By now it should come as no surprise that long-tube headers work better than stock exhaust manifolds. The question now is why? Many enthusiasts point to flow, but they seem to confuse flow with the actual pressure waves that improve power production. Headers don’t offer power gains from an increase in outright flow as much as they improve exhaust flow out of (and intake flow into) the combustion chamber from pulse tuning. Using negative pressure waves, the headers help draw exhaust out of the combustion chamber once the exhaust valve opens. This negative pressure also helps draw the intake charge into the chamber, thereby improving charge filling. The size and length of the primary tubing and collector, as well as other design criteria, determine the effective rpm for pulse tuning. This is why headers can provide substantial low-speed torque gains that have nothing to do with the flow rate of the tubes.
Now that we have a better understanding of why headers work, the question now becomes do they work in the presence of boost? To find out, we decided to run a series of tests by comparing headers against stock exhaust manifolds. To find some answers, we decided to compare the two exhaust configurations on both a naturally aspirated and a supercharged combination. Not only would we see if headers work better under boost, but if and how comparable the gains are to a naturally aspirated engine. The test engine was our tried-and-true 427 stroker. The short-block featured an iron (4.125-inch bore) LSX block supplied by Gandrud Chevrolet. The block was combined with a Lunati 4.000-inch stroker crank, Carrillo Bullet-series rods, and matching CP pistons. Also present was a Brian Tooley Racing Stage IV LS7 cam, Comp Cams aluminum front cover, and ATI Super Damper. The damper allowed us to easily change boost by swapping out the outer damper shell to a different size to affect the pulley ratio of the blower (though no changes were made during the header test).
The LSX short-block was a stout piece but was in need of an induction system prior to testing. We topped the 427 with big-bore, Black Label LS3 heads from Mast Motorsports. Thanks to full CNC porting and a 2.20/1.60 valve package, the 280cc heads from Mast were said to flow 390 cfm. The heads featured 70cc combustion chambers, 0.750-inch-thick deck surfaces, and six-bolt mounting, making them perfect for our supercharged testing. Since the 427 was sporting Mast headgear, we thought it only proper to outfit the naturally aspirated engine with a matching intake manifold. Mast supplied one of their two-piece, CNC-ported, single-plane manifolds for our test mill. The intake featured provisions for fuel rails and our 83lb Holley injectors as well as a 4150 carb flange. To maximize power for our header test we opted to run a 4150-4500 carb spacer from Speedmaster to allow the installation of a 4500-series throttle body from Accufab. All of the combinations were dialed in using a Holley HP EFI management system.
First up was the naturally aspirated testing with the stock exhaust manifolds. The cast-iron manifolds were run with 2 1/2-inch extensions to serve as the exhaust system. This test involved comparing the manifolds to the headers and not so much the attending full exhaust system. Run with the stock manifolds, the Mast-headed 427 stroker produced 661 hp at 6,700 rpm and 564 lb-ft of torque at 5,000 rpm. After installation of the Hooker 1 7/8-inch long-tube headers (and 3-inch collector extensions), the power output jumped to 681 hp at 6,700 rpm and 578 lb-ft of torque at 5,100 rpm. On the naturally aspirated 427, the headers improved the power through the entire rev range, with substantial torque gains down near 3,700 rpm. If the headers just improved the flow of the exhaust, we’d expect the gains to be most prevalent at the top of the rev range, but the biggest gains occurred at the bottom. Such is the tuning effect of long-tube headers. Now it was time to see if this phenomenon held true after adding boost to the equation.
For the next test we installed a Kenne Bell 2.8L twin-screw supercharger on the 427. Designed for an LS3 application, the lower intake was a perfect match for the Mast heads. The supercharger kit featured an air-to-water intercooler, Liquid Cooling (to equalize the temperature differential between the hot and cold sides of the case), and a bypass valve to eliminate pressure buildup under cruise conditions. The Kenne Bell supercharger was run with the same 83lb Holley injectors and configured with a 3.75-inch blower pulley to run with the 8.19-inch ATI crank hub. The combination produced a peak boost reading of 7.9 psi at 6,600 rpm (boost rising with engine speed). Since boost pressure out of the manifolds was a function of the airflow into it, we supplied the Kenne Bell blower with a Mammoth intake and 168mm throttle body capable of exceeding 2,000 cfm. The blower required us to switch over to a different Meziere electric water pump to facilitate the use of the blower belt. Thanks goes to the crew at Turn Key Engine Supply and Kenne Bell for whipping up the six-rib drive system for the supercharger.
