FMIC is this true

[dandan]

B'Have has an awesomely well ducted FMIC, it's better than the SMIC as he had no packaging, parts mouldings, cost, or servicing considerations to worry about. He just sealed it all up with some goop that set hard. I wouldn't like to take it out again, but it doesn't leak air

 

-Ian

 

Charlie used expanding foam inside a "bag" to prevent the foam sticking to everything - so it's removable like a plug.

 

I did a similar thing after speaking to Charlie. I made aluminium sheet ducting top and bottom and then sealed up the sides as well.

 

I went from an old side mount to a good side mount and then to a front mount. Front mount yielded more torque than thr previous two sidemounts - and that's by the "ass dyno". I will get back to the RR for a comparison.

[JohnA]

so Nissan was wrong when they fitted one to the GTR?

Different engine, different engine bay, different dynamics, different weightings in the designers' lists.

Different car.

[TLicense]

OK, I've been meaning to sit down and write this for a little while, but have never been able to find the time / enthusiasm . But seeing as we're talking about it, here goes.....

The following I have learnt during my years designing radiator ducts and radiator core's for the several F1 teams I've worked for over the last near decade.

 

Basically what an intercooler is, or any radiator for that matter, is a heat exchanger. You want to exchange the heat from what is flowing in the radiator / IC, to what is flowing through the radiator / IC.

So the more you can do to increase the rate of heat transfer from what is flowing in the core, to what is flowing through it the better.

 

Now the most theoretically efficient radiator would be one that is infinitely thin, but by the same token, infinitely large. I'll explain why in terms of a water radiator as it's a slightly simpler model to explain (I don't have to keep defining whether the air is flowing in or through the core )

Heat transfer works best when the two mediums have a large difference between their temperatures. So if you have air flowing through the radiator at zero degrees and the water in it is 100 degrees, it's going to transfer the heat from the water to the air better than if there was just a 10 degree difference.

Now for a radiator, the coldest air is on the front face of the radiator. As the air starts to pass through the radiator, the air begins to warm up, and it's ability to absorb heat from the water becomes less. Obviously the more cold air you have on the front face the better, as it will cool more water. Hence why infinitely thin, and infinitely large is the ideal. Unfortunately there's things like engines and bodywork that get in the way of this so there has to be a compromise.

 

So how small can you go? As mentioned always go as big as you can for the duct that the rad is sat in. This helps in two ways. Firstly you have a larger front face, secondly you usually end up filling the cavity that the radiator is sat in.

The reason why, in the case of a radiator or FMIC, this is good is because the air will want to do one of 2 things. Go through the FMIC, or alternatively go around it. What dictates which, is the air pressure in front of the radiator / FMIC, and the "vacuum" (for the sake of arguement we'll call it a vacuum, but it is in fact just a reduced air pressure, and is very unlikely to approach a negative value) behind it.

As the air hits the front face of the rad/IC it's pressure increases dramatically. This is good as this pressure "pushes" the air into the rad/IC. However, without a vacuum behind it, it's not going anywhere. For a given air velocity (or road speed) the way to increase both the pressure on the front face, and the vacuum at the rear is to duct them, in order to prevent the air spilling around the duct at the front, or have air spill in from the sides of the duct at the rear. The higher the pressure and the lower the vacuum the faster the air will flow through the rad/IC which means your getting rid of the hot (not transferring much temperature) air for nice fresh cold stuff.

 

So you want an infinitely thin, infinitely wide, with an infinitely high pressure on the front, and infinitely low vacuum on the rear core right? Well yes, but no.

This is because the moment we start to think about the medium flowing in the core (be that water, oil or air) then you have to start thinking about the velocity and pressure of that medium. This is where radiator start to behave slightly differently to intercoolers. With a radiator, you want the water or oil to pass through the core as fast as possible. The reason for this is for a given bit of water flowing through the radiator, the temperature drop it achieves by passing through the radiator is generally not as important as the volume of water passing through achieving a slightly smaller temperature drop. This is because it's being re-heated by the engine, and there's a target temperature for the engine to work efficiently.

However with intercoolers, you want the air to be as cold as possible as this equates to horsepower. The volume of air flowing through the radiator is usually limited by other factors such as the efficiency of the turbo's or most likely the maximum amount of boost you can run before det starts to occur.

