bonnet vents

[MattDon]

im toying with the idea of cutting vents into the bonnet to aid air flow, and fixing mesh undernieth, has anyone tried this before or have any suggestions? will add a picture in a moment.

[Gazza]

Stevo put a couple in recently into Tango's bonnet.

Gazza

[F1 LOTUS]

Lotusgirlmarie neatly incorporated a Mercedes vent across the bonnet ahead of the windsheild wipers, looked OEM, subtle and neat. For sure it helps exhaust hot air at standstill / low speed - don't know if she verified which way it flows at speed though Very nice job though.

Another member cut-in some vents each side on the bonnet behind the headlamp area - "the grills are from a post facelift subaru impreza turbo uk."

[RayD]

If ventilation were the main thing rather than looks, an easy way would be to modify the rear bonnet seal.

Ray

[Elanlover]

I've been toying with this idea for "another future project" ever since I saw LGM's vent. While I like her's very much I can't help but think that having them mounted lower down the hood/bonnet would make more sense in getting rid of heat. Much like the Subaru ones pictured above. I've looked at thesea few times.

What I like about those ones is that it appears you can simply cut a hole and drop them in thus eliminating the need for body work and/or re-spraying. There may be others that can be installed this way too if you don't like these. However, keep in mind that there's PLENTY of vents out there that look good BUT are only stick on types with no opening into the engine bay itself.

[MattDon]

thankyou for all the replies, all very useful, i do realy like the look of lgm's vent but feel its a little beyond my ability and possibly budget ATM the subaru vents look very effective but dont work for me visualy. what im looking at is a simple hole cut into the bonnet with a mesh attatched, and something like a rubber seal to tidy up the cutting until i can afford to have things painted. although the prospect of a good looking stick in (not on) vents is rather apealing.

[Doug]

sorry to stick a wrench in the gears, but I'll drop in and play the devil and say there's no reason to do this except for appearance!


first show me some concrete proof that it would even help -- and what exactly is your goal and need

we have a composite structured engine bay, not metal, and thus we don't have the heat sink effect of metal cars

how do you know putting vents in the hood will change the airflow or the temperature?

how hot does it even get under our hood and under the hood of a "well vented" car?

maybe you could just do heatwrap around the turbo and exhaust and/or ceramic coat these type parts . . .

[Elanlover]

Awww Doug. There you go again trying to confuse us all with facts after we've already made up our minds

I do remember LGM saying she saw plenty of heat rising from the vent she installed and seemed to "think" the car was running a bit cooler. I don't think she did any serious, scientific-like testing though. Nor has anyone else I'll venture.

And I had neon trimmed vents with flashing LED's ready to go with the "cool light" under body kit

[MattDon]

i have no idea but id assume that there would be high pressure at the front of the car thats why they have the radiator etc there, and providing an exit for that air at a point of lower pressure would create a flow which would draw away heat. my reasoning for looking at this in the first place (apart from the fact the majority of turbo car have vents) is that my engine bay seems to get very hot even after relatively short spirited drives. I also considered removing the heat shielding but id assume that would leave the bonnet pretty vunerable.


(the above is pure speculation)

[jecuk]

Is there any evidence that the engine bay is getting too hot on these cars? Making it cooler might help a bit but this seems more an aesthetic change than a functional one.

[tweetdriver63]

I'll have a look later, but I know I saw somebody had actually done some temperature readings in the bay. It's in a thread somewhere about the virtues of routing air to the intake from somewhere other than the stock wheel arch duct. It was about the effect of the open K&N type intake. Does it really help. Something about getting more air in, but the air would be hotter being ambient air from under the hood, vs outside air. Somebody had readings that showed the area where the intake is doesn't get all that hot, because of the flow of air under the hood, but IIRC, the temp in the rear area (around the plennum) gets significantly hotter. In that thread, the idea of vents was brought up to help remove that heat, rather than putting in some other scoops/ducting to bring in outside air to the intake.

When I get a chance, I'll try to find that thread (if somebody doesn't beat me to it). HINT HINT HINT HINT HINT HINT

[Doug]

well it was Brain MDB who did those


I just don't think it would ever make any functional difference. Shield the heat sources, make sure the radiator is working correctly and you should have no issues.

you have to be sure air would be forced in to know it would get out at speed. yes heat will rise at a stop, but with air flow over the hood it may not extract the heat at speed. The radiator flow likely goes out the bottom of the car. If you cut out some scoops to get ram air in the front then you're more likely to have enough pressure to push it thru the engine bay.

I was waiting for someone to point out I drove an Evo8 for 4 years with a big hole in the hood

[F1 LOTUS]

Guilty
I also found that the heat build-up at standstill took a long time to 'normalize', with very little change occurring at speeds below 40 MPH - this is where LGM's solution should help matters. At higher speeds there's usually a higher-pressure bubble around the base of the windshield - hence my uncertainty if the vent works as expected then - simple tufts of wool should give an indication though

I'd be more inclined to vent the engine bay just ahead of where the hinges are, hopefully tapping into a low pressure area where the airflow is whipping around the sides of the windshield - guesswork of course

[Rambo]

I think Stevo did his for cosmetic appearance rather than any other reason? I think the grilles may be from a Boy Racer's Scooby Doo ? I think they look shite but that's my own opinion

Have a look here for more photo's http://lotuselancentral.com/forum/viewt ... c&start=80

[Elanlover]

That's great info Brian, thanks. I may save the money I was planning to spend on the neon trimmed vents and put it towards more underbody kits and lighting ........or a rear Wilwood brake upgrade (Brian you still there? )

Oh yea........

well it was Brain MDB who did those

I'm sure Brian was thinking "That's my kind of typo!"

Hey "Brain" would side port holes suck air out of the bay better than hood mounted ones? Just thinking there may be a lower air pressure pocket on the sides of the car instead of over the hood.

[F1 LOTUS]

Have a search around this sight, perhaps you'll find some inspiration
http://autospeed.com/cms/search/index.html?keywords=air+flow&x=0&y=0

Their search facility works well, try 'front undertray/spoiler'

Siting hood vents: -
http://autospeed.com/cms/A_2162/article.html

[GeoffSmith]

It's a shame Phil didn't get the FatCat to Castle Combe. I was all ready with 16 channels of thermocouples to baseline the underbonnet temperatures under track conditions.

[F1 LOTUS]

It's a shame Phil didn't get the FatCat to Castle Combe. I was all ready with 16 channels of thermocouples to baseline the underbonnet temperatures under track conditions.

You could always baseline your car first

[GeoffSmith]

You could always baseline your car first

Too good to thrash the bollocks off on track!

Hmm. I can get pressure transducers for 15 quid..........

[surfboardfiller]

I don't really understand this thread. LGM has a heavily modified engine and felt she needed to design a solution for the extra heat created. She also lives in California, a hot place.

There are heat vents for the engine bay, designed by lotus and so tastefully done you don't know they are already there. If you loose the heat you will affect the performance, a warm engine burns less fuel. If you want an ugly car buy a Scooby

If you don't know what you are doing then it's probably best not to do it. Make sure your front lip spoiler is on and in good condition. This will draw warm air from the coolers under the car as it moves.
If the air is too hot for your induction, you should sort out the induction.

If you push hot air onto the brakes it will help cook them.

If you just want to cut holes in the bonnet and put vents in because you feel like it then ignore my opinion and enjoy destroying a nice car.