Just as with the naturally aspirated 427, we started testing on the supercharged combo with the stock manifolds. Equipped with the stock units, the supercharged 427 produced 841 hp at 6,600 rpm (power still rising) and 709 lb-ft of torque at 5,200 rpm. The peak boost reading registered at 6,600 rpm with the stock manifolds was 7.9 psi. After installation of the Hooker headers, the peak numbers jumped to 861 hp at 6,600 rpm (872 hp at 6,800 rpm) and 714 lb-ft of torque at 5,100 rpm. The peak boost registered at 6,600 rpm with the headers dropped down to 7.7 psi (meaning less boost and more power). As with the naturally aspirated test, the headers offered not just more peak power, but power gains across the board. Looking at the numbers, the headers offered less of a power gain on the supercharged application than the naturally aspirated combo, and we suspect the culprit was not boost but rather the shortened runner length on the intake used with the supercharger. I guess this means we have to do another test!
1. Do headers offer more power on a naturally aspirated or supercharged LS application?
2. Our test engine is a 427 stroker that includes an LSX block from Gandrud Chevrolet stuffed with a Lunati forged crank, Carrillo rods, and CP pistons. Also present was a Total Seal ring package, a Brian Tooley Racing (BTR) Stage IV LS7 cam, and Moroso oiling system. Check out the fancy Comp aluminum front cover, ARP head studs, and Fel-Pro MLS head gaskets.
3. Topping the 427 LSX combo is a set of 280cc, Mast Black Label LS3 heads. Offering 390 cfm, the heads feature full CNC porting, a 2.20/1.60 valve package, and 70cc combustion chambers. We finished up the heads with a valvespring package from BTR.
4. Feeding the Mast-headed 427 test mule is one of their two-piece, CNC-ported, single-plane intakes. This manifold was designed for LS3 heads and features provisions for multiport fuel injection and a 4150 carb flange.
5. To maximize the airflow into the Mast intake, we opted to run a 4150-4500 carb spacer from Speedmaster and this 4500-series throttle body from Accufab. Also present are Holley 83lb injectors controlled by a Holley HP EFI management system.
6. To establish the power gains offered by headers on the 427, we first ran the engine with stock exhaust manifolds.
7. The stock manifolds fed exhaust through a pair of 2 1/2-inch exhaust pipes. No mufflers or after-cat exhaust were used for this test.
8. Run with the stock exhaust manifolds, the naturally aspirated 427 produced 661 hp at 6,700 rpm and 564 lb-ft of torque at 5,000 rpm.
9. Next up on the naturally aspirated 427, we installed these 1 7/8-inch Hooker LS swap headers feeding 3-inch collector extensions.
10. Run with the Hooker headers, the power output of the 427 jumped to 681 hp at 6,700 rpm and 578 lb-ft of torque at 5,100 rpm. The headers improved power substantially through the entire rev range, but now it was time for some boost.
11. To test the effect of headers on a boosted application, we installed this 2.8L, twin-screw Kenne Bell supercharger on the 427.
12. Ensuring adequate flow to the Kenne Bell supercharger is this 168mm throttle body.
13. The stock manifolds and extensions were installed onto the supercharged stroker for testing.
14. Run with the stock exhaust manifolds, the supercharged 427 LSX produced 841 hp at 6,600 rpm and 709 lb-ft of torque at 5,200 rpm.
15. We then installed the 1 7/8-inch Hooker headers on the supercharged combo.
16. Run with the headers, the Mast-headed, Kenne Bell-supercharged 427 produced 861 hp (at 6,600 rpm) and 714 lb-ft of torque. A peek at the dyno graph will reveal we revved the header combo 200 rpm higher (where it produced 872 hp), but even at the same 6,600 rpm, the headers offered 20 hp. The peak boost registered at 6,600 rpm dropped slightly with the headers from 7.9 psi to 7.7 psi. It is obvious from the results that headers improve power on naturally aspirated and supercharged combinations.
Graph 1: Stock Exhaust Manifolds vs. Headers (Mast-headed 427 LSX)
Having power gains is always good, but it is even better when those gains occur through the entire rev range. Such is the benefit from the scavenging effect of long-tube headers. Run on our Mast-headed 427 LSX engine, the Hooker long-tube headers improved the peak numbers from 661 hp and 564 lb-ft of torque to 681 hp and 578 lb-ft. The peak gains were nice, but the headers offered huge torque gains down at 3,700 rpm. Stock (cast-iron) manifolds are heavy and offer little or no pulse tuning for performance.
Graph 2: Stock Exhaust Manifolds vs Headers (Supercharged 427 LSX)
Would the headers show the same kind of gains on a supercharged application? The pulse tuning offered by the headers was present regardless of the presence of positive pressure in the intake tract. The same is true of intake manifolds, as long-runner intakes still offer pulse tuning under boost. Tested on this Kenne Bell-supercharged LSX, the headers improved the power output from 841 hp and 709 lb-ft of torque to 861 hp (872 at 6,800 rpm) and 714 lb-ft of torque. Truth be told, the lack of runner length in the Kenne Bell lower intake probably had as much of an effect on the outcome of the header test as the presence of boost, but the blown stroker still worked best with the long-tube headers.