that went into designing and testing the factory parts for maximum efficiency, they didn't just slap some tubing on there and call it good. They are trying to squeeze the most power and fuel economy out of these engines due to the meddling government telling em they need to get 40 mpg in a truck.

[Keith Seymore]

Originally Posted by ironroad9c1

Yep I have never understood why people don't understand all the money that went into designing and testing the factory parts for maximum efficiency, they didn't just slap some tubing on there and call it good. They are trying to squeeze the most power and fuel economy out of these engines due to the meddling government telling em they need to get 40 mpg in a truck.

I started in the group on January 2, 1994 (for a 1999 model year program). There was me, my supplier design engineer (Delphi), one development guy at Milford, one water ingestion engineer and one manufacturing guy.

So there's 5 engineers, full time, for four-ish years, with one engine dyno, one flow bench, one Noise and Vibe cell and both GM proving grounds at our disposal.

It's hard to match that doing a "shade tree" (or aftermarket) design.

K

[Keith Seymore]

There are some "architectural" things we did, too, that you might not notice. These were required to even give us a shot at getting in the game.

The '96 and beyond GMT400 models had the round element air cleaner on top of the fender, with the battery in the RF corner (passenger front) of the engine compartment.

It became obvious to me that I needed a flat filter in that spot to minimize the turns in order to even have a chance at meeting the aforementioned very aggressive flow requirement. So - I started a movement to displace the battery to some other location. Naturally the battery guy wasn't very happy about that.

We were stuck in a stalemate until the Chief Engineer, Ken Sohocki, took notice and called us into his office. He made each of us pitch our idea. In my case, I had actual flow data generated on the bench using rapid prototype material, and could demonstrate the effects with objective test data. The battery guy's response: "but we've always been right here".

The Chief's direction was swift and clear: "Seymore - you get the front corner. Schaule - find another spot".

So he moved the battery to the front of dash (rear of the engine compartment) so that he would have some structure to support his bracketry.

The engine air induction has been in the RF corner since that time, for GMT800, GMT900, K2 and now T1 generations of full size truck.

K

[Keith Seymore]

We weren't out of the woods yet, however.

The next hurdle was that the engine coolant overflow bottle was on the front of dash. That allowed the assembly plants to evacuate and fill the coolant system prior to fender install.

With the battery now on the front of dash that meant the coolant bottle had to move somewhere else, the only other place being top of the wheelhouse on the RH fender. Unfortuately that meant you couldn't fill the sytem until after the fender was on - or - you had to move the filling station. That wouldn't work because it was one brazillion dollars to move a "monument" per plant times 7 truck assembly plants = 7+ brazillion dollars.

So here is what we did: we developed a way to "stage" the coolant bottle on the radiator support temporarily by adding two "buttons" on the rad support and a tab on the bottle. The bottle could be hung in this temporary location, evac and filled, and then moved to its permanent location on top of the wheel house after the fender was installed. Problem solved, with no tooling change and pennies in piece cost.

We briefly discussed if we should remove those buttons or if it made more sense for them to remain on the truck for the life of the vehicle. In the end it was cheaper and didn't hurt anything, so they stayed. If you look at any GMT800 fullsize truck you should see those two buttons on the back of the rad support, just going along for the ride.

K

[Keith Seymore]

One more story: I mentioned earlier that water is the bane of any engine induction system engineer's existence.

The problem with the GMT800 was that not only was the truck new but the engines were a new design, too. That meant there weren't many around and you sure as heck didn't want to damage one.

Water ingestion testing is, by definition, a destructive test. If you put enough water in the cylinder you will break it, the rod, the piston or whatever is weakest. If you don't break it you don't know how far you can push it.

We debated for a couple months about how (and if) we were going to test our design. Finally we hit upon an idea: we found an "old" prototype GMT800 radiator support and fender in the trash, so we added those to a carryover GMT400 pickup, and then installed our new induction system to emulate the new front corner. We remote mounted the engine air cleaner in the existing truck and then plumbed our new system to a shop vac (and generator) in the pickup bed. That allowed us to (a) drive the truck in the water trough, (b) not damage a current production engine (c) flow air through our new system in a somewhat representative environment and (d) collect and measure any water that was drawn in. Pretty clever, I think.

I still remember the first time we hit the 1000 ft trough at 25 mph with 12" of water: water was spraying over the top of truck and flowing big time into the cab through the heater box. I felt like I was on the Titanic, pulling my feet up on top of the instrumentation and screaming like a little girl. But - our basic idea worked and we were able to continue the development process.

