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Louvers
#1
Richardtherodder Richard Mounce
British Columbia, Canada   CAN
I want to add some louvers to my engine compartment, and I saw somewhere a person had put louvers on the inner fenders. How effective would that be as compared to louvers in the hood?

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limey222 Avatar
limey222 Silver Member Michael Cubbon
Portland, Oregon, USA   USA
1969 MG MGB "Mandy"
I was always told that front wheel arches are low pressure areas which you might surmise would tend to draw heat from the engine area if inner fenders were louvred or even drilled in a pattern

MGB567 Avatar
MGB567 Gold Member Barrie Braxton
Sunshine Coast, Queensland, Australia   AUS
1966 MG MGB MkI "Money Guzzler"
1979 MG MGB GT V8 Conversion "Darkside"
There are a number of us who have wing louvres/vents (and there was a long discussion not that long ago about them including those in the bonnet - I think on Swaps). I've added GTR XU1 vents to my GT's wings but as it's not on the road I can't answer how effective it will be. Of course for wing vents to work you have to do something about the splash guards. Rather than remove them entirely I cut about 150mm out of each around vent height and added a piece of stainless mesh (Crimsafe). I will need to keep an eye out for the mesh clogging. My headers also vent through the inner wings.



Convertible: CKD 11/66 first registered 8/5/67. Owned since 3/77. 90% original sheet metal. 18GB +40 balanced with almost all new internals. Peter Burgess big valve fast road head. Piper 285. Fidanza FW. Basil's followers and pushrods. TR7clutch. TT exhaust. ARP everywhere. 123 ign. Needham 4synchro c/r box.. Stock rebuilt/replaced suspension. Superpro bushes. New brakes all round including all pipes in SS flex. Interior redone. CAMS approved roll bar and side bars. Lots more. Hybrid of o/e and show/fast road car. Not for sale - it's my toy!

GT: UK car built/sold December '78. Stripped back to bare shell (with extensive bodywork to come). Powered by 'worked' Rover 5 litre V8 (ex TVR Chimera) with efi. T5 box. FC IFS. CCE rear attached to Salisbury axle with Quaife. And a whole lot more to yet to come. Stealth is the word.

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bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
Inner fender vents can work to advantage. Bonnet vents are a negative unless kept close the area right behind the radiator. The closer you put them to the windscreen (where they admittedly look best) the more likely you will be to start pulling air into the engine bay instead of letting it out (windshield base is a high pressure area).



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

TRY Avatar
TRY Gold Member Tom Young
Georgetown, Kentucky, USA   USA
I bought the MGA louvered inner fender panels for my project.
You might be able to fit these to other models as well.

Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd., USA   USA
In reply to # 3626414 by bills Inner fender vents can work to advantage. Bonnet vents are a negative unless kept close the area right behind the radiator. The closer you put them to the windscreen (where they admittedly look best) the more likely you will be to start pulling air into the engine bay instead of letting it out (windshield base is a high pressure area).

Great for a cowl vent though, or induction as done by Curtis.

Lifting the rear of the hood though, that is an open question. If your hood latch on a TR4 or 6 breaks your hood will lift some at speed. At least an inch, maybe more if the safety doesn't limit it. How much of that is airflow through the engine compartment, and how much is aerodynamic lift? You'd probably need a manometer to know for sure.

Jim

bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
In reply to # 3626848 by Jim Blackwood
Lifting the rear of the hood though, that is an open question. If your hood latch on a TR4 or 6 breaks your hood will lift some at speed. At least an inch, maybe more if the safety doesn't limit it. How much of that is airflow through the engine compartment, and how much is aerodynamic lift? You'd probably need a manometer to know for sure.

Jim

Agree - someone should do some experimentation. Tuft tests have shown that at low speeds the high pressure tends to suck the tufts in if you raise the rer of the bonnet. Ditto for the oval vents on the MGA

Lifting the bonnet works very well when the windscreen is removed or replaced with a race height screen.



