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Old Fri, Oct-14-2016, 08:20:24 AM   #1
LAWLence
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Default E46 M3 Hood Vents

I decided to start producing my own design after not being able to find anything available on the market that was both functional and aesthetically pleasing. Aftermarket hoods are a crapshoot -- they're pricey, you have to run hood pins where you can run the risk of forgetting to latch them, they can delaminate, crack, and most of the time they're not any lighter than the stock aluminum hood. Way too many cons vs pros.




I've always fancied the street GTR style vents. I'm not really a fan of the "GTR Hood" split style vents since they were originally designed to connect to the venturi ducts that vented the radiator on the GTR V8 race cars. None of the production cars have this duct.

After looking at hundreds of photos of M3 GTRs, I arrived at my own design. The corner radii have been tweaked slightly to facilitate riveting as well as complement the design of the slats. These can be riveted on top for an easy installation, or if you wanted to get more involved, you could mount underneath. That would require bonding them to the hood and probably painting or finishing the cut edge somehow. I chose to top mount them on my car because the hood was recently painted.

I did some testing at Road America this past weekend, and my oil temps were down 10-15F from normal and never got above the 3/4 dot on the stock cluster even at the end of a long 25 minute session. I've never had an issue with coolant temps with the Fluidyne radiator, but I can imagine cooling will be improved with a smaller/stock radiator. My aux fan has been removed and electric fan installed with AC retained, for the record. Sitting on grid, you can see the heat flowing out of the vents and distorting the view ahead.

There is a noticeable difference in front downforce at high speeds. The kink at Road America is a 120mph+ turn with very little runoff, and the car used to understeer quite a bit through there. With the hood vents, the car is now neutral, and I could really pitch it in unlike before. Looking at my data, I was able to carry an extra 2mph through the corner compared to before.

The design follows the curvature of the "power dome" as well as the hood lines, the same way the GTR vents do. Again, aesthetics were part of the consideration when designing these. The vents conform to the compound curve of the hood once fastened.

I ended up just spraying them with some Rustoleum semi gloss black paint (in hindsight, should've used some primer as the paint chips really easily from road debris) to match the rest of my aero bits. The fins can be bent by hand with the help of a table edge or block of wood to support the surrounding metal. You can choose the angle you want, although I don't recommend bending them back and forth as that will lead to breakage (think soda can). The only consideration for clearance is the radiator expansion tank cap on the passenger side. The fins would have to be pretty much vertical in order to interfere which is an undesirable angle anyway--I have about 1mm of clearance with a pretty aggressive fin angle.

The tabs on the side are stout at 3mm wide, and the fins won't deflect even when you're going 150mph. I used .063 6061 aluminum which roughly the same thickness as the stock hood in the vent location (1.6mm for the vents, 1.4mm for the hood).





CAD designed and CNC cut. Holes for mounting will be pre-cut:


Few pics of the prototypes going on my car:


Tabs are cut to prevent the cut edge from showing through the gaps. It takes a little longer to cut vs a straight line, but looks a lot better once complete. I used a Dremel instead of an angle grinder due to the care needed to make the tabs. Used 1 reinforced disc per side -- cuts through aluminum like butter!


I used a trash bag to cover the engine bay to prevent metallic dust/debris from falling into unwanted areas. The hood brace just needs to be notched slightly to clear the #1 and #2 fins.


The top of the slats protrude 2-3mm off the surface of the hood to generate a low pressure area behind in order to promote extraction and reduce turbulence. Very subtle and designed to minimize drag.


Vents will come in unfinished bare aluminum. I can't guarantee the aluminum will be perfect -- it's cut from a large sheet that often gets very light scratches from transport / storage from the supplier. There may be stamped markings as well, so I recommend painting them.

Package includes:
- Hood Vents
- Detailed installation instructions for both above-hood and below-hood installation
- Cutting templates
- Black anodized aluminum rivets


1/10/2017: New center vents are new available!









I haven't had time to install them on my own car yet, but these will be similar to the side vents as far as installation is concerned. The shape avoids cutting of any structural bracing underneath and follows the lines for the hood bulge. Cutting templates and instructions will be included. Vent size is roughly 3x16in.

These also allow you to retain the stock intake cold air feed from the kidney grills. Some other designs require removal of this piece which is crucial to bringing cold air to the stock airbox.

If you previously bought the side vents and want a center vent, please PM me for special pricing.

Please inquire about international shipping.

Vents are now available to order directly through my website! http://www.n15design.com/store/

Feel free to reply or PM me with any questions.

Last edited by LAWLence; Wed, Mar-28-2018 at 10:17:01 PM.
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Old Fri, Oct-14-2016, 02:39:50 PM   #2
M3_B
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Default Re: Hood Vents

Excited to receive my pair, will send you some pics when I get them installed!
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Old Fri, Oct-14-2016, 05:09:05 PM   #3
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Default Re: Hood Vents

Those look great!

I'm a data geek, any logged temp data or anything to share with your design?
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Old Fri, Oct-14-2016, 06:00:28 PM   #4
LAWLence
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Default Re: Hood Vents

Quote:
Originally Posted by nholmes View Post
Those look great!

I'm a data geek, any logged temp data or anything to share with your design?
I'll try to log some coolant temp data this weekend on track and will do a comparison with the vents blocked off. It's supposed to be 78 degrees, and as long as it doesn't rain all day, I should have some decent data.

I've only been able to go off the stock needle for oil temps, but they've never crested the 3/4 dot (255F) even in a 25 minute session. It used to get up to 265-270F even with cool ambient temps in those conditions, so there is a marked improvement.
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Old Mon, Oct-17-2016, 01:07:31 AM   #5
mr3
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Default Re: Hood Vents

Money sent. Thanks!
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Old Mon, Oct-17-2016, 01:15:47 AM   #6
LAWLence
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Default Re: Hood Vents

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Originally Posted by mr3 View Post
Money sent. Thanks!
Thanks for your order! First shipment is on track to ship Tues or Weds.
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Old Mon, Oct-17-2016, 03:03:19 AM   #7
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Default Re: Hood Vents

Very nice...might be interested down the road....
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Old Tue, Oct-18-2016, 07:08:59 AM   #8
LAWLence
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Default Re: Hood Vents

4 sets are currently in production and will be shipped on Wednesday. Working on printing templates and instructions tomorrow.
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Old Wed, Oct-19-2016, 06:59:49 AM   #9
LAWLence
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Default Re: Hood Vents



First batch is almost ready to go out!
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Old Thu, Oct-20-2016, 05:32:41 AM   #10
Jitoo
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Default Re: E46 M3 Hood Vents

I'll take a set

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Discussing Hood Vents in the Parts for Sale/Wanted Forum - Post your Parts Wanted, and non commercial bmw related items for sale. We ask that companies selling goods become a Sponsor to advertise your goods. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)