968 filter box top drilled

[enap99]

I'll have an 1993 968 coupe witch I'll start upgrading. The first thing I'll do is to replace the air filter for an K & N. But i heard a story about drilling the filter box so it increases the air flow to the engine. is it true? is it worth? what are the procedures??

thanks to everybody

[SlowToady]

Not really sure, except to say that it was done (an option?) on 993s. From what I understand it doesn't increase HP so much as just makes it sound "meaner."

IIRC, these engines don't have much trouble breathing, and a K&N would be basically a waste of money. There is also a lot of debate about whether or not they are dangerous for engines.

I'd suggest reading a lot about them before putting one in.

[enap99]

Thanks a lot. But you just scared me a lot with your K&N point. I'll study a lot.

[Schumi]

I see no real gain coming from it. I can't recall how the 968 air box differs from the 944, but I know that the 944's box draws air from a cold air tube going to the left fender. If you go and drill holes in the box, you're just negating any cold air coming from the left fender by letting the hot engine bay air into the box. The only difference I would think you would see is the car sounding a bit different up front.

On another note I recently saw someone who purchased a car with silver heat tape lining the outside of the two sides of the box facing the engine to reduce the amount of heat transferred into the box. Don't know what kind of effects all this cold air has anyways considering it's just going to heat the hell up when it hits the intake manifold anyways....

[ERAU944]

the only thing holes in the airbox can do for you are this:

it will make the car sound meaner

if it is behind the radiator (it is on the 944, not sure about the 968) it will let in hotter air and decrease efficiency/power

you won't get much(if any) of a gain by using a K&N, other than not having to buy a new filter for a long time since all you have to do is clean it. the paper filter works just fine. read up!

[Schumi]

^ Great Mikes think alike...

[Dantilla]

The entire power train has to work together as a team. With poorly designed engines, there is usually a "choke point", one specific area that's limiting power. I know on the 944S2 that the factory filter is capable of more airflow than the engine can use, so there is no benefit to changing the filter or box, unless there are other dramatic (expensive) changes. I don't recall if this is the case with the 968, but with most Porsche applications, the factory did an admirable job, and didn't leave any cheap horsepower on the table. Many cars won't benefit from an intake change by itself, or an exhaust change, but will see impovements when both intake and exhaust are modified, allowing the entire system to breathe more freely.

The turbo engines are easy to modify, because all you need to do is increase boost. Porsche did an excellent job with the normally asperated engines, so you may want to do some research before you take a drill or sawzall to your car.

[Techno Duck]

Believe it or not i have read a number of things from credible sources that say the airbox mod really does help increase power of the 968 engine and this has been documented by many people who have done before and after dyno runs. The differences range from 8-10hp and 7-10 ft-lbs. That difference is enough for me to say it caused a noticeable effect and wasnt due to a difference in testing conditions like when someone says they gained 2hp from a K&N filter.

I am not calling anyone out here...but everyone is speculating here as i dont think anyone has a 968 that replied here...

http://www.968engineering.com/airboxmods.html

More importantly

http://www.968engineering.com/pdfs/airboxmods.pdf

But i am a hypocrite, because i am speculating also. If it helps my case, i am planning to put a 968 motor into my car and have done quiet a bit of reading about it.. .

[Schumi]

I read that airbox PDF and realize my error in my assumption...

The 968 airbox IS much different than the 944. It is in the front of the engine not to it's side. What they did what cut hole in the front of the airbox, the part that faces towards the front of the car. I could see this having gains because that air on the frontside of the box is much cooler than the air nearer the other side in the engine bay. I still wouldn't go chopping up your current airbox- grab an extra one from someone parting out a 968 for cheap and try it.

I still stand with my original assumption that there are no real gains to be had from modifying the standard 923S/944 airbox. At least until someone shows me convincing data saying otehrwise on that one, at which point I will be modifying my airbox. :-)

[Techno Duck]

I agree with the 924S/944 airbox.. i drilled holes in the top mainly for sound (it does sound better). I am confident there is no difference in the temperature of the air charge going in, ive felt the top of the airbox after spirited runs and its cool to the touch. The vented nose panel might have something to do with that.

[Eldorado]

to me, there was one flaw with that PDF.

HP numbers, even on identical cars, change slightly. It's surely not unheard of to put two identical cars on the dyno, and get a 10hp difference between them...

they should have taken the exact same car and ran it on the dyno with the stock box, and then with the modified box.

they say a 7hp improvement... I say probably no more than 1... 2 tops.. when all else is equal.

[HondaDustR]

Originally posted by Schumi
...

