[trebuchet03]

Sorry for long post - I want to keep up while I'm away

For a New Beetle, I'd actually recommend a full tapered rear, at least 6 more feet long.

That car is nearly perfect for the tear-drop shape.

But a terrible example of aerodynamics for stability... "Going TT" also applied to the Beetle Hence the necessity of spoilers for the TT and the Beetle - absofreakinglutly necessary With a more gently slope in the rear (to help taper) - this might not be such a big deal, maybe. Aerodynamics are very important, but we must make sure not to lose sight that it's important for more than cutting through the air efficiently

One overriding consideration is that Volkswagen has almost certainly tuned-up this model in the wind tunnel. These Germans know their stuff - Hucho himself may have fine-tuned the Jetta shape. VW engineers are masters in making hardedge, almost boxy shapes aerodynamically efficient through detail optimization. Accordingly, I would bet the flow separates right off the trailing edge of the trunk lid.

There's def. separation shenanigans either on the rear glass or just before (on the roof)... But, I agree with you. The MkIV Jetta has an arguably low cD - low .3's if not .30 (don't recall specifically off hand). I have questioned myself a couple times as to why I'm doing this knowing these numbers From my reading/research (Hucho, etc. etc. etc.), many of the recommended features have been implemented fairly well. At least by naked eye analysis (I haven't actually measured radius to width ratios, etc.).

Based on the CFD from tre and your insight, what in your opinion are good aerodynamic mods for the highly tuned 99-04 Jetta's?

So having just looked at some Jetta photos, and knowing the subtle and easy stuff is already squared away - I would recommend seeing if you can do without the side mirrors. Next, I would consider fairing-in the back wheel wells. Not having a Jetta around to look over, my only other suggestion would be a boat tail to try to reduce the area that the wake projects. Note that these are changes that automakers normally shy-away from because they worry about customer acceptance.

I concur. Fully Fairing the rear wheels is difficult >half the rear wheels extends beyond the bodywork - so you're adding FA while potentially reducing cD. Additionally, the fender edge has been rolled in a quality fashion (no exposed sheet metal edges) with flush well walls making mounting difficult.

I hesitate to recommend a belly pan because I am not sure how it would effect the heat transfer from the exhaust pipes (I would defer to those ecomodders who have tried it). If I had a Jetta to look at, I could evaluate the cooling air flow path and make suggestions. One of these days, I will try to write a general guide to improving the cooling air flow.

A valid concern. VW uses heat shields to slow down heat radiation upwards into the cabin. The Exhaust is inset fairly well. Still on my todo is a belly pan with placed ceramic tiles and submerged ducts for "just enough" airflow. If "just enough" is zero - awesome Alas, the under body design is not conducive to a nice flat panel... Shame on VW for that :/ One day I'd like a thermocouple add in for my multimeter for testing - but for now, the $15 thermistor meat probe has served me well

Seeing that it has been brought-up, I do not agree that hotter exhaust would be helpful (if it makes much of a difference at all). Flow resistance is proportional to the square of velocity.

This is something I have been curious of too.... More velocity means higher head loss (as a function of velocity, density, etc.).... But the question of if the side effects of one outweighs the negative effects of doing so has yet (as far as I know) been empirically addressed....

I know big yachts cover their exhausts (and everything else) with custom blankets - but I'm inclined to believe that's more for sound dampening than anything else. I am aware of header wrap, etc. But I'd feel satisfied with empirical evidence as applied to a fairly stockish road vehicle... Side effects for heat soak, etc. I'll totally buy that - but I'll shoot myself in the foot if I ever think the designers didn't consider heat soak in programming and sensor design


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Sorry for the slow slow progress My sister is Graduating college (funny: she starts a year after me and graduates a semester before me) So I'll be away... Then holiday stuff, dealing with school stuff, etc. etc. etc. etc. I'd love to keep this project on full boil, but I'm content (at the moment) keeping it at a medium simmer

All that on top of figuring out what I want to do for the rest of my life... My two general paths at the moment are: Figure out work/career OR get a Masters degree in I don't know what yet (probably either MBA, Mech Engineering, Industrial Engineering/Mgmt Systems or less likely but a viable option: something like Industrial Design.

Ultimate dream/goal is to have my own start-up.