Questions about FMIC (science questions)

Stuart B

Registered User
I know the main reason for the FMIC is to keep the Air Intake Temps low for performance improvements and engine safety, but these questions are more related to picking the right one?

Okay so I know from the threads that for my S3 when I get my FMIC that it's important the inlet and outlet are the same as the current 63mm I think.

In my simple mind I feel that if they are 51mm then it will generate extra heat on the inlet and I have expect loss of pressure on the outlet and if they are 76mm then it will cause loss of pressure on the inlet and extra head on the outlet? This might not be accurate but just feels right in my head, if you watch water in a river etc.

Say I get a 63mm 300/550/65 intercooler, when the forced induction starts it has to first fill this entire space up before exiting the outlet to go to the throttle body, so I assume this causes lag? Or is the often referred to lag, simply the fact if you are accelerating from 2k the turbo doesn't spin up until 3k so you have to drive 1k rpm on NA?


People say the turbo spins up quicker?
1. How can the air intake flow speed up when the turbo can start as that is initiated from the exhaust flow? Or is the fact there is less restriction than the dual SMIC the turbo has less work to do to push the air through the pipe work.
2. If it does spin up quicker you still have to wait for it to fill up the larger intercooler, before that air can get into the throttle body.

Maybe the above questions are simply nonsense and a turbo would fill this intercooler up in less than 200 milli-seconds


My only real concern is:
I am worried that with the current more restrictive airflow setup of the dual SMIC the torque is limited purely by the pipework and if I add a free flowing FMIC this might mean that the engine would be in danger (connecting rod wise) because more cold air can be delivered in a shorter period. Especially as I have a dubious map on a purchased ECU.

Thanks for any thoughts?
 

vanilla_ice

Registered User
I can't answer your questions but I do believe the infamous Welly bent a rod on his first test run after fitting his FMIC...
 

Stuart B

Registered User
Thanks,
this is my worry that all of a sudden my ECU (with a generic stage 2 map installed) will give more power in one chunk - whereas currently the hardware setup will restrict the flow, obviously the correct way is to have it all free flowing and a decent custom map to ensure the power delivery and fuelling does not blow the engine up.

I am actually wondering whether the dual SMICs are limiting the boost PSI too as with my old Stage 1 MAP it would always go up to 20PSI and peta off to 15PSI - and this Stage 2 MAP struggles to get over 18PSI. Will refit my analogue gauge to get a real reading of these - as I don't trust the Android Torque App for Boost PSI
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
Firstly... don't get hung up on boost... boost is a facilitator, it is not flow or air mass... boost pressure is the result of a restriction of some description... if there is less of a restriction for the same airmass then pressure is lower... fluid dynamics etc..

ME7 ECU's have no real notion of boost... boost is the result of it calculating the load it needs to meet drivers load request (input from the throttle) in colder weather it can get away with less boost as the air is more dense... in summer whne the air is less dense it will use more boost to achieve the same airmass required.

1. How can the air intake flow speed up when the turbo can start as that is initiated from the exhaust flow? Or is the fact there is less restriction than the dual SMIC the turbo has less work to do to push the air through the pipe work.

Overall flow is a contributory factor... less restriction through the whole engine allows increased flow for a given airmass, means its gets out quicker, spins the turbine quicker, less restriction on the inlet tract (B5 TIP is a good example of this) means there is no restriction on the air mass it draws from, larger pipework/FMIC flow means less for the turbo to push against making it spin more easily and the same or more airmass gets to the engine more efficiently... (remember... don't get hung up on boost)

As Bill's mantra goes... its all about the flow.... yes there are caveats to this by going too large, too small, fine tuning to get airspeed etc but in reality unless you are looking for the nth degree of power (F1 maybe an example of this) then there are tried and tested solutions for this already...

2. If it does spin up quicker you still have to wait for it to fill up the larger intercooler, before that air can get into the throttle body.

Airmass is airmass... don't get hung up on boost... obvs you wouldn't fit the biggest FMIC in the world to an engine running a K03 but the reality would be negligible I would expect based on what I have seen... never tried it personally as tried and tested still kicks in here...