I still stand with my original assumption that there are no real gains to be had from modifying the standard 923S/944 airbox. At least until someone shows me convincing data saying otehrwise on that one, at which point I will be modifying my airbox. :-)

Here's what I did to my 924S and it's totally reversible.

It sounds lots meaner and seems to have better throttle response esp. at high rpms (has K&N). It also retains some of the cold air intake properties that the fender snorkel provided. Sorry, no data availible, but I like it.

[The Chris]

It's been dyno'ed and proven. Check out some of the links posted, it's well worth a couple bucks!

[onZedge]

ERAU944 missed one more benefit of the holes - they act as a vacuum break when crossing small streams and rivulets.

[jwade944]

HondaDustr - There was a TSB from Porsche to delete the hose from the airbox to the timing belt cover. They offered a cap to plug the holes at the airbox and the cover. I see in your photo that your hose is still there. As an aside, I removed the K&N cone filter that was on my 924S track car and put a K&N filter in the stock airbox with the fender snorkel intact. I saw better lap times with this "stock" arrangement - probably due to cooler air. Not as scientific as a dyno, but I threw away the cone filter.

[ERAU944]

*laughing* i suppose i did miss that benefit. i realize not everyone fords large flowing bodies of water at full throttle in their 944s, but i live in florida, and if its rainin', i'm stuck using the 944.

if i had a hyundai excel GLS though, i'd probably ford the rivers, streams, and parking lots with that

as for that little hose, i've still got mine on all my cars - still don't see a viable good reason to delete, nor has anyone provided me with solid proof that this TSB exists. i will have to ask my boss if the coolant actually made it into his intake when the WP failed on his '89 944, and whether or not he had the hose.

sounds like you have some research to do on the 968 boards!

[CJFusco]

I'm really failing to see how drilling into the airbox would increase horsepower. The air filter/box is not a major restriction on the 944 (it might be different on the 968, admittedly). The amount of air that gets into the engine is regulated at the AFM box, which is located AFTER the air box. So it doesn't matter if you get more air into the box - the AFM will only allow a specific amount through anyhow.

If we are talking about COLDER air, it is POSSIBLE that colder air would get you better HP numbers, but we are talking about negligable results here. ACtually, I would think this would make a bigger difference on a turbocharged car than a NA one.

If people have done this and have gotten tangible results, then I guess it works (unless we are seeing a Placibo effect here)... I just don't think I understand why it would make a difference.

Homer: "They're speed holes, Flanders. They make the car go faster."

Flanders: "Hmmm. Maybe the old Flandersmobile could use a couple speed holes."

[Techno Duck]

Its amusing that this always becomes an argument.

The first bottle neck on the intake for the 8v n/a is the AFM. Then i would think its reasonable to say the next bottle neck is the cam, followed by the actual cylinder head design.

What the article for the 968 is saying is that the bottle neck is the airbox. ITs evident because only about half of the filter is being used if you look at the dirt patterns on the filter. Remember that the 968 does not use the prehistoric AFM, but rather a Bosch hotwire type MAF, basically the same exact thing that FRWilk was working on for our cars and thats offered by that company out of the UK.

I wasnt going to bother posting again just to reiterate this point, but ill squeeze it into this one. PLENTY of people have dyno'ed the effects of drilling out the airbox on the 968 and done before and after pulls on the same dyno (although on different days) and all have showed anywhere from 8-10hp and 7-10ft-lbs as i said in my first post. Look around on the 968 forums and you will find what im talking about. I agree that different testing conditions can have an effect on HP readings, but that difference is enough to tell me that as long as the air temp charge didnt go from negative 0*F to 100*F then its reasonable to say there is actually a different being made. That goes to say if you post a before and after dyno of something that increased your peak power by 2-5hp...now thats probably because of different testing conditions.

And regarding the service bulletin for the breather hose on the airbox, yes it does exist. Infact i have a copy of it at home and ill be sure to make a scan of it when i get home on friday. Have i deleted mine? No,thats because i see no reason to because i do not run the top portion of the belt cover. Dont even get me started on that debate.

[CJFusco]

Thank you for the post RE: air-flow restrictions ("bottle necks"). This makes a little more sense to me now.

I guess it's not always wise to apply what I know about the 944 onto the 968

[Eldorado]

Originally posted by ERAU944
as for that little hose, i've still got mine on all my cars - still don't see a viable good reason to delete, nor has anyone provided me with solid proof that this TSB exists.

two things I found while searching... Hugh says: "Its in the 1999 Porsche parts catalog I have (#10)", and goes on to explain that it's listed at AllData... I would have got you a link, but AllData requires a paid membership that I dont have...