DIY rear bumper fake vent conversion

Phylanx

Senior Member
Joined
Sep 1, 2017
Threads
4
Messages
183
Reaction score
134
Location
Phoenix AZ
Vehicle(s)
'12 CRV, '17 Si Sedan
Country flag
This.

Every time I see a regular Civic LX I wish they just left the Si body style alone and just added a side skirt and spoiler
Yes, similar to the 8th Gen Civic. I liked that my previous SI (FA5) had a more subtle look to it than the 10th gen.
Sponsored

 

Doc_C

Senior Member
Joined
Jul 13, 2017
Threads
3
Messages
235
Reaction score
226
Location
Omaha
Vehicle(s)
2017 WOP Civic Si Sedan
Country flag
Don't forget that these "voids" or "areas of vacuum" are sometimes intentional and beneficial. Think of pickup beds - driving with the tailgate down allows air to flow through the bed in a way it wasn't intended which actually increases drag. An area of vacuum or pressure isn't necessarily a bad thing.
With truck beds, the air actually comes over the cab and slams into the bed with the tailgate down. They tested this on Mythbusters years ago. I can't remember the exact figures, but it increased downforce in the rear and increased overall drag. It dropped gas mileage as would be expected with an increase in drag.
 

elevated23

Member
First Name
Andrew
Joined
Aug 19, 2017
Threads
1
Messages
20
Reaction score
24
Location
Covina, CA
Vehicle(s)
2017 Civic Si Sedan
Country flag
With truck beds, the air actually comes over the cab and slams into the bed with the tailgate down. They tested this on Mythbusters years ago. I can't remember the exact figures, but it increased downforce in the rear and increased overall drag. It dropped gas mileage as would be expected with an increase in drag.
Closing the tailgate actually improves fuel efficiency because it creates a type of airflow called a separated bubble within the bed of the truck. As wind rushes over the moving truck, that bubble of slow-moving air deflects it over the raised tailgate. By guiding surrounding air over and across the bed of the truck, that vortex effect prevents added drag.
 

4DBox

Senior Member
First Name
Jim
Joined
Aug 24, 2015
Threads
3
Messages
88
Reaction score
68
Location
Oakland, CA
Vehicle(s)
2017 Silver EXT, 2018 Volt
Country flag
Here's the actual findings from Honda R&D. It appears the open vents would effect critical airflow in the region, but for better or worse? Note that there is noticable upwash below the rear bumper which acts as a diffuser effect and that Honda spent considerable effort tuning this area as evidenced by the red dashed oval highlight.

Honda Civic 10th gen DIY rear bumper fake vent conversion upload_2017-9-11_12-45-59
 
Last edited:

Doc_C

Senior Member
Joined
Jul 13, 2017
Threads
3
Messages
235
Reaction score
226
Location
Omaha
Vehicle(s)
2017 WOP Civic Si Sedan
Country flag
Closing the tailgate actually improves fuel efficiency because it creates a type of airflow called a separated bubble within the bed of the truck. As wind rushes over the moving truck, that bubble of slow-moving air deflects it over the raised tailgate. By guiding surrounding air over and across the bed of the truck, that vortex effect prevents added drag.
Yes... That's exactly what I said from the opposite direction.
 


STiTCH87

Senior Member
First Name
Adam
Joined
Aug 24, 2016
Threads
14
Messages
433
Reaction score
280
Location
Southcoast Massachusetts
Vehicle(s)
2016 Honda Civic Sedan, 2006 Scion TC
I really want to swap with a normal Civic. I have already asked in my regional area forum. I really thought someone with a basic Civic would like a sportier looking front bumper but I guess not. I think I will hold out until Mugen makes parts for the car. If they have a body kit with a more appealing front bumper than I will do that. If not I will buy a new bumper.
I would gladly swap front bumpers with you. Same color paint and all, but I live in Massachusetts. Lol.
 

himecraig

Senior Member
First Name
Craig
Joined
Jun 30, 2017
Threads
3
Messages
172
Reaction score
60
Location
Bay Area
Vehicle(s)
01 Mercedes 320slk 08 Ford Ranger fx4 17 Acura RDX adv 17 Honda Civic Hatch ex-l ns
Country flag
I returned splash guards. I feel they aren't aggressive enough and better options and pricing online. I'm going with universal RokBlokz.
Good call...but then can't discuss drag and how big rigs have vented flaps for that reason.
Finish looks very good btw.

