bonnet vents
10-16-2006, 12:20 PM
#31
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Originally Posted by drnick
dont forget the car was originaly an 86 with an engine driven fan for cooling - long since departed. im sure i can improve the fan installation to combat the heat more effectively and as a part of this i also wanted to aid heat evacuation, and i didnt mind cutting the bonnet on my aleady much modified 928. dont get me wrong, for a nice stock car i think this would definitely be the wrong aproach to cooling, but for a pseudo racer... 
On my 85 the stock fan was replaced with a used stock shrouded electric Volvo 15" fan. It draws 80 amps on startup and about 30 amps continuous. It uses 4 gauge wire going to a constant duty solenoid that is triggered by a thermostat Rob made custom stainless steel brackets that mount the fan to the radiator. According to Rob the Mustang Cobra guys use this and have no cooling issues. It has worked well for me even though this past summer temps only got into the 90sF a few times.
10-16-2006, 02:42 PM
#32
Rennlist Member
Thats the DB9, but thats the idea!
on the vanquish, the vents look to be close to the same, but obviously they dont have the downforce added cuts at the front of the hood.
Im now thinking of doing one of those instead . just two big slits and bend the hood down maybe right around the beginning of the intake manifold up front
caddy uses big slits over the hood for downforce too, as does the viper.
MK
on the vanquish, the vents look to be close to the same, but obviously they dont have the downforce added cuts at the front of the hood.
Im now thinking of doing one of those instead . just two big slits and bend the hood down maybe right around the beginning of the intake manifold up front
caddy uses big slits over the hood for downforce too, as does the viper.
MK
Originally Posted by Hacker-Pschorr
The Vanquish has ducts going from the exhaust manifolds to the hood vents. You can see them in the last picture sticking up next to the left throttle body.
Two Aston hood vents:
Two Aston hood vents:
10-16-2006, 02:45 PM
#33
Drifting
Thread Starter
rick, i did have a 16" single kenlowe fan mounted but thought id be clever and go for two 13" fans instead. it seems the single 16" prabably cooled the car just as well if not better and draws less current. i am probably going top remount it, especialy as it mounts from the front leaving more room for the centrifugal unit to fit (eventualy).
as fo the effectiveness of the bonnet vents i can confirm that the car runs at least 5 degrees centigrade lower now, it takes longer before the fans cut in at traffic lights and it cools off more rapidly with them on. no change in warm up time from cold either. you can visibly see the heat soaked air streaming out the top when its stopped at the lights with the fans running im pleased.
as fo the effectiveness of the bonnet vents i can confirm that the car runs at least 5 degrees centigrade lower now, it takes longer before the fans cut in at traffic lights and it cools off more rapidly with them on. no change in warm up time from cold either. you can visibly see the heat soaked air streaming out the top when its stopped at the lights with the fans running
im pleased.
10-16-2006, 02:56 PM
#34
Drifting
Thread Starter
mark check pierre martins thread on fat bully and see the slits he has put across his bonnet. the only problem i can see with them is the fact that the lack of depth below the hood before you hit engine will limit the size of the flap you can cut, also an upturned leading edge will help to direct the airflow over the vent and increase its performance.
the vents have definitely reduced the underhood running temps in my car as far as i can tell from a two hour run today ranging from motorway through to stop start traffic and the ambient temperature is typical for the last few days/couple of weeks.
as far as downforce is concerned im not clear which effect is most responsible - either; bleeding air into the flow across the top of the car , slowing the airstream down and reducing lift - or; reducing the amount of air going underneath and the disruption it causes to the undertray directed flow...
the vents have definitely reduced the underhood running temps in my car as far as i can tell from a two hour run today ranging from motorway through to stop start traffic and the ambient temperature is typical for the last few days/couple of weeks.
as far as downforce is concerned im not clear which effect is most responsible - either; bleeding air into the flow across the top of the car , slowing the airstream down and reducing lift - or; reducing the amount of air going underneath and the disruption it causes to the undertray directed flow...
10-16-2006, 03:47 PM
#35
Inventor
Rennlist Member
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I have a spare hood that I think about putting a large opening directly behind the radiator, with a duct attached to the radiator to direct it up and out. I also considered tilting the radiator for better flow.
The other concept I'm thinking of is to just move the hood back an inch or so (and/or raise the rear). This will create a gap on each side (and the front). Cover these gaps with mesh, or a line of mini outlets.
Check out the vents on the prototype cars:
The other concept I'm thinking of is to just move the hood back an inch or so (and/or raise the rear). This will create a gap on each side (and the front). Cover these gaps with mesh, or a line of mini outlets.
