"Value" of aftermarket outside air induction - LONG!

[Gary - K7GLD]

Brace yerselves - this is a long, but condensed - bit from an earlier thread I started over on the TDR. That was done because there was an on-going string of threads and posts being presented there all operating on the "accepted" assumption that by somehow drawing outside air into the underhood area, or directly into the engine intake, substantial power gains would be obtained.

Testing, by others - and now me - has proved it just ain't so!

In fact, it's so WELL accepted as FACT, that those opposing that view, even with test data, are pretty much candidates for burning at the stake! And since the same sort of related threads and comments are being presented on this board with increasing regularity, I thought I'd resurrect that thread in condensed form, with a few minor changes for photo updates and improved clarity. The complete original TDR thread can be found HERE:

Value of "special" aircleaner ducting... - TDR Roundtable

I had read independent tests done by others, who soon found that the typical vehicle underhood temperature while the vehicle is in motion is usually within 10 degrees of outside ambient temperature! Naturally, a running, but parked vehicle will soon be much hotter underhood than outside air - but even the best "cold air intake" isn't of much value on a PARKED vehicle, is it!

An additional folk tale, is that various hood scoops as typically offered for a street vehicle, will also provide great power improvement from the "Ram Air" effect - cheap supercharging!

While that is of benefit in race vehicles. using physically LARGE scoops and when operating at high rates of speed, it is NOT true of scoops any reasonable owner would want on a street vehicle that seldom sees speeds much above the speed limit. In fact the typical hood scoop, made more for appearance than function, is usually placed FAR away from the proper frontal area location where it would even be most effective anyway!

As I had expected on TDR, my tests and supporting data were met with LOTS of squeals of protest and criticisms - and as soon as I would successfully squash ONE complaint, another was desperately presented - until they finally ran out of ammunition!

SO, what have tests shown to be true in typical and actual real-world operation? Grab a cold drink, settle down, and read on!

[Gary - K7GLD]

This is NOT intended as a "knock" of some of the aftermarket "cool air" induction setups some here are using, only the results of an informal test done on my own truck...

I recently installed a NAPA BHAF on my '02 truck, and in connection with another temperature related project, decided to also see as nearly as possible what the underhood temps were in the area around my BHAF as compared to ambient outside temperatures - here's my BHAF setup:


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SOOOooo, with outside temps at an indicated 91 degrees, and after a 5 mile drive on reasonably level road at 55 MPH or so, my underhood temp over on the inside of the BHAF, next to the turbo, registered just under 100 degrees - an increase over ambient of about 10 degrees.

Now, I gotta wonder exactly WHAT real-world power benefit is to be obtained by hacking holes in firewalls and installing fancy ductwork - all to (hopefully!) reduce intake air by another typical 10 degrees...

Nor is mine the first such test I have read about - and the others also indicate about a 10 degree underhood rise in temperature at common freeway speeds...

Just a FYI to ponder...

Originally Posted by HeavyHauler

Gary, I've always considered you relatively knowledgable on here, but surely you realize that the purpose of "hacking holes in the firewall" is to get more air into the engine to create more power, and not to solely reduce the temperature of the intake air by 10 degrees. In fact, I've never even heard that mentioned as a feature.

You act like you've stumbled upon some startling revelation here, when in fact you're missing the main point.

UMMmm - and exactly HOW does hacking holes in firewalls get MORE air into the engine than a completely OPEN filter under the hood, when there is all the airflow from the front and underside of the truck - the engine is HARDLY enclosed inside and airtight container - HOW much added benefit is there likely to be from another paltry 6 inch or so diameter hole, compared to all the OTHER freely moving air ALREADY flowing thru the engine bay?

The ball's in your court...

AND, before some wiseguy pops up here claiming "ram air effect", has ANYONE installed a pressure guage at the firewall location usually hacked to see what, if ANY pressure is developed there at say, 60 MPH?

YUP - ONE member did, read HIS result down towards the end of this thread.

[Gary - K7GLD]

"Lets see some data from your upcoming towing trip. I'm towing again in a few weeks, and if I can get the fan clutch to kick in [I doubt it here in Michigan] then I will do as I described above and use my laser thermometer to read the filter surface and the filter duct surface as well as the fan shroud and fan blades. I'm sure you will disregard my data. So maybe I won't bother. Maybe I need to get a meat thermometer like yours for matching data."

Sure, no problem, and I had planned to do additional testing and post results, as I mentioned further up above.

"I agree with this statement from you ::a decent low restriction air filter simply mounted underhood will very likely produce as good a benefit as those attempting to draw in additional outside air from the cowl area... "

EXACTLY my point - I just tried to back it up with at least SOME supporting data!

