Deezler's 2003 Jetta TDI Build Thread

[Big Dave]

Also recommended for turbo safety is a pyrometer. Measures exhaust gas temperature.

[Deezler]

Never posted pics from the small mirror that I threw on (same one everyone else was buying up on ebay). It's basically only useful for backing into spaces or parallel parking. With a re-adjustment it should view the next lane ok.





Forgot to snap pics during the tuft test, but was glad to see the mirror didn't appear to be introducing any major flow disruptions anywhere past 5 or 6 inches downstream.


Today I started on a more ambitious project: Rear diffuser.

Would I really cut up this beautiful rear bumper?







I guess so!




You can see how this version of the VW Jetta bumper valence would end up parachuting fairly badly. My crappy coroplast panel wouldn't stay put, so its time for something more serious.

The spare tire well under the trunk actually bends into an 18 degree angle (!). By my measurements, I'll cut it down to approx 10 degrees, and box out the diffuser properly. I know some would say its too steep... But we'll see what happens.

Not sure about fins. Probably not necessary, but they do look pretty sweet.

There's still time for adjustments to the design, so if anyone has some suggestions I am all ears. Will probably cut my abs sheet tomorrow:



Can't seem to keep these things off the roof though!

[Christ]

LOL - Improving aero under the car, so it doesn't quite screw it up as much on top of the car... nice.

I still think your car is one of the cleanest modded I've seen so far. Good work!

[Deezler]

Thanks dood.

So, got the rough build done. I need to tweak it a bit more before I call it done, but it should be doing its thing functionally. Finished it in the dark, late last night. I think the side fins are upside down.... doh. Speaking of fins, would anyone advocate putting a few more in?





The airflow under the car could still tumble quite a bit around the rear axle, but is pretty smooth from the spare tire well back. I think next would be some larger sheet metal (for heat resistance) panels that cover the middle of the car and rear axle.

[Christ]

I wouldn't add any more fins to it, since you'd have to get them perfectly straight for them not to create more area for the force of wind to act upon.

I believe that those diffusers are made in molds created by 5 axis mills and vacuum forming machines.

[Deezler]

So right after switching to pure biodiesel dispensed from a tank at home, my mileage dropped from ~49 to ~46 mpgs. I thought I had verified my fuel measurement upon fill-ups, but it looks like I was off. After taking a road trip this weekend and having to first top off with B20 from the pump, then fill up on B99 from a nearby Mobil station on my way home, things are looking up! Identical driving conditions that measured 46 mpg at home were back to 49 mpgs at the pump last week.

Best ever 52 mpg on a road trip this past weekend across Michigan and back. Cruising speeds anywhere from 65 to 80 mph, with plenty of hard acceleration and a couple high speed bursts. No hyper-miling, but some drafting (its so hard to resist with all the minivans running 80 mph around here). On the exact same trip last year, with better BTU content biodiesel, and driving more carefully (but no aeromods), I only got 49mpgs.

So, I'm pleased. Couple more tweaks coming, hopefully will have pics soon.

[jabb]

I love the way your Jetta looks. It's very stylish and yet aero improved - that's what I'd like to achieve with my Punto...

Is there any noticeable difference in stability with your diffuser?

[Deezler]

Yes, I actually have noticed some good benefit to vehicle stability with the aero mods I've done, especially the diffuser. I try not to drink from the placebo kool-aid, but this is more tangible.

I know its frowned upon to discuss on a fuel saving website, but I can discern the most benefit at high speeds (80mph +). At 100mph, the stock aero made the car quite light and a little scary. Now its butter smooth (and gets there noticeably faster!). Susceptibility to cross winds, semi blow-by and other disturbing aero effects are also reduced.

Couple more aero-mods coming, then I plan to do a few coast-down tests. Unfortunately I don't have a baseline, but the Cd is pretty well known for my vehicle.

[Big Dave]

Bad Deezler!

Two variables (improved aero and biodiesel) in play at once.

BTW, B100 has about 10% lower heating value than dino-diesel, so MPG is always lowerwith bio-diesel.

If you live in SE Michigan 80 MPH is minimum survival speed in a small car.

[basslover911]

Isnt the jetta aero better than the golf?

However, wouldnt it be easier to aeromod the golf? (the kammback seems a lot easier to do than anything to a sedan... other than a rear decklid extension and thats about it i guess)