Gus

Have removed rear bumper assembly to remove replace crank pullies. Noticed the weight of assembly and the lack of venting for the hot air around center muffler to escape.
What steps can be taken to lighten this section?. And has anyone looked at venting the lower section?
Have looked at the vents added in the tail light area - but based on sheet metal behind engine I can't see what this really accomplishes.
Ideas????

HiWind

was thinking the same thing when I reattached new foil/heat shield to line the rear bumper .... Behind license plate and mount plate on 'raised' mount to allow for air?

Gus

I have thought about ways to increase air flow in the area around the muffler. Just a better way to circulate air around the muffler and get it to move on. Thought of adding a directional side duct behind the drivers rear wheel to move area up and into muffler area. Just to try and push the hot air out some.
No one seems to have done anything like this though so must not be a major issue. Can't help but think - better air flow in the area would be cooler -
Real ISSUE - is what can you do it that area to save weight??
I have headers and my muffler sits in this area.
Short of drilling large holes in the bumper beam - not sure of what other weight saving means are available.

PhatPhlatSix

You'd reduce weight and heat in that area with a cup bypass pipe.
With ducting air to it, it is equally as important to be able duct the air out too. Normal airflow under the car may counter act any efforts, so you get a stall in the ducted flow. Hiwind's suggestion of a vent in the licence plate area would work....

Gus

So you think cutting some large vent hole behind the license plate area and then mounting the license plate further out using spacers to stand it out about an inch or 3 cm would improve flow and reduce the hot air build up?

Earlydays

....I think the area around the bumper is probably a low pressure area were the air actually swirls back toward the car

HiWind

That might well be ... Question for Ahab or some aero fiend

Gus

Are we going to have to rent a wind tunnel to figure this out ??

PhatPhlatSix

I'd say if it's low pressure, it's most likely to suck air out from the vented area. Similar idea to the diffusers on F1 cars. Low pressure will suck from anywhere that's higher pressure.

Gus

Then I guess the first thing to do is run a test. Cut the vent slots, attach some light weight plastic ribbon and see how it moves. If it blows out it works. If it folds back against the bumper or concept is false. Any other ideas?

911Jetta

Saw this image and remember your thread.


some other venting ideas:

Gus

911Jetta - Thanks, those are some great pics and offer good food for thought. Not sure how much help the center tail light section vent is/works - but the license plate are certainly appears to have merit. Appears that in the cases where this was done the rear bumper reinforcement section was removed as there is definitely no solid aluminum cross beam showing. Great way to loose weight and allow vent.
Think it is time to start playing with a few ideas.

Bill Verburg

here's mine


and a few others






There's a lot of turbulent detached flow where the rear bumpers curve in, the vents allow air out and smooth the flow

HiWind

nice shots bill - do you still have side mufflers?
or do those side vents (ala 997 gt2) - which look mean! - help with heat anyway
(ie for the centre transverse silencer too?)

Jetta - love that last black one, thanks!

jack.pe

Subscribed...!

This is a really interesting approach.. interested both in saving weight and the venting aspect.

Presumably if the rear beam was removed then a rear end crash would have much more serious consequences and damage to the car?