Undertray / belly pan build - VW Golf MK3 1.9 Turbo Diesel

[Bill in Houston]

please delete this double post. I do apologize for my negligence.

[Bill in Houston]

Originally Posted by COcyclist

My Mk IV has a bunch of 15mm plastic plugs in the underbody. I keep staring up at these on my back trying to come up with a way to attach my belly pan without drilling into the sheet metal.

You could screw into them, OR remove them and put in an appropriately sized expanding rubber freeze plug and put the belly pan material between the big top washer and the nut. You might want another washer in there.... Or, I'd probably use the freeze plugs to mount some simple aluminum cross-pieces and then attach the belly pan to the aluminum.

[COcyclist]

Thanks Bill, Since I posted that response I have done the coroplast belly pan, screwing into the plugs with screws for metal roofing. I have been a slug about starting a new thread but I do have photos uploaded. If you click on COcyclist above my avatar, it will take you to my profile and then open the album "belly pan". Of all the aero mods I have done so far, this seems to make the most difference.

[Bill in Houston]

Oh, cool. I like it very much. The wooden blocks on the jack stands in picture 5 are a little scary... But the belly pan is very nice. Did you do anything to protect it from the heat of the exhaust?

[COcyclist]

Originally Posted by Bill in Houston

Did you do anything to protect it from the heat of the exhaust?

The coroplast is in direct contact with the exhaust pipe in a couple of spots and it hasn't been a problem. The catalytic converter is open to the air but diesel exhaust is much cooler than gas cars.

[lunarhighway]

Nice work

i wonder why did you space the tray from the bumper?
Is this for cooling or venting or to get a certain angle? i have a similar rear tray, but the spare wheel tub extends below the rear buper that's fairly high, and so the tray curves up to meet the bumper

[Bill in Houston]

Originally Posted by COcyclist

The coroplast is in direct contact with the exhaust pipe in a couple of spots and it hasn't been a problem. The catalytic converter is open to the air but diesel exhaust is much cooler than gas cars.

I didn't know that about diesel exhaust. Interesting. My Honday Element's exhaust will melt coroplast allllll the way out to the tip of the tailpipe...

[sallen]

I agree with CoCyclist, my exhaust is not really hot enough to melt it...

If you have a turbo car with an intercooler, which I don't (yet, watch this space for the addition of a Mini Cooper S intercooler) then the exhaust gas temp is drastically decreased.

I like your full width tray CoCyclist. I may extend mine in a similar fashion (leaving the cat open).

Just a 500 mile drive on motorways (nice and hot for engine + exhaust) to test it out, and I'll probably have some MPG results.

@lunarhighway, the spacing is only to allow me to change the angle, my fuel tank sits low and without spacers, the tray goes straight to the bumper at quite a steep angle. The rear portion of the tray is pretty much sealed at the front edge, so not much venting will happen.

The reason for the current gap is simply that was the length of bolt I had lying about. I probably need longer.

[COcyclist]

Originally Posted by sallen

I like your full width tray CoCyclist. I may extend mine in a similar fashion (leaving the cat open).

@lunarhighway, the spacing is only to allow me to change the angle, my fuel tank sits low and without spacers, the tray goes straight to the bumper at quite a steep angle. The rear portion of the tray is pretty much sealed at the front edge, so not much venting will happen.

The reason for the current gap is simply that was the length of bolt I had lying about. I probably need longer.

Thanks, the 4' x8' salvaged sign went from the back bumper to the cat and almost from seam to seam on the rocker panels. I got lucky.

There is a thread on here about diffusers and some charts showing that drag is lowest at about a 4 degree rise to the back edge of the diffuser (belly pan).

[redpoint5]

Originally Posted by COcyclist

Of all the aero mods I have done so far, this seems to make the most difference.

Nice work! Looks like a politicians race car now underneath. My question is, how much of a difference did it make? Could a mod like this cut down on road noise too?

Originally Posted by sallen

Just a 500 mile drive on motorways (nice and hot for engine + exhaust) to test it out, and I'll probably have some MPG results.

... and the result is what?

I like your mod too btw.