Casters450

Just want to give every one on here a warning about POSSIBLE problems that may arise when fitting a WRC style vent in front of the bonnet scoop on a newage (WRX with low scoop).
About 3 years ago i had a genuine WRC vent fitted.

For a lot of the life of the car i have had intermittent problems with it seeming to be very underpower, mainly on hot days and normally on a long motorway run, but each time it does it it only lasts for about 30 minutes max. I get no warning lights and no fault codes. Subaru have changed the MAF. I assumed that it was probably to do with ****e fuel, i sometimes used to put BP in it, but now only V-Power, but the fault hasn't cleared.

I have just put a full de-cat system on it so took it to API for a simtec and re-map. (in preperation for forged bottom end etc).

Whilst mapping, we (the royal we) meaning Pat found that the charge temp out of the standard WRX inter warmer was 117 Deg!! I think it would normally be around 50 Deg. To cut a long story short, we had to bin the session for a bit of head scratching, as it was 8.30 PM (thanks to Pat, David and Nathan). The only logical reason we can see to cause this is that the WRC vent is diverting the air over the bonnet scoop and so little or no cooling air is reaching the inter warmer. This probably could also explain my intermitent fault in hot weather.
I am currently trying to fit a Hybrid FMIC to get the temps down because i'm not sure if an STI scoop would collect enough air.

Hope this may save any problems in the future for any of you thinking of fitting a WRC vent.

Happy tuning!!
Stu

frayz

iTrader: (7)

Strange, i have a friend with a vent as his ACTs are no different to any other WRX?

Neil..

iTrader: (35)

Could it not also be drawing hot air from the coolant radiator out of the vent, and back into the intercooler vent..?

Have you tried blocking up the vent intially and seeing if that cures the problem..?

Casters450

Sorry. forgot to mention, the vent was blanked from fitment, although i am considering opening it up with the FMIC.

ScoobyDoo69

iTrader: (17)

Was yours the Blue one with the WRC wing on it too that I saw Wednesday last week?

Casters450

Quite possibly, was down at API all day - and evening - and night with a few excursions onto the M40 for mapping!!!

Blue blob eye with a 2002 overhang WRC wing, WRC bonnet vent and anthracite 18s.

ScoobyDoo69

iTrader: (17)

Yep that's the one, looks very nice I have to say. Sorry to hear about the temperature problems! Hopefully all goes well with a nice front mount

merlin24

iTrader: (1)

Did see you on the M40 southbound towards Jct 11 last wed - must have been Pat's laptop leads coming out the bonnet and through the window

Casters450

Yeap, i reckon that was me!!! Not sure what we looked like from the outside but it aint so nice sat in the back whilst some one else is caining your pride and joy!!!

ScoobyDoo69 - were you the one collecting an engine to take to Manchester? If so, how did the fitment go and is it being carefully run in??!!

silent running

Interesting. I would have said it was drawing hot air out from the back of the rad and feeding it straight back through the normal scoop until you said it was blanked off.

Best guess I can come up with (and I've actually done pressure and charge temp testing at speed on Clio and Impreza bonnets with my own equipment) is that - even blanked off - the WRC extractor vent (it is that sort isn't it?) is disturbing the airflow over the front half of the bonnet so much that it has stalled airflow through your scoop, or almost stalled it. Charge temps of 119 degrees mean the intercooler basically isn't working hardly at all, these kind of three-figure temps aren't much cooler than what comes out of the turbo...

What you could do to test things out would be to totally 'plate over' your extractor vent with flat cardboard and gaffer tape so that you return your bonnet to its original shape. See what your charge temps are. If they remain the same, the problem is either with some airflow disturbance under the bonnet caused by the vent still sitting there in the way, or much more likely, your intercooler is knackered in a big way.

Casters450

It is the WRC extractor vent. Idealy I would like to have put an STi scoop on to see if that made any difference, although I like your idea of smoothing the bonet with card, but due to time and money limitations, and a desire to sort the problem at first attempt the only logical solution IMO is to go front mount.

I guess i'll have to assume the cooler is ok, can there be much that goes wrong with them?? It doesn't appear to be damaged or blocked.

Thanks for the interest.

Stu

ScoobyDoo69

iTrader: (17)

Nah mate I was the one who cracked his block with his hands on the blue sti Came in a 306 was dropping off some exhaust bits to be fitted while I could!

silent running

I didn't know you could even get those WRC extractor vents on a road car so that's news to me straight away. But generally I've found that aero mods can add up to some weird goings-on if you're not very careful, as you've found out. Just remind me; does the WRC car still run with an open scoop on top, even though there's nothing there? Is your vent exactly the same as the WRC one? Wasn't the WRC vent designed for a reversed manifold with FMIC rather than a standard FMIC?

Butty

iTrader: (2)

Have you got an undertray fitted to the scoop? This should seal with a rubber strip aginst the TMIC.

Nick

Casters450

Hi guys, i'll try and answer both of your queries. Firstly Nick my scoop is standard WRX, not the higher STi, and is correctly sealed around the smaller, standard intercooler with the standard undertray/skirt.
Silent, my WRC vent is a genuine item, fitted by SGM racepaint in Banbury, but blanked off to stop water dripping onto the alternator and air con pump. I think i am correct in stating that the WRCars used an intercooler mounted in the grill rather than low down behind the front bumper, and angled towards the extra vent, also as you have stated with a reversed inlet manifold. There would then be ducting to link the intercooler to the vent to extract the hot air. The bonnet scoop remained but i'm not sure if it allows air into the bonnet area.
My plan is to fit a FMIC (currently ongoing) and then open the vent and put some ducting in there to help direct the airflow out of the intercooler and radiator but also to stop the water problem previously mentioned. The ducting I have in mind is available on the Japarts website for about £115 I think.

