Metro undertray / belly pan

[Pandaf]

Originally Posted by paulgato

I reckon it would be possible to remove the bars in a temporary and easily reversible manner by cutting neat round holes in the head lining (with a sharpened length of pipe in an electric drill?)

I have a different car than you so I'm just guessing but wouldn't there be any plastic cover or part that you could remove from the bars so you could access the bolt(s) from the outside of the car?
It's a bit of a shame to drill holes in the head lining..

[paulgato]

No Pandaf,

Unfortunately a VW Golf Mk4 has roof bars attached by bolts that go through from underneath. You apparently have to remove plastic covers on the bars to reveal the nuts, which can be removed from the outside, but then you have to draw the bolts out from below.

But a few neat holes in the head lining would not be a problem I'm sure, ...just big enough to fit a 13mm socket through to access the bolt heads. I can finish the holes with blanking caps or closed rubber grommets if I drill them the right size.

Mk4 wagon roof bar delete howto? - TDIClub Forums

I'd like to be able to take the bars on and off without removing the head lining.

[PaulB2]

I have my doubts testing tells you anything, at least these short runs. There are just too many variables. Wind can change significantly in a short time. If I were you I'd take my long term data, several tanks or several months, and then compare that with the test version equally long. Or just assume the pan is going to be worth it and don't worry about proving it!

[paulgato]

Originally Posted by PaulB2

I have my doubts testing tells you anything, at least these short runs. There are just too many variables. Wind can change significantly in a short time. If I were you I'd take my long term data, several tanks or several months, and then compare that with the test version equally long. Or just assume the pan is going to be worth it and don't worry about proving it!

I see your point PaulB2, but most of us are going to be trying several different mods over a several-month period, so waiting a long time is also not a great way to tell if a single mod is helping. Also, mpg changes a lot with the seasons, so you'd really have to run the test over a whole year (or two!) to take account of that. And then over a long period like that so many other variables creep in such as age and wear levels of the engine, different tyres, different driving patterns, etc. etc. so waiting for several months/years and for several re-fuels is not a practical way of testing individual modifications, especially if they are expected to have rather small effects.

ABA tests, or even AAABBB tests, can be useful if repeated enough times. Certainly choosing a very calm day for testing is essential. For example, I found that I got a rather small improvement in mpg by adding 0.1% acetone to my diesel tank at fill-up. The improvement was only in the region of 2% but was repeatable. Obviously I could not do an ABA test (can't take the acetone out of the tank!) but repeated AAABBB tests confirmed the small improvement. But if I had not ALSO felt an immediate subjective increase in power I would not have bothered continuing with it or bothered doing the testing. Sometimes you can just FEEL that something has helped.

[PaulB2]

FYI, long range shooters understand that right around dawn is the time most likely to have no wind.

I don't think acetone helps the lubricity of diesel fuel, which is already lubricity-challenged these days.

[YeahPete]

Maybe the belly pans are not helping as much because you guys are trapping the air in your engine and forcing it out through the wrong places like the wheel wells ect...

Look at the audi picture. It has a "large gap" for venting the air that flows through the radiator out the bottom of the car. That is the key most seem to be missing with a belly pan.

[Pandaf]

Originally Posted by paulgato

No Pandaf,

Unfortunately a VW Golf Mk4 has roof bars attached by bolts that go through from underneath. You apparently have to remove plastic covers on the bars to reveal the nuts, which can be removed from the outside, but then you have to draw the bolts out from below.

Actually the bolts remove from the outside, the nuts are welded into the structure of the roof of me Panda. When removing the bars, the holes can be closed by screwing in special plastic bolts.

I guess this time the Italian engineers defeated the Germans

Originally Posted by paulgato

Sometimes you can just FEEL that something has helped.

Yeah, the famous butt-o-meter, never failed me

[paulgato]

Originally Posted by PaulB2

FYI, long range shooters understand that right around dawn is the time most likely to have no wind.

Yes, dawn is often a good time.

I don't think acetone helps the lubricity of diesel fuel, which is already lubricity-challenged these days.

Neat acetone is horribly unlubricious of course, but I don't believe that one part in a thousand (or two ounces in a tank-full of diesel) will affect the lubricity of the other 999 parts of diesel one bit.

You can quite safely put 50 parts per thousand (5%) of petrol in a diesel tank with no ill effects, and petrol is also very unlubricious. I'm not suggesting that putting petrol in a diesel tank is a good idea of course, but the breakdown services people reckon that if you do acidentally put up to 10% petrol in your diesel tank then it's fine to just top up with diesel and drive as normal. (But any more than 10%, then drain the tank and flush all fuel lines before even putting the key in the ignition!) Those 30,000 psi common rail or PD diesel pumps are not to be messed with, but a 99.9% diesel/0.1% acetone mix is not going to mess with them.

(Oh yeah, I did actually put 12 litres of unleaded petrol in my diesel tank just a couple of months back. Day-dreaming at the pump. First time ever, and hopefully the last! I had the car trucked the 3 miles back to my driveway and did the whole drain, siphon and flush thing with a new fuel filter n all. Luckily the tank was just about bone dry when I put the petrol in so I only had about 15 litres of contaminated fuel to dispose of.)

The mechanism by which acetone is supposed to help fuel economy is not totally clear, but I have read that it is something to do with reducing surface tension and thereby helping to atomise fuel coming out of the nozzles.