tath

Fair enuff

For me, FMIC was £350, minimal cutting, already using (and mapped for!) induction kit - happy

JTaylor

FMICs. Available in black . Comes without spastically clenching ring

justanotherperson

So can we say here that there are no vacumes being produced at high speed,meaning,that if the airflow is at such a high pressure at say 120mph+ running over the bonnet,meeting at,what could be described as "an enclosed space"under the bonnet,where the air pressure is different,thus almost bouncing the air away from the TMIC causing a small vacume almost?
We have found simular at work where this does/can happen, This could be avoided im sure by removing the undertray, giving an inlet through the bonnet and a larger outlet under the car.
This could explain why the bonnet lifts at high speed also.

Davey P

iTrader: (1)

If you measure the charge temps at the throttle body, at different speeds, wouldn't that be a good indicator?

NXG

Wouldn't removing the undertray increase air pressure in the engine bay? I would image it increases turbulance under the car, so the air isn't flowing as freely. If the air slows down to swirl, it'll exert more force than fast flowing air.

Edited to say, would the best compromise be having the tray fitted, but putting some rear biased exits into it to suck air out of the engine bay with the air flowing under the car? Something similar to the ones you see fitted to some bonnets....

silent running

Yes I do take the point about a front mount being a lot better, but with all due respect that's getting off the point :-) I'm really interested in what's actually going on in that bonnet scoop and whether anything can be done to improve matters. To which end I've just gone and spent the grand total of £2.40 on two longer lengths of pipe so I can do pressure differential measurements.

Davey - yes measuring charge temps is possible but then you cause yourself more problems because you add so many more variables - throttle position, gear, load, gradient of the road, ambient air temp, boost level, time under boost, etc. etc. All of these affect the charge temp as measured at the TB. The aero properties and air pressures across the Scoob's front end stay the same (or as near as to make no difference) regardless of what the engine's doing- they SHOULD simply correlate to road speed and nothing else.

silent running

Not sure about there being any actual real vacuums present, presumably you mean pressures lower than 'over-bonnet' or lower than atmospheric? But basically the idea of the air 'bouncing away' from the scoop/TMIC is probably quote a good analogy. There's no reason for it to actually go into the scoop at high speed - it's effectively 'full up' and the airflow simply goes straight over instead until the road speed drops allowing more air to enter the scoop. Hence why perhaps the later STi's have the taller scoop to 'catch' more air. Not quite sure how putting another inlet into the bonnet would help though? A larger outlet would work but the problem is, how would you do that, without moving the engine and gearbox somewhere else...

krazy

Hasn't this all been done before? I'm sure someone actually measured charge temps on a strandard car (jdm) and seemed to work fine at 150 ish although it wasn't for a prolonged period, a search will probably find it.
Surely the bonet lifting, (which seems to be more commented on regarding new age cars?) is more likely the force exerted from the scoop deflecting air at 100+ mph rather than a pressurised engine bay?

silent running

Yes my thoughts exactly. The undertray would surely smooth airflow and maintain air velocity under the car, resulting in a lower under-car pressure than you'd otherwise get without the tray. And then you'd want exits at the fastest flowing areas under the car to 'suck' air through the engine bay. You do see the same idea on cars with a rad exhaust vent in the bonnet i.e. Mitsubishi Evo, Lotus Elise, WRC cars - air goes in through the rad, it's ducted diagonally upwards to meet the bonnet and vented out, right behind the leading edge, where you have a low pressure area. Notice that these rad exhaust vents are never in the back half of the bonnet, because this is where air pressure starts to raise again.

Anyone got a picture of the factory undertray or the underneath of a Scoob with its undertray fitted?

silent running

Don't know. Show me the link if you've got it? Although it's not actually charge temps themselves that I'm looking at - it's the airflow past the TMIC that's the focus, good heat management follows naturally from that. I've personally never seen the lifting bonnet effect, but I can't see hwo it would be the force exerted from or by the scoop. If there was that much force on the lip of the scoop to be able to lift a bonnet, surely it would just break it? I'm pretty certain that once you get up to a speed where the scoop is 'full-up' , if you could see the air pressures around it, you'd no longer have a sharp edged scoop cutting into the airflow, instead it would just act like a small bump in the back of the bonnet, acting more like a spoiler than an air inlet.

911

If you could get a real ground effect under the floor (low low splitter and deep side skirts then the rad flow and the scoop flow would be sucked out, or at worst, be able to 'fall' into the low pressure zone.

My Sti v3 has no engine under tray, it is wide open (Jap spec?) and i think the UK/Euro cars have a panel (anti noise panel?) so choking the flow downwards.

Unless there is a relatively speaking lower pressure then the rad/scoop zones will not flow fast (if at all?).
We need to look beyond the front of the (a) car too. The pressure about a mter after the tail of the car/spoiler I think is negative, so I wonder how this zone affects the front of the car??

Taking Paul's point (Zen Perf) I feel he is spot-on with the TMIC.