So for say an engine limited to running at 1.2 bar for example. the actual temperature of the air at the exit of the intercooler is the generally the most important thing.

So how do you achieve the lowest temperature possible. Well again you go for as thin and as large a intercooler as you possibly can. But you have to factor in another important item. The turbo.

The turbo is basically a compressor. If you compress air it get's hot. If it expands it get's cold. So the turbo is heating up all this air and you want to cool it down to get more horsepower. That's the whole point of the intercooler to start with, isn't it? . Now as we've got bits of car, that are limiting how large we can make the front face of the core, we've now got a problem. We're trying to shove an amount of air through a core that's not infinitely large any more, but would still ideally be infinitely thin. This is going to cause pressure at the inlet, as the air is trying to squeeze into the core. This pressure is going to put extra strain on the turbo, which in turn will cause the air it's compressing to heat up more. Making the core thicker reduces this pressure allowing you to flow more air through.

 

Other considerations are the end-tanks and the internal design of the intercooler, as you want the air to flow smoothly through the intercooler. If it doesn't then it's flowing turbulently, which will cause a pressure build up, which will put that strain back on the turbo.

 

So as the volume of our engines is fixed at 3 litres. The pressure of the air is fixed by our wastegates along with the temperature that the intercooler at very best can cool to which is fixed at ambient (remember heat transfer only works when there's a difference between the 2 mediums, if they're both the same temperature there's not transfer) that basically fixes the volume of the air flowing through. Then once you've got the most efficient combination of "large and thick" there's nothing more to be gained.

 

So why do companies sell bigger and smaller intercoolers? Well there's 2 possible reasons. The first is obviously people will tend to buy as big as possible, which they'll charge more for so they'll get more money.

The second and less cynical reason is to match the size of the intercooler with the volume of air flowing through it. What this means is for a given ambient temperature, someone who is running 1.5 bar will get more horsepower using a (for arguments sake) 2 inch core, than using a 4 inch core if they're getting maximum efficiency out of the 2 inch. But someone flowing 3 bar of air would have too much pressure build up in the 2 inch, so would need the 4 inch to flow enough air.

 

Clear as mud? Me too!

 

So which is better a FMIC or SMIC on a MKIV?

OK so we've already said that bigger is better, so a FMIC should be best year? Well only if it's ducted correctly so that the air has no where else to go over than through the core, and also only if it's thin enough that the air flowing through the core doesn't heat up too much, but thick enough so that you aren't putting too much strain on the turbo's.

But then there is the rad that is sat behind the FMIC. This not only reduces the flow through the IC itself, but then has to then cope with the "pre-heated" air that has passed through the IC.

Fitting a larger radiator in this case doesn't really help. As mentioned the most efficient way of increasing the performance of the rad is to have a larger frontal area, but usually this is now limited by not only the rest of the car, but now also the fact that it can't realisticly be any larger than the frontal area of the IC (because it's been ducted right?) and fitting a thicker radiator is relatively inefficient as it further decreases the airflow through both the intercooler and the radiator.

 

So choosing the correct intercooler for your application is a minefield, and unfortunately the only real way you can work out which is the correct intercooler for your application, without a vast amount of computational fluid dynamics and wind tunnel testing is trial and error.

You want one that has a large a frontal area as possible, is thick enough not to impede the air flowing internally, but only thick enough to reduce the inlet air temps to 10 or 20 degrees above ambient. Any thicker then you'll getting into diminishing returns in terms of your heat transfer, and also reducing your flow through too much which will reduce your heat transfer more.

 

Hope that helps

[Chris Wilson]

B'Have has an awesomely well ducted FMIC, it's better than the SMIC as he had no packaging, parts mouldings, cost, or servicing considerations to worry about. He just sealed it all up with some goop that set hard. I wouldn't like to take it out again, but it doesn't leak air

 

-Ian

 

That's as maybe, but you are not including pressure differential across the outside of the core. the SMIC is deliberately vented into the wheel arch, which is a low pressure area, a FMIC vents into the engine bay which is at a MUCH higher pressure relative to the front of the I/C, than the wheel arch. These pressure differentials are crucial to how well a charge cooler or water radiator works. F1 teams go to extreme lengths to reduce frontal area of ducts for radiators, and maximise their efficiency, ignoring this, even on a road car, can give rise to very poor performance from even the largest and most efficient cores.

