Camshaft Selection for your New Engine

[Mark E.]

Cliff Ruggles from Cliff's High Performance of Quadra-Jet fame recently posted these thoughts on his forum about modern camshaft designs. Worthwhile read if you're selecting a cam.

Very consistent with Duke's advice over the years.

https://cliffshighperformance.com/simplemachinesforum/index.php/topic,3650.msg15786.html#msg15786

[Duke W.]

Re: Camshaft Selection for your New Engine

He didn't mention lobe phasing, which is different, today, versus way back when as I explained in the Tale of Two Camshafts article. For example, the McCagh Special cam that is designed to idle just like the OE 300 HP cam while providing more power and another 1000 useable revs (with massaged heads that are REQUIRED for this configuration) has a relatively short inlet lobe, 202 deg. at .050" lifter rise, but it's phased very late. The IPOML is 116 deg. ATC compared to the OE 300 HP cam's 108 deg. ATC.

After the design was complete I compared it to modern LS designs and the .050" duration and IPOML are virtually the same as the inlet lobe on the LS2/3 camshaft.

Similarly when I went to reindex the cams on my Cosworth Vega to eliminate the excessive overlap for NOx control the best average power from 2000 to 7000 required the inlet cam to be retarded 8 degrees and the exhaust to be advanced the same amount. The .050" lobe duration (above the tops of the .016" clearance ramps) is about 220 deg. the IPOML is 110 deg ATC, and the LSA is 114 deg. versus the overly tight 106 with the OE indexing.

Sound familiar?

Duke

[Gene M.]

Re: Camshaft Selection for your New Engine

Clear clean article. But the actual ranges are avoided. The lobe centers for SBC in the range of 110 to 114 degrees and a .050” lift range of no more than 222 to 224 degrees is about the max range for street manners. An L79 327 has a 222 degree cam at .050”. This is in the 10 to 10.5 real actual compression ratio range. Advertised compression is optimistic at best in the 50’s and 60’s. I doubt the 11:1 compression ratio L79 is real unless it is “breathed on”.