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View Full Version : bonnets: just cosmetic?



disciple
25-12-2005, 11:22 AM
hey i was wanting to know if anyone has actually tested any of the vented hoods available for legnums/galants or if it's just for show. my brother and i are working on a few vent ideas to get rid of the insane heat from the rear turbo and so far we're about half-way through testing the standard hood, as in taking a heat sensor and getting readings from 24 engine points, hard work when each test is a 5min run, but he's a pro and we wanna do it right. does anyone have specs at all? a place here in hams was selling glass evo bonnets(with the big wide duct) and he cracked up when i aked him about it. basically i don't like the look of any of the bonnets i've seen, so we'll try and make one that works, even if it's not too pretty. we should be done testing by early feb and by then i'll at least have one on mine. if anyones interested or got any info holla.

You See
25-12-2005, 01:30 PM
Sounds promising! ...I'll be interested if the finished product looks the sh!t and also has a purpose! ...PICS PLS!

Rossco Type-S
25-12-2005, 07:33 PM
A vent for the Pod filter may help too?

bradc
25-12-2005, 09:36 PM
My bonnet vent helps take out heaps and heaps of heat from the front turbo, I've measure air at over 90C coming out of there.

I think that an evo 8 style bonnet vent might be a good idea for the back turbo, placed right at the back of the bonnet. The other option might be a subaru style intercooler intake, but rotated 180 degrees so air come out of it when driving fast.

disciple
25-12-2005, 10:39 PM
that's what we're thinking at the mo, a big wide vent at the back but we want to hide it, so i've got a late model legnum bonnet sitting there and they have a taller bulge so we can cut down(cos my leggies 96), as for the later ones, we'll see when we get there. **** it's hard to do a decent test though! because we wanna sell etc. we want proof that it works, so we're gonna have to spend the next couple of months just testing the origional, before we even get to the prototypes, i guess by then most of the work will be done and testing the types will be easy. still looking for specs on available bonnets guys.

OSiRiS
26-12-2005, 07:36 AM
Check out this page:

http://www.revozport.com/webpics/ptg%20vent%20hood/page_01.htm

btw, isn't this thread in the wrong forum?

Nick Mann
26-12-2005, 10:44 AM
Moved to a more appropriate forum.

Interesting ideas, looking forward to seeing the results.

OSiRiS
26-12-2005, 10:46 AM
bradc how much was your bonnet and where from? I'll be getting one shortly. But I have an idea ;)

bradc
26-12-2005, 01:19 PM
It was from Alfred at speedfactory and it was $750. Tell him you heard about it from me ;)

michaeli
04-01-2006, 08:00 PM
Hi Guys,

Looks like a very interesting project, definately interested in the results!!! :thumbsup:

I read up on aerodynamics over bonnets and it basically said that:

closer to front of car, air will come out of engine bay

closer to windscreen, air will go into engine bay

This means that where BradC has his vents, the air will travel through radiator, intercooler and front turbo, then out of the engine bay

If you have a subaru vent at the back of the bonnet, either way, the air will travel downwards into the engine bay and into the top mounted intercooler


Assuming all of the information that i have read is correct, then that is exactly why mitsubishi vents are at the front (front mounted intercooler) and the subaru ones are at the back (top mounted intercooler)


One could deduct that there is room for both types of vents in our cars to cool both front and back turbos, one could also deduct that the best place for our air intakes are at the back of the engine bay, where there is a natural air ram effect.....


Aerodynamics have been discussed on this forum before, do a search, see what comes up....

Good luck!!!

Regards,

Mike

bradc
04-01-2006, 08:10 PM
Did we ever get SGHOM to attach streamers to his bonnet to see if the air was sucked down on his vents that he had at the back of the bonnet?

Wouter
04-01-2006, 09:03 PM
Did we ever get SGHOM to attach streamers to his bonnet to see if the air was sucked down on his vents that he had at the back of the bonnet?

Will streamers actually prove anything?, to test it properly the car would have to be moving, and then the wind hitting the car from the front will probably be stronger than any force made by the air entering or leaving the engine bay via the vents.

SGHOM
04-01-2006, 09:10 PM
decide for yourselves ??
http://www.clubvr4.com/forum/showthread.php?t=10826&highlight=steady+hand

when staitionary in traffic, the heat haze can clearly be seen from the rear vents. /yes

Kenneth
04-01-2006, 09:14 PM
Will streamers actually prove anything?, to test it properly the car would have to be moving, and then the wind hitting the car from the front will probably be stronger than any force made by the air entering or leaving the engine bay via the vents.