I was still pretty nervous, though, the first few times we had rain once we started driving the trucks on the road.

K

[Keith Seymore]

Your move, K&N...



K

[ironroad9c1]

lol i love stories like this....

[Willie 66]

Keith,

Thanks for the reply. I've read some of your posts before and picked up that they weren't exactly worth the money - but that was after I already bought mine

It's really cool to hear the history of it all - thanks for sharing. After inspecting my own stock intake, I can definitely see the engineering that went into it.

A while back, I bought a K&N drop-in filter (no intake mods) expecting to see some increases in efficiency with it, but alas, the only thing it did was prevent me from buying a new paper filter over the 4 years I had it installed. As a result, the ROI for the drop in came pretty quick, as I picked the filter and cleaning kit pretty cheap.

Without knowing the engineering already put into the intake, I figured that even just a cone-style filter with more surface area would be a quick and dirty way to "let the truck breathe better" and I might see some gains from it in both efficiency and power. Obviously, that kind of thinking put me $250 in the hole!

Even so, I would still like to see some numbers from some real people (not intake manufacturers) before and after cold air intake installation. Might keep the next guy that has money burning a hole in his pocket from spending it unwisely.

[68C15]

Originally Posted by Keith Seymore

Your move, K&N...



K

[68C15]

I see vehicles come in my shop with these aftermarket systems. When I compare them to original designs I see them to be more of a "hot air intake" since it draws air from engine bY, not the fender.

Plus you have to figure in the life of the filter. I'm not going to discuss serviceable filters here, stay with paper type for this discussion. Most "CAI" systems I see come in with dirty filters, yet in all my years of working under the hood I have only replaced 3 filters on the 96-current models. Two were asked to be replaced while the third was due to an operator induced engine fire. In my area (northern plains states) the air inside fender is clean. Pretty amazing considering we have so many trucks driving on gravel roads.

Now, let's talk about performance gains
The gains I see claimed are in horse power. Those gains are shown at high RPMs, and ar far above what most people use. "15% increase in HP @ 5500". That's really pushing it unless you are racing. If you're racing you can kiss your warranty goodbye. If you are full-on racing then you don't care about warranty and will most likely have a vehicle barely resembling original other than body shape

Summary;
Cold air intakes are good for one and only one purpose. To separate money from you

[68c10airstream]

Keith, where were you when i was working as a gmc dealer mechanic in the 90's! Couldn't agree with you more on all accounts! Don't get me started on cleaning mass air flow sensors from K&N oily bug screen filters! A couple of my friends run K&N and call about every 6-9 months with ill running 5.3's. My question is: still running the oily bug screen filter? Cleaned you maf sensor like i told you? Response' ok i'll go do that!

A friend installed an aftermarket cai on his 2004 duramax diesel and said performance was worse! I looked at the system and it was sucking hot underhood heat and possible water (diesel death)! I said to put the stock system back on and draw air from the cooler and schielded inner fender. Haven't seen him in a while for an update.

Thanks for posting! Made my day reinforcing the stock parts working pretty damb good.

[Daubs]

Originally Posted by Keith Seymore

Your move, K&N...



K

Excellent stories...THANK YOU for sharing!!!

[OutlawDrifter]

hard to beat solid engineering. even if you add more flow, the maf sensor will account for this and adjust fuel trims accordingly, therefore no gains. colder air and a cleaner flow path would be the only gains if any, and at low rpm, would be difficult to measure.

[indymachinist]

Originally Posted by OutlawDrifter

even if you add more flow, the maf sensor will account for this and adjust fuel trims accordingly, therefore no gains.

No.

[OutlawDrifter]

Originally Posted by indymachinist

No.

let me clarify, in terms of fuel economy.

[69gmcc10]

I have owned 3 different GMT800s myself and worked/serviced several others of my friends and family members GMT800 and I could not agree with the direction this conversation is moving. I currently have a Spectre "CAI" on my 1500HD 6.0 and have had them on various other 1500 5.3s and 2500HD 6.0s in the past with similar results. All the "CAI" I have insalled have done nothing to improve bottom end torque and drive-ability, but have shown "marginal" butt-dyno results at about 5000 rpm and above. I did see a mileage increases, but that is directly attributed to my drivings style changing to try and get as much economy as possible after I purchased it, and that .5 of an mpg I did get quickly went away after I forgot about mileage and remembered I live in 'merica!

Things I like about the intake system is that the filter is washable (I am ocd so I keep it cleaned up) and when I opened the hood to jump my buddies powerstroke the other day both he and his friends complimented me on the size of my intake! That's about it.