FYI @360glitch pointed out '17 hatch bumper:

Honda Civic 10th gen DIY rear bumper fake vent conversion IMG_0668.JPG
 
OP
OP
Brian17Si

Brian17Si

Senior Member
First Name
Brian
Joined
Jul 23, 2017
Threads
8
Messages
253
Reaction score
279
Location
Hartford CT
Vehicle(s)
2017 Honda Civic Si
Vehicle Showcase
1
Country flag
Good call...but then can't discuss drag and how big rigs have vented flaps for that reason.
Finish looks very good btw.

FYI @360glitch pointed out '17 hatch bumper:

IMG_0668.JPG
Thanks himecraig. Wow I didn't know about vented mud flaps. Great point, I was thinking the same thing. I've attached pic showing tires in direct path of vents. In pic you can see they've cut a curved metal leaving nothing on its path.

IMO all signs point towards diffuser capability. I mean c'mon they've OEM'd faux vents! Probably taken note to Honda racers cutting holes in bumpers for years. Probably said "if there going to do it let's give them a good starting point". For true race applications someone will optimize this location and do same bumper delete as me.

Airflow comes from under carriage to the rear bumper and wants to escape where it's guided. The bump delete vents IMO still increases aerodynamics and downforce. Funny we both thought of the flaps because IMO air is pushed from tire into vent rear bumper location. But for protecting vents from debris I have to apply them.

The next step would be to create a real diffuser for rear and then this baby is fully active. I've attached pics of concept from NSX design. I will be soon posting pics with mud flaps and ez lip for final stage 1 build.

Honda Civic 10th gen DIY rear bumper fake vent conversion IMG_0096.JPG


Honda Civic 10th gen DIY rear bumper fake vent conversion 987E49BB-D635-4161-BA79-56077B2DA116-5850-000004BA66328CD3


Honda Civic 10th gen DIY rear bumper fake vent conversion 8AB19813-7866-4142-A840-AAC06ADB3273-5850-000004BA814F0FE4
 
Last edited:

4DBox

Senior Member
First Name
Jim
Joined
Aug 24, 2015
Threads
3
Messages
88
Reaction score
68
Location
Oakland, CA
Vehicle(s)
2017 Silver EXT, 2018 Volt
Country flag
So Brian, are you saying the stock bodywork behind the bumper vents to wheel well covers is hollowed out or empty from the factory? And what is that tan surface under the wheel? It appears a section of the bottom rear cover has been removed revealing some kind of MDF board on the floor.
 

jakabony

Senior Member
First Name
Jake
Joined
Jul 20, 2017
Threads
49
Messages
1,335
Reaction score
1,424
Location
Pittsburgh PA
Website
www.facebook.com
Vehicle(s)
2017 Honda Civic Si, 2019 Honda CR-V EX-L, 2017 Subaru Forester
Vehicle Showcase
1
Country flag
So Brian, are you saying the stock bodywork behind the bumper vents to wheel well covers is hollowed out or empty from the factory? And what is that tan surface under the wheel? It appears a section of the bottom rear cover has been removed revealing some kind of MDF board on the floor.
MDF aka concrete floor
 


totopo

Senior Member
Joined
Apr 3, 2016
Threads
2
Messages
344
Reaction score
307
Location
CA
Vehicle(s)
'17 Civic Ex Hatch, 370z
Country flag
Airflow comes from under carriage to the rear bumper and wants to escape where it's guided. The bump delete vents IMO still increases aerodynamics and downforce. Funny we both thought of the flaps because IMO air is pushed from tire into vent rear bumper location. But for protecting vents from debris I have to apply them.
There's a reason diffusers have a graded angle and there's a reason they are in the CENTER of the car. First off, if the gradation isn't smooth or not gradual enough you get separation of the airflow and it basically no longer works. Second, you don't want to lose your low pressure zone underneath the car by letting air back in from the side skirts and tires.