Maybe the above questions are simply nonsense and a turbo would fill this intercooler up in less than 200 milli-seconds

Filling the intercooler is not really the issue as once 'full' as such it would become a restriction and therefore require pressure to help force more air through it... obvs the whole point of forced induction is to compress air into a smaller area than normal but you need it to be able to flow as all you have then is lots of pressure trying to push an airmass and a slower rate..

My only real concern is:
I am worried that with the current more restrictive airflow setup of the dual SMIC the torque is limited purely by the pipework and if I add a free flowing FMIC this might mean that the engine would be in danger (connecting rod wise) because more cold air can be delivered in a shorter period. Especially as I have a dubious map on a purchased ECU.

You would do well to be worried... releasing flow restrictions without proper mapping and or other precautions can lead to doing a 'welly'...

I remember when I changed from the AH Fabs v1 to the AH Fabs v2... the resultant increase in flow actually gave me throttle cut due to hitting a safety limit in the map... obvs all I then did was move this map accordingly as I wanted the increased load at that point and retuned the boost profile to suit...

<tuffty/>
 

Stuart B

Registered User
Thanks for your comprehensive replies describing the boost pressure science :)
its all about the flow!, not the boost pressure as I could put a bottle neck in the charge pipe and require 30psi to deliver the same mass of air as 10PSI without the bottleneck. just will have more heat.

I cant say I fully understand how the car requests more air mass from the turbo as the only management are
1. the diverter
- Forced open if the pressure in the charge pipe circuit exceeds the spring / diaphragm rate
- Opened by vacuum, when the inlet has negative pressure (Gear Changes, reducing revs)
2. the internal wastegate
- Actuator Spring (10/12psi)
- N75 / MBC ( I assume an electronically controlled N75 will "hide" the charge pipe boost pressure to avoid the actuator spring action, and an adjusted MBC ball bearing and spring holds back the air from the actuator)

so for a K03 / K04 the exhaust drives the turbine at an unmonitored speed depending on exhaust flow rate (revs?) eg maybe between 20,000 and 120,000 RPM, on a free flowing inlet that may be 15PSI on a restricted setup 20PSI the temps of the air at 20PSI will be higher than 15PSI (thumb over a bike pump burns your skin) making the air less dense - hence the addition of an inline FMIC to improve the flow (smooth curves, no sharp "dust traps" getting in the way of the air from the charge pipe to the throttle body, no variations/bottlenecks in the circuit.) to make the air cooler and denser again.

I don't quite understand how the air mass is really known by the time it gets to the plenum?
The 195 g/s is from the MAF sensor isn't it?, but that is the rate the air is passing through the MAF, that air is pressurised, cooled, etc all before the fuel is added and every car is different so how does the ECU know how much fuel to add to my 195 g/s compared to someone else's 195 g/s?

I know the Map Sensor is close to the throttle body and there is an Air Temperature Sensor (I think in the throttle body itself) - does the MAP Sensor and AIT sensor provide enough information for the ECU to know that the 195 g/s from the MAF is now a carrier bag full of 30 Centigrade air.

Is air just air or is there better quality air eg if you are in traffic and most of the air is other peoples fumes or a hot still summer evening - where you are struggling to breath because the air quality is so bad, as an example people add a "wizard's of noz kit".

My wife has a load of portable oxygen tanks which can deliver up to 15 litres per hour of pure oxygen is that
1. a fire waiting to happen
2. pointless as the air rate would usually deliver 15 litres in 75 seconds (200 g/s * 5) * 15 - so the tiny bit of O2 would be insignificant
or
3. could be used to artificially change the air quality after the MAF sensor, improving ignition

(to be fair regarding the oxygen, considering we need to alert the fire and rescue we have oxygen at home and you need to stay away from naked flames, being anywhere near the canister's or compressors - I am expecting the answer above to be 1 ;) )


Regarding the engine safety when adding an FMIC, there are obviously some precautions I can take eg put in the old ECU with the 240BHP map when fitting the FMIC it to see whether it has any unexpected outcomes on a simple Stage 1 MAP - although that ECU has the DIS Snowflake N75 controller bug and I get the regular P420 cat threshold error because of the 200 cell sports cat - so it would be only for a test - unless I pay out for a custom remap on that ECU to bring the car back up to ~265BHP - the main reason I changed to a stage 2 map is the various hardware modifications I had made meant that the car didn't run as well as it should on the Stage 1 map.

