1988 Pontiac Firebird Custom 4-Inch Inlet Pipe - Breathe, Puppy, Breathe!

As we get down to the wire with our 1988 Firebird project car, it is more obvious than ever that having a big powerful engine alone is no guarantee that big power will come out at the other end. The 396 cubic-inch, ACCEL SuperRam stroker which was built for us at Strope Speed Shop in Washington, Pennsylvania has presented a new challenge for us: how do we actually feed this beast with sufficient quantities of cool, filtered air?

We did some asking around, namely at the message forums at www.thirdgen.org and www.camaroz28.com. We got some great feedback and even some helpful photo links to some other big-inch third-gen Firebirds with custom induction setups. What we found was interesting. It turns out that third-gen Firebirds have a unique problem in that their low hood line and passenger-side-only intake ducting makes it very difficult to route lots of cold air into the motor. This is not really a problem with stock displacement engines with mild bolt-ons or even head/cam packages, but it is a big problem with bigger engines such as ours. Third-gen Camaros, on the other hand, have a higher hood line which simplifies the buildup of a custom intake pipe when one is actually needed. Fortunately, the dual snorkel factory setup found on all tuned-port IROCs and Z28s flows a greater amount of air than the sibling Pontiac setup. The Camaro dual-snorkel is also easy to modify for increased flow for not a lot of extra effort. Unfortunately for Firebird owners, the Camaro dual-snorkel setup cannot be swapped over to the Firebird because of the 'bird's lower hood line. Bummer.

We did find SLP's Firebird dual snorkel unit (part No. 21030) which is a factory part on speed-density '91-'92 SLP Firehawks, but installing this requires removal and relocation of the battery to the rear. We also had questions about the SLP's ability to move enough air (the runners are smaller than what we ended up using) and clearance problems with our larger Evans radiator and SuperRam manifold (it sits closer to the radiator than stock).

The only practical solution was to fabricate something custom out of four-inch mandrel-bent steel tubing. We contacted a local fabrication shop the author has used previously and set up an appointment to have the staff look at the car. We were given an initial estimate of $300, which included the fabrication labor, the mandrel-bent mild steel pipe, the mock-up, painting and installation. This estimate was later revised to $400 after it was determined a custom protective air box was required beneath the undertray to house our 7-inch long conical K&N filter. All together, we spent $511.13, which included flexible 4-inch turbo hose and t-bolt clamps (from Precision Turbo), a K&N filter (from Jeg's), and applicable handling and shipping charges.

Dyno Results
In the January 2002 issue (see "Magnum Returns"), we tuned our Strope Speed Shop 396 using an ACCEL Gen 7 DFI system at Second Street Speed (Perkasie, Pennsylvania). At that time we dynoed Magnum TPI in two configurations: with the stock intake tract (including MAF sensor) and with a completely open throttle body. The results were dramatic; with the stock MAF and inlet, power was limited to 323 rearwheel horsepower. Taking off all the inlet pipes allowed power to swell to 354 rearwheel horsepower, a difference of over 30 horsepower.

At the race track, Magnum TPI ran a quarter-mile best of 12.30/109.4 with a 1.67 60-foot time. This ET was accomplished using 93 octane pump fuel and our Centerline/Mickey Thompson ET Street wheel/tire package from project TGOW. Most notable is the fact that this ET was run with the stock intake tract and MAF sensor (it was nonfunctional except to act as part of the plumbing).

The day prior to our followup drag test (using our new 4-inch custom inlet), we suffered a major setback in the form of brain fade. While changing our tires, the car slipped off the jack and the jack slammed down onto the oil pan, necessitating a trip to the shop for repairs. (Thankfully, no damage was done to the 396's internals. You'll recall we used billet Pro Gram Engineering main caps and Lunati Pro Mod rods, the main reason our engine was saved from damage.)

The second attempt at a track outing was cancelled due to rain, but we did make a trip to the Dynojet at Crazy Horse Racing in South Amboy, New Jersey. Using the same standard correction factor, rearwheel horsepower weighed in at 337.7 (5600 rpm) and peak torque registered 445.6 lb.-ft. at 2900 rpm. That pretty much splits the horsepower difference between our stock plumbing (13.8 rwhp more) and the unrestricted open throttle body (16.3 rwhp less). We had honestly hoped for more, given the large 4-inch diameter of the mandrel bent pipe, but at this stage of the game we feel it's still worth the effort.

Now it's only a question of getting back to the track before the winter sets in. Will we get into the 11s using pump gas, an emission-legal cam/head combo and natural aspiration? Stay tuned, this is getting good!