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| This dyno sheet compares the effects of dyno headers with those actually installed on the car. The importance of testing the engine as it would be installed was not lost on the engineers. |
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COMPONENT SELECTION
Chevrolet engineering performed extensive power evaluations in 1968 on the 302 cu. in. Z/28 engine. These tests were conducted to evaluate experimental components and combinations thereof specifically for “gross” power. Aside from gross power findings, we can also use this information to determine the appropriateness of components and combinations for our different 302 engine applications through the careful analysis of the torque and power curves. These studies lend a good a basis for determining the right “set-up” when preparing our individual 302 using the Cross Ram Induction system.
Test Conditions:
A 302 cu. in. engine was prepared in accordance with the HD engine specifications listed above. The engine was initially set up using Traco-prepared “202” heads, 2X4 Cross Ram, “140” service cam (first-design off-road) and dyno headers (‘67-’68 Z/28 Camaro type). It was then run on the engine dynamometer and results recorded. The same engine was then re-configured and re-run using an experimental cam with a significantly higher lift and a pair of 180 degree headers. The experimental cam used in the second engine configuration later became the “754” or second-design off-road cam. Various header tube diameters, collector lengths, timing changes and carburetor CFM ratings were also evaluated on both engine configurations.
The Results:
The 180-degree headers showed a gain of 15-20 horsepower over the conventional type headers. The report concludes the best power run was 486.4 horsepower from the little 302 cu. in. engine, which is the equivalent of just over 1.6 horsepower per cubic inch. If that weren’t remarkable enough, it also states that these results by no means represent the ceiling on the 302 engines power producing capability...!
CONCLUSION
For Race Applications:
Use of components extracting maximum horsepower as indicated by these tests might be the way to go. However, the point at which horsepower begins to compromise engine durability needs to be addressed. Smokey Yunick found this out the hard way at Daytona in 1968 where his 302 Trans-Am engine, built for sheer power, blew up very nicely. In general, depending on the racing application, track type and conditions, peak torque and horsepower points should be set in accordance with long or short track racing. More specifically, they should conform to where maximum power and torque is needed most. This in large part is the function of the cam and therefore careful selection is in order.
For Show and Street:
It’s important to not sacrifice too much mid-range torque for top-end power for the sake of drivability. Low to mid-range is where we need the most power and torque, therefore, look toward setting up the 302 with the 1967-68 Z/28 type (conventional) headers and the stock “346” or service “140” (first-design) off-road (short track) cam in conjunction with the Cross Ram System.
Header/Cam Combinations:
For street and show use with stock “30-30” (346) cam use 1-5/8 inch O.D. primaries, 26-34 inches long and a 2-1/2 to 3-1/4 inch diameter collector. 302 engines using the off road “140” cam producing over 1.55 HP per cubic inch work well with 1-7/8 inch O.D primaries. Collector size as above.
For Trans-Am racing, use 1-3/4 inch primary pipes, 29 inches long (or 1-7/8 X 35- inch) into a 3-1/2 X 50 inch collector/tailpipe for each side.
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