I can't say for sure and I'm not an expert, but I HIGHLY doubt that delete does much of anything in the positive and would think if anything it would be negative.
 
OP
OP
Brian17Si

Brian17Si

Senior Member
First Name
Brian
Joined
Jul 23, 2017
Threads
8
Messages
253
Reaction score
279
Location
Hartford CT
Vehicle(s)
2017 Honda Civic Si
Vehicle Showcase
1
Country flag
There's a reason diffusers have a graded angle and there's a reason they are in the CENTER of the car. First off, if the gradation isn't smooth or not gradual enough you get separation of the airflow and it basically no longer works. Second, you don't want to lose your low pressure zone underneath the car by letting air back in from the side skirts and tires.

I can't say for sure and I'm not an expert, but I HIGHLY doubt that delete does much of anything in the positive and would think if anything it would be negative.
Two words... "parachute effect" it's a thing. I didn't make it up. The average to even spirited driver might not be aware. But the race community is fully aware, embraced, and conquered it. Everyone reading this should've seen race or drag cars with rear bumper holes. Here's a link to a company that sells products they say have been tested. This is what they say...

Rear bumper diffuser
Honda Civic 10th gen DIY rear bumper fake vent conversion B5365C6A-78D5-4485-806D-2B5F26AEABA4-436-00000035886C6893


"Whether you drive your car to and from work or only drive a quarter mile at a time you will see remarkable benefits with our new diffuser design. At speed a rear bumper cover can increase overall aero drag and promote lift. Neither of these effects are desirable on any vehicle, and as speed increases the problem becomes more pronounced. Think of your rear bumper as a big air brake. Our diffuser removes the trapped air and lets it flow freely through the bumper cover. Our product promotes higher track speed and gives the driver more stability at those high speeds."

"This product has been tested at the drag strip on a 9 second, 150mph drag Civic. Each diffuser is CNC water jet cut, and features a glossy finish. It measures approximately 4"x45", and comes with easy to read instructions for trouble free install and black painted rivets. For those really fast racers out there you will be happy to know we machined a center hole just for your parachute tube. A secondary benefit for some cars using parachutes is faster parachute deployment due to the larger volume of air exiting out the bumper cover."

- Retrieved from http://www.lighterfaster.com/13163.html

All reply's are appreciated because this topic has been a healthy debate. It's reinforcing more research and knowledge that's extremely beneficial. Info is limited but it seems to be a very important aspect of racing. Hopefully we'll discover the truth behind it, literally. We need people with professional expertise to chime in and shed some facts.

UPDATE: FINDING SOME AMAZING INFORMATION

Spoon rear aero bumper product.

"The newly developed Spoon Rear Aero Bumper was designed based on 15 years of S2000 racing experience. The raised bumper height allows air to escape from behind the wheels thus generating rear downforce. The bumper cutouts allow trapped air to escape for reduced drag and aids rear differential and exhaust cooling."

- Retrieved from http://www.gotuning.com/product_info.php?products_id=1775

Directly from Spoon website...
Honda Civic 10th gen DIY rear bumper fake vent conversion F521F14B-ED3D-49FE-B3AB-422A6AB83F0B-770-0000007955B1002C


"Creating down force while reducing drag. These repulsive factors must be balanced at an optimum to produce a truly effective aero part. At Spoon, we combine our knowledge accumulated from all of our years of racing and state-of-the-art CFD (Computational Fluid Dynamics) to develop each of our aero parts for Honda vehicles."

Honda Civic 10th gen DIY rear bumper fake vent conversion 4339D514-46D6-4D8E-9008-554746517D24-770-0000007F19160B7D


"All proto-type products are tested on the track and validated from multiple perspectives. To achieve the highest cornering performance. Stability under any circumstance. Only the blatantly honest policy to develop an aero part with surpassing performance leads to the highest quality product."

