Bonnet vents, Yay or Nay?

Iamzod

Iamzod

Iamzod

Soldato
Joined
7 Dec 2002
Posts
4,075
Location
UK
I'm looking at putting some form of ventilation into the bonnet of one of my cars to get more heat out of the engine bay, this is for function rather than any cosmetic effect.

The thing is, do they actually make all that much difference? And if so is there a best way of achieving said ventilation without it looking stupid.

Is there a best place on a car bonnet for vents to be fitted? For example are they best as far back as possible or nearer the middle?
 
lets start with why you think you need to get more heat out from under your bonnet?
 
I'd say put them where you're going to get more cold air into your intake as a result of doing do.

I don't suppose they make much practical difference if you're not 'charged in some way and your intake temps are going to cause detonation due to heat soak and compression increasing the air temps?

I have no scientific basis for that, just that most cars don't have vents, but any seriously 'charged car will have an intercooler to reduce intake temps.
 
I imagine the only kind of vent that actually works is a scoop like you'll find on impresas or the likes of a front mounted shaped intake like you'll find in the mps Mazda 3 and these will target (I assume) the intercooler
 
Haze said:
lets start with why you think you need to get more heat out from under your bonnet?
Click to expand...

Because it doesn't have the original engine fitted and the width of the new engine (gone from an OHV engine to Quad cam) doesn't leave any room for a battery or an airbox meaning I have to run a cone filter about 10 inches from one of the exhaust manifolds.

This and I am running a radiator that is smaller than the donor cars radiator, I have binned the standard viscous fan for a high powered electric unit, but all that heat only has under the car to go to and through the tiny panel gaps down the sides of the bonnet.

If it won't help then I won't do it as I don't want to deface a good bonnet for no benefit.
 
You'd probably be better trying to insulate the filter from the exhaust heat and run some sort of feed to it.....somehow

The rad should be directly in the airflow anyway?
 
Beechdean_Aston_Martin_Vantage_GT3-021.jpg


That kind of setup will be effective, a shroud from the front bumper to the radiators, then from the rad up to the bonnet vent.

In your situation it sounds like you just want a bigger radiator though.
 
rodenal said:
I imagine the only kind of vent that actually works is a scoop like you'll find on impresas or the likes of a front mounted shaped intake like you'll find in the mps Mazda 3 and these will target (I assume) the intercooler
Click to expand...

Yup on the Mazda's they direct the air to the TMIC.
 
Iamzod said:
The radiator is, but the cooling pipework & expansion tank aren't, I was going to heat wrap the manifolds but have read about it causing fires?
Click to expand...

Depends entirely on the quality of the material you use. Heatwrap will help reduce intake temps, but not drastically. A pic of the engine bay layout would help this situation though.
 
Friend had them on his scooby... you'd be amazed at how much hot air escaped, even I was surprised after mocking him for having them
 
bJN said:
A pic of the engine bay layout would help this situation though.
Click to expand...

Unfinished but just wiring to tidy up, yes it needs a heat shield around the filter but that is only going to protect it from radiative heat I would presume.

Besides, the cooler the engine bay the better, right?



 
Timing/fueling will help it run cool if set up correctly.
clean out the water ways in the block, they will be old and full of crud.
re-core the rad
better fan
better mix of coolant/water

Then start cutting holes in the car :D
 
That really doesn't look bad to me at all from the pics. In terms of the filter, it looks like you should be able to run an air feed straight to it ?

The rad does look a bit undersized in there mind, but even so does it actually create an issue or are you anticipating there being a problem? Would more cores help? Looks like there's room
 
Last edited:
Best place for evacuation depends on car design but is generally the very front of the bonnet, or the rear corners near the windscreen. Everywhere else is unlikely to have a practical pressure differential.

From the pic above I would go with vents in the far corners, which will likely minimise stagnation from around the ancillaries (assuming that's the issue).
 
You must log in or register to reply here.
Back
Top Bottom