Out in a Blaze of Glory - Low Dollar 318
Cam Timing vs. Compression Analysis
"*V/P (Volume/Pressure) Index is a mathematically-derived figure, the product of the corrected volume and cranking pressure. It’s a very useful barometer of the motor’s low-speed power, and may be solved with new variables for a “before & after” analysis when modifications are contemplated. Anyone planning a cam or compression ratio change would definitely want to know how much the low-speed flexibility would be affected. Some useful insight may also be derived as to the motor’s tolerance of pump-quality gas (ping & knock resistance). The results of these comparisons are generally quite surprising!"
I can say going from the stock 340 cam to the comp 268h 218 218 454 110 106 its alot better low end cam and iam sure it raised the v/p index.
I did put a set of used 2.02s on to replace the tired x heads when i did the cam this was @100k miles on stock 68 340 other then weiand stealth tuned 650 dp 2 1/4 thru manifolds and a unilite . All stock@80k miles it went 14.3ish@97 even though fisherman says it bs id guess 13.7 now with 3.91s up from 3.23s That comp cam puts the stock 340 cam to shame. Didnt measure the cc of the heads so that could have helped or hurt the swap it still had good power the valve seals were junk. Building a motor today i would use the vp/index as a tool to get the best of both worlds.