[adam bell]

thats what i was going to say but i was making a brew lol

[jevansio]

That's as maybe, but you are not including pressure differential across the outside of the core. the SMIC is deliberately vented into the wheel arch, which is a low pressure area, a FMIC vents into the engine bay which is at a MUCH higher pressure relative to the front of the I/C, than the wheel arch. These pressure differentials are crucial to how well a charge cooler or water radiator works. F1 teams go to extreme lengths to reduce frontal area of ducts for radiators, and maximise their efficiency, ignoring this, even on a road car, can give rise to very poor performance from even the largest and most efficient cores.

The thing is we have no control over the frontal area of our car so may as well make best use of the gaping hole we have, yes????

[TLicense]

That's as maybe, but you are not including pressure differential across the outside of the core. the SMIC is deliberately vented into the wheel arch, which is a low pressure area, a FMIC vents into the engine bay which is at a MUCH higher pressure relative to the front of the I/C, than the wheel arch. These pressure differentials are crucial to how well a charge cooler or water radiator works. F1 teams go to extreme lengths to reduce frontal area of ducts for radiators, and maximise their efficiency, ignoring this, even on a road car, can give rise to very poor performance from even the largest and most efficient cores.

 

Correct. Except we don't try to reduce frontal area's of the inlet duct. We try in INCREASE it as much as possible, as you effectively increase the free flow velocity into the rad. but you can only go so large before it becomes aerodynamically inefficient to do so. You end up disturbing the air flow going around the sidepod and into the rear wing and also rear duct too much. Plus the biggest consideration is the fact you have to fit an upper and lower side impact structure above and below the duct, which again limits the size.

[TLicense]

The thing is we have no control over the frontal area of our car so may as well make best use of the gaping hole we have, yes????

 

 

Yes but you still need to do it efficiently, which is the trick.

[Pabs]

just my 2p, but when I fitted a Forge FMIC to my car, when stuck in traffic jams in hot weather my car used to overheat, causing the enginebay fans to kick in at double-speed. This made my car feel more sluggish until it had been driven for a short distance, getting the airflow going again.

 

This never happened without the FMIC.

[jevansio]

Yes but you still need to do it efficiently, which is the trick.

Most definately, ducting is one of the things on my list of DIY jobs to do when all the post single turbo conversion bugs are ironed out

[jevansio]

just my 2p, but when I fitted a Forge FMIC to my car, when stuck in traffic jams in hot weather my car used to overheat, causing the enginebay fans to kick in at double-speed. This made my car feel more sluggish until it had been driven for a short distance, getting the airflow going again.

 

This never happened without the FMIC.

Something doesn't make sense there as overheating is related to water temp which would indicate the only reason a FMIC could induce that is by hampering the airflow over the rad. When sat in stationary traffic is the FMIC going to warm the air that much as opposed to not having a FMIC there (bearing in mind in stationary traffic you're not at WOT with the turbos kicking out massive amounts of heat)?

[Pabs]

Question on this topic (kind of)...

 

Intercooler spray/cooling systems - would an SMIC with one of these be as good as an FMIC? Would the water/whatever would cool the air to lower than ambient temps, although you'd need to be constantly using the spray to benefit???

[Pabs]

Something doesn't make sense there as overheating is related to water temp which would indicate the only reason a FMIC could induce that is by hampering the airflow over the rad. When sat in stationary traffic is the FMIC going to warm the air that much as opposed to not having a FMIC there (bearing in mind in stationary traffic you're not at WOT with the turbos kicking out massive amounts of heat)?

 

Well Forge didn't understand it either. It has been put down to the FMIC blocking too much airflow to the rad, even though at a standstill there isn't much of an airflow?!?

There were only a few similar cars suffering from this problem - certainly a very small percentage of the customers with the FMIC's anyway.

 

EDIT: Coolant temps (normal) are around 90 degrees on my car - with the FMIC they were reaching in excess of 105 degrees, sometimes as high as 110, which is just under the warning level.

[TLicense]

If I sit idling for a long amount of time my inlet temps can go as high as 60 degrees with my SMIC, but my coolant temps never go higher than 85 degrees.

