In fact, typical moderate street performance profiles will readily respond to the tuning effects of headers. Primary pipe length is a consideration, as well. Even at the speed of sound, it takes time for the pressure wave to travel up the pipe. The primary has to be at a length to time the event for the overlap period, but the period of time between cycles varies with rpm. As a result, a given primary-pipe length will tune to a given rpm. The optimal primary-pipe length will vary with the operating rpm range of the engine. Primary lengths between 28 and 42 inches cover the range from high-rpm race engines to tow rigs. Cast-iron exhaust manifolds and shorty headers are at a disadvantage here.
This whole theory has been proven in dyno results on high-output engines, and now we know why. We wanted to explore the question of headers versus manifolds in a much milder setting, a pussycat of an engine if you will-the type of engine that would have a guy questioning whether to use headers or manifolds. To find out, we brought a Mopar Performance 300hp Magnum crate motor to Westech to run some variations. The 300hp crate is a real puppy, with a new-car-like idle (to us) and over 19-inch Hg of vacuum. Its docile nature is the result of a mild cam, with minimal overlap and stock .385/.410-inch intake and exhaust lift, respectively. Spec'd to drop in and go with no hassles, the 360/300 crate will happily pull a full package of accessories, power brakes, air conditioning, and a tightly-converted automatic while idling along effortlessly.
We brought along a wide range of exhaust manifolds and headers, running the gamut from puny stock 318 iron manifolds to the bigger log-type 360 pieces, and even the highly-sought-after and revered 340hp iron units. We also brought a range of headers to see how things would compare. We found some of the results surprising, if not downright shocking. Read on for the results of our exhaustive research.
Left with the choice of banging...
Left with the choice of banging clearance into the headers or clearancing the block, we pulled out the grinder and hacked away at the block. It took quite a lot of material removal to gain the required clearance.
Late-model truck blocks, on...
Late-model truck blocks, on which the crate 360s are based, are cast with large motor-mount pads behind the traditional mounting ears found with earlier production blocks. With the Hookers, we found tube interference on the driver side, preventing it from bolting to the head. This was not surprising since the headers were designed long before the change in block-mounting provisions.
The Hookers feature a layout...
The Hookers feature a layout similar to Hedman's full-length tubes, with the number 3 tube passing up along the valve cover, crowding the plug wires to cylinders 5 and 7. Also, the number 1, 5, and 7 tubes are routed low to go under the steering drag link in the chassis, hindering ground clearance. The 1 5⁄8-inch full-length headers provided quite an improvement in torque, with 423.9 lb-ft on tap. At 319, horsepower up top was down fractionally compared to the shorties. We would expect the results to be different if the engine was equipped with more cam duration, but at this mild spec, the tuning advantage of the long-tube header is largely lost up top due to cam timing.
We swapped the 1 5⁄8-inch...
We swapped the 1 5⁄8-inch Hookers for a set of tti 1 5⁄8x1 3⁄4-inch step headers. We immediately realized there was clearance for a standard box-end wrench to be used at the header bolts. The tubes also cleared the late-block's mounting bosses much better, bolting up without binding, although it was close.
The passenger-side tti header...
The passenger-side tti header will clear either a stock straight oil-filter arrangement or a production-style 90-degree oil-filter adapter.
The layout of tti's headers...
The layout of tti's headers is unique, with none of the low-hanging tubes of the other designs and ample clearance for the plug wires up top. Past experience has shown they have excellent chassis fit. Power output with the tti's was the best of all the systems we tested, clearing 327 hp and producing a healthy 425.5 lb-ft of torque.
With the positive response...
With the positive response in output gained by going to the step header, our next change was to determine if even bigger would be even better. We went to a pair of 1 3⁄4-inch Hooker Super Comp headers. The Super Comps are race-style headers with slip-fit collectors. With this 360's mild combination, the Super Comps proved to be overkill, with output lagging the step header, posting 321 hp at 3,700 rpm and 420.7 lb-ft of torque at 3,700 rpm. As a point of reference, we have seen the Super Comps add 10-15 hp to a standard 1 5⁄8-inch header in engines of the 450-500hp level.
Unlike the Hooker street headers,...
Unlike the Hooker street headers, the Super Comps tubes were routed clear of all spark-plug wires.