Engine Build and Dyno Testing - How to Pass a Lie Detector

In which our small-block LS7-killer divulges its performance secrets on the dyno

Dave Young May 6, 2011 0 Comment(s)
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To actuate the valvetrain, we chose a combination of a Comp camshaft, lifters, and pushrods; with Jesel shaft-mounted rocker arms and a Jesel adjustable beltdrive timing set. Knowing that accurate valve timing is one key to making consistent power, our Dart block features a raised cam location and 50mm cam journals. This allows the camshaft to be ground from a larger core, eliminating torsional flex. The raised cam location also allows the use of shorter pushrods, which are less prone to bend and flex under load, keeping the valvetrain more stable throughout the rpm range.

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Additionally, we decided to take advantage of Jesel's shaft-mounted rocker arms, which are the industry standard in terms of valvetrain stability. Although we're giving up a fair amount in terms of intake runner volume, valve size, and valve material to the LS7 (which uses a titanium intake and sodium-filled exhaust valves), our combination of Comp and Jesel products will capitalize on the design of the SBC, allowing the use of items that aren't available to production LS engines.

Our Comp cam is a solid roller with 0.680 intake lift and 0.652 exhaust lift after lash, which we felt was an even trade-off given the LS7's superior intake-runner volume, flow, valve angle, and intake-valve size. We also chose the LS firing order, which swaps the No. 2 and 3, as well as the No. 4 and 7, cylinders in relation to the standard SBC order. Though it's difficult to find data to support that this swap makes more power, the Winston Cup (or is it "Sprint Cup" now?) NASCAR teams are currently using it, so we feel it must be worth something. It will also help our engine more closely mimic the design of the LS7.

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Further, we wanted our engine to make its peak torque and horsepower at approximately the same rpm as the LS7, rather than over- revving it to meet our goals. The LS7 has a 7,000-rpm redline, and we chose our cam to make peak power well under this limit, along with peak torque right at 4,800 rpm—just like the LS7. To feed our small-block, we chose a Dart single-plane aluminum intake matched with a Quickfuel Technologies Q-series 950-cfm carburetor. Remember that this is an "old-school" build, and our car is already set up for a carbureted fuel system, further simplifying final installation. Despite what you may have heard, quality carburetors are very reliable, and a top-notch piece like the one we chose from Quickfuel won't give up much in terms of driveability and throttle response. Even better, it'll actually make more peak power than would fuel injection.

With the pieces for our LS7-killer in place and the necessary machine work accomplished, we decided to assemble our engine in the clean room at APE, rather than performing the task in our shop and then transporting it for dyno testing and tuning. While we were hoping to out-power the LS7 by a significant amount, the closer we got to finishing our engine, the more nervous we became about making the necessary 505 horses, let alone topping it substantially.

An engine dynamometer is like a lie-detector machine, and it's very difficult to cheat. Further, APE's dyno is known to be a little stingy, and owner Kevin Willis won't fudge on correction factors simply to get a big torque or horsepower number. We either had our combination right or we didn't, and we were about to find out.

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With the engine bolted up to APE's Superflow 901 dyno, we filled the fuel cell with 93-octane gasoline from the station up the road and installed a smallish 750-cfm shop carb for the initial startup. Using a known carburetor is generally a good practice on a fresh engine, eliminating any surprises during break-in. We also took the necessary precaution of priming the oil system. This step not only ensures adequate oil pressure, it also fills the oil galleys before the distributor is installed and the engine fired for the first time.




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