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

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Richardtherodder Richard Mounce
British Columbia, Canada   CAN
I think the hood lifts up from the wind passing over it. The same airflow that will lift a plane, will lift your hood. That is why I believe the most efficient (what happened to I before E except after C?) rear spoilers, at high speed, are the ones that sit above the air flow over the body. From the information I received from this thread, I came up with an idea of putting ducting behind my rad, sealed off, with the openings in the wheel wells. So all the air passing through the rad, flows into the wheel wells. So will this work, any thoughts.

bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
Yes, that should work.

Have to be careful about adding any undersheilds (usually sheet metal that smooths the underside of the car to prevent turbulent flow). Modern Cars (including my Z4M) often have this sort of thing, more to jack up fuel mileage than speed, but on old cars doing this can cause overheating - we found that out on an MG that someone tried a full belly pan on.

Making sure all the air coming in the front of the car goes through the radiator is basic. The air that gets in will go out the tunnel, or if you louver the inner fenders, some will get out that way.



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

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Jim Blackwood Avatar
Jim Blackwood * BlownMGB-V8
Gunpowder Rd., USA   USA
Finding accurate info on exactly what causes lift with a wing is difficult. Who knows, maybe even the experts consider it too complicated to lend itself to an easy explanation, but the old standby Bernouli principle theory has by now been pretty thoroughly debunked. I never could see that accounting for the modern wide body tiny wing airliners anyway.

But the bottom line is, for the car to be pushed down, an equal mass of air has to be pushed up. Apparently a rear diffuser can be the most effective way to do that. Why? I think it is because you already have a fairly stable mass of air at ground level that you are lifting a considerable distance by having the car go over it. (remember, the air is not moving. The car is) So you lift that air as far as you can and the result pulls the car down.

In some ways wind tunnel studies do us a disservice. They invariably portray the wind moving past the car, because that is what happens in a wind tunnel. But what we really have is a predominantly stagnant mass of air, or more usually turbulent air from other vehicles passing through it directly ahead of you. But it's usually not moving any significant distance at any great speed. Then comes the car body plowing through, throwing off a bow wave and all sorts of weird currents in its wake. Unlike water, the effect is more localized but does follow much the same pattern. You see in those smoke tests that the smoke spreads after leaving the tail of the car. But you also see that in that particular test on that particular car the airflow does not smooth out until it is several inches above the bodywork. Bear in mind, that body was designed to minimize the air disturbance. That distance between the body and the smoke trace is the boundary layer and it is composed of turbulent air which is going in all directions at once. On the MGB that boundary layer is much thicker due to the steep windshield and top rear angle as well as a hundred other tiny details. (This is also why most hood scoops are generally not considered effective in producing ram air.) Not that you couldn't lift the turbulent air, just that it isn't as effective.

Now the spoiler unlike the diffuser, does not lift the air to produce downforce, but rather it prevents it from being sucked back down by the bodywork dropping away as the car goes by. You can think of it as a big mass of air that has been compressed upwards by the car body and is now trying to spread out in all directions. As the car goes by it is also trying to move back downwards into the space it formerly occupied. If you prevent that aerodynamically the forces balance around the rear of the car and do not try to push it upwards into the space left by the top. If you do not, the air under the car tries to push upwards into that space. It's just another way of looking at it, but the important thing to remember is that you are as mentioned, filling that momentary void with a bubble of air that has been scraped up by the spoiler and dragged along with the car, trying as it does so to spill out to the sides and over the top of the spoiler. Because you are dragging that mass of air along with you through stationary air, this is in fact the very definition of drag, and now we can see why the steep upward blade of the NASCAR spoiler is effective. Side blades on the rear quarters would make it even more so.

