You can't make a 5.7L DOHC engine the same external size (I assume thats what you meant by 'profile'?) as a 6.2L pushrod. They're a couple inches taller & wider. To compensate, you'd have to take a couple inches off the stroke. Now you've got half the displacement as the pushrod engine. You could make up a little bit of the 'lost' displacement by boring it out. But even then, there isn't much room to increase the bore on a small block over the 4.06" on the current 6.2L engines. The overall displacement limit would be somewhere between 3 and 3.5L. You could increase the bore spacing, but that a) makes the engine longer and b) causes a massive increase in cost. But besides that, the resulting engine would be redicously oversquare. Something like a 5.6" bore on a 1.75" stroke. It could be done, but the thing would be wildly impractical for street usage.
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Originally Posted by Firefighter
GM can and has made these types of motors they simply choose not to for cost/weight/overall dimensions.
Personally I'm not looking forward to the thought of having to buy 2 or 4 cams and a 30' timing chain because I want to do a cam swap. Never mind 32 valves to have to get worked on and start thinking about buying all of those in titanium or sodium filled, what about checking all of those springs and retainers etc... just too much to achieve a similar goal IMHO.
They can be cool though. There is another thread around here comparing the Coyote motor to the LS3 and it's a never ending thread of tit for tat. Someone pointed out the AMG 6.3L making 631hp and 468tq with an 8k redline what I find interesting is that it's TQ number is down so much compared to HP.
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Yep, its not like DOHCs are a magic bullet that simply make an engine better. They are heavier, taller, more complicated, and more expensive than a pushrod engine. Its also much harder to implement cylinder de-activation, though it can be done (I think it involves shutting down an entire bank of cylinders). Now, given the fact that the 'ancient' pushrod engine in the C7 has managed to provide the best combination of power and fuel economy of any car ever (which, by default, includes everything with a DOHC) I don't think they made a mistake by sticking with pushrods.
as for the AMG 6.3, its not that torque is down (it makes about the same as the new LT1), its that it has a very high redline. Since horsepower is a function of rpm's and torque, an engine that spins faster while making a similar amount of torque is going to make more power.