Stu

silent running

Have you thought about going the whole hog and fitting an FMIC in the WRC position with the proper WRC ducting? With a standard FMIC, low down and out in front of your main rad and aircon rad, I predict you will see very little benefit from the WRC extractor vent and possibly even enough airflow disturbance (if you open it up) to actually lessen airflow through the FMIC/rad/aircon rad stack. Cool-looking as the WRC extractor is, it is designed to do a specific job in conjunction with repositioned FMIC and ducting. I don't think it can be of any benefit with any other setup. Best option in my book if you're not doing the full WRC inlet tract would be to fit your standard FMIC but keep the extractor blanked off.

Casters450

Point taken mate - in all honestly I don't really know what to do!! Obviously I would like the proper WRC set-up, but I suspect this would run into thousands to convert, when things like buying the cooler, ducting, possibly different radiator, brackets/ fabrication along with losing my air con etc,etc I don't think it would be worth it, well financially!!
Not wishing to cause an argument, BUT do you have any grounds for stating that the airflow may lesson through the FMIC/rad etc, ie during the testing you carried out above, because I would have thought that if you can give the air flow an 'escape route' ie an open extractor, then it would pass through quicker??? I appreciate that if you can smooth it's flow through some sort of ducting then obviously the benefits would increase due to less turbulence, but surely an extractor is better than no extractor isn't it??!!

silent running

LOL that's fine argue as much as you like. :-) Makes a change to chew something over that (AFAIK) hasn't been dealt with on SN before (or at least recently).

What I mean is that airflow is generally pretty well managed on a standard car by the designers of that car - they have wind tunnels and millions of pounds to spend on getting aero right. It is difficult for the amateur (i.e. not the manufacturer) to improve airflow to do what you want, and very easy to mess it up. The principle that I have seen work is tight ducting or 'shrouding' every rad that you want to flow air through. Basically a lot of people make the mistake of thinking that if you put an intercooler out in the airflow for example, air will go through it. In fact if you could see the flow you would see that most of the air will go around the sides top and bottom of the IC rather than through it. So how do you encourage air to flow through a heat exchanger core like an IC? Make sure the pressure in front of it is higher than the pressure behind it. This can be achieved by shrouding the front side so that air cannot go around it (high pressure on the front) or siting the rear in an area of low pressure, or ducting the rear out to a low pressure area. This is how your WRC extractor vent works - high pressure on the front of the IC because there are few alternative routes for the air to take once it's in through the grille; low pressure on the rear because just behind the headlight crease in the bonnet is a classic low pressure area on most cars (as is the rear tailgate or windscreen). Result - air has no choice but to flow through the IC efficiently. My testing btw has been done by fitting extractors, intakes, ramscoops, shrouding etc on my old turbocharged Clio and measuring air pressures and charge temps. On my Subaru it's been limited to disproving the idea that airflow through the standard bonnet vent stalls at certain high speeds, again by measurements of pressure and charge temp.

Now I can't claim to know what the effect of an open extractor would do to your airflow behind the rads in a Subaru engine bay. I would guess that yes at a standstill, and perhaps at low speed it will help to draw hot air through, more because hot air rises than anything else. But once you get moving the main expected route for hot air off the back of the rad is under and around the sides of the engine, not over the top. Stick an open vent right there and I wonder whether you would simply have your airflow pulling in two different directions and end up stalling it in there or at least not have it working as well? By all means if there are any aero experts who have tested this and have hard data, let's hear it.

I think you're right that a full WRC conversion would be ridiculously expensive. Fit a standard FMIC, get some kind of charge temp device in your throttle body or just before it, monitor your charge temps and water temps with the vent closed. Then after a few days of that, try opening up the vent to see if it improves things or not.

Casters450

Yeap. Can't disagree with what you have written there mate. I'm an aircraft engineer by trade, so I hopefully (20 years ago when I did my training!!) still have an understanding of airflow, albeit over a wing or gas turbine blade, but the principles are the same. I do like your idea of fitting a sensor to monitor charge temps. The problems have arisen whilst mapping with a Simtec, am I correct in thinking that a sensor is put into the system, in my case screwed into the top mount to measure these charge temps, which is how Pat (the mapper) new the temp was at 117 deg???? So I would assume that this sensor will still be fitted, but obviously elswhere, with a FMIC, which would allow me, over time to try what you suggest??
It would be nice to eventually use the vent as intended, rather than eye candy!!!! Maybe I won't be putting this discusion to bed just yet!!!

silent running

LOL hope I've not been teaching you to suck eggs then! There are so many variables with this kind of thing that the easiest way to bring it all down to one easily monitored variable is to use charge temp; after all the final result of the exercise is to lower charge temp so why not use a 'see what works' approach, whether the theory is right or wrong?

I have my Power FC mapped using the STi air temp sensor as one of the inputs. Because of this I can also get a readout on my FC Commander as well. All I did was get an old brass plumbing bung, drill the middle out and set the sensor in it with araldite, then tap the FMIC pipe just before the throttle body for the bung thread, job done.

Casters450

Sounds good to me, hopefully i'll sort the fittment of a FMIC this weekend, then i'll have a word with the guys at API when it gets mapped on Wednesday. Thanks for your input, happy engine building!!!

Stu