Quote:
Originally Posted by Grape Ape
The V8 will have - a heavier block (might be on part with a 3.8 straight six)
- a greater total piston circumference (more friction)
- two extra rod journals and one extra main journal on its crank (more friction and weight)
- longer cam(s) with four (or eight) extra lifters and maybe rocker arms(more friction and weight)
- a bigger oil pump to keep all this lubed (greater parasitic loss)
- and probably a bigger water pump to serve the bigger, more complex cooling jacket(greater parasitic loss).
And there is a fair chance that the V6 will have greater total valve area which would reduce pumping losses relative to the 3.8 V8.
Fuel efficiency aside, a V6 will always be cheaper to build (and buy) than a V8 with the same tech (GDI, DOHC, Turbos, etc). |
Points of contention.
1: Assuming the V6 and V8 have a similar bore/stroke relationship, and identical displacement, then there is no reason to assume that a V6 engine of comparable displacement will be any lighter, particularly not when you take into consideration the fact that the increase in stroke the V6 will have to undergo in order to maintain a similar bore-stroke relationship will be relatively large. That means a significantly increased deck height which adds weight to any engine in a hurry.
2:Adding insult to injury, a V6 will absolutely be both taller and wider than a V8 of similar displacement, all else being equal. That means a higher cowl height for any cars using the same, making the car itself heavier, and positoning more of that weight higher up in the car precisely where you don't want it. Not good.
3:As for greater friction losses. More cylinders do mean more surface to surface contact, but they likewise mean a smoother firing order and, in the case of the cross plane V8, more torque down low and a better overall torque curve due to the nature of the design and the counterweights used to balance the same. Also worth mentioning, assuming identical displacement and bore-stroke relationship a V8 will always rev to a higher rpm than a V6 since the mass of the pistons and piston speed itself limit potential rpm, which in turn leads to greater power potential.
4: Also, assuming similar bore-stroke relationships and overall displacement a V8 will
always possess more valve area than a comparably sized V6. (This relates indirectly to the nature of how bore and stroke relate and the reality that displacement increases faster when bore is increased than when stroke is increased, meaning that this is linked to why the V6 will be considerably taller as well) Even more, in the case of the V8 port velocity will be higher on both the intake and exhaust sides as well since, while overall valve area is larger, each individul valve and the port design leading to it will be smaller.
5:I also don't buy into the notion that a V8 will always cost more. First, the split throw cranks mandated by any V6 intended to be relatively smooth running are far more costly and complex to manufacture, even moreso if you intend to garner comparable strength when comapred to a crank from a crossplane V8. And of course, the fact that the V6 crank runs on fewer bearings doesn't help here either. Ford uses a forged crank in the new 3.5L EB V6, but given the compromises inherent in the split throw design it is unlikely that this is significantly stronger, or any stronger, than a good cast crank would be for the typical V8. As the crank is easily the most expensive part of the engine next to the engine block itself this is no small issue.
Yes, the V8 has more individual parts, but given the increased valve area, greater inherent smoothness, greater ability to rev, and better potential for torque there can be little doubt a V6 will have to possess more tech to match a V8 quality for quality, adding yet more costs to the equation.
IMO V8 versus V6 is no comparison at all. Frankly, I'm not sure why manufacturers even bother with the V6 design at all.