3.2 Dyno Tests: Airboxes and Mufflers

[LJ851]

The whistling doesn't annoy you? I put a stock airbox lid back on after a listening to the whistle for a few weeks. What seems odd to me is that i have removed airbox lids on several other cars and there was no whistling, does everyones AFM equipped 911 sound this way?

[Por_sha911]

I wonder what is the amount of opening in the air box to get the advantage before it becomes overkill. I use my SW chip, B&B 2 in/1 out, and this cover to get the stock look with more air flow:

My thought is that the horn is the greatest restriction so I'll have at least the same volume of airflow but with a direct path.

[nkotselas]

I also got whistling after cutting off the entire face of the airbox. At first I was disappointed that this was part of the "great" sound everyone talked about. But once it got going the sound was pretty cool. I've gotten used to the whistling and I can't even hear it with the radio on.

I also washed my car before changing the box. It didn't seem like water would be a problem but I would still recommend being careful.

[LJ851]

^
Aha! That's my problem, i don't have a radio.

[nkotselas]

Well some people compare it to the sound of a turbo. So just tell people that's what it is and since its bring in a whopping 5 horses it works almost as well

[clutch-monkey]

Originally Posted by Por_sha911

I wonder what is the amount of opening in the air box to get the advantage before it becomes overkill. I use my SW chip, B&B 2 in/1 out, and this cover to get the stock look with more air flow:

My thought is that the horn is the greatest restriction so I'll have at least the same volume of airflow but with a direct path.

i always thought the airbox wasn't really a restriction until you get serious with mods? i have a 964 3.6 in my car and wanted to try something like the fabspeed setup.

[Brando]

Originally Posted by Por_sha911

I wonder what is the amount of opening in the air box to get the advantage before it becomes overkill. I use my SW chip, B&B 2 in/1 out, and this cover to get the stock look with more air flow:

My thought is that the horn is the greatest restriction so I'll have at least the same volume of airflow but with a direct path.

I swiss-cheesed mine like that, but at the next opportunity I will just cut the rest of the cover off. Now i just need a glass-pack muffler and a couple G's for steve to tune the chip

[Dreamer52]

From perception comes reality- If I sound fast I'm fast... but before I start drilling holes or buying new performance covers must I also get my SW chip redone to take advantage of the increased air volume?

Thanks

Carl

[Steve W]

Originally Posted by McLovin

I'm not sure I'm getting it right, but this doesn't seem like a straight comparison of "stock" engines.

That test would be to take a stock Carerra, test with stock airbox cover, then test with no airbox cover.

But from what I could see, you altered the chip tuning for the tests.

So it's not really a comparison between "stock" engines. To me, "stock" means unaltered, including unaltered chip tuning.

Did you run any straight tests? I.e., stock engine, stock chip, with airbox cover, and stock engine, stock chip without cover?

Valid question, but the objectives are as previously posted was to see what if any gains or losses are attributed to the restriction or lack of, of the stock airbox cover and muffler.

In order to do this properly, the air/fuel ratios need to be corrected to the same ratios for each test, eliminating that as a variable. The stock chip runs lean at the low and mid rpms, and very rich at upper rpms. If I for example, with the stock chip, take off the airbox cover and measured a gain of 8 hp at 6000 rpm, but the AFR there also leaned back from 11.5:1 to 12.3:1, well how much of the power change would you attribute to the airbox cover vs the leaning of an overrich air fuel ratio? You see a test like that does not achieve the objective and becomes subject to debate because of it's flaws.

Originally Posted by paulgtr

hi Steve, interesting thread. do you have any contacts on the east coast who could dyno tune a car with one of your chips?

search for one here:
Dynojet Automotive Dyno Centers

But before you do that review the basic instructions here and contact me with any questions:
http://www.911chips.com/Dyno instructions.pdf

Originally Posted by Maxhouse97

What are the dangers of water ingestion (without carrera tail) from rain w/ little to no cover on the air filter?

I have never heard of anyone having such a issue, stock filter or aftermarket setups. But even if possible, it would be no problem for the engine. Water injection has been around forever especially with for turbos motors which increases the effective octane of the fuel to increase boost, further increasing power and torque.

Originally Posted by ivangene

OK ..I didnt see where the question of combining the two tests (remove stock box cover and stock muffler) were addressed...would you expect a combined HP gain?

someone asked early one and someone else said it was addressed but I couldnt see that either

BTW I am pulling off my cover today and driving around with a bungee cord!!!

(help for the blind reader here )

Ed, reread post #10 and you'll find your answer.

[Maxhouse97]

Thanks for the answers Steve!

What are everyone's thoughts on the statement below (from a prior post on airbox mods):

"The "horn" was to provide a clear and clean path for "cool" air that was being forced in from the lid vent at speed. The air in the way back of the compartment is warmer and more turbulent.

So I think this would be in effect while in motion and not really in effect during idle."

So maybe there is a gain on a dyno when not in motion, but not at speed with a heat soaked engine?