Crank vs. rear wheel

A-BOMB360 said

in 1972 compression ration went down to 8:1 for most engines. thats a BIG hit from 9.5:1/ 10:1 engines. the difference in HP on a 1970 340 compared to a 1973 for example is 16%. how much of that is becouse of the lower cr. then the difference would be from parasitic loss from the engine accessories.. that would be what? 5% at most. so i don't see how prior to 72 you'd get a 40% drop to the rear wheels. 5% difference at most prior to 1972. ie: instead of they typical 18% drivetrain loss factor in the 5% NET hp loss and it would be a 23% total hp loss.

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The performance difference between a 70 340 A-body car and a 73 340 A-body car is minimal which suggests the engine are putting close to the same amount of power to the ground. There is certainly not a 35 HP difference in performance (the difference between a 73 340 and a 70 340) which suggests that the change in the measurement system accounts for the bulk of the difference. You have to remember back in the late 60's horsepower wars the HP number in the sales brochure would make or break a sale but the vast majority of folks would never know the difference so the motivation to test engines in a way that gives the marketing types the number they wanted was great. If this was not so the government would not have stepped in and madated a standard testing method.

It's easy to accept that an engine with open headers, no engine driven accessories no air cleaner (and possibly a non stock carb) could make 16% more power on a dyno compared to the same engine with factory manifolds (and exhaust), all the factory engine driven accessories and air cleaner.

So you add the loss due to engine configuration changes (16%) and the 18% most have been stating for drive train loss you arrive at 34% difference. I previously stated you could approach 40% and there is quite likely some engine configuration that would support that.