Re: Well Written Restorer Article
That's a conventional design cam - tuned to the E/I flow ratio of OE machined heads with split overlap at about 5 deg. BTC. There's no new thinking here. The inlet side lobe is nearly identical to the McCagh Special, but it's indexed 9 degrees earlier. This means it will not tolerate as high compression, or the centrifugal curve might have be slow, or both, both of which will cost torque in the lower range, and the earlier closing inlet valve will cost power up high.
EVC is about the same as the McCagh Special, but EVO is a whopping 20 degrees earlier, so it's throwing away a lot of useable energy. The higher exhaust port flow efficiency of massaged heads allows the exhaust valve to open later and turn more heat energy into useful work at the crankshaft.
I plugged it into EA for a 327/300 with typical massaged heads and 10.25:1 compression and the McCagh Special beats it from off idle to valvetrain limiting speed with the greatest advantage at the top end.
Effective overlap is 2.3 sq-in-deg, so I question that its idle behavior is indistinguishable from the 929.
A chassis dyno test and manifold vacuum check at 500 in neutral will tell all.
BTW there is a '64 327/300 in work that will carry the McCagh Special. I'll write an epilog after this engine is completed, tuned, and chassis dyno tested.
In the meantime if anyone has any real data on a better 300 HP configuration that has identical idle behavior and no visually detectable non-OE components, you can always post it here.
All you need to simulate the McCagh Special is in the article, assuming you know the lobe lifts of the 929 and understand that the McCagh Special just swaps the lobes with the different indexing shown in Table 2.
Duke
P. S. Joe R. - you have the best flowing heads in my library of massaged head data, so the McCagh Special would work very well in your engine, but you'll give away about 5-8 percent across the range with your low compression ratio relative to the near 10.5:1 that the McCagh Special can tolerate with an aggressive centrifugal spark advance curve.
That's a conventional design cam - tuned to the E/I flow ratio of OE machined heads with split overlap at about 5 deg. BTC. There's no new thinking here. The inlet side lobe is nearly identical to the McCagh Special, but it's indexed 9 degrees earlier. This means it will not tolerate as high compression, or the centrifugal curve might have be slow, or both, both of which will cost torque in the lower range, and the earlier closing inlet valve will cost power up high.
EVC is about the same as the McCagh Special, but EVO is a whopping 20 degrees earlier, so it's throwing away a lot of useable energy. The higher exhaust port flow efficiency of massaged heads allows the exhaust valve to open later and turn more heat energy into useful work at the crankshaft.
I plugged it into EA for a 327/300 with typical massaged heads and 10.25:1 compression and the McCagh Special beats it from off idle to valvetrain limiting speed with the greatest advantage at the top end.
Effective overlap is 2.3 sq-in-deg, so I question that its idle behavior is indistinguishable from the 929.
A chassis dyno test and manifold vacuum check at 500 in neutral will tell all.
BTW there is a '64 327/300 in work that will carry the McCagh Special. I'll write an epilog after this engine is completed, tuned, and chassis dyno tested.
In the meantime if anyone has any real data on a better 300 HP configuration that has identical idle behavior and no visually detectable non-OE components, you can always post it here.
All you need to simulate the McCagh Special is in the article, assuming you know the lobe lifts of the 929 and understand that the McCagh Special just swaps the lobes with the different indexing shown in Table 2.
Duke
P. S. Joe R. - you have the best flowing heads in my library of massaged head data, so the McCagh Special would work very well in your engine, but you'll give away about 5-8 percent across the range with your low compression ratio relative to the near 10.5:1 that the McCagh Special can tolerate with an aggressive centrifugal spark advance curve.
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