Installing bonnet vents to reduce engine bay temps

[TCJBOLDIE]

Has anyone done this and what were the results ??

Am considering installing them to help with reducing temps at the track as the IC pipe that is in the engine bay gets very hot but the outlet that is in front of the radiator is quite cool compared to the inlet side.

If I fit them they would be positioned with the leading edge just behind the radiator which would appear to be best place to position them after looking at Evos and Cosworth turbos.
The pipework is ceramic coated and have thought about winding on some heat reflective tape to help against heat soak.

Constructive thoughts and actual experiences appreciated

 

[obi_waynne]

You need to be careful not to upset the flow through the engine bay. Vents can cause turbulance or direct the cooling air away from where it's needed.

Personally I'd only add one for air intake purposes, but I'm not really going to be at the cutting edge of engine tuning anyway. Otherwise I'd buy a pre vented bonnet where significant R&D development has gone into it.

We did an article on this some time ago, it probably needs updating a little now but it gives an overview.
https://www.torquecars.com/tuning/bonnet-intake-vents.php

 

[old-git]

The IC inlet pipe is hotter than the outlet pipe? That is good as it shows that the IC is working

If you wrap the inlet pipe this will trap the heat in and raise the IC outlet temp.

The air pressure over a bonnet varies. Generally it is low over the front and high at the rear. Therefore place exit vents at the front and intake at the rear. Placing a vent in the wrong pressure area can result in the air flowing in the opposite direction to what was intended!

A rear facing vent located behind the IC in a low pressure area with a Gurney flap attached to the lip will draw air out pretty well. If you have room to fit a deflecting plate to the underside of the vent that will direct more air out.

I am suggesting this, of course, without knowledge of your engine layout and guessing that you know this anyway

 

[TCJBOLDIE]

You need to be careful not to upset the flow through the engine bay. Vents can cause turbulance or direct the cooling air away from where it's needed.

Personally I'd only add one for air intake purposes, but I'm not really going to be at the cutting edge of engine tuning anyway. Otherwise I'd buy a pre vented bonnet where significant R&D development has gone into it.

We did an article on this some time ago, it probably needs updating a little now but it gives an overview.
https://www.torquecars.com/tuning/bonnet-intake-vents.php

Obi I am wanting to reduce under bonnet temps by drawing hot air out thru the vents so the vent louvers would be facing rearwards. IIRC that is the way the Cossie RS Turbos have the vents installed.

There are no vented bonnets made for this model The vents in the early JA bonnets were cosmetic and not functional BUT I have opened them up.

I do have a cold air intake pipework from the air dam opening directed at the filter.

I have already read the vent article.

 

[TCJBOLDIE]

The IC inlet pipe is hotter than the outlet pipe? That is good as it shows that the IC is working

If you wrap the inlet pipe this will trap the heat in and raise the IC outlet temp.

The air pressure over a bonnet varies. Generally it is low over the front and high at the rear. Therefore place exit vents at the front and intake at the rear. Placing a vent in the wrong pressure area can result in the air flowing in the opposite direction to what was intended!

A rear facing vent located behind the IC in a low pressure area with a Gurney flap attached to the lip will draw air out pretty well. If you have room to fit a deflecting plate to the underside of the vent that will direct more air out.

I am suggesting this, of course, without knowledge of your engine layout

Steve thanks for your input but I may have not explained myself as clear as possible, sorry.

The inlet pipe I mentioned is the IC outlet / TB inlet pipe that I was considering wrapping in a heat reflective tape to resist any temp increase due to hi engine bay temps and to assist getting the cool IC air into the manifold with minimal temp rise.

My motor is a North South conventional RWD layout and the IC is mounted in front or the radiator in place of the AC condenser.

 

[old-git]

Ah, right. Wrapping this pipe is a good idea, especially if it's aluminium.

Any photos of the engine bay/IC layout?

 

[obi_waynne]

I would imagine that venting the heat from the radiator and intercooler would be priorities here. So it makes sense to place them just behind these areas with a deflector to pull that hot air up.

Wing vents can then be added to pull cooler air into the engine bay from the sides. (again depending on the car and application and a host of other things.)

 

[davalav]

No bonnet?

What about running bonnet raisers? You fit them up by the hinges and it raises the rear. So as you drive, the hot air pushed out up the wind screen! Great for when its cold.

 

[obi_waynne]

No American car has a bonnet interestingly! They do come with a Hood though

 

[old-git]

No bonnet?

What about running bonnet raisers? You fit them up by the hinges and it raises the rear. So as you drive, the hot air pushed out up the wind screen! Great for when its cold.

The trouble with this, Dave, is that the opening is in a high pressure area, so you can actually get air being pulled into the engine bay rather than out. This is why manufacturers place the interior heater intake at this location

Apart from that, it also looks naff................IMO

 

[old-git]

No American car has a bonnet interestingly! They do come with a Hood though

No boot, either.

 

[crowley]

This is interesting, I'm might eventually ad vents the the drift demon. If for nothing ells then just to make it look more Maaad.

 

[old-git]

You run the risk of falling into the AFANS class of vehicle

 

[TCJBOLDIE]

All Fart And No S##t
Did I get the correct interpretation

 

[old-git]

Yes

 

[davalav]

The trouble with this, Dave, is that the opening is in a high pressure area, so you can actually get air being pulled into the engine bay rather than out. This is why manufacturers place the interior heater intake at this location

Apart from that, it also looks naff................IMO

Oh, I didn't know that! I figured it was a good location as it was more or less at the front! Thanks TCJ for the info.

 

[TCJBOLDIE]

Well I have fitted a pair of Cosworth copy vents where they did not affect the structural integrity of the bonnet and have colour matched them with rattle can paint and can report that on a 120k test drive yesterday on a 30deg + day the temps were 75-78 deg on the highway and backroads so will report on the track day temps soon.

 

[SLEEPER]

Rrather than fitting bonnett vents I fitted a custom made cold box screened from the exhaust and turbos by kevlar panels covered is gold reflective material . The panels are shaped so that when the bonnett shuts it seals at the top with door seals cut to size.
Air is ducted through the nismo bumper vent directly into a chamber via aluminium trunking . this is where the filters are , air can exit down into the wheel arch .
None of this is for pressurising the air itself , it is simply all about keeping cold and hot apart .

 

[TCJBOLDIE]

Oh, I didn't know that! I figured it was a good location as it was more or less at the front! Thanks TCJ for the info.

I might add that raising the rear of the bonnet would be fine for low speed 4x4 off road situations due to almost no airflow/speed over the bonnet so the radiator fans would be able to push hot air out. IMO

 

[TCJBOLDIE]

Brian nice set up
I have my filter mounted to the side and clear of the radiator with cold air piping from the front spoiler that directs cool air onto the filter at speed.

I also have the ceramic coated pipes from the turbo and from the cooler to the TB gold heat reflecting wrapped as well and have installed the bonnet vents that will,at speed reduce the under bonnet pressure,thereby increasing the airflow thru the IC and radiator and reduce the hot engine bay temps.