- Retrieved from: http://www.spoonsports.jp/philosophy06.html

Spoon Rear Aero Bumper - S2000 AP1/2

Honda Civic 10th gen DIY rear bumper fake vent conversion EA477F8B-2960-4E66-9608-333A9E61FA9A-436-0000004CAF36C47F

Honda Civic 10th gen DIY rear bumper fake vent conversion 7B1DAC75-962E-4C6E-8B43-B5272D9A1F6F-938-000000D35EDCA169


Spoon Sports S Tai Rear Bumper ‑ Honda S2000 AP1 AP2
Honda Civic 10th gen DIY rear bumper fake vent conversion F1612DDD-3474-44C8-B924-831DE8291307-938-000000D3FB0859D3

Honda Civic 10th gen DIY rear bumper fake vent conversion 91C29610-1E0B-407B-AB32-792F59B534EA-949-000000D68B5CF738

Honda Civic 10th gen DIY rear bumper fake vent conversion D1023349-5D86-4F49-9634-8CD0FCD4E1FC-938-000000D3B4A8813D

Honda Civic 10th gen DIY rear bumper fake vent conversion BD8D3038-4BFE-4332-B303-7BA763141366-938-000000D37812D858

Honda Civic 10th gen DIY rear bumper fake vent conversion 12E1E2C3-FADB-4395-B503-727C72FC90C5-938-000000D3CF323828


Spoon s2000 Racing (CUT OUTS LOOK SIMILAR TO SI)
Honda Civic 10th gen DIY rear bumper fake vent conversion BA9B1E41-6604-46CA-84BB-A7B5B6E67143-436-0000002B9F62450A

Honda Civic 10th gen DIY rear bumper fake vent conversion 5AA4A9FF-5B62-4F1A-9BA8-76CDF875077E-436-0000002C063E86A1


Miscellaneous pics
Honda Civic 10th gen DIY rear bumper fake vent conversion 88845C52-208B-4196-A9A8-800DA7CDF121-436-0000002D9C7C39CC

Honda Civic 10th gen DIY rear bumper fake vent conversion 7A6A5E83-3339-4A8B-8095-F200F7AAA6C5-436-0000002E439103DC

Honda Civic 10th gen DIY rear bumper fake vent conversion DDD14D7B-3B62-497F-B0CD-118A545D3CB0-1116-000001591837DE5E

Honda Civic 10th gen DIY rear bumper fake vent conversion ACD06C8E-BB92-4808-A615-6CA15443D875-1116-000001593108A326
 
Last edited:
OP
OP
Brian17Si

Brian17Si

Senior Member
First Name
Brian
Joined
Jul 23, 2017
Threads
8
Messages
253
Reaction score
279
Location
Hartford CT
Vehicle(s)
2017 Honda Civic Si
Vehicle Showcase
1
Country flag
So Brian, are you saying the stock bodywork behind the bumper vents to wheel well covers is hollowed out or empty from the factory? And what is that tan surface under the wheel? It appears a section of the bottom rear cover has been removed revealing some kind of MDF board on the floor.
Hi 4DBox, NO the bumper needs to be cut but behind that everything is clear to the tire as seen in pic. Jakabony's correct, what you're referring to as MDF is my concrete floor.
 

Giltibo

Senior Member
First Name
Gil
Joined
Jul 30, 2017
Threads
0
Messages
214
Reaction score
103
Location
Alliston ON Canada
Vehicle(s)
'08 Accord Coupe 5MT. '18 Civic Sport Touring 6MT (Both Red!)
Vehicle Showcase
1
Country flag
Your a life saver. i am currently opening up the driver side fog lamp area for a CAI vent. i was looking for a mesh grille and this looks perfect.
On the HS models (i.e. most Civics with CVT), that's where the radar module for the ACC / Auto High Beam) resides...
 

Civic416

Member
First Name
Adam
Joined
Oct 25, 2017
Threads
3
Messages
35
Reaction score
15
Location
Toronto
Vehicle(s)
2018 Honda Civic Sport Touring
Brian, thanks for working on this and sharing.. so you were able to salvage the original vent garnish - and the backing/hex/mesh strips can be swapped? Sorry if I misunderstood.What was the cost at your body shop to remove replace and install, assuming you provided that universal hex vent?
We have lots of options - A) opening up the vents, adding a custom mesh pattern - see thread here:
http://www.civicx.com/threads/any-photoshoppers-hb-faux-vents.7463/#post-307255
B) rear bumper, possibly vented, C) rear bumper diffuser
Sponsored

 


 


Top