THEN, Scotty pops in with:

"Reverse cowl induction or taking air from the bottom of the windshield nets a lot more then you think.

A "lot more"? Exactly how MUCH more, in tested and documented PSI? A "LOT more" doesn't really quantify anything or prove much, does it?

Its the best place to take air for trucks towing or BOMBed in order to maintain low exhaust gas temps. Wonder why that is? Gary, you figure it out. "

Really, under the circumstances, *I* shouldn't HAVE to "figure it out" - guys like you SELLING the cowl-induction systems SHOULD have already MADE the appropriate tests, and have test documentation readily available - do you?

[Gary - K7GLD]

Scotty said

I've always said the results that I give are from real world use. Such as reduced Exhaust gas temperatures, faster spool up, quicker cooldown.
My air intake simply works and I have no technical jargon to post publicly on this.

That's convenient - you KNOW it works - but have done NO testing, and have NO documented test results or data to back your claim...

I have had several people conduct their own tests or use reference to tests and results of reverse cowl induction that concur that what I have designed does as I claim.

Anecdotal, here-say "evidence" is usually not worth the breath it takes to state it - claims without SOME degree of independent test data are WORTHLESS!

When someone starts a thread like this and uses such words as hacking [cheap shot]. I tend to look at what that relates to in their own efforts.
I do not see cutting a 4.5" hole in the cowl with a holesaw as hacking.

Gary, this is 'your' thread. Have fun. You have a lot of time on your hands...some of what you post is good info.

Scotty

(MORE BELOW)

[Gary - K7GLD]

FIRST, and for the record, thanks Scotty for taking the time to respond - as originator of one of the type setups I am comparing my BHAF with, you are in a unique position to speak from greater experience and authority on the subject - I had HOPED you might also have research data you could provide as well.

As to my terminolugy, and use of "hacking" - that wasn't particularly intended as a cheap shot, just a reasonably accurate description of what a lot of guys under that backyard shadetree end up doing, just as *I* did on my old '91 when I had to use a metal hole saw to install a Banks intercooler - perhaps a bit too "colorful" description for some, but maybe closer to home for others!

NO, it isn't "MY* thread - it's a backyard test/research thread for ALL members here - and yes, opposing viewpoints ARE encouraged, so we can ALL maybe learn something new and useful - just keep it clean, on topic, and if at all possible provide something to the mix over and above idle speculation and preconceived notions.

Contrary to suggestions, I had no such preconceived notions - I had simply read previous such tests, and since I was already under the hood anyway taking other temperature readings, figured to refute or verify those other test results in the process - it made/makes NO difference to me which way results go, and why SHOULD it?

I certainly have NOTHING to gain or lose from the results!

But for the record, I too saw a radical reduction in EGT's - about 200 degrees across the board - when I installed my BHAF as pictured in this thread - along with the same faster turbo spoolup and cool down - I suspect that will be pretty common when ANY significant improvement in air filtration is made, regardless of type - such as my current one:

.

I only hope to determine what additional benefits, if any are available from typical outside ducting - and hell, I may be muddying my own water, since I still use the factory fender air inlet to my BHAF - who knows what added benefit THAT is already providing?

ANYWAY, I *do* have a common, wired, inside/outside digital temperature setup here at the house - I'll look into installing that on the truck for a few around town and local runs - if it seems to work OK, and has enough temperature range to be useful, it will provide the added benefits on our up-coming RV trip for greater on-the-run accuracy that seem to be a hanging point for some here.

Later...

[Gary - K7GLD]

OK, thanks to LSfarm for motivation to obtain improved temp data for futher tests - I have done as he suggested, and have installed a digital inside/outside thermometer on the truck - it is a real time instant reading job with -58 to 158 degree range.

But some of you critics are NOT going to like the results!

Here's the monitor section, displaying absolutely the WORSE upper temperature reading, engine fully warmed up from a 15 mile drive at the speed limit, sitting in the sun in my driveway with the engine at an idle with the A.C on - the LOWER reading is underhood temp - disregard the UPPER reading, that is the inside cab temp, but the inside cab sensor is right there in the sun next to the windshield - so reading higher than actual in-cab or outside ambient temp:



OK - worse-case underhood temp with the vehicle PARKED for a few minutes out in direct summer sunshine measured almost 109 degrees underhood temp.

So what WAS the ambient outside temp?



HMMmmm - a difference, or increase in underhood temp of slightly LESS than 30 degrees - worse case scenario!