Yes they will. if you hang the streamers over the vents, obviously if the streamers were pushed into the vent then you have more pressure on top of the vent than underneath. in this case, air would be entering the engine bay. the reverse is also true.

The idea behind the aerodynamics is that air accelerates over a curved surface (front of the bonnet) creating a LOW pressure zone. if the air pressure inside the engine bay is higher than this, then the air will move from the high pressure engine bay out to the low pressure on the bonnet.

The engine bay gets a fair bit of pressure as you have an air dam at the front that is designed to force air through the heat exchangers. unfortunatly if the pressure in the engine bay at any time matches the pressure at the air dam, you will get no flow through your heat exchangers and thus they are almost useless.

if you are standing still and radiating heat out through your vents, thats a different story.

Kenneth
04-01-2006, 09:25 PM
decide for yourselves ??
http://www.clubvr4.com/forum/showthread.php?t=10826&highlight=steady+hand

when staitionary in traffic, the heat haze can clearly be seen from the rear vents. /yes

I would expect this to be good for drag racing... while stationary (or nearly so) between runs you would get good convection from the heat of the turbos.

Track times and general longer trips I would expect this to be bad. if the air DOES go down into the engine bay, you will be increasing the engine bay pressure and reducing the effectiveness of the front heat exchangers.

My money would be on the air going into the engine bay area when you are in motion (and at a reasonable speed)

Ollpen
05-01-2006, 04:46 AM
I had the CF EVO on my old Bitchie, and it didnt help crap.

michaeli
07-01-2006, 10:38 PM
Did we ever get SGHOM to attach streamers to his bonnet to see if the air was sucked down on his vents that he had at the back of the bonnet?

If you look on google at bonnet aerodynamics you will see that what I have said above is supported when the car is moving above 20mph...

If stood still, in traffic or at traffic lights, you will see heat escaping through the top of the vents at the front and back, as heat rises...

/Steeringw :smug: :thumbsup:

I'd tried to find some info where one guy did the streamers on his bonnet thing with pieces of wool.

he then did cut holes in several bonnets and measured the effect inside the engine bay and as previously stated by Kenneth the pressure was equalized with just vents at the back causing heat issues as air flow was non existant.

I think the best way is to put spacers in the back of the bonnet to raise it slightly, Air to back turbo and over top of engine, and cut vent just behind the radiator and fans which will aid the air from the front of the car to escape and increase dissapation..

But above all MAKE IT YOUR OWN DESIGN!! That's the fun part!!

OSiRiS
08-01-2006, 11:34 AM
I think the best way is to put spacers in the back of the bonnet to raise it slightly, Air to back turbo and over top of engine, and cut vent just behind the radiator and fans which will aid the air from the front of the car to escape and increase dissapation..

I put a few washers in there to space the bonnet up where it hinges and removed the rubber seal.

My goodness has it made a difference. Even with the car parked up for 30 minutes I can still feel hot air pouring out the gap I have just created. I wonder where it all went before I put the washers in /Hmmm

You See
08-01-2006, 12:04 PM
You can get spacers from here (http://www.redlineperformance.co.nz/main.cfm?id=2&pid=647) tho I using washers would save you 40 bux! :thumbsup:

OSiRiS
08-01-2006, 11:04 PM
My set of washers only cost $3.99 from the Warehouse lol :P

Kenneth
09-01-2006, 12:05 AM
... I wonder where it all went before I put the washers in /Hmmm

It sat there keeping your engine all cosy and warm.

My personal opinion is that in winter a little bit of heat isn't too bad. If I leave my car for 30mins and come back I don't want my engine cold.

However heat-soak isn't good for rubber components and stuff... I like the idea of having a way to close the vent (like on Pescha's bonnet where it has an insert you put in) for when its cold in winter, but being able to remove it for summer.

bonnet spacers sounds like a good idea, you can then adjust it as per your needs / weather conditions.

As my step father is an enineer I should be able to get some spacer plates made up... what is a good thickness?

disciple
22-01-2006, 10:31 AM
spacers or washers to raise the bonnet are the best and most cost-effective way to release heat from the engine, we found that out real quick. like michaeli described you end up with air rushing into the back of the engine bay when moving at speed cooling it down nearly 20 degrees in some of our tests, but it looks really goofy and i can't get around the look so we're still at it.