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Engine Bay Vent Fitting 
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Post Engine Bay Vent Fitting
If I fitted a raised vent (or two ) on my engine bay cover should it face forward or backwards? This may seem like a daft question but if the back of the car is a low pressure area then it may be more effective to draw hot air out rather than try and force cool air in where it is also partly shielded from the air flow by the driver and passenger. Aerodynamics are not my strong point.........

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Sun Aug 16, 2015 10:12 pm
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Post Re: Engine Bay Vent Fitting
I suppose there are 2 options, the easier one is to get a hole saw and put holes where you think it may do some good, or duct air in to an oil cooler, or air box around the carbs and have an outlet in a low pressure area, expect the engine cover to be a low pressure area,
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John


Mon Aug 17, 2015 4:45 am
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Post Re: Engine Bay Vent Fitting
Likewise, I'm no expert...but it's Friday afternoon and I needed to think about cars for a minute!

I think the airflow depends on a couple of things, but in this instance it'll be mostly the difference in pressure above and below the engine cover. It's hard to know exactly what all will be going on under the cover. The flat floor followed by the "opening" for the engine/box will cause some turbulence in my mind. I imagine at roadspeed it'll be mainly low pressure in the majority of the engine compartment.

That said, I think with the shape of the back window, at any speed above about 45mph, my guess is the majority of the engine cover will be under lower pressure than under it. I'd put the vents facing backwards.

If it was me, I'd cut about 10 bits of string 3 or 4" long and tape them to the boot cover, then go for a drive with someone watching. Or they drive and you watch. That'll let you know exactly where to put your vents and what direction.


Fri Oct 02, 2015 4:12 pm
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Post Re: Engine Bay Vent Fitting
Willie wrote:
If it was me, I'd cut about 10 bits of string 3 or 4" long and tape them to the boot cover


Like the thread (sorry about the bad pun) in "Libra / Spyder" at the mo' then

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Fri Oct 02, 2015 7:17 pm
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Post Re: Engine Bay Vent Fitting
I've just submitted a reply to this and it's disappeared :? Must have been put off by Malcolm's terrible pun....

Anyway, here goes again. I agree with your comments, Willie, because my own gut feeling is that the vents should face backwards and I've actually bought a pair of louvred aluminium panels from CBS which should look pretty good once they're painted but the problem is where to put them. I'm reluctant to cut holes unnecessarily but needs must, I suppose, and they look well placed either side of the landing pad affair on the back panel but it's double skinned there with stiffeners underneath so I'd rather not cut into it. The easiest place is actually on the single skinned landing pad itself but then it looks boy racerish. So, I'm now thinking about drilling a row of holes along the back lip of the pad so they will still face backwards but be more discrete. Decisions, decisions.

I read Pete Silcock's post with interest so that's something to consider but I'LL be doing the driving, thank you :mrgreen:

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Fri Oct 02, 2015 7:51 pm
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Post Re: Engine Bay Vent Fitting
Hadn't seen the post in the Libra forum. That's the ticket though. I can see legions of GTM owners now pinching their mother's knitting and getting mates to hang out car windows taking photos.

What is the purpose of these vents? Is to cool electricals or vent exhaust heat? Would that help decided where to locate them? Would you rather do without vents? How about some ducting from heat build up area to underneath the car? That should create a similar effect I imagine.


Sat Oct 03, 2015 8:49 pm
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Post Re: Engine Bay Vent Fitting
When the car is stopped in traffic there is a heat build up in the engine bay because there is no ventilation to it apart from underneath. Cooling has been a general issue for a while and I have improved it by sticking a number plate on the bonnet and drilling 5 holes each 3" in diameter in the number plate space which I then finished off with a grill. This has dramatically increased the air flow to the radiator so there is now no steady increase in temperature while the car is moving and I also have a pair of 9" electric fans to replace the old Metro one so the front end is sorted for the moment. I haven't tried it in really hot weather yet (that will have to wait till next year now :roll: ) but if there are still problems then the next step will be to fit an electric water pump but that's an expensive option! I'm now looking at ways of keeping the engine from getting too hot by drawing out hot air while on the move and also giving it a way out while stopped. I have a 4" in line fan in the boot at the moment but when I switch it on all it seems to do is move hot air around although, having said that, it does bring the temperature down a little bit eventually so again I need to get some cold air in. Coupes and other versions of the Rossa have an opening just behind the carb and I'm trying to do something similar but the style of the Mk1 makes it a bit harder to do without spoiling the look of the car. I'm also looking at a way of ducting cold air to the in line fan through the boot floor but, of course, the exhaust is there to pre heat it so it looks like I will need to reverse the flow of the fan to make it an extractor so I could really do to get some cool air in across the engine otherwise the fan will just pull air up from underneath and over the exhaust manifold which I don't feel will be enough. Sorry for the long story..........

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Sat Oct 03, 2015 10:40 pm
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