Air Flow Debate
Discussion
One of the most debated areas regarding rear-clip engine-bay temperature and flow to the air-filter for good consistent performance.
The former being the biggest ticket...
With more and more of us moving to LS based, or more modern engines, I for one am still a little confused sorting out the anecdotal information vs the established factory position. The factory have had the advantage of using wind-tunnels and the like, to try to get the optimum from their design, and you would have thought that being the end of it, but then, why do people add side-scoops and any number of mods to presumably keep the engine bay even cooler than standard? Does it actually make a difference?
OK, like many, I prefer to have(removable)floor plates under the engine area (not the gearbox), and this is mainly to stop crud and protect the sump from a chance thump on our UK roads. But, this means I may have compromised the airflow in or out of the bay areas doesn't it!
And so, without the benefit of a wind-tunnel, I have to re-consider if or what mods I might need to do to compensate!
1. Looking at the back half of the car, the clip slants down from the roof, and so I make the presumption that this will produce a low pressure area over the Clip, and thus, provided the engine bay is at a higher pressure, I assume that hot air will leave the bay through the oval holes in the top of the canopy. There isn't a very large area of venting going on here, but I again presume this is enough given other vents. Should this be bigger? But then how do we increase the pressure inside the clip to make this useful?
2. The side vents - now these are interesting... I don't know how efficient these are
a) with the engine bay bottom open, or
b) with the cladding I have in place?
Some have added side-scoops...but do these actually work? The theory I presume is that when in motion, the scoops collect air more efficiently, ramming more through the side vents.... Do they actually?
3. The big rear oval - I can guess again that there is a lot of low pressure behind the car, so any hot air passing through the engine bay, heated up by the exhaust bits and the engine, will readily flow out from this area, provided there is sufficient pressure created by other vents inside the clip. Again - what factors are in play here if we clad the underside of the car....
Any air-flow experts out there?
K
The former being the biggest ticket...
With more and more of us moving to LS based, or more modern engines, I for one am still a little confused sorting out the anecdotal information vs the established factory position. The factory have had the advantage of using wind-tunnels and the like, to try to get the optimum from their design, and you would have thought that being the end of it, but then, why do people add side-scoops and any number of mods to presumably keep the engine bay even cooler than standard? Does it actually make a difference?
OK, like many, I prefer to have(removable)floor plates under the engine area (not the gearbox), and this is mainly to stop crud and protect the sump from a chance thump on our UK roads. But, this means I may have compromised the airflow in or out of the bay areas doesn't it!
And so, without the benefit of a wind-tunnel, I have to re-consider if or what mods I might need to do to compensate!
1. Looking at the back half of the car, the clip slants down from the roof, and so I make the presumption that this will produce a low pressure area over the Clip, and thus, provided the engine bay is at a higher pressure, I assume that hot air will leave the bay through the oval holes in the top of the canopy. There isn't a very large area of venting going on here, but I again presume this is enough given other vents. Should this be bigger? But then how do we increase the pressure inside the clip to make this useful?
2. The side vents - now these are interesting... I don't know how efficient these are
a) with the engine bay bottom open, or
b) with the cladding I have in place?
Some have added side-scoops...but do these actually work? The theory I presume is that when in motion, the scoops collect air more efficiently, ramming more through the side vents.... Do they actually?
3. The big rear oval - I can guess again that there is a lot of low pressure behind the car, so any hot air passing through the engine bay, heated up by the exhaust bits and the engine, will readily flow out from this area, provided there is sufficient pressure created by other vents inside the clip. Again - what factors are in play here if we clad the underside of the car....
Any air-flow experts out there?
K
Edited by V8 Vum on Monday 24th October 11:26
Keith, simply using low pressure area's to extract or draw through the clip (from even flat/panel or flush intakes) is the way to go..
Big additional induction scoops will only produce drag and pressurize the rear clip (a disadvantage and usually countered by rear wing adjustment producing further drag ... Duh!!)
2-4 times extraction area to intake ratio works well (after heating air expands considerably and rises) ... there are many examples of both air and water cooled race set-ups being dialled in around these basics.... in a variety of machines.
The combination of light weight, aero efficiency and consistent running (hint temps) usually achieve best performance results.
Big additional induction scoops will only produce drag and pressurize the rear clip (a disadvantage and usually countered by rear wing adjustment producing further drag ... Duh!!)
2-4 times extraction area to intake ratio works well (after heating air expands considerably and rises) ... there are many examples of both air and water cooled race set-ups being dialled in around these basics.... in a variety of machines.
The combination of light weight, aero efficiency and consistent running (hint temps) usually achieve best performance results.
Keith,
Living in Spain I guess I have the best temp.testing laboratory available here (in the forum).
What I have experienced is:
- Flat underneath is good for aerodynamics in combination with a good front airdam design and a proper rear diffusser.
- Bigger air scoop on clamp may be good in running conditions.
- Extra louvres on clamp bring good results in terms of disipate engine bay temp.allowing the hot air to flow out.
BUT :
The temperature problems start each time the car stops with engine hot. At this point flat underside panels, large scoops, more louvres.....bring very small help.
But anyway...our Ultimas are midengined race cars (some with HiFi set) and race cars run hot "very often".