[jevansio]

Well Forge didn't understand it either. It has been put down to the FMIC blocking too much airflow to the rad, even though at a standstill there isn't much of an airflow?!?

There were only a few similar cars suffering from this problem - certainly a very small percentage of the customers with the FMIC's anyway.

Yeah, does sound a bit strange, could be your cooling system was always on the verge of overheating and the very hot days coupled with the ever so hampered air flow was just enough to overheat it. How long after fitting the FMIC did these hot days occur??

[TLicense]

Don't forget that when at a standstill the fan is still drawing air through the radiator. They have a massive effect. We're not allowed to use them in F1, the result of which means we can't have the car sat still for long as the coolant and oil temps start to increase. It makes that much of a difference.

[Pabs]

Yeah, does sound a bit strange, could be your cooling system was always on the verge of overheating and the very hot days coupled with the ever so hampered air flow was just enough to overheat it. How long after fitting the FMIC did these hot days occur??

 

I don't want to harp on about it as this is a really interesting thread, but running the car with a laptop plugged into the ECU using VAG-COM, we'd see the temps rise quite quickly.

The problem occured about 3/4 weeks after fitting FMIC, when we had some really hot weather (last yr i think). However, I've not really seen the problem this year, but then I'm rarely in traffic jams in the hot weather (earlier journeys to work, later journeys home)

[jevansio]

Well Forge didn't understand it either. It has been put down to the FMIC blocking too much airflow to the rad, even though at a standstill there isn't much of an airflow?!?

There were only a few similar cars suffering from this problem - certainly a very small percentage of the customers with the FMIC's anyway.

 

EDIT: Coolant temps (normal) are around 90 degrees on my car - with the FMIC they were reaching in excess of 105 degrees, sometimes as high as 110, which is just under the warning level.

What did you do about it in the end Pabs?

[jevansio]

Don't forget that when at a standstill the fan is still drawing air through the radiator.

It is, but the air passing through the FMIC will be at a lower temp therefore as you said before, less temp diff between air passing through FMIC vs over FMIC therefore less heat transfer therefore the air reaching the rad at standstill shouldn't have warmed up much as opposed to air that reached the rad without passing through the FMIC. Just found it strange that at standstill a FMIC could be the cause of a car overheating

 

PS sorry for labouring this point but thought while people with Tony's experience in these fields are reading the thread, would love to hear their input

[Pabs]

interestingly, I actually had another problem with the cooling system about 2 months after the FMIC and eventually had to change my thermostat, and change the upper FMIC hose. (The Samco hoses split around the MAP sensor) I also had the chance to remove the coolant and change it, ensuring there were no airblocks etc. So it could have been any of the above that resolved the issue.

 

However, the other people with the same FMIC issue eventually changed their thermostats for aftermarket models (Neuspeed i think) which opened at lower temps. This seemed to sort them out fine.

[TLicense]

As mentioned it largely depends upon the thickness of the IC though. If it's a real thick one, then the rad can't pull enough air through it, even if there isn't much heat transferred to it.

If there's not much air being pulled through, then it reduces the effectiveness of the fan.

[jevansio]

As mentioned it largely depends upon the thickness of the IC though. If it's a real thick one, then the rad can't pull enough air through it, even if there isn't much heat transferred to it.

If there's not much air being pulled through, then it reduces the effectiveness of the fan.

Understando

[Chris Wilson]

so Nissan was wrong when they fitted one to the GTR?

 

No because it's fully ducted, and is of quite modest thickness.

[Chris Wilson]

As mentioned it largely depends upon the thickness of the IC though. If it's a real thick one, then the rad can't pull enough air through it, even if there isn't much heat transferred to it.

If there's not much air being pulled through, then it reduces the effectiveness of the fan.

 

Assuming the thing *IS* ducted, otherwise, at low speeds, the stock (ducted at the rear of the water rad) fan will pull air from around the (un-ducted) FMIC. The problem starts at higher road speeds where the ram effect from the bumper opening is crippled, as the air firstly takes the path of least resistance, and secondly the ram effect is drastically reduced by a big sod off core of a FMIC being in the path of the water rad air flow. IMO it's a problem at higher road speeds and high engine loads, whih I think you agree with, anyway Tony

[jevansio]

I maybe half cut, but I'm having trouble working out why it's OK for a Skyline to have a FMIC & not a Supe