Here's where the underhood sensor is mounted:



SO, what's not to like, if you are a true believer in the value of drawing in outside air to counter that nasty underhood, superheated stuff?

Simply this, the WORSE CASE down the road temperature differential registered was the *SAME 10 degrees* as displayed by my "meat thermometer" (actually, it is an air conditioning service thermometer - it just sounds more laughable and demeaning for critics to describe it as a "meat thermometer"...).

Fact is, depending on the state of the A/C and engine thermostat, the difference was frequently as low as *5* degrees!

Yeah, stopped or slow traffic raises temps somewhat, and heat soak when the engine is shut down goes even higher - but AS SOON AS the vehicle speed resumes anything above 25 MPH or so, underhood temp drops like a rock to that same 5-10 degrees temp differential!

NOW, I have absolutely NO illusions this latest test will in the slightest change the mind of ANY of the critics - their "opinion" is set in stone - and NO test I can do will change it. They will insist I wasn't driving fast/slow enough, have the sensor in the wrong place/position, or my truck's the wrong color - ANYTHING to deny the rather obvious and strengthening conclusion that typical and average down-the-road underhood temperature differentials are not NEARLY as high as they THOUGHT, or were led to believe they were!

SO, where do all those radical claimed power improvements with the ducted intake systems come from? If it isn't actual cooler air, well, damn, it must be that vast amount of pressurized air from the cowl area, right?

We'll see!

It's rather easy to install a water-column sensor down in the cowl area where the air intake mods usually drill that access hole, and get the ACTUAL down the road pressure buildup - and then we'll see how much pressure there REALLY is down there to "pressurize" the engine intake tract...

So, all you critics get your objections and preconceived notions ready, and line up for the NEXT round!

Actually, it will probably be a couple of weeks - we have company here all next week, and the week after that, we all take off for the Oregon coast for a week of RVing, but then....

( yeah, yer right - I'm having WAYYYyy too much fun with this!)

[Gary - K7GLD]

Originally Posted by HeavyHauler

Gary, frankly I don't see how that "test" proves any theory of yours. You have yet to get out and work your truck, under load, and report the temperatures. It has already been submitted that a 55 MPH cruise isn't going to yield much of a difference.

Let us know what the difference is when you get out there and really put a load on your truck. The only thing you're doing now is repeating what you've already claimed.

No, I have provided ADDITIONAL proof for the benefit of previous critics who insisted my test equipment and methods were flawed - the SAME critics who have now seen earlier criticisms proved wrong, must rest all their remaining hopes on the results of a heavy haul/steep grade scenario - and that's OK too, because in about 14 days, I get to yank THAT rug out from under you all as well, I have NO doubt that the heavier towing situation will result in essentially the same results!

Get those objections ready, your time is running out!

[trik396]

I know for a fact that in the 60's GM tested a Corvette (I believe) on a road course with a big block. Don't remember the engine size but it was a big block. Then they installed the cowl induction system and it knocked a few seconds off of the lap times. There is higher pressure air at the base of the windshield. I believe when this denser air was sucked into the cowl induction systems back in the day, with naturally aspirated engines, they experienced a mild supercharging effect and raised horsepower. I had this very setup on a 70'Chevelle SS396. It was a pretty radical street car, that I "tricked out" with a 509bbc... Hence the name "trik396"...

What does this have to do with our trucks? Absolutely nothing. Just thought it was pretty cool stuff, especially back in the day...

[Gary - K7GLD]

Curtis wrote:

Gary the starting point to your thread was to see the actual air temperature going into the turbo...... CORRECT ???

NO, that is INCORRECT - it is to determine underhood temperature under varying conditions AVAILABLE to the aircleaner and intake tract, and also determine if various aftermarket "cool air" and "ram air" devices have any significant potential to provide enough power increase to be worth what they cost.

I have no safe or easy way to determine actual turbo inlet temperatures - and given the temperature of air immediately adjacent to the aircleaner, that should be sufficient for my purpose - if I can read the temp AT the aircleaner, as compared to outside ambient air temp, that meets my goal!

Does your latest temperature probe have a long enough shank to actually stick through the air filter somehow ? Maybe a pic of the end, please.

You already HAVE a pic of the end probe, up there in my last picture post!

Gary nobody doubted you or your readings.

HAH!

LsFarm was simply stating it is better to actually monitor the air temp during the same scenario that our trucks are built for *TOWING, HAULING, WORKING* The way i took he only wanted to see more accurate readings for the above conditions.

