Last month, we outlined the premise of a budget-oriented big-block Chevy buildup that would put out close to 700 hp for around $7,000 using a combination of massaged stock components and modestly priced off-the-shelf parts. Although the compression ratio of 12:1 dictates the use of some race fuel, the idea is to run mostly pump gas on the street, with only a splash of race fuel. Alternatively, 100-octane unleaded can be used without a stretch. Considering the high cost of pump gas and the limited street use of the engine, it's not the huge cost you might imagine.
The idea of this engine being a do-it-yourself project was brought home by a trio of UNCC Motorsports students under my tutelage. Bruce Greer, Nathan Bornitz, and Dusty Kennett brought the short-block to completion with the help of T&L Engine Development, which supplied the necessary machining processes. We completed part one with a check of the completed short-block's static turning torque, a good measure of an engine's mechanical efficiency. The 482-inch big-block turned over with a scant 16 lb-ft. In a world where 30 to 35 lb-ft is the norm for a street-bound big-block, we knew we were on the right track.To review, let's take a look at the budget build-sheet for this project, then move on to the induction, final assembly and dyno test.
UNCC Motorsports student Nathan Bornitz performed the porting and assembly of our project engine's Dart Iron Eagle heads from start to finish leaving only the job of bolting them on to Bruce Greer. (For more on these affordable performers, review the story "Iron Clad Horsepower" in the August 2005 issue.) Check out the sidebar "Choosing The Budget Iron Eagle Heads" to see what they produced in the way of flow. We used FelPro gaskets throughout the build, as they are very much a tried and tested deal, especially in terms of the head gaskets.
The next operation was the installation of the pushrods and guide plates. Because of the repositioned valves, the Iron Eagle heads are best used with Dart's adjustable guide plates. This allows the correction of what would otherwise be about 200 thousandths of rocker misalignment.
Selecting pushrods proved to be a very critical job. If you've an idea to use stock pushrods, forget it. They will simple not work and in the process will probably chew out the end of the rocker. The most critical area by far is the intake pushrod. It needs to be of a length that produces the correct sweep across the valve tip, but there is more. This length inevitably produces an excessively acute angle between the pushrod and rocker in the closed position. If the sweep is correct, the rocker/pushrod angle is greater than the pushrod seat in the rocker can accommodate. The key here is to use as long a pushrod as possible to move out of bind on the rocker's pushrod seat, but not so long as to move the contact patch too far off the valve tip center. To get things to work, it proved necessary to make a trade between a centrally located sweep patch, and avoiding bind at the rocker's pushrod cup. This left us with a sweep patch that was biased toward the exhaust port side of the valve tip.
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Here's one of our Dart Iron Eagle heads with basic porting. We used the new COMP Cams big-block beehive springs because they deliver more rpm on less poundage. |
ARP head bolts and FelPro head gaskets ensured our cylinders would hold out against the 12:1 compression ratio being used. Before installing, the ARP bolts were given a coating of FelPro hi-temp sealer. |
The repositioning of the valves on the Dart Iron Eagle heads means using Dart's adjustable pushrod guide plates. |
The pushrod length needs to be set to achieve a centralized roller contact patch. A compromise with rocker geometry had to be struck on the intake. |