[swineone]

I've been hypermiling for almost 15 years now (I recall hanging out at CleanMPG around 2007-2009 or so), but I just decided to create an account here because my current car has been leaving me puzzled. I posted something similar at the CleanMPG forums back when I bought the car, but apparently the forum is not very active currently.

As everyone knows, the latest trend is in downsized, turbo direct injection engines. I bit the bullet last year and bought a VW up! TSI sporting a 1.0 l, 3-cylinder turbo engine with 105 hp and a manual transmission.

While I'm getting nice figures (about 12-13 km/l tank averages with E100 fuel, all-city driving, with very short, 5-10 km trips), I get the feeling I could be doing better. Especially from the kinds of mileages that I see reported elsewhere

I obviously follow the usual hypermiling tips: reduce speed, properly inflate tires, remove weight from the car, time traffic lights, avoid putting yourself in a position where you'll need to brake, no air conditioning, etc.

As for driving style, I use P&G with engine on (trust me, this car doesn't like to do EOC -- I'm quite familiar with EOC as I used it on my previous cars), try to stay in a 1700-2700 RPM band more or less, and target 70-80% of max load during pulses, which means using some boost. I installed an analog boost gauge on the car, which connects to the MAP sensor of the car (not to OBD-II), and seeing as the car can reach about 0.7-0.8 bar of boost, I try to run it at 0.2-0.4 bar of boost. I've seen people say you should avoid boost like the plague on turbos, but on the other hand, the BSFC maps that I've seen appear to contradict that advice -- sadly I've yet to find one for my engine.

A few days ago I decided to look at the throttle position reading using an OBD-II app for my smartphone and found that, at about 0.2 bar boost or a little bit over that, I already reach the WOT condition at 88%. Further pressing the throttle pedal will take boost to 0.7-0.8 bar like I said, while the throttle position stays fixed at 88% -- I believe the wastegate valve may be controlling the exact amount of boost. I've always understood that a partially closed throttle reduces efficiency through pumping losses, so it appears to me the 0.2 bar boost for pulses may be a good choice.

Also, I've got a lambda gauge (rich/lean) on my OBD-II app, and monitoring it as well as PID 03 appears to indicate that my car stays in closed-loop, lambda=1 mode even at WOT and high boost values of 0.7 or 0.8 bar. I've mostly tested this at low to mid RPMs, which is the range of interest to hypermilers anyway. From this it appears that fully flooring the car (at least at low RPMs) shouldn't harm fuel efficiency.

I welcome comments on what I'm currently doing and advice on what I should be doing better. Also, if anyone who advocates avoiding boost on turbo engines could explain to me the technical reasons behind this, I'd also be grateful, because I'm really not convinced that I should be avoiding boost -- at least that's not I see in BSFC maps for turbo engines.