It is in the wrong place, it is small also compared to the Hybrid FMIC. It has cast alum end runners which, when hot, stay that way for ages. Quenching them with scoop air is difficult as the rubber seal ring under the scoop goes around the perimeter of the matrix and seals the runners off into the engine bay!

When i ran my car at Well Lane rr last year, the TMIC (sti v8 type) roasted after 3 power runs despite 'forced cooling' to the radiator of the car.

I hillclimb against a fast Nissan Pulsar with a TMIC, 2 x the size of the Sti v8, and he gets huge heat-up to.

The EVO5 who ALWAYS beats me has the FMIC but and API one I think, and his is cool after a run....and that's with 500bhp and all that goes with it.

Popping back to air flow:

Some have the reverse scoop when running a FMIC, now, there's an interesting discussion coming up!

Good thread this, thanks for starting it.

Graham

bugeyewrx

On a VW beetle there is an area in front of the windscreen running out along the bonnet by about 12" that at 60-70 mph has no airflow as such ie a stagnant area . You could watch flys and wasps walk around on the bonnet with no problems at all , until they strayed into the area with airflow when they would suddenly disapear . The inlets for cabin ventilation were also in this area . Could explain the vast number of beetles with misted up windscreens

From the small amount I know about aerodynamics it's very difficult to extrapolate airflow effects from one speed to another . Just because the airflow is a certain way at 100 , 110 and 120 mph it does not follows that at 125 mph it will be the same only more so .

For example most aerofoils at high speed suffer from separation bubbles ( an area on the surface where the airflow detatches , leaving a small turbulent area , before reattaching ) . These bubbles are not always present but have a critical speed at which they start to form . If you ever see a glider at high speed , and low enough , the high pitched whistle you can hear is the airflow being torn apart as it encounters the the separation bubble . Also just because airflow detaches at 120 mph it does not mean that when the speed drop back below 120 mph the flow will reattach , some times the speed has to drop well below that level for reattachment to occur .

Now all this happens with an aerofoil that has been designed purely to provide lift with the least possible drag , so you can imagine how much more complicated the airflow is over a car bonnet .

I think that it is quite possible that there is a critical speed at which the scoop stops working , to some greater or lesser degree .

I think it's also worth remembering that the load on the engine is much greater at 130 mph that at 120 mph than at 110 mph . The drag increases as a square of the speed and therfore the power needed to overcome it and the load on the engine . I noticed when I was on an autobahn , determined to reach top speed that each extra mph took much longer to reach !

Martin

NXG

911. Agreed on the air flow (1) and the end plates (2) because:

1. The idea of taking advantage of the vacuum effect with shaped ducting in the undertray assumes there is sufficient, directed air flow under that area in the first place. Also, what impact will the ducting have on ground effect at the front of the car and hence stability?

2. Went to Powerstation with the Wales contingent yesterday for a rolling road day, and after spending 20-30 mins in the queue with the engine running the APS top mount was quite warm. The engineer managing the run said the 341bhp the car made would easily be 10bhp more with a TMIC with less dense end plates, though this only applied on the rolling road. Out in the day to day world, with 'normal/spirited' driving, i.e. not hill climbing, where there is nearly continuous air flow, the heat build up woudn't be much of an issue.

I'd be very interested to to see the results of some practical testing of a TMIC showing charge temps vs speed. The methodology of testing will be critical to meaningful results though.

ZEN Performance

The surface area of the end tanks is small in comparison to the surface area of the finned core of the intercooler.

With an intercooler of over double the volume of a v4 TMIC, I see over 60deg with over double the sort of power commonly put through a v4 TMIC, but this is only on a prolonged application of WOT.

In the height of summer i wouldn't be suprised to see over 70ºC intake temps at WOT in a TMIC, which can have a significant effect on the engine depending on the mapping and what the ECU does about det (if anything).

NXG

bugeye

I'd expect to the charge temp go down as speed increases due to ram effect, then tail off as aerodynamics messed up relative air pressues either side of the tmic, reducing its efficiency.

NXG

Hi Paul. Did you see the results of the RR day at Powerstation yesterday?! I do very good rates on advertising if you'd like 'As tweaked by Zen' on the car

On UK roads, taking into account the way the TMIC allows earlier spool than a FMIC, would the diff in intake temp be cancelled out?

Steve

tath

I think it's only RAs that don't have them.

banny sti

iTrader: (68)

Most people have them removed, during oil changes and leave them off.

911

My thoughts are really aimed at the hillclimb situation which can be different to road and drag racing driving.

Heat soak is a real problem, and then you have to get rid of that heat too while blasting the car for 50/60 seconds, or 6 times longer than Paul on the strip!
With runs taking only a minute and sometimes much less(ie 33 secs), it would be hard to get temperature readings without some kind of multi channel data logger.

common engineering sense could get you a long way:

A big light FMIC well in the air stream with atomised cold water spray (I put ice cubes in the water to chill it) will be about as good as it can get within the confines of the car's bodywork.
A CO2 spray will really chill things, but can a decent ecu (ie Apexi FC) respond fast enough to give an advantage?

Maybe a MAF in the scoop (TMIC) front grill (FMIC) opening would be interesting and chart MAF against speed/accelleration?
Similarly, a MAF down by the bottom of the D/P and the other side of the box would be good too.

