Quote:
Originally posted by rcfast
Snoman- what do you consider a modern high compression engine?? To me 9.3-9.5ish compression isn't all that high. Most the engines that require high octane are around 10:1, like most of the sport cars
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I consider the engine with TBI or Vortec "modern" and from 73 till 86 carb'ed ones not as they had 8.5 to one or less as a rule. 9.3, 9.5 is plus territory for sure. 87 octane was born for a few reasons. One was when they took lead out it lower octane of fuel and auto manufactures chopped ratios for it and the lower compression also helped reduce NOx emissions (Nitrous Oxides) by lowering peak combustion temps. As cats improved anlong with engine cotrols they started to raise compression back up to improve thermal efficency of engines (power and MPG) and increase octane requirements of engines. 87 is a vestage of old times and should not really be used in modern engines, especailly in hot weather