john d 81SC

When I was changing the air filter in my 88 Carrera, I noticed a small elliptical hole approximately 3/8" long and 1/8" wide in the bottom right hand corner by the clip. It is very smooth, no rough edges. Is that supposed to be there?

Thank you in advance!

Mike Murphy

I don't think so. I assume this hole is on the cover and not the airbox? I wouldn't worry about it, unless you think it weaken the cover. If someone was trying to improve the performance of the airbox cover, that small of a hole wouldn't have much effect on sound or horsepower.

I actually sawed off the entire cover, aside from leaving about 1" with clips on my Carrera, thus exposing the entire air filter. This gives my car a great induction sound. Additionally, it does slightly improve horsepower on the 3.2, probably to the tune of about 1 or 2 HP. Even though many people disagree with this claim, I found an article that proves it in another Rennlist thread found here: https://rennlist.com/forums/showthre...9&page=2&pp=15

bmcallister

Very strange. Mine does not have one. If you want to replace yours I have a spare cover. bryanmcallister@email.com

Mike Murphy

Ooooohhhh, a spare airbox cover! These are hard to come by, so I would jump on it

jet911

I purchased a new air box and the hole is there as is it on my old original box.

Regards,
Jim
'86 Coupe

john d 81SC

Gentlemen,

Murphy's - yes, it is on the cover and not the airbox itself.
Bryan, thank you for your generosity, but I don't need to replace the one I have.
Jim, thank you for clarifying this. The hole is "too perfect" and strategically placed in at the corner to look like it was from wear.

Thank you all!

Corrales911

Isn't that a drain hole?

ajmarton

Mine has it too and I was wondering about it but did not give it much thought as I replaced the cover with the cut out version sold by Performance Products.

Loaded

i have covered the air horn with my hand at idle and it sure seems to suck a lot of air just at idle has anybody done dyno test removing or modifying and then adjusting the mixture timing etc to take advantage of the extra airflow?

I understand that if you just remove it the hp increase is limited and you actuallyneed to do more to make it count

Mike Murphy

Loaded, to answer your question, I found an old Panorama article (August 2000) where a tech article explains the mod. Below is a transcript:

Q: This is a question about the power flow and MSBS type or air cone in filters. Is there a real gain in having any one of those on a fairly stock 3.2?

Jerry Woods: A: "I have done some work on this. I had a stock 3.2 motor on the dyno and was running it without an air cleaner. I thought this would be interesting. I put the air cleaner back on and we lost a little power. At that time Automotion was in business in their former facility which was about ten miles away from us. I knew the general manager and he lived nearby and he brought a K&N filter over for me to try. He stood there was watched while I tried it because that was one of their big product lines. We found the same power as with the paper element. We did find that by taking a two-inch hole saw and putting three two-inch holes in the outside plastic cover, it was like there was no air cleaner. All of a sudden the power came up. There was virtually no difference between the K&N and the paper. I strongly recommend the paper elements for road going cars. They do the best job of filtering out the fine small dust-type particulates. Protect your engine. K&Ns are nice; yes, you can wash them out but they take a lot of maintenance to do a good job. They are suited for a race car but not for a road going car in my estimation. That's how I see it."

Loaded

sound's like something I will try........tonight

KC911

With all due respect to Jerry Woods, I wonder if his comparison was 'statistically valid'...(i.e. one dyno run each way doesn't validate his conclusions imo). I remember reading that someone (I don't recall who, but someone that I held in high regard) had performed his same dyno analysis (stock filter vs. no filter at all), and there was no significant difference between the two. Hence the conclusion that a stock 911 isn't constrained at all by the airbox, stock filter, etc. I do have my airbox drilled...'cause I used to put baseball cards in my bicycle spokes too...I like the sound, but I doubt seriously if there are any hp gains. Discuss....

Keith
'88 CE coupe

Loaded

I would assume over past experiences with other cars that it may increase top hp by a smig. I think most stock cars are programmed for some restriction, I am unsure if the computer can adjust enough to make it worth while until you add a new chip that has this in mind. It appears the wong chip may address this. Agian judging by previous experiences it would need/use more initial ignition advance and then enrichen the top end. More air/less restriction would cause the af mixture to lean out............ah then we have to address the exhaust.

I am personally going to use the fab cat replacment and dump sans muffler that would allow much more flow in the exhaust couple that with free intake it would absolutely need a new fuel map. I have found most stock fuel maps especially in motorcycle drag racing (my specialty) count on and rely on restricted intake and exhaust. Once you place a pipe and filters on a drag bike or car it reduces the induction airflow/speed so we improve this by advancing the timing either initial ignition or....if I remember correctly advancing the exhaust cam creating more neg pressure/exhaust scavaging in the cylinder for better intake air speed.

In theory its sound, if the other variables...........fuel/ignition.........can adjust accordingly.


I make these statements from motorcycle/car drag racing tuning.

Mike Murphy

I have read the same thing as you, KC911, and thus, I have come to the conclusion that "someone" is less of a credential than "Jerry Woods." Others on Rennlist also say that "there is no horsepower gain", but most who make this claim only have the "butt dyno." The ones that actually have a dyno are not professionals, just amateurs.

To each his own, regardless of who is right and wrong, but I made the change due to the sound more than anything else.

Mike Murphy

Most cars' HP varies by up to 5% because of manufacturing tolerances, so most computers can compensate by that much

Agreed. In fact, when you buy a new motorcycle, you usually have to take it right back to the mechanic and have them "fix" the tuning that the bike comes with in order to pass emissions testing.

My classic & antique cars & trucks also exhibit similar behavior. Sometimes even changing the muffler can cause the engine to run lean or rich, and thus the carburettor jets may have to be changed. The good news is that most modern car computers can adjust to a small degree, and I think the Digital Motor Electronics on the 3.2 is one of those. Anything beyond a small percentage may require a significant number of mods, including intake manifold, exhaust manifold, fuel pump, fuel injectors, camshaft, etc...