We would then see the changes in air flow against speed/accelleration.
I wonder also how the airflow changes with accelleration (a transient period) and the steady state of stable speed levels.
Just how quickly do aero conditions and hence pressures stabilise, ie

Car accellerates like Paul's to 100 mph in about 6 secs (or faster Paul?) but are the MAF readings the same after 15 seconds at 100 mph?
You would need a run in both directions over the same course to negate ambient wind speed.

Graham.

silent running

LOL there's some great stuff here, keep it coming guys. Looks like we better all put our hands in our pockets and chip in for some wind tunnel time at MIRA :-)

There's far too much for me to comment on here, but just looking at your last post Graham, yes a CO2 spray would work very well and being an air-air I/C no danger of actually freezing anything! The problem I see with putting MAFs here there and everywhere is that they would only measure the flow through the MAF body and not over the whole zone that you're targetting. In something like a small brake duct this would work really well, but in a bonnet scoop or down by the bottom of the downpipe, I wonder if it would be very representative of what was really going on? It would give you an idea, but would the accuracy you'd get make it worth the effort of trying it out?

The comments in general about the different effects of acceleration / deceleration on aero are interesting too. Not having done my measurements with much accuracy yet, I did notice that the high pressure areas I measured did seem to linger more on the way down than when I'd been accelerating. I put it down to not paying proper attention. But actually maybe it was a real, if not huge, effect.

Martin - yes a Beetle's aero profile is weird. We used to have an old '66 and had the same problems that everyone does with misting etc. I'd imagine with the curve of the bonnet, the big front wings on either side and the almost vertical windscreen, it's totally different to modern cars.

Well it looks like I need to get some more pressure results from other places around the engine bay and start noting them down properly. What would be interesting would be a chart of pressure differential across the TMIC vs. charge temp differential internally. Problem is I can't have two channel charge temp reading, unless someone else has an SPA temp/temp gauge with the intercooler probes to allow up to 255 C air temp readings? I could do a single temp reading at the throttle body pipe but that would have nothing to reference it against so there would only be a very loose correlation to pressure differentials.

ZEN Performance

My temp figures are for a top speed run of some 30+seconds, with no breaks for the engine at all. The temp drops to less than 40deg under braking in a few seconds.

If you go for a blast in your car, you will find when you stop you have a warm and cold end of the intercooler!

paul

justanotherperson

I believe as figure that if you keep the ACT's down below 40 degrees you can claim you have a good intercooler set up...?
I think im right in saying this

911

Yes, understand.
When I worked on the heater stuff in motorhomes at 55mph etc we used airmeters, but moved them through a prescripive grid according to the standards.
We did the same with the wind tunnel, we had a huge fan, about 2 meter across and measured air flow in about 100 places to ensure laminar air flow was present.

So, in my 'experiment' above you would take the MAF in the zones and progresivly move the MAF's across an imaginary gride over the FMIC, but to basically understand the 'flow path' you would only need a few co-ordinates.

Paul:
I have my FMIC water spays pointed at the hot end of the matrix, other end I hope will be cooler!

I thought this subject would be a bit boring, but not so...taking me back to when my professional job was techie rather than a sea of emails and deadlines (or is that like building a Scooby to a date?..thinking of David and Steven et al)

Graham.

Andy.F

The std TMIC is only let down at speed by its capacity(size) in my opinion.

Most tmic's are way too small for the power/boost level and under sustained wot the charge temp increases continually.

My car has run to 175 mph at Elvington on a number of occassions on a tmic without issue. It was however a massively uprated core which was bigger than some fmic's.
I was not aware of any cooling airflow issues at high speed and I monitored IAT at the throttlebody for that very reason.
In fact the only reason I went fmic was that the bigger turbo i fitted left no room for the intercooler.
Some fmic installations can be worse than a good tmic such as the APS (nice result NXG )
An example of this would be a car that retains the undertray, has an open tmic scoop building backpressure behind the engine and has an A/C radiator further reducing the cooling air flow through the stack of 3 cores.

Andy

ZEN Performance

Spray it on the cool end too, and you may be able to reduce the output temp below ambient in low stress situations!

Paul

Andy.F

Grahams car - low stress ? nah, that will not happen

NXG

Cheers Andy

assam

'the engines blowing up i have been told is to do with the full pump. When u get to high speeds well over hundred the fuel pressure is not high enough. causing the car to not get enough fuel then in turn cuts the air which leads to a blow up'

written as few posts up, i have heard exactly the same thing somthing to do with the fuel pump/mixture
my mates engine went whilst doing 145......on a private road of course

ZEN Performance

With increased power over standard, comes a requirement for more fuel, and usually at a high total pressure than standard. This is often too much for the stock pump, and you get a drop in fuel pressure as the flow increases. In some cases, the fuel pump is fine, to start with, but as the demands on it increase, and it heats up on a run, it will begin to die off. It should come as no surprise that Prodrive uprate the fuel pump on the PPP for the STI.

assam

thanks for that makes perfect sense