The wing otoh is somewhat like the diffuser. It creates downforce by lifting the air it passes through while creating a minimum of turbulence but it does not have the added boost the diffuser gets by separating the air from a solid unmoving surface, in effect creating a partial vacuum in the process. The angle of attack must be less than what will cause laminar flow separation on the back side of the wing, in this case the bottom. If flow separation occurs it progresses up the wing surface until it reaches the point where the wing no longer produces lift or in this case downforce at which point the wing has stalled and can do nothing except produce drag. Up to that point it is a rather efficient device and depending on the wing profile and size can create considerable downforce at a minimal cost in drag.

I found it interesting that the Superbird wing was found to be optimized for height aerodynamically after they reputedly designed it for trunk lid clearance. Sort of makes you wonder. But, sometimes form does follow function.

Jim

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
In reply to # 3627410 by Jim Blackwood Finding accurate info on exactly what causes lift with a wing is difficult. Who knows, maybe even the experts consider it too complicated to lend itself to an easy explanation, but the old standby Bernoulli principle theory has by now been pretty thoroughly debunked. I never could see that accounting for the modern wide body tiny wing airliners anyway.

Jim

I always doubted the Bernoulli business. I noticed that changing the angle of attack (pitch) on a propeller was the SOP for increasing thrust(lift in the Bernoulli camp) rather than changing the props airfoil.

Try getting a trike geared airplane off the ground with a short nose strut... with a negative angle of attack it makes little difference how fast you go down the runway.

On rear bonnet openings... if there is suction into the opening from the low pressure created just ahead of the windshield... where does the air go once it's sucked in? Under the car? Some other place? Who cares as long as it goes "away" ?

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

bills Avatar
bills Bill Spohn
W. Vancouver, , BC, Canada   CAN
In reply to # 3627494 by pinkyponk
On rear bonnet openings... if there is suction into the opening from the low pressure created just ahead of the windshield... where does the air go once it's sucked in? Under the car? Some other place? Who cares as long as it goes "away" ?

Adrian

High not low pressure at the windshield - air piles up there and will go into the engine bay and out down the tunnel or under the car. remove the windscreen and the high pressure region disappears. I have much of the air exiting the race car via a bonnet raised at the rear (gives you early warning on any leaking fluids too, though that can be a mixed blessing).



Bill Spohn www.rhodo.citymax.com/carstuff.html
Current: 1958 MGA Twincam (race car (170 bhp)),1962 MGA Deluxe Coupe (98 bhp)
1957 Jamaican MGA (200 bhp)1965 1971 Jensen Interceptor (350 bhp)
2009 Pontiac Solstice GXP Coupe (350 bhp)
2007 BMW Z4M coupe (340 bhp)
Recent: 1969 MGC roadster (175 bhp),Jensen CV8 (375 bhp),
1969 Lamborghini Islero S (350 bhp), 1988 Fiero GT turbo (300 bhp)
North Vancouver BC

pinkyponk Avatar
pinkyponk Gold Member Adrian Page
Berwick, Nova Scotia, Canada   CAN
Yup... got myself all backwards. So if there are louvers at the back of the bonnet air would enter the louvers and go out through the tunnel or under the car... taking heat with it...? (the purpose of the exercise)

Adrian



Home built Eaton M62 Supercharger with 9psi boost, "stock" high ratio rocker arms, 8:1 compression, Piper 270 cam, ported head, matched manifolds, CB Performance computerized ignition.

Richardtherodder Richard Mounce
British Columbia, Canada   CAN
I am curious whether one can draft a car, if it has a diffuser.

metalhead Avatar
metalhead Andrew F
NSW, Australia   AUS
In reply to # 3627586 by pinkyponk Yup... got myself all backwards. So if there are louvers at the back of the bonnet air would enter the louvers and go out through the tunnel or under the car... taking heat with it...? (the purpose of the exercise)

Adrian

The issue is the air goes into the engine bay, reducing the pressure differential across the radiator, which reduces airflow through the radiator, and then exits under the car, increasing lift. All negatives really.



Edited 1 time(s). Last edit at 2017-11-15 09:46 PM by metalhead.

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