Jonttt's 993 C4S Journal

jonttt said:

Fabspeed Cup Airbox.......

I already have the "sports" airbox fitted but was intrigued by the cup car option.

There is some "controversy" over this items but my thought process was as follows:

- dragging hot air into the combustion chamber is a no no :hand:
- dragging more air into the air chamber is a plus
- dragging air under pressure to the air chamber is a plus

so the simplistic ideal is to fit an induction system in such a way as pressurised cold air is fed into the engine. Thats why your car feels faster on a crisp winters day :wink:

I have no evidence of the following but my simple logic based on the above simple ideals is that the 993 air induction is flawed in some ways as it drags air in which has been warmed at least to some extend by the engine. The only way to improve this is to protect the external air from the engine heat as it enters the combustion chamber ie extend the intake up to the engine grill. I believe their is an option to do this via a "trumpet" for the fixed winged cars. However this will not fit the retracting grill for obvious reasons.

So unless I want to go fixed wing (which I don't) I have to accept a compromise in engine heat transfer to the air induction.

With regard to pressurised air the OEM 993 airbox is split into 2 parts. The back part is specially disigned to increase air pressure into the combustion chamber so the ideal is not to lose this feature ie retain the back part of the OEM airbox.

This leaves air volume. The OEM sports airbox allows more air through compared to the stock airbox by simply putting more holes in the front part of the airbox. nb the side affect of this is a "induction" noise which most regard as pleasing under full throttle

It appears that Porsches own solution to this on race (cup) cars was to effectively remove the front of the airbox altogether thus allowing as much air as possible to enter the combustion chamber

However you still need to fit an air filter to stop contaminents entering the engine and the OEM front of the airbox was how this was retained in place. The solution was to simply provide the skeleton of the front airbox which sole purpose is to retain the air filter.

Fabspeed seem to have simply produced a version using he same logic.

In summary the pluses are supposed to be maximum pressurised airflow into the combustion chamber. The side effects are increased induction noise.

Note: To maximise the benefits of the increased airflow in the extra air volume needs to be able to exit easily. Therefore reducing any "blockages" to the exhaust side of the engine helps. This is why sports cats and mufflers help with performance ie less obstrucition to exhaust gases leaving the car. my car has sports (RSR) mufflers but not sports cats (still has OEM cats).

One of the problems reported of the cup airbox design is the skeleton frame holding the air filter offers less support to the filter. There have been reports of OEM air filters collapsing. Therefore it is recommended fitting sports "free flowing" air filters. These are designed to allow more airflow but as a a consequence tend to be more rigid and therefore less prone to collapse.

So that is my simple, none scientific, none engineered man logic which led me to want to try the Fabspeed cup airbox. The only part of my logic which does not really make sense is why did Porsche not fit the trumpet style solution to their fixed wing cup cars :dont know:

Anyhow it was a nice ebay project for me to source a second hand one.

One came up advertised from america with a buy it now option but the buyer would not accept my offer. It was the first one that I had seen come up on Ebay so a bit disappointing. So imagine my delight when within a week one came up from a UK seller and my offer was accepted.

It arrived today.....






I make no apologise for the gratuitous opportunity to show my GT2 poster in the new man cave :wack:

Unfortunately my new garage is not quite ready and so the 993 is not at home at the moment so trail fitting / running will have to wait for now but I will complete the write up when fitted.

Here is the Fabspeed youtube video of the installation / running etc....



ps I have no interest in a debate over BHP etc.... its all about how it sounds and the car feels on the road to me :thumb:

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