Michael Galimi
December 15, 2009

The past few issues we have been following a supercharged 2000 Mustang GT as it received a new set of Trick Flow Twisted Wedge Street/Strip 4.6L cylinder heads, the latest Anderson Ford Motorsport (AFM) F82 camshafts, and a larger ProCharger D1SC centrifugal blower. The '00 GT is fairly basic with a built short-block (cast crank, forged rods and pistons) and the aforementioned induction components. The heads were worth 34 rwhp over CNC-ported OEM heads, and we finished at 571 rwhp.

We were expecting 600 rwhp but a slipping six-rib blower belt hampered our lofty-but realistic-goals. The boost gauge touched 17 psi, but the engine fluttered in the upper rpm range. Mike Dezotell of Dez Racing was also disappointed, as the engine should be revved up to 7,500 rpm in order to take advantage of the larger AFM cams. The rwhp level fell off at 6,500 rpm.

Since we couldn't end on a sour note, we are back at it. Our original goal for this issue was to add a ported Fox Lake P-51 intake and also have the company run our TFS heads through its CNC-machine. That would help our engine ingest more air and get to our goal of 7,500 rpm.

Another trick on our list for the 600-plus-rwhp club was to-finally-upgrade to long-tube headers. Kooks whipped up a nasty set of stepped headers (1 3/4 to 1 7/8-inch primary tubes) with 3.5-inch collectors. We also ordered a 3-inch X-crossover, which has provisions to mate to the Magnaflow 2.5-inch after-cat exhaust. The headers and X-crossover are made from stainless steel. Until this point, our test car has employed a set of Ford Racing short-tube headers and 2.5-inch X-crossover.

Deadlines prevented us from adding the ported heads and intake, so we focused solely on upgrading to the Kooks long-tube headers. We made two changes since the car was dyno-tested last issue; the first was the addition of a ProCharger eight-rib blower pulley setup. The unfortunate part was that ProCharger's smallest blower pulley is 3.40 inches, while our six-rib one was 3.20 inches. That meant our baseline would have less boost through the entire curve.

The second difference is that last month Dez knocked off 2 degrees of timing (15 versus 17 degrees), due to the Stang seeing street time. He wanted a safety margin should some low-octane fuel come through the station's pump. In this trim, boost barely touched 17 psi at the top of the pull-thanks to the belt-grip. That was the same boost we peaked at last issue but less timing advance brought output to 549 rwhp and 465 rwtq.

We had high hopes for the long-tube conversion and larger X-crossover due to the supercharged nature of this Mustang."The shorty headers are not worth it," said Dezotell. "They are a major restriction at 500 rwhp and here we were trying to push 600 rwhp as well as rev the engine to 7,500-both goals were not previously achieved and we hoped this exhaust would help us remedy flaws in our system." These headers are of the stepped variety, which means the header tubes start at 1 3/4 inches and then open to 1 7/8 inches-more on that in a bit.

Adding a better exhaust system is a simple concept, what goes in must come out. And this being a supercharged engine means that we have a lot of air getting crammed in to the 281ci powerplant that has to make it way out. But what does that automotive cliché mean? An engine is an air pump and it has to get rid of the spent gases from the combustion process. As the exhaust valve opens, the pressure in the exhaust tube is lower than that in the cylinder, so gases will rush into the cylinder head port and into the header tube(s), to eaqualize the pressure. As this is happening, the piston is moving upward, helping the process by pushing the exhaust past the valve. As the piston is thrust upward, there comes a point (near top dead center) when the intake valve will begin to open. This valve event is called overlap and the rapidly exiting exhaust gases actually help pull-in the fresh air/fuel mixture from the intake valve.

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