Steviem

Hey,

On my N-reg WRX jap import the vents on the bonnet have a sealed back plate, meaning there is no air getting in through them. Should it be like that?

What benefits would it gain if the back plate was replaced by say, close nit wire mesh, to stop stones getting in and at the same time allowing air to the filter, as the driver side one sits directly above the cone air filter. Would this effect the set up of the air flow?

Thanks,

Sweet as!!!!

bryhp

the plate is there to stop water getting in. If you run an induction filter the water from rain or spray would end up killing your maf sensor. There is no real advantage to taking out the plate just more hassle

Brian

adzer

iTrader: (13)

i knew they had the plates to stop the water but why did they put vents on if they had no function

bryhp

just for looks. fine with standard box to open it up but no gains, maybe with dry day and induction kit you may get some cooler air.

APIDavid

iTrader: (4)

1, The under bonnet aerodynamics are correct with the blocked off vents in place.

2, Letting air in also allows rain in and it is possible to do 600 - 800 quids worth of damage to the relay panel electronics, just by the suspension turret, if you get a decent amount of rain or carwash or hose or jetwash water in there.

Convinced to leave them on ?

There, don't you feel better now ?

David APi

Steviem

LOL, yea well convinced

Many thanks for the info guys, ill leave it well alone. £800 a could do without thankyou

Sweet as!!

joz8968

iTrader: (13)

I fitted the 22B-style bonnet vents and have kept the backplates fitted for the exact reasons that APIDave has sited. Common sense really.

Also, as a footnote (and unless I'm mistaken) the vents were put in by Subaru for the homologation of their 93-96 Gp.A spec. world rally cars, where they were indeed fully open to help the great underbonnet heat to escape...

harvey

iTrader: (48)

Exactly as Joz and David said.
The vents would let air out and homologation.
In tests I actually found under bonnet temperatures rose by an average 6 deg.C with the vents removed.

joz8968

iTrader: (13)

harvey, are you saying that with the backplates, or indeed the whole vent assembly, removed, the underbonnet temp increased by 6deg?!!!

If so, would this be because the open vents have reduced the air pressure differential between the air entering, and the air exiting, the engine bay, and as a result this had a detrimental effect on the underbonnet temp., because the air was more static?

If not, what would be the explaination?

andyxros

took mine off last year and no diffrence, plus (and a big plus) it miss fired like mad for first 10 mins of warm up due to water/damp dripping on to ht leads at plugs as there is a hole in the plate to divert this. put them back on and no misses since, keep them on nothing but trouble imho...

kyah710

iTrader: (10)

This is a very interesting topic! I have had the vents open on mine since I purchased it 2 years ago and no problems so far.

If closing the vents really does reduce air temps then as I have a fmic I may as well get an impreza sport bonnet. What are the views on turning the main bonnet scoop backwards facing the windscreen to let hot air out if NOT running a top mount?

dazdavies

iTrader: (22)

I had my vent open on mine (was ruuning a big K&N on my rotated GT30R)

Nothing but hassle. If it rained as soon as the car came on boost it sucked the water in and missfired like hell. They were quickly put back on.

As for the bonnet vent with an FMIC look at the vent on RCMS's Gobstopper.

Four or five vents facing the windscreen letting hot air out.
Does, the job, looks awesome but quite expensive.

harvey

iTrader: (48)

That is exactly what I found. With the vents open, underbonnet temperature was higher.

When Subaru designed the car, the intention was for air to flow in from the front, over the engine and down the transmission tunnel aided by air coming throught the bonnet scoop and TMIC. When the blanking plates are removed the effect is to suck air out of the engine bay, not to let cold air in. I think this disruption effects the smooth flow of air over the engine and down the transmission tunnel.
I have also noticed that when fitting a six speed transmission to a five speed car, the undrbonnet and running temperature will increase and this must be because the bigger bell housing takes up much more space in the transmission tunnel.

joz8968

iTrader: (13)

Yes, I thought that must be the reason.

There you go folks, keep those backplates well and truely ON! ... All pros; no cons.

fabulous555

I take the one above my induction kit off but only on a dry, rainless day.

ginger321

Hi
I fitted spacers under mine so there is a small gap around the edges to let some hot air out. Any water still draines through the hole in the cover. Been like that for 2 years without a problem, cars been jet washed etc with no issues - Im just running a standard airbox though.
In heavy traffic u can see a heat haze comming from them in winter. Probably not made one blind bit of difference to temp under bonnet but I like to think it might!!!

Wurzel

iTrader: (1)

I have been running my MY00 classic with the vent backplates removed for the last 8 years with no problems what so ever! Never had any missfires or water loggied filters blah blah, and it rains like a biatch here however I am thinking of refitting them again purely because API suggested I do so. I will refit them at some stage when I get round to it.

Gregsti01

iTrader: (1)

Scooby did not spend millions on design as a job for the boys,over the years of car modding I found that air ducting is very complex in the middle is called compromise I have argued many times about Newage under tray.If you leave it off you screw up the air flow big time,under body temps increase up to 8 deg

joz8968

iTrader: (13)

Indeed. harvey measured the temp increase (when car's in motion) with the vents removed - see above ^^^

richscoobylove84

nope there comin off lol thanks mate

NOSSY_89

Was running a Pipercross induction kit on my classic. Took the plates off to open the vents in the summer months but put them back on when it was snowing etc.

APIDavid

iTrader: (4)

P1Drifter

iTrader: (7)

go for it mate, people like you keep garages in business, obviously David and Harvey have no idea what their on about

NOSSY_89

I would have to agree with the above comments. I know I didn't have covers on mine all the time but like I said that was summer and it was fine no issues at all with it. But this is the time that I would have put them back on. Mate its winter. Think of the ice, water etc.

joz8968

iTrader: (13)

lol @ David

But I share the 'frustration'

AshMurc

Yeah, for the past couple of years i have been running with the back plate removed on the induction-side vent without issues, including last winter, but the theory along with the observed data presented by API is difficult to argue with! Now where the hell did i put it....

Galifrey

iTrader: (3)

Surely the big LOL in the middle of his reply meant he was joking?

joz8968

iTrader: (13)

Not necessarily.

Since when has lol ONLY EVER been used 'in context'.

APIDavid

iTrader: (4)

We've been going around buying them all up waiting for the day when the world listened.

In singles or pairs £250.00 each + VAT and carriage.

Form a queue here peeps.

David

harvey

iTrader: (48)

What's the point? Even if a few people on here can read it doesn't mean they can understand the written word.
Air like water always flows downhill. Downhill in terms of air is from a high pressure area to a low pressure area. The area above the bonnet vent is low pressure and this pulls air out of the engine bay. Please do not jump to the conclusion this is good. Air is pulled out of the engine bay, not cold air going in and pulling the air out of the engine bay in this area interrupts the gas flow as Subaru designed it in through the front of the car, over the engine and down the transmission tunnel.
If you want to run without vent covers that is up to you. I have collected a pair of blue facelift vents and two sets of undercover from scrap bonnets if anybody wants them but if you have an alternative theory to the above please invest in a couple of minimum and maximum thermometers and some knitting wool and do your own experiments.
Do them carefully and pleset let us have the results.

I don't know for sure but apart from styling it may be that Subaru fitted vents to the bonnets for homologation reasons on their rally cars but they operate substantially differently to your everyday road car.