(sorry, I need to brush my english)
Cheers,
Living in Spain I guess I have the best temp.testing laboratory available here (in the forum).
What I have experienced is:
- Flat underneath is good for aerodynamics in combination with a good front airdam design and a proper rear diffusser.
- Bigger air scoop on clamp may be good in running conditions.
- Extra louvres on clamp bring good results in terms of disipate engine bay temp.allowing the hot air to flow out.
BUT :
The temperature problems start each time the car stops with engine hot. At this point flat underside panels, large scoops, more louvres.....bring very small help.
But anyway...our Ultimas are midengined race cars (some with HiFi set) and race cars run hot "very often".
(sorry, I need to brush my english)
Cheers,
Edited by srreck on Monday 24th October 14:23
Zo...Maybe we cut ein massive gert hole each side of the centre hump, and fit 2 humungous hi-power Pacet fans underneath that power up when the bay reaches a certain temperature?
Can't remember - but I think I experienced this arrangement when walking past a recently parked Lambo and got the fright of my life when a massive fan WHooshed into life!
Hmmm...sounds like a plan....
Can't remember - but I think I experienced this arrangement when walking past a recently parked Lambo and got the fright of my life when a massive fan WHooshed into life!
Hmmm...sounds like a plan....
Steve_D said:
Mounting a pair of fans in the rear grill are on my modifications list.
Sadly they will not be large as the exhaust exits and the gear linkage get in the way.
Even so they will not be efficient unless they are ducted as they will just draw air from around the side of the fan.
Steve
Maybe the fans should be mounted nearer the front of the clip at almost the highest point, with a partition separating the engine airscoop? It will only be on when stationary. I rather fancy this fanciful idea!Sadly they will not be large as the exhaust exits and the gear linkage get in the way.
Even so they will not be efficient unless they are ducted as they will just draw air from around the side of the fan.
Steve
A couple of rectangular vents on the top rear edge under the wing was the route I settled on... a very slight aerofoil section to them so even when driven at low speeds there would be extraction via the created venturi..... lots of it at high speed too.
A couple of small circular fans incorporated in adjacent top-surface flush vents to run via a stat when stationary, pulling out the rising warm air from the silencer/trans area etc.
A couple of small circular fans incorporated in adjacent top-surface flush vents to run via a stat when stationary, pulling out the rising warm air from the silencer/trans area etc.
I would think that the best and most relaible bang for the buck on reducing underhood or bonnet temps would be to coat your headers and exhaust with the best available materail. If the hot air is going out the back its sure as heck not getting into the engine compartment. Next up would be to mount the A.C. radiator in the nose like RATGTR has done, same idea, less hot air in. I have constructed a very good scoop to feed my Kinsler injection on my LS and have the data from the Motec that says this is a very important mod. Lee
ROWDYRENAULT said:
I would think that the best and most relaible bang for the buck on reducing underhood or bonnet temps would be to coat your headers and exhaust with the best available materail. If the hot air is going out the back its sure as heck not getting into the engine compartment. Next up would be to mount the A.C. radiator in the nose like RATGTR has done, same idea, less hot air in. I have constructed a very good scoop to feed my Kinsler injection on my LS and have the data from the Motec that says this is a very important mod. Lee
The idea is that the low pressure area at the back of the car causes the high temperature air to be 'sucked' out of the rear of the car. This is replaced by air entering the clam from the side grills (and from under the car) which in turn dissipates heat as it flows through the engine bay and is expelled out the back (constant mass flow rates etc).Can you please post a pic of your scoop.
The noble guys have done some really intresting work in to helping get air tomove through the engine bay. The best mod on them is to fit a much less drestrictive rear mesh and this alone is said to make a marked difference. They then tend to go for opening up the side scoops to try and feed more air in.
On the GTR you could look to add more vents in the rear clam (near the top intake) to try and vent any hot air out. Vent could possiable be added lower down beneth the rear opening to try and remove air.
The main problem with all this is without wind tunnel testing its all guess work! Also you have to remeber that although you might solve the aero problem in one areaa you might be creating another further down the car.
Chris.
On the GTR you could look to add more vents in the rear clam (near the top intake) to try and vent any hot air out. Vent could possiable be added lower down beneth the rear opening to try and remove air.
The main problem with all this is without wind tunnel testing its all guess work! Also you have to remeber that although you might solve the aero problem in one areaa you might be creating another further down the car.
Chris.
Didn't Racecar Engineering print a wind tunnel analysis of GTR in the past? I would bet Ted and Richard have access to it.
It would be nice to have an easily removable belly pan as a factory option (like the alloy firewall). Ideally it could be fastened to the square section frame rail with U-clamps eliminating the need to drill more holes in the frame.
It would be nice to have an easily removable belly pan as a factory option (like the alloy firewall). Ideally it could be fastened to the square section frame rail with U-clamps eliminating the need to drill more holes in the frame.
spatz said:
i see you removed the back mesh, which I am very close to do myself, i am tired of removing the clamp for simple things that can be fixed if the mesh would not be there or at least removable.
I removed my rear mesh as soon as I bought the car. It looks far better and lets heat out quickly, plus you can hide your rear view camera ontop of the gearbox rather than drill the bodywork.Dom
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