Brainstorming a vented rear bumper cover

denpo

denpo

Carburated Nihilist
Joined
Jul 14, 2010
Messages
2,522
Location
Montreal, QC
As the summer come and go, it seems less and less likely that my car would hit the paint booth this year. The flares are a couple of days away from completed but I still have the rear window mod on my list.
So, considering I may have one more winter to spend on the body, I'm starting to list additional modification I could do before next spring.
So far I have :
LT-1 hood scoop, '68 gill and vented rear bumper cover.
And that's on the lastest I'm asking for your inputs, technical and/or aesthetic.
Did anyone tried that?
How big is the "parachute ass" effect it? / How big should be the opening to prevent it?
What is you favorite vented rear bumper design?

Feel free to go wild, this is brainstorming.
 
You are further along than I and I still hope to get a tech inspection this year...
These are ideas I've been kicking around:
126953daa796c4804.jpg
I am eliminating the rear bumper entirely - so need to "face" the open area and have a means to mount tail lights. The Chaparral 2H has a nice look.

To avoid a parachute effect - a diffuser of several varieties:
126953daa7ece03bd.jpg

That one is pretty radical (but I like -- and will use -- the Diff cooler plan). This a little less so - even though it is on a "wide body.":

126953daa7ecacf29.jpg


Here is sort of how I'll work the rear inside the car:

126953daa7ec77797.jpg

My "tin-man" is folding my rear bulkhead this week.
.

BTW: let me know when you're finished with the Flare "tools" I'm getting ready to make my flare mold this next week. Then splash 4 to mount.

Cheers - Jim
 
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That's some good ideas you're bringing.
By the way I removed the last flaring tool yesterday.
PM me your address, I'll send them to you next week.
 
The first pix with the blue/silver stripes, and the holes in the rear looks the coolest for a street machine, but I saw a pix some years ago where the holes were higher and more of them, just under the rear 'spoiler'.....on the flat surface, I have done my 'body work' as of some years ago, and so I wonder about how to trim out the holes.....but you know, I have the vents from the astro vent system that used to be on the back deck behind the convertible top lid....filled them in long ago....be cute to mess with vette owners and put them on the rear just above the tail lights....hummmmm.......:smash::thumbs:
 
1965ChevyVetteGrandSportFastFiveCars-2.jpg
 
The widebody cars of Greenwood's had some mesh in cutouts.
 
Thanks everyone for the input.


May I shoot some ideas of mine:


I like the upper vent shape
80-ferrari_458_italia_back_090a8742031f5aeba4d7f8e723e16527f8fa41cd.jpg



Here is two render I did :


In this one the idea would be to join the two taillight holes, and mesh the bottom, so air could flow around and between the taillight.
80-rearventidea1_zpsac2cf37f_ec9a27479e45ccf72bb140e9469e6e7598d784a1.jpg



Here are idea of more subtle vent, above the taillight, of beside.
80-rearventidea2_zpsa560f5a3_22abb1d5b155e9a5af608039513f0a6eab05230c.jpg
 
rtj said:
Why not two below the tai lights?
Click to expand...
Excellent question.
I've been asked the same on "the other forum".
The actual question is : how high (or low) those holes need to be to be the most efficient.
 
Why not two below the tail lights?
Click to expand...

And use your mesh idea from above - include the Back-up Lights - kinda sorta like the Ferrari.

I'm thinking the upper section is largely blocked with the fuel tank. If you look at the rear wheel well - it kinda blocks some air I suppose. If you removed the inner well, then a lower set of air exits should be more efficient, than all the air jamming up in the wheel well. If you have a look at many of the Sports Racers, they are all "open-ended" no parachute at all. Many (including Formulas) have a diffuser too. theory being, get the air out - through the "holes"; control the flow and generate downforce with the diffuser.

Cheers - Jim
 
Last edited:
phantomjock said:
You are further along than I and I still hope to get a tech inspection this year...
These are ideas I've been kicking around:


To avoid a parachute effect - a diffuser of several varieties:
126953daa7ece03bd.jpg



....................

Cheers - Jim
Click to expand...


If it weren't for my reluctance to cut up the bodywork/structure I've always wanted to run some "large" ducts from under the car (at the storage compartments or under the seat/footwell areas) upwards towards the astro-vents behind the rear window. This would/should partially fix two problem areas in these antiques. The area behind the rear window is a turbulent/low-pressure area, and the undercar area is a higher pressure area. Sucking some air out from underneath the car and supplying it to the large horizontal surface of the rear deck should have an effect on reducing drag and reducing lift.
 
Just now at a car show, a fellow showed up with a super NICE blue and USA Flag '73 vert, parked next to me, super nice car, and I pulled out one of my vent caps that went to the old 'Astro Ventilation' setup......my car being an old show car, came with the AV console panel and the two slots on either side for the control levers, the driver side was closed off, as was the pass side, and any flappers removed in the rear, what I have is the deck vent grill, my side windows have old GM Astro Ventillation on them...

at any rate, since the two grills were closed in and removed some time ago, I happen to have them hanging around.....

