MPG, WHP, and GDI

Friday, June 25, 2010 - 3:55pm

The green movement...Plug in hybrids...Toyota Prius…

These phrases may excite the typical tree hugger but they put the average automotive enthusiast into a boredom induced coma. All this environmental crap is just going to kill our hobby, right? Well, not necessarily.


MPG and WHP are not mutually exclusive. We (the collective auto enthusiasts) are always wanting more power out of our cars and whether we think about it or not, increased efficiency is usually how we get it. For example, look at the most basic mods we do… free flowing exhaust and high flow intake. Both not only yield you more power, but also improve your gas mileage. This efficiency/power model carries over to fuel injectors too. Many of the people I talk to about DeatschWerks wrongly assume that when our highflow injectors are installed MPG takes a nosedive. They are shocked to hear most of our customers retain the same MPG as they had before the injectors. In fact, many of our customers enjoy BETTER gas mileage after our injectors are installed along with a good tune. And why not? You’ve upgraded from an often poorly balanced set of injectors with a generic from-the-factory tune to a set of injectors balanced to within 1-2% variance and a custom tune made specifically for YOUR car.

A more timely fuel injection-related example is Gasoline Direct Injection (GDI). GDI, what it is, and how it works could easily be its own blog post. But briefly, for those of you unfamiliar, put simply, it is the relocation of the fuel injectors from the intake manifold to the combustion chamber (see diagram).

There are many benefits to this new location, both from an efficiency perspective and performance perspective. However, I assure you, the recent push towards small displacement GDI engines in many new cars was born out of the green movement, not the desire for the automobile manufacturers to bring us cars we can easily modify for more power. But we benefit from the performance aspects nonetheless. For example, GDI creates a very significant temperature reduction in air charge and we all know colder denser air leads to more power. Also, since the injectors inside the cylinder and do not have to travel through the intake valves, injection timing is free to be manipulated however the programmer or engineer would like. Without GDI the new breed of factory forced induction cars such as the Mazdaspeed3, BMW 335, Cobalt SS, and VAG 2.0t would never be able to achieve their high compression ratios and fat torque curves. It may take us a little while to completely crack into and manipulate this new technology but it is certainly worth it.

So, next time you pull up next to a Smart Car or a Prius at the stop light, don’t laugh. Instead, nod and say thank you.