DIY rear bumper fake vent conversion

[Brian17Si]

What are you attempting to gain by doing this modification?

Cosmetic improvement, reduce drag, increase downforce.

No. Front vents are better left shut for reduced drag. That's why we see active front shutters on some models which close at higher speeds to improve fuel efficiency.

Venting out the rear bumper cover helps by reducing drag, which is why it's of common practice in drag racing... Weight savings are of course negligible.

It already looks better because the rear vents are no longer fake. It does also look lighter. It will look great once it's finished and opened up behind.

Thanks Invader and he's 100% correct with his posts. All the super cars and race cars have openings in rear bumpers and diffusers to reduce drag and increase downforce. Air gets trapped in that area of the bumper causing drag to the vehicle's airflow and aerodynamics.

Do you have actual test data to support that? Opening up those spaces would save weight and material. If it would improve fuel efficiency or performance even by the tiniest imaginable amount, don't you think Honda would have done that from the factory? I can't think of anything better for a manufacturer than saving weight, material, and money while gaining performance and fuel efficiency at the same time!

In a worst-case scenario, allowing air to flow through areas not intended could actually create additional drag and decrease efficiency and performance. It may also alter the airflow characteristics in such a way that causes exhaust fumes to be drawn into the vehicle. We'd need a wind tunnel and several hundred thousand dollars worth of test equipment and fluid modeling software to validate these wild guesses.

Thanks for your reply. Like Invader said it will improve in a positive way small or larger. Something moving with a wall on it's rear end will trap and restrict air flow. Think if you ran with a parachute open behind you it would definitely add resistance and make it more difficult to accelerate. If you were to cut holes in the parachute you would be able to accelerate and move more freely and quickly.

I feel Honda was really itching to make these vents real but for whatever reason decided to go the more conservative route. Who knows but I got the hint because they started it! One thing I'm sure about is I don't like big fake vents.

Here are a few good links related to this topic...



Porsche forum - https://rennlist.com/forums/964-forum/820881-rear-bumper-venting-2.html

Its Monday, so I'm a little slow. But are the pics above of the actual conversion or are they just photoshoped images?

PS, I think it looks good. Might have to do some black paint mitigation behind the vents but thats no big deal.

Hey, this is real no Photoshop and here are some images of the work in progress. I'm going to be cutting the bumper and struggling if I'm going to cut the entire section or just the slanted thinner section in middle and spray additional section flat black behind vents.

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[Design]

Unfortunately, after knowing how Honda tests their vehicles these days, I doubt you'll find much if any improvement. CAFE regulations have forced all manufacturers to pay much closer attention to flow dynamics. And while the rear bumper is slightly exposed, the entire underbody is designed to minimize turbulence as evident by the lower skid plates. Is not like the EGs and EKs that were notorious for flexing rear bumpers

Were this really an issue, Honda would have added a small lower diffuser before and after the mufflers. But will keep an open mind for the sake of pioneering.

My 2 cents.

 

[T_A_H]

I definitely wish Honda went more conservative with those things on both ends

They are a real pain in the ass to clean especially since they are black and have so many surface angles.

 

[HayaiKuruma]

Hey, this is real no Photoshop and here are some images of the work in progress. I'm going to be cutting the bumper and struggling if I'm going to cut the entire section or just the slanted thinner section in middle and spray additional section flat black behind vents.

Oh, I thought you were just going to do the vents. Wow, your going all out, the full Monty, eh? Either way, it looks bad ass.

What part did you use for the grill?

 

[zroger73]

They are a real pain in the ass to clean especially since they are black and have so many surface angles.

I hear ya. I not a fan of "complex" shapes on vehicles and all the resulting, impossible-to-get-to nooks and crannies. So far, I've probably washed my Si a dozen times in the last 2-1/2 months and haven't found the fake vents to be a problem. The biggest issue was the water they retain after drying, but the secret there is just pressing a folded towel against them for a few seconds to wick the water out of the hexagons.

 

[das borgen]

Do you have actual test data to support that? Opening up those spaces would save weight and material. If it would improve fuel efficiency or performance even by the tiniest imaginable amount, don't you think Honda would have done that from the factory? I can't think of anything better for a manufacturer than saving weight, material, and money while gaining performance and fuel efficiency at the same time!

In a worst-case scenario, allowing air to flow through areas not intended could actually create additional drag and decrease efficiency and performance. It may also alter the airflow characteristics in such a way that causes exhaust fumes to be drawn into the vehicle. We'd need a wind tunnel and several hundred thousand dollars worth of test equipment and fluid modeling software to validate these wild guesses.

