3.2 Dyno Tests: Airboxes and Mufflers
 

We recently were tuning a stock '89 Carrera and ran some runs on the side that I though could also be of interest here.

First what we have here is a comparison on the stock 3.2 motor with and without the airbox cover. The blue curves are the motor with the stock airbox cover, red with it removed and just a bungee cord holding the air filter on. In each case the chip mapping was re-optimized to ensure the power differences were not due to the excess or inadequate fueling. Results show an average 5-6 rear wheel hp gain at the upper rpms with no filter cover restricting the intake:


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Next we have a comparison between the stock 3.2 muffler and the muffler removed, essentially a open exhaust right off the cat. Blue curves are with the stock muffler, red is with it removed. Differences are at the upper rpms averaging 6-7 hp at the wheels, which gives you the maximum theoretical restriction of the stock muffler. The total power achieved on this motor with no muffler, open airbox and chipped is 206 hp to the rear wheels, or accounting for a 15% transmission loss is (206/0.85) 242.5 hp at the flywheel.

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That is awesome Dr Wong!

Thanks for the graphs.

Now if i could figure out a way to stop my airflow meter from whistling at light throttle openings i would put the open lid back on my airbox.

Great Steve,

Finally some substantiated data ... should get a lot of people talking ... lol
There were many skepticals regarding the airbox !

Cheers !
Phil

For those now wanting to rush out and spend much money for a cup air box cover for the 3.2...take your cover off and head to a table saw...cut off just enough to keep the clasps for the filter and install.

Cleans up the entire area...and enjoy the sound track during WOT.

Steve - one question...does this mean if you have an older chip without compensating for the removed cover you do not see the gains?

Hi Steve,

What would you expect with running both air cover off and muffler with your chip?

Jim

He stated that, read Steve's post again. :D

I think Jim's question is valid. The first run is the airbox mod with optimized chip. The second run states, muffler off, airbox open, & chipped. So it is not clear if the improvement in the second run is due to the airbox or muffler. And I assume this is the same optimized chip also for both runs.

I think there is some confusion here. Steve states the mods were done to one car but both "after" dyno runs are the same number and appear exactly identical in shape and even down to a tenth in peak HP and torque. (both run #8) Perhaps Steve can clarify.



.

Yes for the sake of clarity, I kind of described the before and after with each for a simplistic comparison. However if you want to look at them another way, the red curves in both graphs, runfile_008.drf are the same run with no filter cover and no muffler. In each graph, the stock muffler or stock airbox cover were reinstalled to measure for possible loss or gain if any. In each case there was a loss, representing a restriction.

awesome info. And, I think you just solved the "I can't reach the rear airbox clips" dilemma for 90% of Pelican posters. :)

Cool post....time to drill some holes. :)

Is it reasonable to expect similar improvement on a 3.0?

YES!!! I have the cat bypass, SW Chip, and modified air box (cut lid, only left area with clips)..Love it!!

Steve, to continue the possible restrictions, do you have any data on barn door vs. firewire?

Jim

Is this temperature corrected?

That settles it... Chopping my airbox cover and ditching the muffler for a glass-pack.

Watch out car-alarms, here I come...

Dyno
 

Just spent the afternoon with Steve with my car on the Dyno. great experience and custom tuning a chip is the way to go. Every run yielded more and more positive results.

I've heard a lot of negative feedback about changing out the stock airbox with a "cold air intake" (K&N cone filter with elbow), but never seen a dyno chart confirming the truth or myth about these things.

How about a test?

Yes but differences depend upon the quality of the design of the MAF sensor setup. Well designed, MAF such as the setup I used to have available, is +6-8 hp over the stock AFM after 4000 rpm, +12 or so at 6500, and that's the stock AFM optimized with a big throat velocity stack intake with cone filter.

Yes, all runs are SAE corrected. Dynojets have a internal weather station in them to correct for atmospheric conditions from temps, humidity, and barometric pressure.

Located a fault too in your computer and it's fixed now. You can be sure to cause trouble now at the next event! :)

I think most of the negative is that gauze type filters such as the K&N let more fine dirt into the motor than the stock air filter. When new, the stock filter and a K&N flow the same. Through use, the K&N may flow more than the stock filter after a while, but that's because the stock filter captured what the K&N let through. I have a stock factory filter on my personal car, not only for the filtration quality, but because it's lighter. :D