Reply #16: Well, HP is just one relatively meaningless statistic for an engine. [View All]

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You've got an entire torque curve to consider when evaluating engine performance and max HP is just a tiny little snap shot of when the engine is performing the most work ((pound feet of torque x engine RPM)/5252). So, this number doesn't mean very much for applications where great amounts of low end torque are required (as in trucks designed for towing) or for accelerating large sedans from a stop. V8s excel at low end torque and without turbos, V6s still can't match V8s in that category.

And six cylinder engines have been putting out that kind of power for a while now. Porsche makes either the GT2 or GT3 (I forgot which) which is a normally aspirated, horizontally opposed 6 cylinder which makes about 420 hp. So max output is only one reason why V8s continue to be made. As far as fuel economy goes, GM's V8s (other than the NorthStar) already set the world standard for fuel efficiency in V8s. Many competitors' V6s get worse fuel economy while making less power. Owners of the C5 and C6 Vette (as well as the Z28 and Trans-Am when they were still being made) would regularly get 30+ MPG out of their V8 vehicles. So it's a mistaken assumption to assume that most V6s get equal or better fuel economy than these V8s.

One last thing. Let's compare GM's NorthStar V8 to their more modern "High Tech" DI V6. Both make about the same amount of HP, yet the V6 does so with a liter less displacement. Because torque in normally aspirated engines almost entirely corresponds with that engine's displacement, in order for the V6 to make as much power as the V8, it needs to do so at higher RPMs (remember, TORQUExRPM/5252). So, if you're going to drive the V6 like you were to drive the V8, you're going to spend more time in the upper rev ranges than you would in the V8. More time at higher revs generally means that the engine isn't going to last as long. Of course you can add turbo(s) to increase low and mid-range torque, but that adds a whole new level of complexity to the engine and is yet another thing that can break (also, turbo lag sucks).

So, there are a large number of characteristics which determine which engine is best for a particular application. Fuel economy, torque curve, max power, reliability, smoothness and vibrations all factor in the decision making process. V6s are definitely getting better, but so are V8s. I certainly think there is less of a need for V8s nowadays, but they're certainly not defunct.