Debunking Tuning Myths
From the July, 2010 issue of Import Tuner
By Luke Munnell
Photography by Luke Munnell
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Regular readers will recall last month's testing of two Motordyne bolt-ons that successfully proved Helmholtz resonance can be used to increase exhaust gas scavenging and help your ride put out a few extra ponies compared to other aftermarket offerings. What we didn't get into was how problems on the intake side of our test-car equation nearly negated our power gains altogether, giving rise to the possibility that fitting your car with the wrong intake might bring power to below stock levels. Before we were finished with one tuning uncertainty, we had unwittingly unearthed another:
Can Certain Performance Air Intakes Decrease Power? We had actually come across this problem before, when installing one reputable manufacturer's short-ram/cone filter intakes on a G37 for Power Pages back in June, '08, resulted in a loss of nearly 15 whp over stock. Since the G's VQ37DE was an all-new engine, we attributed the phenomenon to a tuning issue, re-installed the factory airbox, and left it at that. But when the problem reared its head again while testing Ken Kojima's '04 350Z last month-powered by a single-throttle VQ35DE engine-our curiosity was piqued.

The prevailing hypothesis is that cone-filter-equipped aftermarket intakes have a tendency spin incoming airflow into a vortex. If an engine's mass airflow sensor (MAFS) is positioned too close to a cone filter and doesn't feature a screen or grid before the sensor element to diffuse airflow (the 350Z one doesn't), the incoming intake charge can either strike it at a faster-than-normal velocity, tricking the MAFS into overestimating airflow, or flow around it, causing the MAFS to underestimate airflow. In the case of the MAFS reading too much airflow, too much fuel would likely be injected as a result, making for rich air/fuel ratios (AFRs) and decreased power. If the MAFS reads too little fuel, lean AFRs could occur, causing knock-sensor-tripping pre-ignition, and again, a loss of power.
"Another possibility," explained Tony Collette, Motordyne lead-man and innovator of last month's successful ART products, "is that certain short-ram intakes experience some high-speed air separation if they don't feature a built-in velocity stack." Like our hypothetical vortex spinning airflow into a fast, concentrated stream, the separation Tony's referring to occurs when air enters an intake with high speed and angle, and without the aid of a velocity stack to provide a smooth transition into the intake tubing, can't adhere to the walls of the tubing and causes air to condense into a fast-moving stream which could also prompt a MAFS to overestimate airflow. Since our AFRs became increasingly rich as engine speed increased, and the power loss was mostly top-end, "I'd bet that's what's happening," hypothesized Tony.



If either of these theories proved to be true, our logic was that cold-air intakes with more tubing would provide enough room for airflow to straighten out before contacting MAFSs, avoiding the problems described above. We also theorized the same would hold true for the Z's factory induction equipment, since its flat-panel air filter would induce air in a more linear fashion, avoiding the vortex and air-separation issues. To test, we rounded up examples of all three systems-our suspect short-ram intake from previous testing, the car's OEM induction stock, and an AEM Cold Air intake-and strapped Ken's '04 350Z down to the rollers of Mavrik Motorsport's Mainline dyno in Fullerton, CA, to power test it with each configuration in place. AFRs were monitored throughout.

Immediately noticeable with the short-ram intake was that its filter features a "twisted" design-something we've seen other manufacturers tout as a benefit that spirals airflow for increased power. Also apparent was that its inverted cone-designed as a part of the filter's housing to direct airflow into intake tubing-stopped short of the filter's inlet into the tubing, which could allow for air to sneak in perpendicularly from the filter's sides and cause the separation Tony theorized. More importantly, neither the filter nor its intake tubing featured a velocity stack.


Our AEM filter did incorporate a velocity stack in its design, and coincidentally fit onto the tubing of our short-ram system. To prove or dispel Tony's air separation theory, we installed it on the short ram tubing for a round of testing.


Sizing up the car's stock equipment, we noticed that like our AEM filter, it also utilized a velocity stack at the start of intake tubing.


Our final test of the day was with the complete AEM Cold Air intake installed.


It's important to note that while on the dyno-with hood propped, bumper removed, and supplementary fans blowing at full-blast-changes in intake charge temperature between short-ram and cold-air alternatives are insignificant.

Eyeing its restrictive design and panel filter's comparatively small surface area, it's no surprise the 350Z's stock intake brought the lowest average power and torque. What's interesting, however, is that as rpm increased, the benefits of the short-ram diminished, even falling below stock levels in the upper realm of the Z's powerband, as AFRs fluctuated and fell into far richer territory than with the stocker-clear evidence that while providing more airflow, our short-ram intake was doing so in a way the MAFS didn't like. Factoring in the benefits to both power/torque output and AFR found with simply swapping the short-ram's native filter with AEM's velocity-stack-equipped one, we had evidence in support of air separation interfering with MAFS function. Finally, installing AEM's long-tube Cold Air intake vastly improved power and torque, and brought AFRs into leaner territory than the short-ram, at much smoother rates.

