Engine Efficiency and Power

>>14712528
power, efficiency, and size requirements make for hugely different engines

DOHC isn't more popular in smaller engines because of efficiency nor are are large displacement V8's pushrod due to cost or complexity

the simple answer is that pushrods give a much narrower angled block in V8's and DOHC I4's are pretty nicely packaged to fit under the hood of a FWD shitbox
EGR's increase the amount of fuel burned given a certain amount injected, however they rob overall power and increase complexity/maintenance

>>14712593
Egr does not recycle fuel. Or at least that is not the goal of it. This is obvious because on most engines it is only ducked in off of 1 exhaust manifold runner. It is inert gas. Meaning that putting it into the engine doe not affect the fuel air mixture. Therefore you are essentially displacing the engine's displacement and saving fuel. A properly functioning egr valve is only open when you are at idle or very light load. The downside is that it is a valve that has unburnt fuel traveling through it and will always eventually stick open which robs power and makes the overall system more complex

>>14712593
>>14712883
Sorry, meant to reply to op not you

>>14712528
The only modern company where dohc v8s are rare is gm. Ford, Dodge, Toyota, Nissan, etc all use dohc.

>>14712883
Pretty sure EGR is for NOx emission regulations only. It will not save fuel. You save fuel by putting in less fuel.. Period. It actually hurts power and economy, which is why EGR delete is so popular.

You're right about it being combustion-inert, but the purpose of that is to have gasses in the chamber which take up some of the heat from combustion, lowering cylinder temperatures and preventing NOx from forming.

The problem with that is your exhaust gasses are hot, or at least relatively warm compared to normal intake air (still cold compared to cylinder temps though). Hot intake gasses means lower compression ratio means less efficiency and power.

Theoretically, it can increase efficiency, mostly due to the fact that it's using energy heating the gasses (which expand, more power) and not wasting energy dissociation the gasses (at high temps). But in reality, how cars are tuned from factory for NOx reduction, they hurt efficiency overall.

>>14713412
You're absolutely right. It is mostly for nox emissions. But displacing volume which would otherwise have to be filled with fuel air mixture does save you on gas. Even if only like 2 mpg. Also the lower cylinder head temp is better for reliability. The biggest point to make though is that a properly functioning egr valve will not be open when you are accelerating, ie when you are actually trying to make power. It's only open when you don't need the extra power, want to reduce Temps, and reduce emissions.

>>14712528
Dohc isn't rare in v8's. Why are americans so stupid?

>>14712901

DOHC v8s are common even under GM. Don't forget about the Northstar engine family.

>>14714773
Didn't even think of that. Just thought of Chevy pushrod stuff. So, yeah. Op didn't do any research at all.

>>14714773
They're kinda ass though and GM aren't making them anymore. Because they're ass.

>>14713412
there are two ways of reducing nox on cruise.
egr or running rich.

>>14712901
Dodge uses ohv.

>>14712528

A little bit off topic, but what are the advantages/disadvantages to using a rocker arm layout on a DOHC head versus a shim under bucket layout?

>>14714907
because swapping any engine that isn't a 5.3/5.7 into an american car is rare as fuck
>>14714946
this