Ted
The pilot formerly known as Twin Engine Ted
- Joined
- Oct 9, 2007
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iFlyNothing
This is more for the car guys/gearheads on here (aren't most of my threads these days?).
Back in the 90s (also known as "ancient history" to some of you kids), most new design automotive engines you saw followed the formula of 500 cc/cylinder. 2.0L 4-cylinders, 3.0L 6-cylinders, 4.0L V8s. The theory was that, through a bunch of engineering mathematical wizardry, it was determined that above and below the 500 cc/cylinder mark, an engine inherently was going to be less efficient, coming down to some balance of rotating assembly mass, square inches of combustion area for the combustion chamber at the top. Smaller cylinders would produce a revvier but less efficient engine, and larger would produce a torquier but also less efficient engine.
In the late 90s and through the 2000s we tended to see cylinders move to larger displacements (which as I understood it came about because of some shift in the optimization curve between fuel economy/efficiency and emissions), but we've been seeing this formula return in the past several years, often with some complex turbocharger setups to boost horsepower numbers as needed.
It didn't occur to me until recently, but I've driven (and owned) a number of engines that have fit this mathematically perfect equation. And none of them have been my favorites to drive. Even with varying significant levels of tweaking (my 3000GT VR-4 being a 3.0L V6 that I very heavily worked on), they all remained... boring. Even the 4.0L supercharged V8 in our XKR isn't a particularly exciting engine to me.
Here's my theory: This mathematically perfect engine also creates a mathematically boring engine, because it is too balanced. Not in terms of physical balance, but in terms of performance. These engines are decent at everything, but not great at anything. Start to diverge in either direction - bigger or smaller displacement per cylinder - the engine will get to be more enjoyable to drive.
Smaller: You get an engine that's revvier and will happily rev to higher RPMs. This is fun for winding it up and getting some serious revs.
Larger: You get an engine with bigger torque pulses that create a stronger visceral sensation of torque and performance.
Just like the idea of 500 cc/cylinder being mathematically perfect, diverging from it is an over simplification and there's a lot more to it. Undersquare vs. oversquare, cam profile, cylinder head and combustion chamber design, compression ratio, forced induction, engine calibration (fuel and ignition). If you look at the Cobra build, it's a Ford 351 (so 5.8L or figure 725 cc/cyl, and oversquare on dimensions at 4.0" bore and 3.5" stroke). I'm doing everything I can to make it really responsive and revvy. In some ways I do think the engine may not be ideally suited for it as far as size/weight/displacement go, but it will be an interesting engine.
There are other similar theories about number of cylinders as well, and all of these things come together. I think for motorcycles the equation changes some for various reasons. But for cars, I think this is true.
So don't be boring - buy a car with a displacement that's not 500 cc/cylinder.
Back in the 90s (also known as "ancient history" to some of you kids), most new design automotive engines you saw followed the formula of 500 cc/cylinder. 2.0L 4-cylinders, 3.0L 6-cylinders, 4.0L V8s. The theory was that, through a bunch of engineering mathematical wizardry, it was determined that above and below the 500 cc/cylinder mark, an engine inherently was going to be less efficient, coming down to some balance of rotating assembly mass, square inches of combustion area for the combustion chamber at the top. Smaller cylinders would produce a revvier but less efficient engine, and larger would produce a torquier but also less efficient engine.
In the late 90s and through the 2000s we tended to see cylinders move to larger displacements (which as I understood it came about because of some shift in the optimization curve between fuel economy/efficiency and emissions), but we've been seeing this formula return in the past several years, often with some complex turbocharger setups to boost horsepower numbers as needed.
It didn't occur to me until recently, but I've driven (and owned) a number of engines that have fit this mathematically perfect equation. And none of them have been my favorites to drive. Even with varying significant levels of tweaking (my 3000GT VR-4 being a 3.0L V6 that I very heavily worked on), they all remained... boring. Even the 4.0L supercharged V8 in our XKR isn't a particularly exciting engine to me.
Here's my theory: This mathematically perfect engine also creates a mathematically boring engine, because it is too balanced. Not in terms of physical balance, but in terms of performance. These engines are decent at everything, but not great at anything. Start to diverge in either direction - bigger or smaller displacement per cylinder - the engine will get to be more enjoyable to drive.
Smaller: You get an engine that's revvier and will happily rev to higher RPMs. This is fun for winding it up and getting some serious revs.
Larger: You get an engine with bigger torque pulses that create a stronger visceral sensation of torque and performance.
Just like the idea of 500 cc/cylinder being mathematically perfect, diverging from it is an over simplification and there's a lot more to it. Undersquare vs. oversquare, cam profile, cylinder head and combustion chamber design, compression ratio, forced induction, engine calibration (fuel and ignition). If you look at the Cobra build, it's a Ford 351 (so 5.8L or figure 725 cc/cyl, and oversquare on dimensions at 4.0" bore and 3.5" stroke). I'm doing everything I can to make it really responsive and revvy. In some ways I do think the engine may not be ideally suited for it as far as size/weight/displacement go, but it will be an interesting engine.
There are other similar theories about number of cylinders as well, and all of these things come together. I think for motorcycles the equation changes some for various reasons. But for cars, I think this is true.
So don't be boring - buy a car with a displacement that's not 500 cc/cylinder.
