Cold Air Intake

Ford Focus ZX4 ST Modifications - Cold Air Intake - Phil Usher - May 2006

May 18th: Got a call from Focus Sport today.  The Cool-Flo CAI system is on backorder - Might be month! I upgraded to the more substantial and expensive (and available) Cosworth Cold Air intake system (Cosworth @ FocusSport).  The Cosworth CAI is CARB approved (pending) - read "emissions legal".  Cosworth claims a 10hp gain - that's about a 9% increase - should feel that!  The acid test will be the dyno.

May 19th: Amazing shipping speed - Product has arrived.

May 20th: Step 15 in the instructions was an unpleasant surprise:  'For cars with manual transmissions, it will be necessary to trim the lower air box cover inlet hole for proper clearance.  It will be required to remove approximately 28mm as measured from the air box opening as shown in.....'

May 23rd: Exchanged email with Cosworth.  I complained that their instructions were not available online.  Cosworth replied that they're working to get the instructions up on their web site.  Why do most of these companies fail to recognize the support cost savings to be had by maintaining a decent website.  Last week the Cosworth site was actually down for quite a long while.   I just hope their engineering proves to be more trustworthy than their internet technology.

May 31st: Josh at NRP removed the improbably large and complex stock air intake system (see picture left) and installed the Cosworth system.  The Cosworth system is so much smaller by comparison that there is now a gap in the engine bay.  Fortunately the cutting described in "step 15" of the instructions proved to be unnecessary and the whole install took Josh a little over an hour.

After install we ran the car on the Dyno and made some small adjustments to fuel at high revs and the end result was a jump from 133hp to 141hp.

Gain in power = 6% (~8hp).

Some notes about driving the car. It's worth noting a three things at this point.  First there are two sets of changes here, the Cold Air Intake,  the Hypnotic engine tune and the minor additional tune elements courtesy of NRP.  

• The Hypnotic adjustments seem to include some changes to throttle response (need to check this with Wayne) which produces an effect of "peppiness".

• It's louder, much louder.  A large part of the stock intake solution is about eliminating noise.

• It pulls much more cleanly at high RPM. Previously there wasn't much value in holding a gear beyond 6100 revs, now the car pulls almost all the way to the Hypnotic tune increased rev limiter.

In practice these little changes combine to produce a considerable change.  Now a jump to wide open throttle is rewarded with a growl as the system ingests a less restricted airflow.  While only slightly quicker acceleration is more consistent and rewarding. The experience feels and sounds faster than it actually is. 

The increase in usable rev range (at the top) is very useful allowing one to remain in gear a little longer if needed.  To put this in value into an example consider imagine a tight turn followed by a short straight followed by another tight turn. The increased usable rev range now provides an opportunity to hold 2nd on the straight and eliminate two gear shifts. This example also provides an opportunity to use the left foot to brake for the second turn.

Conclusion

If you're seeking performance improvement then changing the air intake system should probably be your first modification.  It is my understanding that the factory air intake system design goal was to go 100,000 miles between servicing and be quiet.  Having studied the size and complexity of Ford's efforts I'm impressed but an aftermarket air intake (like the Cosworth one shown here) will provide a marked increase in power and provides the necessary the groundwork for subsequent modifications. 

Notes

• Those concerned with emissions should note that the Cosworth air intake is currently the only one CARB approved. 

• Those who live in very wet climates where the roads often have deep puddles may want to consider a cold air intake which draws air from higher in the engine bay.