gravelexpress

just done this (dont ask why). has anyone else done this it cant cause any problems can it?

Attu

My only worry is that the holes are over the air flow sensor and fuse box, Ok it it didnt rain all the damn time but as we live in the UK (presuming you live in the UK that is ) its all ways bloody raining

Andy

Scott.T

iTrader: (2)

I normally remove them for the summer months, as it helps when stuck in the holiday traffic.

refit them over winter tho' to stop too much water getting through...

dhorwich

Hi,

I thought it would be a good idea a bit back but found out that under bonnet temps increased because heat from the exhaust was been drawn up into the engine bay.... si i put em back on...

Dan

gravelexpress

thanks for the sound advice chaps..

(i took them off because of all the leaves and stuff stuck underneath.... then thought ..they look rubbish anyway)

gravelexpress

oh .. ive just seen your post Mr Horwich,

and i thought it would help the cooling effect... how did you discover the adverse effect?
so i gather it could damage the car?

Alberick

I actually thought too it would draw hot air out, as I'm having the big WRC type outlets (not the 22b ones).
How could the exhaust temps be drawn up when driving?
On hot days, when I stop the car with running engine and the fan kicks in, I can feel loads of hot air being blown out of the engine bay through the outlets.

Dan, I would alos be interetsed how you found out that under bonnet temps increased?

Thanks,
Ramon

dhorwich

Hi,

Someone else on here also noted it.... he did actual under bonnet temp readings... i have an induction kit (blitz SUS) on my car and found if i took both vents off and went for a drive, no traffic just a straight drive and opened the bonnet up straight away the induction kit felt hot to touch even with a cold air feed.... when i put the covers back on it was cool.... and didnt feel that warm...

The air flows through the front bumper and needs to escape from somewhere usually with the vents on the air just passes through the bumper, rad e.t.c... and as hot air rises with the vents covers off the air is drawn up throught the vents from the air passing under the car which is heated up from the exhaust manifold... thats what ive read....

The only advantage is like someone mentioned is sat in traffic the hot air can escape...!!

I was all for this simple mod but decided it was not such a good idea when you have an induction kit fitted.... because the kit is right near one of the vents and the hot air was rushing past the air filter on its way out of the vent...

Dan

harvey

iTrader: (48)

Dan: I think you have seen a previous post where I gave considerable info on experiments I did on removal of one or other or both blanking plates.
Do not do it. To my surprise the biggest temp rise was with drivers side only removed.
I measure temps at throttle body and ambient on an on going basis. You can repeat this experiment yourself with a min/max horticultural thermometer(cost about £10 from B+Q or some gardening shops)
The results surprised me as there was an under bonnet temp increase of 6-10cent in the vicinity of the air filter while on the move. I also found the coolest under bonnet area of relevance to me was just behind the driver side headlight.
I repeated the experiment several times to satisfy myself that my initial findings were correct. (Not done any more experiments since the Doberman ate the thermometer. Glass and mercury has given it a very mean streak)

dhorwich

Thanks harvey... you were right..!!!

Dan

gravelexpress

oh dear....
best put them back then

Trout...

MMMM - just fitted an FMIC kit and you have to remove them otherwise the pipes won't fit!

Might just get a scoopless bonnet now!

Trout

gravelexpress

thats a good point..
harvey u have a FMIC are you taking the scoop off or blanking it?

paul corrigan

what air filter are you using ? if you are using an induction kit where the filter in the engine bay leave them on as it will draw air past the filter not leaving much for it to suck under heavy driving
i was told to put a cold air intake inside the intercooler scoop on the bonnet there is about 4 inches of space where it is blanked off and run a pipe down to the filter

Trout...

Paul,

the area in the intercooler scoop is not in fact blanked off - it is vented and specifically designed to cool the turbo!

It is all swings and roundabouts - in my car I had a big pipe feeding up from under the indicator (where the orange plastic grill bit was) onto the induction kit.

Trout

PS You can off course get bonnet scoops that drive the air in and stop all the sucking

gravelexpress

funny that trout .. when i was looking at the grilles it looks like you can face the louvres forward to create a positive force to the engine bay.

(i never thought this thread would cause such a debate)

What is the origin of the grilles? I have only seen them on cosworths and subarus. If you look at the WRC it has really large holes (none louvred) where the grilles are. Thet cant be purely cosmetic can they??

Scott.T

iTrader: (2)

The Subaru is the only car I have had that actually blanks off the bonnet vents.

Previous cars which include Cosworths and RS Turbo's did not blank-off. Which leads me to believe that the RS Vents served a purpose, yet the Subaru ones are just for looks.

With the Cosworth Vents you could get you fingers through them, so letting water through can't really be an issue.

harvey

iTrader: (48)

When I found to my surprise that opening the louvers caused a temp increase I concluded that it was because the design intends air to flow in through the radiator and other frontal areas especially behind the headlight, over the engine and turbo and out down the gearbox tunnel. Opening the louvers disturbs this flow and there may be a low pressure area above the slats.
Trout can you put flat plates back on to blank off?
When I fitted my APS FMIC + Cold Air Kit it did not interfere with the louvers. I was going to remove the scoop. Bettr aerodynamics = more absolute velocity.
Jonny Gav bought the TMIC and against my better judgement he persuaded me to let him have the steel pressing assembly that fits in the underside of the scoop.
Temps were 1-3c over amb. but then went to 6-10 over. No prob. I thought. Off came the scoop. Even worse. Blanked the hole. Worse.
Did various experiments including blanking different parts of the scoop mouth.Best result was with scoop in position fully open.
Had something else gone wrong? Still 6-10c over.
Bought another pressing which wrankled me. Fitted.
As happy as pie. Temps Amb +1-3c
Hope this helps others to improve their motors and not waste an evening and a bit and the uncertain concerns I experienced.

Charlie H

I believe the purpose of the vents was to do with Group A rally regulations. For homologation purposes, a rally car could not have holes in the bonnet that the road going version didn't have, hence the blocked off vents. Not a problem now with WRC regs hence no vents on new models. Still would have thought it would be better without them, otherwise why did ( and still do) the rally cars all have them? Surely they wouldn't have removed them if underbonnet temp actually increased

gravelexpress

oh god dare i ask.....
i want to take off all the sound proofing/insulation stuff from the underside of the bonnet...

what will this do...

yours nervously
mark

harvey

iTrader: (48)

Mark: Why take it off? Does not weigh a lot unless wet. No experience of this but it will make an already loud car louder.
I wonder if temperature above the turbo on the bonnet paint work should be considered?

gravelexpress

Harvey i am sort of working on a little bit of a project at the moment.. i will send you a mail

Markus

I've not got blanking plates on mine (also MY94) and never had a problem, however, I have a set of Stuart Knight's mini vent scoops, which mean that when the car is sitting getting rained on the water does not go down, as it normally would do.

pics of the scoops can be found here

RICH WILD

Hi,

I took the sound deadening off mine as I had seen a lot of the Ali bonnets had none.

It looks better and there are no issues with heat, just a lot more engine noise. I did it for looks really as I'm not bothered about noise, but if you are, don't do it. If you want to save weight, get an Ali bonnet like I have now

Cheers

Rich

David_Wallis

Whats your project GravelExpress??

David

gravelexpress

yeah ive got the ally bonnet and noticed a pic of an RA with the deadening taken off. mines all tatty and want rid of it.
simple project - WRX to STI (without the expensive bits!!)