Not surprisingly, the peak gain was only 1 hp and 1 lb-ft of torque. But, like the previous run, gains were as high as 10 hp and 15 lb-ft of torque over the rest of the graph. More impressive was how much smoother and consistent the graph was throughout the run. Also, this combination caused a spike in horsepower at our cutoff of 6,250 rpm. A small hike in the maximum rpm may have produced greater horsepower at the peak, but the car owner didn't want to turn up the rpm.
Last on our list was BBK long-tube headers and matching X-style mid-pipe. Since this combination was going to be last, and permanent, we opted for the BBK stainless steel long-tube headers (PN BBK 16415) to couple with the X-style mid-pipe with cats (PN BBK 1637).
The long-tube headers, like the shorties, are also available in chrome (PN BBK 1641) and ceramic coated (PN BBK 16410). With the long-tube headers and mid-pipe in place, Grieves strapped our GT down for one last spin of the rollers. True to form, the long-tube combination yielded yet another 4 rwhp and 8 rwtq, bringing our running totals to 397 rwhp and 378 lb-ft of torque. More noticeable, though, was the big increase in torque from 3,650 to 5,500 rpm.
Clearly we made the most power with the long-tube headers and matching mid-pipe. However, this is not a perfect world. As the graph shows, low-end torque was reduced slightly. It was recovered higher in the rpm range, but it must still be noted.
The final results against the baseline test show a maximum increase of 9 rwhp and 12 lb-ft of torque at the peak, but none of us drive at a constant rpm, and certainly not at the redline, so overall power is what you must look at. What we liked most was the significant gain in torque from 3,300 rpm and up. At 4,200 rpm, the gain was over 25 lb-ft-and that equates to better throttle response and a noticeable seat-of-the-pants feel, even on a near-400-rwhp supercharged steed.
With the BBK shorties and...
With the BBK shorties and mid-pipe in place, a quick run on the Brothers Performance Dynojet yielded 4 rwhp and 4 lb-ft of torque over the stock exhaust manifolds and mid-pipe.
Next up were the long-tube...
Next up were the long-tube headers. We opted for stainless steel (PN BBK 16415), but chrome and ceramic-coated are also available.
To install the long-tube headers,...
To install the long-tube headers, the steering shaft must be disconnected from the steering rack and moved aside.
Grieves installs the BBK mid-pipe...
Grieves installs the BBK mid-pipe to the long-tube headers.
O2 sensor extension harnesses...
O2 sensor extension harnesses are included with the purchase of the long-tube headers.
A final run on the chassis...
A final run on the chassis dyno yielded 397 rwhp and 378 lb-ft of torque, but there were much larger gains in the mid-range.