Re-animator

He has a point. By ingesting hot under-hood air,the temperature difference can exceed 100° F in city driving or waiting in line for your autocross run. SAE correction factors for temperature give a horsepower loss of about 5% for a 50° F increase, 9% loss for a 100° F increase. It may be worthwhile to measure temps in the airbox pre and post drilling. Moving more air may sound better out the exhaust; but if that air is hotter and thinner, it will not pack as much power in the combustion chamber at velocity as a colder denser charge. My vote is for scientific theory over conjecture until proven incorrect by placebo controlled clinical trial. Or, if you love the sound; who gives a rip.

inactiveuser92616

quite a bit. the trick is turning it into steam first.

mtnman82

I remember the same thing (nice throaty sound) happening after replacing stock carb's with Weber carbs on Datsun's when I was a kid. The cars always ran better (because of the better carb, of course), but they sounded real coooool too, with no mods to the exhaust. It's just the sound of the engine breathing (not the exhaust) is more audible because there's less in the way. The Weber's used re-usable cloth K&N air filters vs. the big sealed donut air filters of yesteryear. It does sound cool (everyone who rode in one of the Weber-ized Datsuns always commented on that). Not sure what it does for performance, though.

Porsche-O-Phile

Not to be an ***, but can you substantiate this with any numbers other than a butt dyno? I'm just trying to help you from avoiding being flamed ruthlessly for what otherwise might be an interesting idea.

PennyWise

I saw an 944s2 where the guy removed the whole filter and put chicken wire mesh over the intake pipe..... he managed a weight saving of a couple of hundered pounds.. but that was after he had to have the engine removed for a rebuild. :-)

DanG

Someone needs to get some actual numbers or this is just going to be a "no, I'm right", "no I'm right" kind of discussion.

The numbers need to be Intake air temp measurements (ie: inside the intake plumbing). I don't give a hoot how hot these scorching underhood temps can get. Show me that the intake air itself has risen by a significant amount and I'll reconsider my airbox modifications.

Also, was the comment about water ingestion sarcastic? There's no way holes in the intake would increase your chances of water injestion beyond the stock system. The only way a car will injest water is if you submerge the inlet under it for a few seconds while running. I don't go swimming in my 944 that often. Rain or splashes from wet roads/puddles aren't going to hurt the car at all. Check out the search term "water injection" and you'll get more of an idea why.

I'd take the intake temp measurements myself, but my engine is out for clutch/tbelt. If someone wants to beat me to it, go for it.

joseph mitro

once again i ask......do you have a dyno graph to back up your statements? if there's one thing my 13 years of higher education taught me, it's not to accept opinions without proven documentation. so saying you "lose power" by drilling the airbox because it's "common knowledge" doesn't quite meet my level of acceptability. biased rhetoric is one thing......proven documentation is another.

i agree with re-animator......show me a dyno graph of proven hp loss before and after drillling the airbox and i'll believe it. until then......leave those of us alone who have the freedom to modify at will.

Oddjob

I doubt a dyno chart would be the final answer to this, since a dyno is performed stationary and we are concerned with engine bay temps and air flow while the car is moving.

Placing a thermo couple downstream of the airbox and driving the car at operating temp with and without holes in the airbox cover (back to back) would probably give the best indication of what effect this will have. You should check it at several speeds and engine rpm and could probably make a quick graph for comparison.

Blue S2

Ok so how does an S2 factor into this. We have the airbox OUTSIDE the engine bay. If i were to remove my airbox and add a cone, air would be hitting my filter as direct as it does an intercooler on the turbos.

Even if i were to swisscheese my box, how could my temps possible go up, up or make me lose power. Where my filter is, its always getting hit directly with ambient air pretty much.

wombat7

I know I'm a little late, but liquid water is definitely an incompressible substance. Now on the water ingestion topic, the amount of water that you could possibly get into the air box because of a few small holes or even one large hole would not effect your engine's performance.

I could possibly do the intake temp measurements before and after. I need to find the hardware to do it though. I'm sure I can find it if I knew what I needed, I do go to an engineering school where we have departments (electical, mechanical, civil, and biomedical jsut to name a few) of parts and equipment that we can use for stuff like this. If someone can tell me what I need, I will do the temp measurements.

944CS

everyone here is talking about temperature...but we are forgetting another thing when it comes to power...pressure...by drilling the holes, you are not letting the air inside the airbox pressurize when you are driving down the road at 60 mph...this mod probably won't affect performance in around town driving, but one of the reasons these cars pull pretty good with only 150hp is because the airbox becomes pressurized when you reach a certain velocity. the reason porsche updated the airbox by removing the piece that goes into the fender is because people would drive through water and blow their engines up because water traveled into the combustion chamber...now one argument people are going to make is that the door on the air flow meter is restricting flow anyway so the pressurized air cannot possibly be getting to the valves....and my response is that the air is not pushing the door open, the absence of air is opening it (vacuum from the pistons).
not that i really care if you guys do it, i like that sound personally but i like to extract as much hp as i can and i just couldnt sit comfortably knowing that i might be taking away from the performance of the vehicle, no matter how big or small i may be taking it away.

Re-animator

On my ex- '01 S4, I drilled one big hole saw sized hole in the box on the bottom away from the engine. With my VAG-COM, intake temps at idle were 30 degrees C higher. Using SAE correction statistics as a baseline, performance was markedly impaired. It sounded really cool, though. I have a little trouble comprehending how this mod may out engineer the boys at Weissach, but they may have had constraints in their design like sound limitations and such. Bottom line, it is your car; be happy with it via whatever means.

cas951

I've actually done this to my car and I have a spare airbox cover. I drilled several 1/2" holes on top of the airbox. I also took temp measurements inside the airbox but mostly during California winter months and early spring. Outside temp were @ 60 deg and inside airbox temp while moving is the same. At stoplights 1-2 minute stops the inside airbox temp rose about 15-20 deg but dropped back to normal temps as the car moved. I used a dual digital thermometer from Radio shack to measure. The unit measures outside temp and it has a probe that has a 20 ft wire you can route anywhere.

Summer months is a different story. Temp differences is a lot. At 90 deg outside temp I saw as much as 130 deg inside airbox temp. As the car moved the temp slowly drops but the time it took to drop was fairly long. I've never measured for performance gain but more experimenting with it.

Mongo

I haven't posted a pic yet, but Geoff, Randy V and Ibkevin can vouch for how many holes I drilled in the airbox. I can't give you an exact temperature reading since I didn't use any equipment, but I can tell you that there has been no lag on take off (which is common with a cone filter equipped 944), not flat spot under 3500 RPM due to hot air being sucked in, and absolutely no improvement in performance.

I didn't get to post pics or a video last night because a freight train of brandy and kamikazes hit me quite hard (thanks Randy... )

Mighty Shilling

It does sound REALLY nice. I'm thinking about picking up a spare airbox so I can do this with mine.... :drool: