club.liberty.asn.au

Season's cheer to all! Hope everyone is or is going to enjoy a well deserved rest over Chrissy.

Right, straight to the point: I'm looking to fit bonnet vents to my 3RB. I'll be fitting a custom radiator from PWR over the break and wanting to avoid the potential heat wall between said radiator and the front of the EZ30. I've designed vents out of 1.0mm 316 stainless sheet metal to fit into these gaps in the bonnet's support layer:



They will end up looking like this, somewhat (it's a image mock-up so not necessarily perfectly to scale):



The key difference between these vents and other similar ones on the market are that they will have a wall that holds back the insulation (so it can be maintained to preserve the bonnet's paint) and strengthening strakes that give them rigidity and vandalism deterrent look. (Zoom into the second image). The final weight of each vent will be about 300 grams, including powder coating or painted finish.

These vents will fit all Gen IVs. So, whilst not my primary motivation, and given that I couldn't find something to simply purchase that I could just fit, I'm curious to see if anyone else would be keen to purchase such an item for their Gen IV?

I will update this post once manufacturing quotes come back, but I'm fairly confident I'll be able to offer them as a pair for considerably less than what you could find similar items online.

montyLalor wrote:Season's cheer to all! Hope everyone is or is going to enjoy a well deserved rest over Chrissy.

Right, straight to the point: I'm looking to fit bonnet vents to my 3RB. I'll be fitting a custom radiator from PWR over the break and wanting to avoid the potential heat wall between said radiator and the front of the EZ30. I've designed vents out of 1.0mm 316 stainless sheet metal to fit into these gaps in the bonnet's support layer:



They will end up looking like this, somewhat (it's a image mock-up so not necessarily perfectly to scale):



The key difference between these vents and other similar ones on the market are that they will have a wall that holds back the insulation (so it can be maintained to preserve the bonnet's paint) and strengthening strakes that give them rigidity and vandalism deterrent look. (Zoom into the second image). The final weight of each vent will be about 300 grams, including powder coating or painted finish.

These vents will fit all Gen IVs. So, whilst not my primary motivation, and given that I couldn't find something to simply purchase that I could just fit, I'm curious to see if anyone else would be keen to purchase such an item for their Gen IV?

I will update this post once manufacturing quotes come back, but I'm fairly confident I'll be able to offer them as a pair for considerably less than what you could find similar items online.

I would have thought a ram air type vent (reverse the louvers in pics), would work better than the suction method.
Just my thoughts, I am no genius.

I do apologise for the image. It's not very clear. The louvers will be on a 45° backwards angle, so high pressure hot air will be drawn out as low pressure air outside rushes over the bonnet.
When I return from holidays I'll upload an image of the CAD model...

montyLalor wrote:I do apologise for the image. It's not very clear. The louvers will be on a 45° backwards angle, so high pressure hot air will be drawn out as low pressure air outside rushes over the bonnet.
When I return from holidays I'll upload an image of the CAD model...

So the air is going through the radiator, flowing into the engine bay, then using the Venturi effect over the bonnet to suck air out?
Have you calculated at what speed it will become most effective?


EDIT: not trying to be a smart ass. just hate to see you put holes in your bonnet only to regret it if it doesn't work.

No calcs as yet. I'm not an engineer. Just a bloke with a parametric CAD package.
Despite this, I will be able to back it up with empirical data as I'll be installing ambient sensors in the engine bay. I'll be recording data before and after installing the vents. The vents will be located just behind the radiator thermo fans at the front of the engine where, given the EZ30's girth, I believe a bit of a heat wall could potentially be an issue. Because hot air loves to rise, the vents should be well placed to negate the potential heat wall that the larger radiator might create, so even at standstill, the fans will push air out through the vents. Yes, it's conjecture, but something I believe the data will confirm.
Watch this space...

Just a thought - what would be your solution for rain through the vents? A lot of aftermarket hoods with vents I've seen (at least higher end ones) have a cover underneath to install for rain or if not in use. Curious to see how this works out with your testing!

This has definately been a consideration I'll be working on a solution for. Infact, over dinner tonight this very challenge was spoken about with extended family. I will be studying as many factory vent designs as I can to attempt an adaptation that has a suitable amount of clearance.

Whilst not a totally duplicatable solution, I personally will be investigating ways to replace the aircon compressor and power steering pump with electric units and moving these to behind the engine. To supplement these relocations, a mate had an idea to replace the alternator with a higher-output model and move it to up near the firewall and run a flex-drive from a pulley driven off a shorter multi-v belt. This is primarily to move weight rearward and unload the engine of parasitic losses, but would have the benefit of removing electrical items from beneath the vents.

Those replacements won't happen until later next year, so my focus will be on duplicating OEM vent's water management designs first and foremost.

Is there any feasibility in moving the vents to either side of the bonnet (like the old GC8 WRX) so the exiting hot air isn't being blown straight into the intercooler for bonnet-scoop turbo models?

Yowie wrote:Is there any feasibility in moving the vents to either side of the bonnet (like the old GC8 WRX) so the exiting hot air isn't being blown straight into the intercooler for bonnet-scoop turbo models?

Yes. There's gaps in the bonnet's substructure layer outboard of the centre ones pictured in my previous post.