Things I don't like about the intake system is that on one of my 5.3s and my fathers 6.0 it created a drone at a certain point in the rpm range that while sounded "fun" for a month got real annoying and both quickly found there way back onto the garage shelf. The MAF needs constant cleaning especially 50 miles after the filter has been cleaned/oiled. My filter is constantly trying to inhale the insulation pad on the hood and the top of the filter turns black! Finally, it provides almost no benefit at all unless the engine is running over 5K rpm and I just dont travel down the road at the rpm very often.

The only reason I have the CAI still on my 1500HD is because I had a custom tune done that was done after my CAI and my Magnaflow exhaust system was installed and I don't want to change the variables of that because it runs so well with the current set up. Almost want to weld the hood shut.

In my current 2wd 5.3 and my brother-in-laws 4wd 5.3 I installed AFE dry stock replacement filters and just the filter was every bit as good or better than the CAI on the other 5.3s I have owned without the oily MAF issues and it saved hundreds of dollars.

I will never buy another aftermarket intake system for a stock vehicle again! Exhaust, yes and a custom tune, HELL yes (best thing I ever did), but never again an aftermarket intake.

[Willie 66]

UPDATE:

Just put the stock intake back on, and I am enjoying the truck behaving as it used to. Would have liked to see the true gains/losses either way for posterity's sake.

Next time I'll get a custom tune. Or a cam. Or a big block. Or I'll just buy a Corvette. I dunno. Something with real results.

[andrewmp6]

I remember years ago on a f150 forum they took a stock truck and dyno tested every single cold air intake made for it.Only 2 out of the whole lot made more hp and it was like 3hp.The rest either lost power or didn't gain any over the stock pulls.

[ironroad9c1]

Yea a clean aftermarket air filter oiled or not tends to let alot more particulates into the engine than a paper filter.

[69gmcc10]

Originally Posted by ironroad9c1

Yea a clean aftermarket air filter oiled or not tends to let alot more particulates into the engine than a paper filter.

Absolutely! The only way to increase air flow through a filter is to reduce restriction, so you must add more holes to the filter or increase the size of the holes that are there. Either way it is more ability for "stuff" to pass through the media.

[ptc]

Originally Posted by Willie 66

UPDATE:
Just put the stock intake back on, and I am enjoying the truck behaving as it used to. Would have liked to see the true gains/losses either way for posterity's sake.

Next time I'll get a custom tune. Or a cam. Or a big block. Or I'll just buy a Corvette. I dunno. Something with real results.

As the OP - I think this thread may have helped you out the most in your learning curve on "Truck Performance".... but if you really want performance then go with your idea above!!! a new C6 would be nice way to achieve both torque and HP and good mileage (in comparison to your truck!)

Originally Posted by ironroad9c1

Yea a clean aftermarket air filter oiled or not tends to let alot more particulates into the engine than a paper filter.

I would certainly beg to differ with this statement (and many others of yours) So you are saying that BECAUSE its "aftermarket, clean and oiled or not" its worse than a stock paper filter? Without googling it do you even know what a K&N filter media is made of since 1969? or any of the other brands of non-cellulose media filtration are? There are many much more durable, less restrictive and more performance friendly filters types than just paper... do your homework before making bold statements.

Originally Posted by 69gmcc10

Absolutely! The only way to increase air flow through a filter is to reduce restriction, so you must add more holes to the filter or increase the size of the holes that are there. Either way it is more ability for "stuff" to pass through the media.

Not necessarily..... Intake filtration system resistance to airflow is restriction. Restriction is typically measured in units called inches or millimeters of H2O vacuum, and is defined as the difference in static pressure between the atmosphere and the outlet side of the system being measured. The higher the restriction the harder an engine has to work to obtain clean air for combustion.

So if the total AREA of filtration was enlarged then you would have less restriction without just making 'bigger holes'.... you think these two trucks have the same size filters?

[OutlawDrifter]

Originally Posted by ptc

There are many much more durable, less restrictive and more performance friendly filters types than just paper... do your homework before making bold statements.


So if the total AREA of filtration was enlarged then you would have less restriction without just making 'bigger holes'.... you think these two trucks have the same size filters?

i want to step in and say the most factory replacement paper elements will provide more than ample airflow for your typical daily driver that isn't driving around at red line all the time. therefore no need for a higher flowing material.

**also, thank you for taking the time to use a picture of a mechanical drive 797 vs. an electric drive heavy truck. that would have been an extreme oversight.**