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 In this "before" photo, you...  In this "before" photo, you can see the restriction imposed by the stock inlet elbows and stock MAF meter. This is how we ran Magnum TPI at the track for its best-to-date run of 12.30/109.4. The heavy-breathing 396 tuned-port motor had already been converted to speed-density via a Gen 7 ACCEL/DFI, but the MAF was retained for plumbing. A 3-inch "Home Depot" PVC pipe and 3-inch conical K&N filter did alleviate some restriction, but it was still far from ideal. |
 One big challenge was finding...  One big challenge was finding enough clearance to run a 4-inch pipe between our big Evans radiator and the A/C compressor. Making things more problematic was the third-gen Firebird's sleek hood line, lower than the Camaro's. Another difficulty was getting around the radiator overflow "nipple," which was easier to bend out of the way rather than to weld on somewhere else. |
 We're skipping a lot for space...  We're skipping a lot for space reasons, but here's the finished 4-inch pipe, welded and painted with Krylon black crinkle paint. If you're looking to do this yourself instead of having a fabricator do it, the mandrel bent 4-inch mild steel pipes can be special-ordered from NAPA (it's actually exhaust tubing) for about $70 per bend. We used a 5-inch radius bend and an 8-inch radius bend with straight pipe in between to get our final shape. |
 Our third-gen Firebird required...  Our third-gen Firebird required part of the hood support frame on the passenger side to be cut away in order to provide ample clearance for the 4-inch inlet pipe. The notch in the hood was then sealed with a urethane adhesive sealant from 3M. This will keep rubbing to a minimum and protect the exposed metal from rusting. |
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!
 We cut a 4.5-inch hole in...  We cut a 4.5-inch hole in the undertray, using a hole saw. Note the relocated charcoal canister. |  This 4-inch diameter, 7-inch...  This 4-inch diameter, 7-inch long K&N filter (part No. RF-1015) was obtained from Jeg's mail order for $39.99 (it was actually $57.97 including handling and shipping). Note the length of 4-inch tubing clamped to the filter neck. This pokes through the undertray where it can be clamped to the inlet pipe from the top side of the engine compartment. |  Not wanting to have the filter...  Not wanting to have the filter exposed to water, mud or other road detritus, we had our fab shop build us this drained, vented and shielded filter box. The box fastens to the fender and undertray using existing panel holes and a few new sheetmetal screws. |
 In this comparison, you can...  In this comparison, you can see the difference in the throttle body inlet area. The old one fabricated out of our stock inlet tube and a piece of flattened pipe is on the right, and our new 4-inch tube is on the left. Note that a 4-inch round pipe conveniently flattens to exactly the size of a standard twin-blade GM throttle body. The section of new pipe attaching to the throttle body (right) is on a 5-inch radius--not ideal but it was the most gentle radius that cleared all the obstacles. |  Here is the finished pipe...  Here is the finished pipe installed. To connect everything up, we obtained a foot-long section of flexible black turbo hose (cut into two parts for each end) from Precision Turbo for $22.26. The four t-bolt clamps we used (also from Precision) are really high quality and ran $5.91 each ($23.64 total). Finally, we can give the old MAF the heave ho! |  We've found an amazing degree...  We've found an amazing degree of consistency between Dynojet chassis dynos, particularly those equipped with automatic atmospheric data acquisition (both our test dynos at Second Street Speed and Crazy Horse have this). Nevertheless, dyno numbers are no substitute for ET slips. Is 337 rearwheel horsepower (roughly 420 hp at the flywheel) enough to go 11s with 3,625 lbs.? Soon, we shall see. We've certainly got lots of torque to get us moving. |
 Here is the end result of...  Here is the end result of our new 4-inch inlet, taken on a different Dynojet (Crazy Horse Racing instead of Second Street Speed), but using the same standard correction for atmospheric conditions. The custom pipe produced 337.7 rearwheel horsepower (5500 rpm), or about 14 hp more than the stock pipe. Note how fat our torque curve is: no less than 400 lb.-ft. from 2000 rpm all the way up to 4200 rpm. Torque peaked at 445 lb.-ft. (2900 rpm). |  The two graphs here represent...  The two graphs here represent the power produced with the stock inlet pipe and MAF in place (323.9 hp) and the same 396 engine with a completely open throttle body (354 hp). This rearwheel power figure is the bogey for our custom fabricated 4-inch inlet--the closer we get to that number, the better our design. | |