Aftermarket Parts - Are Premium Parts Worth The Price?

Induction, exhaust, and cam timing are the three big power players for street engines. We thrashed for three days to test this pile of parts to make you smarter.

'This was dyno thrash week, and we went through the Summit catalog like kids at Christmastime. The conversation went something like this: "This will be great-test that tunnel-ram against a single four-barrel manifold . . . See that new Edelbrock dual-quad setup? Test that too . . . Hey, Holley's got three different 750 mechanical secondary carburetors. Which one will make the most power and which one costs the most? Run 'em all and find out . . ." It was like combining stream of consciousness with dyno testing. Before I knew it, I was staring at a 6-foot-tall pile of parts in my shop that took two truckloads to haul to Westech for a marathon dyno session.

We also enlisted Car Craft's brand-new JMS-built 383 small-block Chevy for the beatings, which would consume 35 gallons of pump gas and three long days of 6,500-plus-rpm blasts. At the end, we had Westech's Steve Brul asking, "You're not coming back again for awhile . . . are you?"

After cleaning the last bit of synthetic oil out from under our fingernails and pondering whether we qualified for the Guinness World Record for the most small-block Chevy intake manifold swaps in a single 48-hour period, we did manage to compile a rather sizeable database for the parts we tested. We discovered all kinds of surprising stuff. We learned that Wilson tapered carburetor spacers rock; that 7,000 rpm can tweak a set of valvesprings in one pull; that tailpipes cost power but not where you think; that Weiand makes a very strong dual-plane Air Strike intake manifold; that an Edelbrock nostalgic dual-quad setup looks pretty cool on any small-block; and finally that Dart's CNC 227 heads matched with a big cam can make wicked horsepower. All told, the thrash was a total success. And you're the big winner, because now you have all the information you need on these parts to decide if they're worth emptying your savings account in the name of horsepower.

JMS' Jeff Johnson dropped the Lunati 4340 forged 3.75-inch-stroke crank in the freshly machined block after all the clearances were checked for compatibility. Meticulous prep work eliminates much of the drama during final assembly.

The Power Source
All the tests in this section were performed on the same 383ci small-block Chevy machined and assembled by JMS Racing Engines. Since this small-block was destined for a very hard life on the dyno, it made sense to plug in a rock-solid rotating assembly that could take the abuse, which led us to a complete bottom end from Lunati. One small shift from the norm was to start with a one-piece rear main seal block of '88-and-later vintage. To give it a fighting chance to survive, JMS added steel four-bolt main caps to the center three main bearings, requiring a careful boring operation to make the bearing housings all round. We opted for the standard 3.75-inch-stroke steel Lunati crank with a one-piece rear main seal, along with Lunati's forged Pro Mod rods and a set of flat-top, forged Wiseco Pro Tru pistons with two 5.4cc valve reliefs.

Stroker packages, especially the 383 Chevy, often need a little clearancing around the bottom of the cylinders, and this block was no exception. Once the block was cleaned and the forged pistons assembled on the Lunati rods, it all slipped together with the 11/416-inch rings and bearings supplied with the rotator package. We selected a pair of Dart Pro 1 Platinum 215 heads as the starting point for our small-block test mule combined with a Comp Cams Xtreme Energy XR280 mechanical roller cam (cam specs can be found in the Dart cylinder head test sidebar). Compression came in just a hair under 11.0:1, but even with the smaller cam detonation was never a problem. We also planned on testing a larger set of Dart CNC 227 heads combined with a bigger XR292 cam, so Comp supplied 0.080-inch-thick-wall pushrods along with some lash caps we needed to ensure the rocker arms would clear the larger-diameter valvesprings. After that bit of custom engineering, the engine came together very quickly, including a three-piece front timing cover and a Hamburger oil pan from Summit Racing to button everything up with Fel-Pro gaskets and ARP bolts.

JMS also installed the Comp XR280 cam and degreed it in to ensure it was opening and closing where the timing card instructed. This required advancing the cam 2 degrees using Comp's billet timing set.

We began this quest with a set of Dart 215cc, Pro 1 Platinum as-cast heads complete with 2.05/1.60-inch valves and 1.550-inch-diameter valvesprings. Dart stuffs 0.200-inch-longer valves in these heads with the big valvesprings, necessitating longer pushrods.

Here's our lineup of carbs from tame to terrific. On the left is the classic 750 with its choke horn still in place. In the middle is the new Holley Street HP, priced in between the original 750 double-pumper and the new HP on the right. All three carbs are rated at 750 cfm. In the upper righthand corner is a 950-cfm HP Ultra that we also tested, although on our 383ci it offered no power advantage.