The first mod that many performance-car owners make is to replace the factory air filter with a K&N filter. This can allow more airflow into the engine, promoting better performance and efficiency. Letting your motor breathe freely is usually a good idea.

Decisions, Decisions

There are several ways to approach this issue. One is to install a direct-replacement K&N into the stock airbox, and while this is inexpensive and simple, I figured it would be better just to get rid of that funky airbox with its narrow snout poking into the fender and run an "open" filter in its place. I could have installed a K&N FIPK or a new Mass Air-Flow meter (MAF) such as a Pro-M or C&L, each of which can replace the airbox with a large open filter, but the filter would be exposed in the engine bay and take in hot air (no good). An even better idea is to position the entire filter in the cooler space of the inner fenderwell, running a pipe from there to the MAF intake. This is what the Roush Performance Cold Air Intake kit does.

The Roush Solution

The Roush kit includes a big (8.5" long x 5" diameter) cylindrical K&N and a 90-degree curved steel pipe that goes from the opening in the passenger-side fenderwell to the MAF. While it's possible to fabricate your own pipe from PVC and such, I wanted a more professional look -- the Roush pipe is a nicely-finished piece and fits perfectly. Cost was about $170, which isn't cheap, but the K&N FIPK isn't much less and it leaves the filter exposed in the engine bay. Besides, the Roush kit is much cheaper than a new MAF ($250-400), which may or may not give you any additional benefit -- I've yet to see convincing evidence that an aftermarket or modified MAF unit, apart from the new filter or electronics, provides any improvement when used on a normally aspirated engine. And don't talk to me about so-called "Ram-Air" kits -- for about $150, you get a device that sucks water, dirt, bugs, and other debris into your air intake! No, thanks.

Installation was done in less than an hour; the most difficult part was pulling the stock airbox out. The (very detailed) instructions tell you to remove the MAF and mount the new pipe and filter on it before bolting the entire assembly under the hood, but I found it much easier to leave the MAF in place, slide the filter into the fender (it fit fine -- doesn't seem to hit anything in there), mount the pipe to the filter, and then the pipe to the MAF. It's a snap with a couple of wrenches (8mm and 7/16") and a screwdriver. I also disconnected the negative battery terminal while I worked so that the engine computer could reset and adjust itself to the increased airflow.

Impressions

I'm not sure exactly how much more power this kit gives you, but my buttometer tells me it's more than enough to justify the cost. There's a subtle but definite power increase throughout the RPM range. Idle smoothness is unaffected, and there is just a hint of additional noise -- kind of a deep hissing sound -- under hard acceleration.

Now, even though I have no hard before/after figures from a dyno or dragstrip, I always try my best not to let my prior expectations color my impressions. So take my experience for what it's worth -- a subjective improvement -- though I'd be surprised if this thing didn't add pretty close to the advertised 9-12 rwhp. Thumbs-up to Roush -- I'm very happy with their quality and service. Usual disclaimers apply: just a customer, YMMV, etc.

The only thing that concerned me after putting in the kit was that there was a pretty large gap left between the fender and pipe -- it looked like hot air could easily find its way into the filter from the engine bay -- so I sealed the gap with some black duct tape. It doesn't look too bad. ;-)

Note that the Roush pipe will NOT fit on an aftermarket MAF such as the Pro-M 77mm without some sort of custom adapter -- it's meant to bolt right onto the stock MAF (the new Pro-M 87mm will probably work, though). Also note that the K&N filter that comes with the kit is of a special size (8.5" x 5") that is available only from Roush (or so they say).

I bought this kit back in Spring '98, and I'm not sure if it's still available. Try Dallas Mustang or another Roush dealer in your area. Or take a look at the similar part offered by Western Motorsports, which is less expensive and which also can be ordered with a matching Pro-M 87mm MAF.

Postscript

While it's a matter of some controversy, with plenty of biases on both sides, I suspect the K&N filters do not filter airborne particles as well as other types, including basic paper OEM filters. If you agree, consider the AEM Dryflow or Amsoil Ea filters, both of which may work with a cold-air induction kit. Also take a look at the Purolator Pure One air filter, which fits in the stock Mustang airbox. This would necessitate giving up the cool air pipe, but hey, if you value the longevity of your engine, it might be good to think about.

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