While your *MEAT THERMOMETER* may have been accurate enough for around town driving, is it accurate for the above mentions conditions. We'll only know from your findings. *THANK YOU*

UMMMm - you musta MISSED my last picture post up above clearly showing the digital remote reading thermometer I used for my last test run... And it WASN'T a damn "meat thermometer" I was using earlier - it's an air conditioner test thermometer used by A/C techs to test A/C temperature differentials

G-Day

Curtis

[Gary - K7GLD]

OK guys, I have been largely just been giving you a hard time - hopefully, we are all friends here - and no hard feelings on my part - just a slight annoyance that my methods and motivations should be so agressively questioned and resisted just because some don't like results that differ from long held assumptions!

IF, when I started this test, I had asked in open forum under what driving circumstances special intake ducting to outside air benefitted engine performance, I'll flat out GUARANTEE you the overwhelming response would have been "why, under ALL driving conditions of course!"

Now that THAT seems to have been largely disproved, NOW the cry is, "well, the GREATEST benefit is under HARD work, heavy loads up steep grades, yeah man, that's it"...

Well, even if that WAS true, how often do you actually USE your trucks in those scenarios? Would you REALLY pay the $$$ for a product or mod that only delivers marginal gains over extremely LIMITED conditions that the vast majority of us only rarely see, percentage wise, in daily or towing use?

Face it, the VAST MAJORITY of typical truck operation is lightly loaded around-town and freeway driving - where the special ducting SEEMS shown to be pretty worthless as a performance booster, at least as compared to other commonly used intake filter setups that are far less expensive and physically intrusive to the vehicle!

BUT, in 2 weeks, we'll be towing our 15,000 lb GCWR RV setup over several pretty decent grades on our way to the Oregon coast - and we'll SEE what differences in temperature differentials occur when we do. I suspect precious LITTLE difference from that already seen locally and out on the open road!

And if I'm wrong, I'll simply have to publicly eat my words!

(been there, done that - it ain't fun OR tasty!)

NOW, if any here still question my tools, integrity or methods, these digital remote thermometers are pretty common and inexpensive - why not go buy your own, run lots of tests under varying conditions, document your findings and post them, complete with supporting pictures here on this board. Shucks, I'm SURE you will get enthusiastic welcome and support for your info - just as *I* did...

I too had a well-drilled airbox and K&N - it was vastly better than the stock setup - but when I recently went to the BHAF, I immediately saw an additional 150-200 degree drop in EGT.

As far as reduced EGT is concerned, I suspect any of several approaches will improve over stock - and so when guys make a move from stock, to say, a Scotty system, no doubt a big improvement over the stock setup they just came from, and they are understandably impressed and tend to give all the credit to the fancy sheetmetal and ducting - but their largest SINGLE improvement was quite likely the better air filter!

What I am curious about, is any who went from a properly setup BHAF to something like the Scotty or similar type outside ducted system - what no-doubt-about-it added gains were seen then?

Believe me, I'm NOT trying to pick on Scotty or similar setups - just trying to nail down what's worthwhile, and what isn't, and separate the BS and wild assumptions from actual, provable FACT!

[Gary - K7GLD]

TOD T said:

Gary, a few years back I had performed the above prescribed tests using two MAP (Manifold Absolute Pressure) sensors and a simple volt meter with correlating readings charts and conversion charts from Pascal to PSI.

The first (#1 sensor) was installed in the cowl area where the air is drawn from for the cowl type system. The second was mounted in the intake tract ahead of the filter (dirty side). As I did, you should also find that you'll consistently see, at all road speeds nearly zero pressure readings in the cowl area (a few spikes of pressure (.5) but nothing sustained). Additionally, under light boost levels (6PSI and above) a slight negative pressure (vacuum) from this sensor (about those of the small pressure spikes (.5-3/4 but a bit more measurable during a boost condition). This will also be supported by actual vacuum levels measured by the #2 sensor in the dirty side of the intake tract (this reading will be consistently about 4PSI lower than a boost gauge installed in the intake manifold and level off just before boost starts to level out (drop)).

These tests were performed first with the HVAC system in the off position, next in vent mode and third in recirculation mode on the A/C cycle.

THERE you have it! An independent test, using quality test equipment - and the result - a PALTRY BEST of .5 PSI boost measured in the cowl at the base of the windshield, and even THAT was only momentary!

Using a cowl induction system (CIS)* that utilized only the 4.5" cowl hole, I theorized that the HVAC system with its series of vacuum operated doors do not allow for a good enough seal to actually hold pressure in the cowl area also the seal around the cowl and CIS area is not enough to hold back pressure.

