The short-tube headers were...
The short-tube headers were tossed. The short-tubes do not promote scavenging.....
Once the exhaust valve closes, the gases in the header tube lose velocity due to the loss of that force from the piston and from the fact that the pressure equalizes. However, the slowing gases in that tube are helped by the scavenging effect of the header collector (and X- or H- crossovers). The other cylinders that are pulsing exhaust through the appropriate tubes merge at the collector and actually help draw the slowing gases from the tube that has the closed exhaust valve.
The tubes of our new headers feature two different sizes, a primary size and a secondary size. The step increase is a trick that is more popular in racing applications but is becoming more common on the street. "When the tubing diameter is increased in size the gasses decrease the tract pressure and increase positive exhaust flow. That creates a raised scavenging effect and allows more air and fuel to be utilized. That is the more air in, more air out effect," said George Kook Jr. of Kooks Custom Headers. "Also, a stepped header helps on collector scavenging as well because it cancels the reflective frequency back to the cylinder head. An increase of horsepower and torque is obtained because the efficiency is elevated because the clean cylinder charge is not re-burning the unused fuel."
.....nor allow the exhaust...
.....nor allow the exhaust to expand and exit the port efficiently.
Dez Racing's Brian Machie handled the installation and it was easiest for him to drop the K-member and A-arms in order to get the headers in. We encountered one problem-in our excitement, we goofed the order. The stepped headers utilize a race-style collector that measure 3.5 inches. The X-crossover is designed for use with a Kooks 3-inch collector due to the ball/socket technique for bolting it together. The two pipes wouldn't mate together. Luckily, Dez Racing has stockpiled old exhaust pipes-small and large. Machie fired up the welder and built a conversion pipe to go in between the two. The Kooks 1 3/4-inch long-tubes (PN 6000S) are designed to work with the 3-inch X-crossover, not the stepped headers with the 3.5-inch collectors (P/N 6002S).
Once back on the dyno with the new Kooks stepped headers and X-crossover, we noticed the air/fuel ratio changed down low and the engine pulled to a higher rpm. "It leaned out down low as the header helped the engine. Up top we were fine because I have it tuned a little rich for the supercharger. Torque increased as much as 10 lb-ft in some areas and it always made more torque up to the redline over the shorty headers," said Dezotell of the more efficient exhaust. Peak torque went from 465 rwhp up to 476 rwtq. We also saw a healthy increase of rwhp, to 579 rwhp with the long-tubes and larger X-crossover versus 549 rwhp with the short-tubes and 2.5-inch X-crossover.
"I pulled the car to 7,100 rpm with the long-tubes and it rolled over at 6,600 rpm. But you can see the power is flat from 6,600 to 7,100 on the graph. It didn't fall off and carried it through. You can definitely rev the motor higher at the track. But now, unfortunately, the exhaust is no longer the restriction. It is somewhere else and we think it is the intake manifold," proclaimed Dez.
I stuck my hand above the...
I stuck my hand above the collector to show that there is ample room between the underside of the unibody and the headers.
Right now, the engine wears an unported P-51 intake that is typically used in applications up to 6,600 rpm. Dez also said he didn't change the timing and the more efficient exhaust would allow him to do so safely. The exhaust gases move out of the chamber faster-keeping it cooler and allowing more ignition timing before pre-ignition occurs. But for this test, the timing was kept consistent for a true A-B comparison.
Our search for more power continues-next month we will be getting our boost and timing back, then we will add ported heads and make a change in the intake department. How far can we go? Stay tuned as we add one last dose of horsepower.
The headers fit flawlessly,...
The headers fit flawlessly, except in one spot-Machie attributed it to a cheap set of motor mounts. A little wiggle of the tube with a pry bar solved the problem in about 10 seconds.
The 02 sensors were installed...
The 02 sensors were installed in the collector.
The 02 extensions didn't fit,...
The 02 extensions didn't fit, as we needed to cutoff a tab on the stock connector. Machie said this is a common problem and easily fixed. As you can see in the photo the green tab doesn't line up with the black slot for it.
Our only major bump in the...
Our only major bump in the road to more horsepower was mating the X-crossover and the collectors. The X-crossover uses a ball/socket setup while the collector is designed for a slip-on set of pipes. Machie fabbed up an adapter, it wasn't pretty but it worked.
The exit side of the X-crossover...
The exit side of the X-crossover has the male end of the ball/socket. It is designed to mate to the 2.5-inch female side of most after-cat exhausts. Here the fancy stainless steel Kooks is bolted to our crusty and well-used Magnaflow after-cat system.
The Kooks headers hang down...
The Kooks headers hang down but still offer nice ground clearance. Just eyeballing it, we think the long-tubes are also wide enough to clear most aftermarket bell-housings.
Kooks includes longer bolts...
Kooks includes longer bolts for the X-crossover.
Here is a peak inside the...
Here is a peak inside the X chamber. This type of system helps exhaust waves balance out, in turn helping the scavenging effects of the exhaust system.
Our baseline produced 549/465,...
Our baseline produced 549/465, it was down from our previous results due to two degrees of ignition timing. We will call it our street tune.
The addition of the more efficient...
The addition of the more efficient Kooks headers added 30 rwhp and 11 rwtq (579 rwhp and 476 rwtq). The tune was left identical to our baseline. Dezotell said, "It (ed note: the headers) leaned it out down low and we saw a huge gain in low-end torque. Up top, we were fine because I had it rich to begin with in that part of the curve. But down low we went from 10 rwtq in some areas and the torque was always above the baseline from 4500 up to peak."
Dezotell added a ProCharger...
Dezotell added a ProCharger eight-rib pulley system, which replaces the blower pulley, accessory pulleys, and idlers. An Expedition balancer from a junkyard motor completed the eight-rib conversion.
He also bolted on a larger...
He also bolted on a larger ProCharger race bypass due to the expected big boost from the D1SC.
In review, our test engine...
In review, our test engine is a 281ci Two-Valve mod motor with TFS Street/Strip 4.6L heads, AFM F82 cams, Fox Lake P51 intake, ProCharger D1SC, and now Kooks headers and X-crossover.