Fletcher

I have seen a few of these mod's mainly on race/track cars. I was told by those who use it that it does make good power gains. You eliminate the air runners to the air box, expose the back of the box or modify it and trim the metal firewall down so the air can flow more easily from the back of the hood (colder air I'm told). I have an idea how to make the mod look clean enough, but would like some feedback.

Anyone tried it, and with what results?

bergstsm

Darren,

Search the archives (or maybe the thread was on S4VR), but those that have gone that route have mentioned the problem of water getting in the intake when they have done what you suggested. If you have a solution, I am sure there are people that would be quite interested.

Shawn

Update - Found it. Look at these replies.

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=000113" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=000113</a>

Jeremy B

Just a matter of opinion on the topic I think that the power gains wouldn't be all that much since the origional design by porsche was to take cold air from in front of the radiator area through teh intake tubes, the colod air that is rushing in as your driving, i have noticed that even mark anderson from 928 international uses the stoke air inlets for his race car, i bought some larger intake tubes than the stock ones that work great they were only 10 dollars a peice at 928 international, also just a thought if you bought one of those thermometers from radio shack or somewhere and measured the temp of teh air taken into the tubes and the temp of the air where the back air inlet is by the winsheil compare teh two see if the temp difference is worth all the hassle of getting water inside, take care and good luck

Jeremy 84 928 S

Mike Schmidt

There's already been some intake air temperature testing done. There were readings taken comparing the ambient air temperature to the air temperature at a couple of different points along the path of the stock intake system. After idling at a stop for a short while, the air temperature was considerably higher at the air filter than the ambient air temperature was. Most of the temperature increase was taking place as the air flowed through the intake tubes. Temperature readings were taken at different car speeds. The faster the car went, the closer that air temperature at the filter got to ambient temperature. I don't have the test readings here, but at right around 20 mph or so the temperature at the filter was already pretty close to ambient. If you're sitting at idle and floor the gas pedal with the stock intake system, you'd be down on power some compared to something like a cowl induction hood. If you're going more than about 20mph the cowl induction won't provide much if any cooler air. If you're going way above the speed limit, the cowl induction hood will provide some ram air effect, but so will the stock system. Don't expect too much though. I think the Devek white car was getting .3psi with the cowl induction setup at around 200mph.

If you insulate the stock air intake tubes, the increase in air temperature as it passes through them at idle and very low speeds is reduced quite a bit. Porsche used insulated air intake tubes on the GTS. Those are the type that Mark Anderson had on his car the last time I saw it.

Steve Cattaneo

The plastic tubes are not a ram air system; they just guide cooler air from the front. The plastic tubes were designed as a venturi nozzle to dampen the engines intake noise. Go with GTS tubes. Until you find a better way. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Fastest928

watch out for water injection it is noncompressable!

Marc

Mike Schmidt

It wouldn't have any great effect, but if they're well sealed the stock intake tubes should technicly provide some ram air effect. The location of the openings is in an area of high pressure with the car at speed.

Fastest928

The stock inlets are very good, if not the best pending pressure drop across the rad at speed. Like mike says, stickw ith stock and use the GTS tubes or make some yourself at substantailly lower cost.

Marc

Steve Cattaneo

Mark,
A picture is worth a 1000 words.


marc@DEVEK User Rennlist Site SponsorUser # 5789 posted 06-09-2002 21:23 watch out for water injection it is noncompressable! Marc --------------------

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

sweet928

I searched all over and cant find much on how/why my PO came to the decission to cut down the cowl behind the airbox. I didnt even notice it when I bought the car two months ago. When I noticed it, I called him. He said he did it because the guys online were doing it to deal with OB's running hot. He had the car 13 years and I think he did it a deade ago...Later on he bought a alluminum radiator and the car runs on the lowest bar on the temp guage.

So I only found this one and only post from 2002 which refers to this step. I cant find anything else on the subject. The cowl was cut down about 3 inches from the top and about the width of the airbox. So now I cant mound the plastic cover or the weather strip at the front of the cowl and seal off the engine as Porsche intended.

Anyone know more about the pros and cons of this choice by the PO. I am inclined to correct this, but not sure how to best go about it. Any ideas? I just ordered the 75cover plus the weather stripping and thought a metal fabricator or welder could put some metal back using the cover as a guide. Or should I just leave it as is? Hard to get a good picture, but here are some.

i am worried about someone trying to get into this spot and weld something back in. It seems like a hard spot to get to and dont want someone messing up my fenders, airbox, etc. Maybe I should leave it alone? The car is not a daily driver and will never see rain and I don't think it ever has in 30 years.

Lizard928

I would just leave it and fugedaboutit.

ew928

Do you have A/C?
Right now with the cut down cowl, HVAC will ingest hot air from the engine compartment and try to chill that hot air.

mark kibort

Ive done the pressure tests. the tubes, sealed with even just tape, provide the same ram effects as the back of the engine. I use both! This reduces the pressure drop of the air box under WOT conditions.
I did all sorts of pressure sensing along the air path, and its all about .2psi at near 100mph.

danglerb

I bought an OBDII scanner to trouble shoot my wife's Lincoln. Hooked up to an old laptop I could monitor various sensors, and I was shocked to see intake temperature at an idle (as measured in the plastic tube between the air filter and maf and the throttle) was 135F. Turns out that is normal, and it does drop quite a bit under a load, but this is a modern car and it is really well sealed.

Air filter box on the 928, and the tubes leading too it do NOT seal all that well.

I suspect unheated air is possible from something at the cowl or tubes to the front, whats most practical I think remains to be seen. Doing it well may be more important than front or cowl.

Could be its all moot unless the intake to the heads is also insulated.

sweet928

Yes, I have cold AC.