Secondly, with a CIS that uses both a cowl hole and factory fender hole you cannot sustain pressure due to the obvious factory hole leaking it by. So basically, with either system the air flow to this area was pushed out of the area through numerous leaks including those not related to the HVAC system. Fresh air? YES, Ram air: NO! Louder turbo whine: YOU BET YA! More than my family could tolerate during extended towing.

*Note: Not claimed to be a benefit of the either type system, just an observation that pressure is not detected or sustained with either system in place.

Ram air? Id rather call it Cold Air Induction. The trouble with 'ram-air' systems is that often they aren't. Ram-air, that is. By the time you collect enough air and shove it into the airbox, negative pressures lurking around corners in the intake duct and at its entrance have probably assassinated the pressure gained by the forward movement. Plus, how d'you know that the place you're trying to pick air up from is under positive pressure anyway? With proper CAI siting on our trucks you can easily equal out the intake tube and filter restrictions of the intake system under a no boost condition and that would certainly help, but i still wouldnt call it 'Ram air!'. I don't have data for our 5" tube or the BHAF or K&N type filters but would speculate the siting would need to be just about dead center on the trucks grill at the bumber line area similar to DF's location.
The true benefit of cold air intakes (CAI) or cowl air induction is to eliminate the draw of under hood air at take off and provide plentiful clean cold air during operation however the effects on under hood air temps at speeds greater than that of a regualar surface street (35MPH) are nearly identical to those you've reported already. IMO void and null, when compared to the trade-offs (louder turbo whine or risk of water ingestion) There's radiant road heat to think about here on take offs too. but we have forced induction and aftercoolers. do you really think its a DMDPC (Dwyer Magnehelic Differential Pressure Gauge) measurable difference? or better yet, the ol' S.O.P. meter detectable faster spool up? like i said void to null IMO.

As with any non-factory intake system utilizing a larger filtering surface element you will see reduced EGT's and freer air flow to the engine resulting in better performance be it cooler EGT or better MPG's or both.

Conclusion: Aftermarket air filters that provide a greater filtering surface to that of the factory element will result in better performance and reduced EGT's. So pick your poison fella's. Me? I have twins and a nice K&N stuffed under the hood drawing in nice hot air and spitting out piston melting performance. come and get you some, is all i can offer! loaded or not.

SO guys, exactly how MUCH added power do YOU think .5 PSI boost is going to give you - even when accompanied by a 10 degree reduction in intake temperature?

PRECIOUS LITTLE!

======
OK, Just returned from about 1200 miles of RV towing from eastern Oregon to the Oregon coast - several decent mountain ranges and grades involved. But as mentioned previously, typical actual time and distance on those grades was a pretty miniscule percentage of the total miles involved.

So how did underhood temps read?

Well, the VAST majority of the time and miles, underhood temps ran about 5 degrees above outside ambient temps - that's right, *5 DEGREES!*

Toss in some rolling terrain, and a slow rise to 10 degrees.

Fairly long climbs at 60 MPH or so delivered about 20 degrees rise - and that was IT!

Of course, once hills were crested, underhood temps quickly returned to the lower ranges - and while coasting downhill, usually approached ambient outside air.

Turning on the A/C while maintaining 60 MPH only raised underhood temps by about 1 degree, if that.

Just to try a "worse case scenario", I tried purposely artificially loading the engine up a long 7% or so grade in overdrive to see what temp rise I could generate - running at about 1800 RPM, EGT at 800 degrees, and boost at 28 PSI generated about a 45 degree underhood rise in temp - and that MIGHT represent RVers with heavier rigs than my 7000 lb. setup - or guys whose engines must work harder than mine. My power mods REALLY make it hard to stress my engine other than the above deliberate lugging abuse - which was WAY outside of anything *I* would call "normal" truck operation!

I *really* love and appreciate the recent power upgrades I had done - the 1.6 injectors and full 4 inch exhaust, combined with the free flowing BHAF, and other power mods, REALLY make this a delightful tow vehicle - during this trip I rarely used the Edge Comp - and when I did, it was on 1x1 to turn power DOWN, rather than up - all the rest of the time, it was off since I had all the power I needed - other than another burst on 5x5 up another 7% stretch to see what would happen.

Let me tell ya, those big Oregon pines started flying by REALLY fast, before I ran out of road and grade!

SO, let the reader judge for himself the need or value of "special" ducting to lower air delivery to the Cummins - I've already made my decision, and where I'm at is where *I* will STAY!

[LinemanTater]

Nice write-up. :thumbsup


I concure!!!!


I think we often post things that we hear from manufactures, and think of our words as Gospel (I'm Guilty) (same goes for the " 5" exhaust systems make you Loose power")claim. And there is absolutley no proof to back up the claims.