Now at least I understand when people upgrade some of their hardware - they sometimes run with an unplugged N75 until they can get to remapping.
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
I was wondering whether a non turbo engine would also benefit with an intercooler fitment?
doubt it... it would be too restrictive on flow... forced induction allows for inefficiency of the inlet tract... NA tuning is generally affected more my inlet and exhaust design than forced induction

Cold air intake is the realm of NA... people believe it to benefit forced induction but ROI is substantially less... better off with a decent FMIC and WMI for forced.

<tuffty/>
 
I got my fmic fitted bout 3 months ago but have still not been to get the map tweaked. Is this a bad thing cause i have other mods i wanted to do first but dont want to hurt the engine while im waiting.
 

Stuart B

Registered User
I think it will be fine whilst making the other mods as the existing map will limit the power.

My original concern was I bought the car with the normal stage 1 map and then I added a 3inch downpipe, B5 TIP and some PCV delete etc - I didn't think the car was as smooth as before the downpipe (I reckoned the components outgrew the map). so I got a stage 2 generic map ECU and the car runs really well currently (fingers crossed, salt over the shoulder etc etc, its got a bit of an exhaust blow at high revs on the back of the middle box - but it's responsive and fun to drive). so now my worry is the stage 2 generic map is maybe at 250 lb/ft Torque and 265 BHP but is advertised as much higher than that - if I add an FMIC - I don't want the first drive to be 280 Torque and a tow home and new engine (or a convenient fire) - but if I don't add an FMIC and the ambient temperature increases much more it will be too hot.

Maybe Welly already had a high performance map, restricted by the inlet standard pipework and then adding the FMIC suddenly freed the extra power, whereas the correct thing to do is what you are doing and make the stage 2 mods first then get a safe map to suite the components.

I think this is why some of the big turbo conversion threads on here say the car is running bad because they added a load of components but don't want to risk the N75 causing a boost spike so they unplug it until it is mapped correctly.

When I read the link "S3 Highlife" kindly provided it sort of explains that extra power is made available with the use of the intercooler over the stock setup - but I don't think it created new power on a standard setup - it was only after the map had been adjusted but was lost in heat on the stock intercooler. http://www.enginebasics.com/Advanced Engine Tuning/Intercooler Efficency Test .html

I will of course get an FMIC and roll the dice - this is why I haven't bought a new wing to replace the rusty one yet ;)
 

badger5

www.badger5.co.uk
Site Sponsor
I think much of what you have written is incorrect based on poor assumptions of how its working.

Seperate ecu control from the engines mechanics.

AFR is simply that, Air Fuel RATIO.

DV is not "overcome" by boost just by its spring.. Boost/Vacuum operate directly onto the DV so its boost + spring which holds it shut not just spring pressure to point out one of the error's in your scribblings
 

Stuart B

Registered User
I trying to learn so it's good to be corrected.

My visualisation of the crap splitter dv is the turbo sends the air down the charge pipe that pressurises the DV and n75 in addition to throttle body.
The N75 may pass the pressure to the actuator if greater than map setting.

But I thought the only thing stopping the DV from sending the charge pipe pressure back into the tip was the spring and if the pressure is more than the spring, as a safety mechanism it will relieve the pressure? Hence why you tighten it another 5 clicks if the car is mapped. And the vacuum opens the DV on gear change to relieve the pressure again.

It might explain why I can't visualise how a standard DV orientation can get forced open by too much pressure.
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
It might explain why I can't visualise how a standard DV orientation can get forced open by too much pressure

Mainly due to there being a larger surface area presented by the base of the piston in the direction the piston needs to move that sees boost pressure... if boost pressure is inside the piston chamber itself the design of the piston means it has nothing large enough to push against in the direction the piston moves to open...

