QuestionHi, I'm actually asking this for my stepfather who rebuilds cars as a hobby. If you could help that would be great. Thank you for your time...
I have a 1962 Thunderbird with a 390 cubic inch eight cylinder engine that is rated by the manufacturer at 300 horsepower . During a recent rebuild of the engine , I had the machine shop bore each of the cylinders .030 oversize. The original bore size of each cylinder was 4.05 inches . What is now the total cubic inches of the engine , and what is now the rated horsepower ?
Answerengine cubic inches are figured by this formula:
Bore X PI X Stroke X number of cyl.
Your 390 is 4.052 bore by 3.784 stroke. That works out to just under 390 cubic inches.
When you add .030 more bore, you get about 6 more cubic inches.
This is not enough to change power enough to worry about.
You have increased engine size by .015% and if you take that times 300, you get just over 4.6 So you could say you now have a 305 hp engine I guess, but for purposes of car shows and judging, you want to keep calling it a 390/300. Judges will just think you are wierd if you call it a 396/305!
Besides, for a Ford fan, 396 is a Chevy number!
:)
It is a 390 with a clean up bore during rebuild.
Don
