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383 Chevy Small Block Engine - Make 59 LB-FT and 33 More Horsepower For Almost Free!

More power and it's practically for free.

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The performance world is full of good tuning ideas. One place that is often overlooked in the search for more power is the exhaust system. For decades, knowledgeable drag racers have been using header collector extensions to improve torque, so we decided to test that idea on our hot street small-block.

The premise was simple enough. Stick an engine on the dyno and run a couple of headers with and without collector extensions and see what happens. This exhaust test involved using our trusty dyno-proven and Westech-flogged 383 small-block Chevy. With lots of valve timing and overlap, our roller cam motor made as much as 530 hp with a set of chassis-style 1 1/4-inch headers. Since this was a header test, at first we decided to run the engine without mufflers. Our first test ran without collector extensions compared to a second test with a set of 18-inch collector extensions installed. The difference was staggering.

This got us to thinking about larger exhaust systems and how a 3-inch system might be an advantage even for a 450hp engine, because the larger-diameter exhaust is in some ways just like a long collector extension. We've also included a dyno test that first appeared in the September issue, but this time we're looking at it from an overall power standpoint. When we quizzed Flowmaster muffler guru Kevin McClelland, he suggested necking the system back down to 2 1/2 inches before entering the muffler to limit the noise that occurs from 3-inch systems. The results may not surprise you if you've been around high-performance engines for a while. But if this is your first foray into the wild world of hot gas tuning, this should be an eye-opening experience.

The Test Engine

We used the 383ci small-block Chevy from the September issue for this test because the little Mouse just loves to run. The short-block retains the same Lunati 4340 steel rotator with its excellent 4340 steel Pro Mod rods and Wiseco forged pistons. We did change things up a bit with the XR286 Comp mechanical roller only because we didn't want to spin our little motor all the way to the moon just for a header test. That will come later. Completing the Comp valvetrain are the same Endurex roller lifters, Comp Magnum 1.5:1 rocker arms, and roller valvesprings. We stayed with the alpha-dog Dart 227 CNC heads, however, and also retained the Holley Keith Dorton single-plane intake manifold. We did do some minor alterations with a move to a larger Barry Grant 850-cfm Mighty Demon carburetor. Combined with the Hedman 1 1/4-inch headers, a fresh set of Bosch spark plugs, and our requisite MSD distributor, we were ready to test.

Length Does Matter

If you look at a typical set of V-8 street headers, there is a large tube that connects all four primary pipes called a collector. Most collectors are relatively short, roughly 4 to 8 inches in length. The collector ends with a flat flange used to connect to the rest of the exhaust system. The baseline for Test 1 ran a budget set of 11/4-inch headers that feature a relatively long 8-inch collector. For Test 2, the only thing we did was bolt on two 18-inch-long collectors.

Between 3,100 and 4,500 rpm, the additional collector length was worth a maximum of 59 lb-ft of torque at 3,900 rpm. In between these rpm points, the average torque increase was more than 34 lb-ft. If you consider that this rpm band is the flash rpm point for a typical street torque converter, adding 30-plus additional pound-feet of torque has got to drastically improve the 60-foot times. We also evaluated the power averages of both rpm curves from 2,500 to 6,700 rpm. The collector extensions won that battle too, with a better horsepower curve and an additional average increase of 9.7 hp. Just to support the effect of a collector extension, we performed a second test using a smaller set of Hedman 1 1/4-inch primary tube chassis headers. With these headers, the collector extension increased the torque between the 3,500- and 4,800-rpm band with a maximum gain of 26 lb-ft but also an average of 14 lb-ft of torque over that entire 1,400-rpm span.

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