For my N/A H6 I decided to reject developing these for the following reasons:
1. From a purely aesthetic standpoint, if I make use of all of the frontal outboard substructure gaps, but avoid dipping into the soft fold of the style line (so the vent doesn't sit on a void) the shape of the vents looks a bit wonky-eyed. I'll revisit my original design for these ones and correct the look of them so they don't make the gorgeous Gen 4 look stoopid.
2. The driver's side outer vent is directly over what would predominantly be the OEM intake scoop, pretty much negating any airflow benefit. Should a CAI or somesuch be installed, then it could potentially increase the vent's effectiveness, but also possibly lead to rain/washing water ingress into any CAI pod filter that could be in the vicinity.
3. The passenger side's outer vent is directly over both the dipstick and oil filler cap, potentially causing water ingress issues, again, where they're not wanted.

In my previous post I mentioned how water management is something I'll be looking into to, in an attempt to rectify water ingress concerns. In my research I've found many references from people both claiming that water ingress into bonnet vents isn't such a big deal and that it's a consequence large enough to negate any benefits gained from fitting vents. The curious thing is that those that claim the issue to be a storm in a teacup, tend to back it up with more empirical data and observation than those who attempt to poo-poo the whole idea outright.

Granted, when I install my centre vents I will need to create a shield over the alternator to protect it from water ingress, but this is a solution that I believe is the best compromise. Particularly, too when teamed with a run of pinch-weld around the perimeter of the hole cut in the bonnet insulation. I reckon this pinch weld would press into engine bay furniture and create a semi seal that attempts to control the vent's 'wet bits' zones. I believe this would be a better solution than significantly reducing the vent's efficiency by having a gutter designed and installed, which would reduce the vent's effectiveness. The only major issue I see with this result is water over the OEM thermo fans motors. I'd expect them to be designed to be as waterproof as deemed necessary by Subaru, but what that means, though, could be debated ad-nauseam.

if you have the spare time you could always design some sort of sliding seal plate under the vents and connect them to an actuator. Could be controlled with a switch in-car.

Or even better, make the vents themselves working louvers and have them triggered to close by a moisture sensor

Going to make some assumptions (correct me if I'm way off here).

I think realistically the use case of the vents will only be during warmer weather or where you're driving relatively hard. Therefore we can assume that water will not be any issue when they are actually in use. During all other times, the vents can safely be closed up.

So my personal solution would be to disregard any water issues in regards to their design when open, but have a method to close them when not in use. This seems to be how most aftermarket vents tackle the issue from my limited understanding. It doesn't need to be a perfect seal by any means.

So, I can finally share images of the fitment of my bonnet vent prototypes.

Here are the vents, prior to painting, sat in the freshly cut holes of the cheap, sad-looking bonnet I bought some time back:



And here is the post-painted and riveted completed project (for now).



These are prototypes only. The final version will be 3D printed in nylon, as nylon is fairly fine with heat. That said, final material selection for the prints will be made rather whimsically, as it'll depend on the price and heat resistant characteristics of the selected material at the time of ordering.
I'll be opening up the holes in the bonnet to accept a plastic peg (that is part of the print) in lieu of the riveting of holes. This way the pegs will accept some sort of retainer clip underneath and the finish on top of the bonnet is smooth and as flush as possible. The rivets just look too back-yard-hack-ish. Which is what it is, but doesn't need to look like it

Now, empirical data:

@ 30°C ambient temperatures, max water and oil temps, whilst sitting in traffic, rise to mid nineties: I've seen 94°C for water and 96°C for oil. It doesn't rise beyond this. Looking at traffic through a column of heat haze is very satisfying. Under-bonnet temps rise to over 50*C (my gauge's max for these two sensors) sitting in traffic too, but cool to low forties when travelling at 60kph for a few minutes. Oil and water cool to low-to-mid eighties when travelling at 60kph for a few minutes, too. The under-bonnet temps used to climb into the 50+°C range and never return under all conditions prior to fitting the vents. I have noticed that 60kph is the minimum speed to start to reduce temps. This must be when the Bernoulli effect starts to draw air out through the vents properly.

I can confidently say that my rig is now Queensland-proof as far a general heat management goes

As far a water management goes, the vents ended up sitting further forward than I had feared and only expose the very front of the power steering pump, alternator and A/C compressor. It essentially has the pulleys and drive belt exposed. One day, whilst parked at work, it drizzled all day and the water ingress was as expected, but to very little detrimental effect. It started up just fine. One pulley had a tiny smidge of surface rust on it that the belt would have eaten quick-smart.

The 3D printed versions won't be louvered. The rear surface will extend forward and the internal opening will be more of an internal snout, with the rear surface draining water in front of the drive belt, into the gap behind the fans. This will also neaten up the look and make it seem more OEM, IMHO.

All in all, I am very stoked that this has worked as well has it has. I shall post images of my final design when completed.

Looks great, do keep us posted on any updates!

I'd love a set.

Yes looks good. For aesthetics another pair towards the windscreen and a similar distance from the fold would might (at least) look better but may also get more of the hot air out from around the back of the engine? Not much electronics under there being just inside the shock towers?

Close to the windscreen is a high air pressure zone. That's why a lot of cars take in cabin air at that point. Extra vents close to the windscreen would probably force air into the engine bay.