Pretty much my thoughts. it would have cost Honda literally no extra $$$ to mold holes in the bumper making tool, and they definitely would have molded those holes into the bumper if there was a benefit to drag, and consequently fuel efficiency.
Well said

 

[zroger73]

Pretty much my thoughts. it would have cost Honda literally no extra $$$ to mold holes in the bumper making tool, and they definitely would have molded those holes into the bumper if there was a benefit to drag, and consequently fuel efficiency.
Well said

This modification makes me think of K&N air filters - if a simple air filter would actually increase fuel economy and performance of a stock engine while maintaining the same level of durability, Honda and every other manufacturer would equip every vehicle with one as standard equipment from the factory. Think about it.

 

[Brian17Si]

Unfortunately, after knowing how Honda tests their vehicles these days, I doubt you'll find much if any improvement. CAFE regulations have forced all manufacturers to pay much closer attention to flow dynamics. And while the rear bumper is slightly exposed, the entire underbody is designed to minimize turbulence as evident by the lower skid plates. Is not like the EGs and EKs that were notorious for flexing rear bumpers

Were this really an issue, Honda would have added a small lower diffuser before and after the mufflers. But will keep an open mind for the sake of pioneering.

My 2 cents.

I can agree with you. On the type r every vent or hole are functional. Even if there is little to no improvement I don't feel there will be negative impact. Then I'm happy because hopefully it will look better. Still not finished so

Pretty much my thoughts. it would have cost Honda literally no extra $$$ to mold holes in the bumper making tool, and they definitely would have molded those holes into the bumper if there was a benefit to drag, and consequently fuel efficiency.
Well said

Yes, but then they would have to consider appearance of what's behind the big vents. This would cost additional $$$ for presentation. On a mass production level who knows why they decided to do this. It can't be ignored that some designer or engineer visioned real vents here. For me I'll be happy with an improved appearance and hoping improved aerodynamics. If diffuser comes out I'll add that to get aggresive look and any performance edge.

 

[kritz]

This modification makes me think of K&N air filters - if a simple air filter would actually increase fuel economy and performance of a stock engine while maintaining the same level of durability, Honda and every other manufacturer would equip every vehicle with one as standard equipment from the factory. Think about it.

Even if it cost 30 bucks more per car? Bean counters bitch over pennies.

 

[jakabony]

I'm also guessing that any benefit you receive from this mod will not be measurable, unless you turn your car into a 350 whp track car, or auto cross. For every day driving, and what 99% of the people on these forums use their cars for, this mod is going to give a visual advantage at best. Just my opinion.

 

[360glitch]

I'm also guessing that any benefit you receive from this mod will not be measurable, unless you turn your car into a 350 whp track car, or auto cross. For every day driving, and what 99% of the people on these forums use their cars for, this mod is going to give a visual advantage at best. Just my opinion.

If it looks good and does not negatively impact anything someone could sell a LOT of them.

 

[jpuhl777]

aesthetically go for it, but I don't think there will be much functional gains.

However if you are concerned with aero functionality you could craft yourself a belly pan. That will net you some measurable difference in function and a few extra MPG. And hey, if you live in an area with tons of snow that belly pan will probably help there too.

 

[Brian17Si]

I'm also guessing that any benefit you receive from this mod will not be measurable, unless you turn your car into a 350 whp track car, or auto cross. For every day driving, and what 99% of the people on these forums use their cars for, this mod is going to give a visual advantage at best. Just my opinion.

Yes, visual advantage is what I'm going for and anything additional is a bonus. This is my daily driver but the next mod is Hondata flash.

If it looks good and does not negatively impact anything someone could sell a LOT of them.

Yes, sorry y'all. Just to clarify the original intent of doing this was for aesthetics and realness. Like many, I love the Si looks with exception of the rear vents but was happy to live with it. I wouldn't spend the money but the opportunity presented itself and I had a vision decided to go for it. A healthy and interesting debate started about the impact of aerodynamics. Anyways I'm dropping my car off at the body shop tomorrow and I'm nervous and excited. I'll update post with pics of finished product hopefully on Sunday. Thanks for everyone's input!

 

[jgreen16]

Looking forward to seeing the results.

 

[Brian17Si]

Oh, I thought you were just going to do the vents. Wow, your going all out, the full Monty, eh? Either way, it looks bad ass.

What part did you use for the grill?

Purchased off ebay. It's a great product I strongly recommend.

https://www.ebay.com/itm/331531229976

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