SO the thought struck me to mess with vette folks, and mount them in the rear maybe up top, or on the back with the tail lights.....then JaxNorb said to use just ONE, and put RED LEDs in the slots for a center brake light.....

hummmm.....not to block the air flow, just to keep it real.....one in the center just below the flip up/spoiler :smash::eek::twitch::cool::thumbs::loveletter:
 
A look at the "problem" SIDEWAYS

Maybe not make holes - but fill holes...

The charts are from somewhere - I've misplaced the source - maybe Katz/MacBeath? I'm "whipped" from sanding 'glass so not going to check just now...
ANY way, a slight weight penalty (69427 will be sensitive to that), but less drag and more downforce might be worth a few ounces.

126953dd5e1bbd577.jpg

IMPORTANT DISCLAIMER: The background image is not associated with the test results posted. I only provide as representative of the possibilities.​

Note the "kick-up" at the rear - a diffuser. Venting the "parachute" would still be useful I'd think. Look closely - you'll see the rear bumper through the wheel well.

Cheers - Jim
 
phantomjock said:
126953dd64daa777d.jpg
Might be a useful pic for these discussions...
Click to expand...
Even more than you think, at the bottom of the bumper cover, there's the bumper.
So, even if the lower part should make more sense, vents would just be and opening to an alumunium flat surface.
OTOH, being a '80 style bumper (futher away from tank), the upper area may offer better flow.
I expect air to hit the back of the bumper and move up.
 
69427 said:
phantomjock said:
You are further along than I and I still hope to get a tech inspection this year...
These are ideas I've been kicking around:


To avoid a parachute effect - a diffuser of several varieties:
126953daa7ece03bd.jpg



....................

Cheers - Jim
Click to expand...


If it weren't for my reluctance to cut up the bodywork/structure I've always wanted to run some "large" ducts from under the car (at the storage compartments or under the seat/footwell areas) upwards towards the astro-vents behind the rear window. This would/should partially fix two problem areas in these antiques. The area behind the rear window is a turbulent/low-pressure area, and the undercar area is a higher pressure area. Sucking some air out from underneath the car and supplying it to the large horizontal surface of the rear deck should have an effect on reducing drag and reducing lift.
Click to expand...
Interesting thinking.
Those duct could be the volume of the arch around the back window. It would take some glassing from the inside.
Basically those duct would come from the areas at bodymount #4 and would end at openings in the inside the arch, at each side of the back window.
I hope I make sense.
 
phantomjock said:
Maybe not make holes - but fill holes...

The charts are from somewhere - I've misplaced the source - maybe Katz/MacBeath? I'm "whipped" from sanding 'glass so not going to check just now...
ANY way, a slight weight penalty (69427 will be sensitive to that), but less drag and more downforce might be worth a few ounces.

126953dd5e1bbd577.jpg

IMPORTANT DISCLAIMER: The background image is not associated with the test results posted. I only provide as representative of the possibilities.​

Note the "kick-up" at the rear - a diffuser. Venting the "parachute" would still be useful I'd think. Look closely - you'll see the rear bumper through the wheel well.

Cheers - Jim
Click to expand...

I hated to add weight to my car, but I'm hoping the reduced drag and lift might make up for it. Right now I'm just band-aiding the underside of the car (several cuts and modifications, depending on the changes to the trans crossmember shape and the exhaust system iteration). It certainly would have been easier if I could have started with a clean sheet of paper regarding the frame and floor pan design. I'm also trying to figure out the most sensible way of getting an accurate answer to my question of when the aero helps more than the weight hurts.

IM002298_zpsec3ff5b8.jpg
 
denpo said:
69427 said:
............

If it weren't for my reluctance to cut up the bodywork/structure I've always wanted to run some "large" ducts from under the car (at the storage compartments or under the seat/footwell areas) upwards towards the astro-vents behind the rear window. This would/should partially fix two problem areas in these antiques. The area behind the rear window is a turbulent/low-pressure area, and the undercar area is a higher pressure area. Sucking some air out from underneath the car and supplying it to the large horizontal surface of the rear deck should have an effect on reducing drag and reducing lift.
Click to expand...

Interesting thinking.
Those duct could be the volume of the arch around the back window. It would take some glassing from the inside.
Basically those duct would come from the areas at bodymount #4 and would end at openings in the inside the arch, at each side of the back window.
I hope I make sense.
Click to expand...

Yeah, I follow you. :thumbs: My intention was to try to pull air out from under the car as early as possible (as forward as possible), but I do like the packaging efficiency of your idea to incorporate the current bodywork in ducting the undercar air.
 
That bumper venting kept ticking in my head.
I watched a vid on the Challenger Hellcat, describing how they hollowed out one of the headlight to make room for supercharger intake that it all came clear to me.
I'm gonna do hollow taillights.

80-hollowtaillight3_zps9c63a268_58a84a05d2b49c8720b2f1e9a8c8a56f509696ab.jpg


80-hollowtaillight1_zps5b83ba7d_4c91c143eef09a49b44bd89466580a053d77bd86.jpg


80-hollowtaillight2_zpsf4d565d6_47bb7d92844645aa7b4cb535b6a757cb6533dd1e.jpg


LED rings are of the 'COB' style, as smooth as CCFL rings, and damn luminous.
The support is gonna be aluminum, and there will be a grid in the middle.
 
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