Here's a list of eco mods I've already done to my van:

[Synchronicity]

Thanks for the reply-

Probably because, in all honesty "I can't be stuffed". I used to be a scientist, with a PhD in fact, so I'm kinda over the testing phase.

These days I'm more into prototyping, component design as well as materials. I like to get my hands on things to keep busy.

A more serious answer:
It's extremely difficult to find a straight, flat piece of road with no traffic on it here in Tenerife. Just look anywhere on google maps. I don't think quantifying the changes would be easy. I'd be out practically every other day and this would take up a lot of my time...

I don't have a scangauge, but I do have something equally as good:
It's a bluetooth enabled OBD thingamajig which links to an android app called "torque". Not only can I see instant and average fuel consumption, but a whole host of other engine parameters such as coolant temp, boost pressure, intake temp, etc etc.

Another reason for not doing proper testing is that since signing up, my driving technique itself has changed... I used to get 800km or less on a tank of fuel and when I started measuring it, my average fuel consumption was 8.9L/100km. I haven't tested that lately, but I will do when I finish the diffuser.

Just by driving around slower and adding a partial bellypan I was able to get that range figure in excess of 900km.

So I prefer to say "I can get up to 1000km on a single tank of fuel" rather than "add this this and this to your car and you'll get a certain % improvement". 1200km is my goal but I don't think I'll get there before the end of the year (if ever).

It's true that some things deserve proper testing procedures.
But this is mainly for fun.

I know that overall, I'm using less fuel than before. For instance, I can feel the overall effect of my modifications most notably in reduced cabin noise and increased coasting distance (and I can glide on flatter and flatter roads). I usually do mods one at a time so at least I can eliminate combined effects.

Lastly, I think what this forum needs is a bit more emphasis on QUALITY mods. Ones that stay put and don't fly off on the highway at 100mph. I feel that is a real and present danger for other road users. What if they swerve to avoid a piece of chloroplast (thinking it's made of sheet metal) and there is a resulting accident. Who is really at fault in that case?

[Synchronicity]

Well the latest news is that I filled up the tank. So far I've got 490km on 4/9ths of a tank of fuel. Fuel tank is a digital gauge & I am fairly certain the last "tenth" is the reserve. Total fuel tank capacity is 90L. I'm getting 120km per tenth.

This is without the front & rear undertrays but the van is lowered now.

I'm not sure what the reserve is, but it looks like I'll be getting an estimated 7.5L/100km, in this configuration. Not bad for the most powerful version of the engine. I'm hoping to get down to 7L/100km and call it a day.

[slowmover]

Sorry to have missed this thread earlier. I admire what you've done. And believe the attitude toward the thing (idle hands are the Devil's work tools) and that it be fun as well as permanent make a good approach to the whole of the problem (however that may be envisioned).