<tuffty/>
 

Stuart B

Registered User
it is as simple as this isn't it? - maybe I am overthinking the safety pressure relief feature from too much pressure in the charge pipe - and it is always operated by the vacuum?

Dv
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
There is also a spring that 'returns' the piston to its closed position... pressure will equalise both sides of the piston and it will stay shut until vacuum is present... this is why you only need a weakish spring as the vacuum will have a job to over come the spring pressure and slow the release of pressure as it won't open as quick or as much

<tuffty/>
 

Stuart B

Registered User
This is why the splitter seems easier to understand in my brain - the orientation of its placement has the charge pipe pushing directly against the piston and spring rather than at 90 degrees. but even with a new spring it doesn't seem as stiff as the standard - but I need to forget about it being forced open by pressure when the boost is too high and instead being vented by the vacuum.


Dv



Interestingly, I was looking for a picture of a cut up 710N and on this post

http://www.audizine.com/forum/showthread.php/360423-710N-DV-Install-(Reverse)-Pics-and-Tips

there is a comment saying Audi originally fitted the 710N in reverse but people complained about a noise so they switched the orientation, don't know how much truth is in that?

Dv
 

superkarl

MAN OF STEEL
I trying to learn so it's good to be corrected.

My visualisation of the **** splitter dv is the turbo sends the air down the charge pipe that pressurises the DV and n75 in addition to throttle body.
The N75 may pass the pressure to the actuator if greater than map setting.

But I thought the only thing stopping the DV from sending the charge pipe pressure back into the tip was the spring and if the pressure is more than the spring, as a safety mechanism it will relieve the pressure? Hence why you tighten it another 5 clicks if the car is mapped. And the vacuum opens the DV on gear change to relieve the pressure again.

It might explain why I can't visualise how a standard DV orientation can get forced open by too much pressure.
A DV in the right orientation can't blow open. It may rupture if diaphragm type, or leak if piston type. But the boost seals the DV.
IMO the spring is just a helper for closing after it's lifted open with the vaccuum. Vaccuum can vary massively from car to car hence the need for diff springs.
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
As for banging on about split-a*se... I am gonna send one in to these guys I think..



<tuffty/>
 

badger5

www.badger5.co.uk
Site Sponsor
I trying to learn so it's good to be corrected.

My visualisation of the **** splitter dv is the turbo sends the air down the charge pipe that pressurises the DV and n75 in addition to throttle body.
The N75 may pass the pressure to the actuator if greater than map setting.

But I thought the only thing stopping the DV from sending the charge pipe pressure back into the tip was the spring and if the pressure is more than the spring, as a safety mechanism it will relieve the pressure? Hence why you tighten it another 5 clicks if the car is mapped. And the vacuum opens the DV on gear change to relieve the pressure again.

It might explain why I can't visualise how a standard DV orientation can get forced open by too much pressure.
forget the split-r thing its shyte

Think OE dv or piston forge equivalent if that pleases you.

vac + pressure goes into top port.. ie above piston/diaphragm.. so has boost acting onto to holding it closed under boost. Also has spring to push it back closed again when vacuum is applied sucking it up. So Spring + boost is what holds it closed.. More boost more pushing it closed pressure. Stronger springs blah blah is BS and always has been.
 

Stuart B

Registered User
Thanks :)

so to be clear in my head!
if the turbo goes mad and is 50PSI or the vac line to the DV is pinched / clamped... the DV does or doesn't open to save the circuit?

The actuator via EBC/MBC/DIRECT connect is the only method by internal wastegate.
More than likely a hose popping off.

or can the OE DV be forced open or emergency diaphragm split (like my electric shower has a "too much pressure" release valve if the shower head is blocked)

Karl answered this above - that's what was doing my head in :)

"A DV in the right orientation can't blow open. It may rupture if diaphragm type, or leak if piston type. But the boost seals the DV."



