Words And Photos: Richard Holdener

Before a performance enthusiast steps up to make a modification, the question he wants answered is, does it make more power? After all, why go to all the expense and trouble to make a modification if it doesn’t add any power, right? For our testing, this question was applied to headers, but the problem with any question is that it needs to be specific. The question isn’t so much do headers work (they do), but rather how well do they work on your exact combination? Obviously, the only to tell for certain is to test them on your combo, but we did the next best thing by testing them on a pair of combinations, both stock and modified. By comparing the results of our testing on this stock and modified LR4, we covered much more ground. Using the data on these two applications, we can come to some conclusions about what might happen on others. In addition to whether the headers would be more or less beneficial on the stock or modified combo, we would answer a number of others questions as well?

To prepare for the header test, we needed a few important things like headers and a test motor. Naturally we would start out our testing with the cast-iron exhaust manifolds, but we decided to compare them to more than just one set of headers. Knowing that shorty headers are a common upgrade, we included them in the mix as well as two sets of long-tube headers. The QTP and DNA headers not only represented different ends of the price scale, they also differed slightly in configuration. Both headers featured 1 ¾-inch primary tubing, but the QTP headers also offered a 3-inch merge collector. By comparison, the QTP headers offered a more conventional ball/socket 2.5-inch collector feeding a 2.5-inch collector extension. Given the minimal power level of our test motor, we doubted either represented a flow restriction, but the difference in pulse tuning might be interesting. Our plan was to run the four different headers on a (nearly) stock 4.8L then again after subjecting it to further modifications.

First up was the testing on the stock truck motor. The 4.8L had been rebuilt using a set of forged SRP pistons from JE. The JE slugs featured a 7cc dome to increase compression slightly, but otherwise the LR4 truck motor was kept stock, meaning stock heads, camshaft, and intake. Feeding air and fuel for the test was an Accufab throttle body and Holley 50-pound injectors, controlled by a Holley Dominator ECU. Also present during testing was a Meziere electric water pump, Lucas synthetic oil and K&N oil filter. Equipped with the stock cast-iron exhaust manifolds feeding 2.5-inch open exhaust, the 4.8L produced 330 hp at 5,700 rpm and 335 lb-ft of torque at 4,600 rpm. Swapping over to the JBA shorty headers added a few horsepower, with peaks of 333 hp and 338 lb-ft of torque. The long-tube headers offered slightly more power, with the DNA headers posting 339 hp and 342 lb-ft of torque. The final run with the QTP headers produced 336 hp and 345 lb-ft of torque. Tested on the stock 4.8L, the largest power gain offered by the long-tube headers was 9 horsepower.

After testing the four different exhaust systems on the stock motor, we upgraded the little 4.8L with heads and a camshaft. The stock heads and camshaft were replaced with a set of CNC-ported Gen X 205 heads from Trick Flow Specialties and a healthy Crane hydraulic roller grind. With flow numbers exceeding 280 cfm, the TFS Gen X 205 heads were capable of supporting over 550 hp, or more than enough for our little LR4. Working with the Gen X heads was a Crane camshaft that offered .590 lift, a 224/232-degree duration split (at .050) and 115-degree lsa. Mild by most LS standards, the 224 cam was plenty healthy on this smaller 4.8L, pushing peak power up near 7,000 rpm. Equipped with the Gen X heads, Crane cam and stock manifolds, the 4.8L produced 427 hp at 7,000 rpm and 370 lb-ft of torque at 5,600 rpm.

After adding the JBA headers, the peak numbers jumped to 433 hp and 374 lb-ft of torque. Once again, the long-tube DNA headers added even more power, pushing the peaks to 443 hp and 379 lb-ft, while the QTP headers countered with 442 hp and 380 lb-ft. With a peak difference of 16 horsepower, the power gains offered by the headers on the modified combination were much greater. This test demonstrated a number of things, first that shorty header do indeed make more power than the stock manifolds, but long-tube headers make more power than shorty headers. In addition, don’t expect huge power gains by putting your stock motor on the pipe, but those gains will be increased with other modifications.

Illustrating four different power curves on one graph makes it difficult to distinguish the subtle differences, but that was actually the point of this exercise. Tested on this stock 4.8L LR4 truck motor, the largest power difference offered by any of the headers tested was less than 10 horsepower and this only occurred at one point on the curve. The shorty headers offered an additional 3 hp over the stock manifolds, while the gains from the long-tube headers were as high as 9 hp. Oddly enough, the low-cost stainless headers from DNA offered more power than the QTP headers. The DNA headers featured a 2.5-inch exhaust while the QTPs exited to a 3-inch system.

After adding ported TFS Gen X heads and a Crane camshaft to the mix, the power gains offered by the headers increased. Naturally the stock cast-iron exhaust manifolds made the least power, but the JBA shorty headers improved the peak numbers from 427 hp to 433 hp. The gains offered by the shorty headers were consistent through the entire rev range. Once again the scavenging effect of the long-tube headers offered even more power on the modified motor. The headers were worth as much as 16 horsepower over the factory exhaust manifolds. The major difference between the QTP and DNA headers was at the beginning of the curve. This was a function of the size (length and diameter) of the exhaust used after the collector.

Sources

Crane Cams
cranecams.com

DNA Motoring
dnamotoring.com

Holley/Hooker
holley.com

JBA Performance
jbaheaders.com

JE Pistons
jepistons.com

Lucas Oil
lucasoil.com

Trick Flow Specialties
trickflow.com