Quote:
Originally Posted by replicat
I read this post with two freinds of mine that go to tech school with me and it was agreed that that the BER will not change MPG. AT ALL! PERIOD. Its for less robbing of HP.
Just my opinion, and yours is yours.
And Restrictive headers...now that I think about it..I dunno? Maybe im just an idiot..or maybe the fact that typically a more restrictive exhaust yields more MPG than one that doesn't have it...example stock USspec headers for M3 vs...EU spec headers.. C'mon think about...don't try to make me look stupid, I do cars for a living u piss-wad.
(Not to mention other things that aren't required for EU as opposed to US and CARB emissions, egr, evap. All those systems are alot more restrictive and give less power..which I usually see as more MPG.
My opinion so move on or F*ck off...  |
Easy there. No need to get rough. And, you're still in school, so you haven't mastered anything although you have a point...
Let’s try to think through this rationally:
1) During regenerative breaking, some of the energy that would have been otherwise dissipated as heat will be used to charge the battery.
2) Assumption: Since the batteries will be well charged, the alternator, if designed to do so, will be offline for some time during regular driving FOLLOWING regenerative breaking. It should not matter if the alternator is offline during breaking as it would not make sense to break and burn fuel in the cylinders simultaneously. In other words, taking the alternator offline during breaking does not save any fuel.
Now we’ve done regenerative breaking, battery is charged up, alternator is offline, and we are sitting still immediately after coming to a stop. (You could also imagine you are kind of coasting at steady speed after decelerating, but the full stop example makes things more dramatic and explicit.) Let’s think of two scenarios:
3.A) We accelerate out of the full stop normally—meaning we don’t floor it. The full capacity of the engine is never utilized. Whatever energy that would be transferred from the shaft to the alternator to generate electricity and charge the battery is not expanded since the alternator is offline. In short, we save “some” energy, and therefore, fuel. Unless someone pulls out pen and paper and calculates everything to see if a significant amount of energy would be saved, we would be speculating. And, of course, that would all depend on what one means by significant.
3.B) We floor it, and use whatever the engine can generate. The engine burns all the fuel it can possibly burn. Whatever energy that would have been used to run the alternator is now available, and is used to accelerate. So we have “slightly” more power, and accelerate slightly faster than we would have if the alternator was still running. In other words, the energy freed up by putting the alternator offline is transformed to higher performance (and it is still expanded not saved). There is NO net energy savings, and mileage is not improved.
So, if my assumption is correct, the affect of regenerative breaking of this kind on fuel efficiency depends on how you drive. This is not the same type of regenerative breaking system used in a hybrid, where the energy stored during breaking always ends up being used to accelerate the car eventually, which results in net energy savings.
To your second point about restrictive headers. There probably is a possibility that a more restrictive header will indeed result in higher fuel efficiency. If the header restricts air flow into the cylinder, the ECU should inject less fuel in the cylinder. Therefore, the power output would decrease, and so would the fuel consumption. It would be like driving with an engine with a smaller displacement, or would it? I am not sure if it is that simple as the thermal efficiency of the engine might he affected as well due to combustion chamber dynamics. Volumetric efficiency would definitely decrease, but that might or might not affect fuel efficiency. Someone who knows more about combustion should comment.
Regards,