Incidentally, if a diaphragm does split on OE DV does it ever find its way through the TIP into the turbo, or is that protected by the OE DV design.

I thought that was going to be one question - but it is just another bunch of ramblings :)
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
DV won't operate without seeing vacuum... this is pretty impossible under boost hence the reason the N249 setup is there to enable switching to a vacuum reservoir... the ECU will cut throttle and operate the N249 if it needs to... and if you have it of course...

<tuffty/>
 

Stuart B

Registered User
DV won't operate without seeing vacuum... this is pretty impossible under boost hence the reason the N249 setup is there to enable switching to a vacuum reservoir... the ECU will cut throttle and operate the N249 if it needs to... and if you have it of course...

<tuffty/>

yeah that was my understanding - if you have an accident and the cars on full throttle in a hedge the N249 will keep the DV open - mines in the shed :D

I suppose if you blow a hose off on constant full boost that's a fire waiting to happen.

Thanks for all your help and patience, I knew what the question was, but since I live near a main road (dementia) couldn't construct it in a simple enough sentence :)


My sister's Renault Laguna diesel turbo went mad a few years ago, she turned it off, took the keys out, took the kids out the back and stood at the side of the road for 10 minutes whilst it was running on full power for 10 minutes and finally broke - I think a turbo seal went and the engine was somehow running on its own - maybe on oil?
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
if you have an accident and the cars on full throttle in a hedge the N249 will keep the DV open

N249 is a protection circuit for over boost situations...

I knew what the question was, but since I live near a main road (dementia) couldn't construct it in a simple enough sentence

Tru dat...

My sister's Renault Laguna diesel turbo went mad a few years ago, she turned it off, took the keys out, took the kids out the back and stood at the side of the road for 10 minutes whilst it was running on full power for 10 minutes and finally broke - I think a turbo seal went and the engine was somehow running on its own - maybe on oil?

Yes... its known as runaway... it will combust its own oil and rev its t*ts off until either the oil runs out, engine explodes or you deprive it of air

<tuffty/>
 

badger5

www.badger5.co.uk
Site Sponsor
Thanks :)

so to be clear in my head!
if the turbo goes mad and is 50PSI or the vac line to the DV is pinched / clamped... the DV does or doesn't open to save the circuit?

The actuator via EBC/MBC/DIRECT connect is the only method by internal wastegate.
More than likely a hose popping off.

or can the OE DV be forced open or emergency diaphragm split (like my electric shower has a "too much pressure" release valve if the shower head is blocked)

Karl answered this above - that's what was doing my head in :)

"A DV in the right orientation can't blow open. It may rupture if diaphragm type, or leak if piston type. But the boost seals the DV."



Incidentally, if a diaphragm does split on OE DV does it ever find its way through the TIP into the turbo, or is that protected by the OE DV design.

I thought that was going to be one question - but it is just another bunch of ramblings :)

The ECU, should go wtf in the event of overboost and attempt to open the DV, turn off N75 and close throttle... Presuming of course things have'nt been deleted.... *cough* N249 etc
 

Stuart B

Registered User
I wonder whether it would fail "scrutinising" at a race track with the N249 in the shed?

If I remember rightly from the n249 delete thread because my version of S3 has Fly By Wire - it was relatively safe to remove the N249 - as the ECU would close the throttle.
 

<tuffty/>

Badger 5 Edition...Its all about the flow...
Staff member
Moderator
I wonder whether it would fail "scrutinising" at a race track with the N249 in the shed?

Only if it was in the MSA rules to run one for the series the car is entered into... which it won't be...

Like most 'safety systems on modern ECU's its there for litigation mitigation more than anything else... pretty sure there are plenty of manufacturers running turbo's with less kit than VAG plaster their engines with...

<tuffty/>
 

badger5

www.badger5.co.uk
Site Sponsor
I wonder whether it would fail "scrutinising" at a race track with the N249 in the shed?

If I remember rightly from the n249 delete thread because my version of S3 has Fly By Wire - it was relatively safe to remove the N249 - as the ECU would close the throttle.
nope - msa would have nothing to say about it - obviously
 
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