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Dutch924-racer · Joined: 23 Jul 2007 Posts: 1081 Location: The Netherlands

The standard 931 airbox is strange. The cold air comes in at the front but the airbox sucks air at the rear.

Has anyone modified the original airbox to get cold air in? Pictures ???

Or would a replacement cone filter be a better option ? Pictures ??
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

tuurbo · Posted: Wed Sep 03, 2008 4:29 am Post subject:

I don't know if you're going to get any change in performance with a new cone filter or something other than stock.

I hooked a vacuum gauge up to my air box, near to the CIS, and once far from the CIS over near the opening. Sealed up the unit as best I could. Then I took the car for a drive.

At zero (0) through seven (7) PSI we observed no vacuum.

No vacuum, if a true reading, would mean there's no restriction, I think.

I think the existing box has enough flow.

Corky Bell says to expect some vacuum from the restriction of a filter, some pressure change at the box, but it's small, like a couple of PSI at best, at full boost. It's not really avoidable.

I've tried the KN route it doesn't make any difference. Unless it's dirty.
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.

924RACR · Posted: Wed Sep 03, 2008 4:34 am Post subject:

I would (and will) definitely go for cold air.

Saw some good easy versions for use with cold air, using sections of foam board from the hardware store such as used for building insulation - only cut to provide a cold box for air intakes. Have to get around to doing this to my car...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

tuurbo · Posted: Wed Sep 03, 2008 5:12 am Post subject:

Yeah but is that for the NA or a turbo Vaughan? I'm asking cause I'm thinking of that plate on the floor of the turbo engine compartment...how are you going to get around that? Or do you?

Cold IS good!
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Vaughan is definitely referring to a 931

One modification I've read about somewhere here on this board is to cut off the "horn" on the stock 931 airbox, and seal up the hole; then cut holes in the front of the airbox so that they receive direct cold air from the vents on the front of the nose panel. Seems really obvious to me, not sure why the factory would have done it differently. If I were sticking with the stock airbox, this would probably be the approach I would try first. I have a spare airbox for sale if anyone wants to try it (so that you don't cut up your good airbox).
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erstwhile owner of just about every 924 variant ever made

924RACR · Posted: Wed Sep 03, 2008 6:36 am Post subject:

Sorry, no, I was referring to the racecar/NA. The 931 will be using a CGT hood scoop, in the less-common placement.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

OK, I stand corrected

I thought you were referring to your daily driver.
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erstwhile owner of just about every 924 variant ever made

tuurbo · Posted: Wed Sep 03, 2008 7:05 am Post subject:

We'd want to get low to the ground for colder air.

I suppose the cutting of the airbox would make up for any restriction issues, but again, I'm not sure we've got a very restrictive box. Maybe some other measurements besides mine would help.
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.

Cedric · Joined: 27 Aug 2004 Posts: 2805 Location: Sweden

hm, the 931 box isnt that bad, the filter is very large and not so close to the warm things under the bonnet. What you could to is to connect a tube from the existing inlet to the airstream somewere, that would probably get you more and cooler air.
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1980 924 Turbo
www.instagram.com/garagecedric/

924turbo_sout_africa · Joined: 29 Oct 2007 Posts: 215 Location: Sout africa

well...this was actually debated a couple of years back when i got here i read it i think it was a rick dude but as far as i know he sold his car to his daugther or something....

well he send me pic's where he grinded the front of the airbox open to get the cold air ....we have a dude racing a 924 turbo here and he did it he said look at idle there is no diference in power but as soon as he takes off he said it is much beter moving so my plan is to do this with my intercooler when i place that in to cut by box and just put in a performance filter that can be cleaned.
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Porsche ...where dreams are a reality
'79 924 turbo canada spec
'98 Formula Vee (M3 eater)

Time in the 931 is a dream come true !!

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

I cut the square hole in the front of the air box and have it directed at the four openings. I left the regular opening as is.

My thought is to get cold air in. Igf it rains I can close off the front opening at any time.

Second thought is to insulate the entire airbox being it sits on top of the radiator. You can do this to the inside or the outside. I prefer the inside. Less noticeable.

Did I notice any change? I have not driven the car in two years because of my move to FL and have not registered the car. Soon though.
_________________
"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

I cut the square hole in the front of the air box and have it directed at the four openings. I left the regular opening as is.

My thought is to get cold air in. If it rains I can close off the front opening at any time.

Second thought is to insulate the entire airbox being it sits on top of the radiator. You can do this to the inside or the outside. I prefer the inside. Less noticeable.

Did I notice any change? I have not driven the car in two years because of my move to FL and have not registered the car. Soon though.
_________________
"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I haven't thoroughly perused these articles, but I generally find the Autospeed content to be very insightful. These might serve as a good reference for this topic:

Siting Cold Air Intakes
More on Siting Cold Air Intakes
Building & Testing an Air Box
Getting Air In & Out
We Have a Record!
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erstwhile owner of just about every 924 variant ever made

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Here's a couple more relevant reads:

Dual Pipe Induction Part 1
Dual Pipe Induction Part 2
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erstwhile owner of just about every 924 variant ever made

924RACR · Posted: Thu Sep 04, 2008 12:15 am Post subject:

Excellent links, thanks Dan!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype