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Originally Posted by Excaliber
Why don't they leave them 427's?
I mean after all, if 427 is good, 480 something MUST be better, ie, bigger is better is the American way! 
But actually the original bore\stroke numbers of the 427 side oilers were carefully thought out and chosen for specific 'race' inspired reasons. The basic equation of a 'good race motor' has ALWAYS been BIG bore in relation to a SHORT stroke. Porsche and Ferrari are two examples that to this DAY employ that reasoning. Short stroke means higher rpm potential. Higher rpm means more HORSE POWER while sacraficing 'torque'. While some say 'torque' is what wins races, I disagree, it's HORSE power that wins races, and history is filled with example after example.
Todays small engines (Honda and other 'ricers') are based on horse power, you simply can't get BIG torque numbers out of a tiny motor. 'Torque' is what the driver FEELS when first accellerating, it's TORQUE that pushes you back in the seat and makes you 'feel good'. 18 wheeler trucks have MASSIVE torque, but there kind of slow on the race track...
You want FAST? Go small block, short stroke BIG bore. You want 'feels awesome' BIG torque? Go with a LONG stroke, big cubes and smaller bore. To each his own. A 427 compared to a 500 plus incher is a much smaller AND POTENTIALLY faster motor! |
The Ford 427 is actually 426 cubic inches. Ford basically took the FE block and put the biggest bore possible in it, still with a full water jacket, and the stroke was what they were already using for the 390 / 406. 7 liter displacement was the limit imposed by Nascar, which is why Mopar had a 426 and chevy had a 427. Ford called their new 426 a 427, because Mopar had already taken the 426 name and promoted it. I don't think there was alot of engineering in coming up with the exact bore / stroke numbers.
Horsepower is torque X rpm's. Torque is a measure of engine displacement and engine volumetric efficiency/mechanical efficiency. A normally aspirated small engine can never have big torque numbers because it cannot consume large volumes of fuel per revolution.
When you say low end torque puts you back in your seat, it's actually low end HP that puts you back in your seat. If your accelerating at any rpm, you're feeling both torque and HP.
A while back, Hot Rod did a comparison of a small bore long stroke BBC and a big bore short stroke BBC, same displacement, using the same heads, cam, intake, etc, and ther was real no difference in torque / HP up to I think 7000 rpms where the test ended.
I think the key advantage to a bigger bore is the bigger valves you can use, better flow, to make the engine run more efficiently at higher rpms, ie, more high rpm torque and HP. I don't think ther is any magic in a particular bore/stroke assuming everything else is the same. Can-Am cars ran stroked fuel injected 454 chevy's.
Increasing the displacement of any engine, keeping all other factors the same, will lower the rpms of max torque and HP, but the curve will cover more area under the larger engine, and the larger engine will out power the smaller engine at every rpm. Give me the 500, unless you want to stay original.