The Verdict:
While the amount of air flowing into a carbureted or MAP-sensor-equipped engine may be the only point to mind when selecting its aftermarket intake, how that air flows is every bit as important to a MAFS-governed engine. While we're still not sure if it was air vortices or air separation that tricked our 350Z into miscalculating mass air flow (or both), we do know two things: It was happening, and switching from our previous short-ram intake to AEM's long-tube Cold Air unit increased peak output by nearly 12whp, and gained power and torque from idle to redline. They say the proof is in the pudding; we say it's in the testing.

 

I wanted to know if anyone has had this problem with the TC2 and a short ram intake and its mafs

 

Great find! Good info…I learned something...thanks

 

I'd bet money that is why Descendant has not released a SRI and has tested their CAI so thoroughly. If it does not work, they don't sell it..It would explain why TRD is taking so long to release the CAI. Descendant is the only aftermarket company I have seen that is willing to show true dyno results and will not produce/sell products that do not work. That's why they and no other company will get my hard-earned 4 grand for a turbo kit later on. I knew about the above stated issues, that is why I chose a plain old K&N filter. If you look closely at our intake, you will notice the only real restriction is the intake snorkel on the side of the box. It has roughly a 2" opening to breath through, a larger snorkel will drastically improve air flow. The rest of the intake is a smooth flowing 3" rubber pipe. I see no major power increases happening from changing that part. A better flowing filter and a larger air inlet to the box are all that is needed imo. Scion did a heck of a job squeezing all the power they could from this mill while keeping engine noise low. There really is no real major performance gains to be had with bolt on intake and exhaust systems. The engine is already operating very close to max. performance. Forced induction or expensive internal engine modification are the only ways you are going to squeeze significant h.p. AND torque out of this engine. Well there is NOS too...

 

I did the same thing for now just a drop in K&N

 

Key to remember if your increasing air in you need to adjust air out ie exhaust. And without pcm tuning you shouldn't expect noticeable gains. My car as an example put weapon r true cai and lost 6 HP. Put a borla exhaust on made that 6 back and an extra 9 past that. Remember kids knowledge is power and knowing if half the battle

 

Sigh. There is so much wrong in this thread right now I really don't know where to begin. I will say the descendant racing theory is false however. Look at previous cai threads. Also, a 350z is no tC by any means. I respect that your trying to give a little more info but every car is ENTIRELY different. MAF position, factory restriction, MAF design throttle body size, etc are all so different from this car to the tC. There are a hundred factors that are being left out. Note that this says AFR's go far rich as RPM increases... has anyone looked at any of the intake dyno's with provided AFR readings?? Let's just say this is for sure not the case on the tC. I never want to knock on any one providing information, however if the information is false or is misleading to information that is completely irrelevant (this current sitiation) then people are going to have a completely false theory or not fully understand something. For expample if I put a WRX dyno here with any intake then everyone would assume that all intakes will make your car go lean which is false. The last thing people need is more info with cold hard and irrelevant facts
to confuse everyone.

 

this is an interesting post though.. like mentioned there tons of variables so this may only apply to setup tested, but the main thing to consider is about how the mod affects airflow and the tune.

 

It's always interesting to see what sort of numbers come out from different intakes. Once a new model has been out for awhile, and a variety of makers have intakes (SRI & CAI etc) and someone can throw them all on the same car on the same dyno, we can actually see a decent gauge of changes to the car.

Overall, it seems like the sound is the biggest draw, hydrolock is the fear, and the butt dyno is always a fun test.

I'd love to slap on an intake just to get a better 'vroom' from the engine, but it really seems that for now, stock is best.

(We have a running gag in the office, anyone talking about mods, we yell STOCK IS BEST)

 

I put this thread up to show the difference from a cheap intake to a name brand and different filters for a certain car to show people facts for a certain car in this case a 350z now you say this is not the case for the tc show me the dyno numbers I dont know for fact if this applies to the tc
it might not but have you done the same kind of test on a tc as they did above now my point is I put this up to see if anyone has had the same problem with TC2

 

There are two intakes available so far for the new tC, both of which have dyno graphs which show a lean AFR. There are not that many intakes even available for the new tC so you could not do a test like this either way. There is also a thread on here with plenty of info why they are going lean as well. So in our tC case this test on a totally different car does not apply because our community already had the information needed about the only 2 intakes available.