Check out the vents on the prototype cars:
10-16-2006, 04:16 PM
#36
Rennlist Member
both! the air going in and out of the radiator goes under the car as most sit stock. this just adds to needless lift. routing the air out the hood, puts more air on top of the car, helping with downforce up front. as you can see from the 928 aero curves, we naturally have a vacuum on top of the hood. thats not good for down force (ie lift) so, by routing air to that area via a vent, you can increase pressure up top, take it away from underneath. a double whammy. Its why all the real race cars have it.
MK
MK
Originally Posted by drnick
mark check pierre martins thread on fat bully and see the slits he has put across his bonnet. the only problem i can see with them is the fact that the lack of depth below the hood before you hit engine will limit the size of the flap you can cut, also an upturned leading edge will help to direct the airflow over the vent and increase its performance.
the vents have definitely reduced the underhood running temps in my car as far as i can tell from a two hour run today ranging from motorway through to stop start traffic and the ambient temperature is typical for the last few days/couple of weeks.
as far as downforce is concerned im not clear which effect is most responsible - either; bleeding air into the flow across the top of the car , slowing the airstream down and reducing lift - or; reducing the amount of air going underneath and the disruption it causes to the undertray directed flow...
the vents have definitely reduced the underhood running temps in my car as far as i can tell from a two hour run today ranging from motorway through to stop start traffic and the ambient temperature is typical for the last few days/couple of weeks.
as far as downforce is concerned im not clear which effect is most responsible - either; bleeding air into the flow across the top of the car , slowing the airstream down and reducing lift - or; reducing the amount of air going underneath and the disruption it causes to the undertray directed flow...
10-16-2006, 04:38 PM
#38
Defending the Border
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Rest In Peace
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Rest In Peace
I've been looking a while now but I can't find the thread about under hood temps where Laust Pedersen of the 951 forum achieved increased cooling just by removing the weatherstrip between the firewall and the hood.
Given the width of the 951's hood, I can imagine some annoying vibration being created with it removed, but the 928's hood may be better suited for this.
David Floyd did a nice set of stamped louvers under " Hood Louvers are in( More pics added )". A 968 Turbo RS vent may fit nicely!
Given the width of the 951's hood, I can imagine some annoying vibration being created with it removed, but the 928's hood may be better suited for this.
David Floyd did a nice set of stamped louvers under " Hood Louvers are in( More pics added )". A 968 Turbo RS vent may fit nicely!
Last edited by ibkevin; 08-01-2013 at 01:07 PM.
10-18-2006, 04:30 PM
#39
Drifting
Thread Starter
one side effect i have noticed is that the warm air coming out of the vents flows up the bonnet and into the hvac intake so i get luke warm air when set on cold. this is ok now heading into winter but i will have to figure something out for summer!
10-18-2006, 11:20 PM
#41
Burning Brakes
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found a carbon fiber scoop site
I was thinking of mounting this 18" x 10" carbon fiber heat dissipating vent more towards the rear of the hood and painting it to match the cars color.
Its the same exact design as the orange car, but 5" wider vent and I am only thinking of using one of them.
I found them on the site, www.carbontrix.com - no affiliation.
Its the same exact design as the orange car, but 5" wider vent and I am only thinking of using one of them.
I found them on the site, www.carbontrix.com - no affiliation.
10-19-2006, 03:47 AM
#42
Drifting
Thread Starter
warren those are the vents i am using, as you say mine are 13" wide each. i was originaly thinking of the size youve shown here mounted centraly but after cutting out some black coloured paper and laying it on the bonnet i went for two seperate vents.
10-19-2006, 10:02 PM
#43
Burning Brakes
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I like the way yours looks, but you have a more bolder color and it works for your car. I may end up with the two vent layout too. Anybody have thoughts on that? The 968 single vent look or the drnick callaway look?
10-19-2006, 11:32 PM
#45
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If the problem is, as implied, overheating due to poor air flow, one of the first things to check is recirculation - hot air from behind getting back to the front of the radiator. A missing bottom cover (belly pan) can cause this...
In addition, it would be interesting to speculate on whether you will run hotter if you dump the radiator air out the bonnet, or if you route it over the engine and exhaust on the way out the bottom.
Given the pressure map, I would not expect lifting the rear of the bonnet to help any - instead, I would expect air to flow back under the bonnet and down.
Even the factories sometimes have problems. BMC discovered far too late that the new outlet vents on the bonnet of the MGA 1600 Twin-Cam were actually inlets...
And, as a matter of interst, we can thank Roger Penske for starting all of this, on the Zerex Special.
In addition, it would be interesting to speculate on whether you will run hotter if you dump the radiator air out the bonnet, or if you route it over the engine and exhaust on the way out the bottom.
Given the pressure map, I would not expect lifting the rear of the bonnet to help any - instead, I would expect air to flow back under the bonnet and down.
Even the factories sometimes have problems. BMC discovered far too late that the new outlet vents on the bonnet of the MGA 1600 Twin-Cam were actually inlets...
And, as a matter of interst, we can thank Roger Penske for starting all of this, on the Zerex Special.