SetH
Member
Registered: 15th Jul 01
User status: Online
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pros and cons of each?
in particular on the VAG 1.8T engine.
I thought you could only use a recirc on the VAG engine as the atmo throws up loads of ecu fault codes.
There is a guy at work saying recirc is shite on this engine and that you should use an atmo with an electronic compensator???
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DAZ1985
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Registered: 3rd Sep 06
Location: Scholar Green, Cheshire
User status: Offline
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quote:
Originally posted by SetH
There is a guy at work saying recirc is shite on this engine and that you should use an atmo with an electronic compensator???
thats bollocks im sure
i think on them its the twin piston type you need something to do with the afm me thinks.
one makes a noise the other dont thats all thier is
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SetH
Member
Registered: 15th Jul 01
User status: Online
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must be more to it then just the noise surely? or wouldnt all turbo cars have the same type of DV?
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DAZ1985
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Registered: 3rd Sep 06
Location: Scholar Green, Cheshire
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Not all turbo engines have the same specs though
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SetH
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Registered: 15th Jul 01
User status: Online
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true
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DAZ1985
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Registered: 3rd Sep 06
Location: Scholar Green, Cheshire
User status: Offline
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http://www.max-boost.co.uk/max-boost/intake/DV.htm
have a read of that
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abdus
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Registered: 23rd Feb 06
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most of the 1.8T VAG are same though
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Dave A
USER UNDER INVESTIGATION - DO NOT TRADE
Registered: 10th Dec 03
Location: County Durham
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we had a focus RS on the rollers on the weekend with an atmospheric, was causing all sorts of problems.
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abdus
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Registered: 23rd Feb 06
User status: Offline
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I have one of these:
http://www.forgemotorsport.co.uk/content.asp?inc=product&cat=1703DV&product=FMCL007P
and nothing wrong atm...just waiting for the remap
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Cupra Steve
Banned
Registered: 7th Nov 06
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Best to stick with a recirc on the 1.8t. There are so many threads explaining why not to use atmospheric dv's on www.seatcupra.net i think it's been made a sticky so have a look.
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Rob B
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Registered: 8th Jan 04
Location: Area Motorsport Drives: Race EP3
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ive heard that atmospheric shouldnt be used on 1.8T, my mate has a forge Split R 60% recirc and 40% atmosphric
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SetH
Member
Registered: 15th Jul 01
User status: Online
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found the post, all clear now.
incase anyone interested :
Eventually it will cause problems, took mine 8 months but it did, you will definately have a fault code relating to a pressure drop between the turbo and throttle plate, your ECU sees this as a leak, doesn't always throw an engine check light though.
The main concern is 'bore wash', unburnt fuel from venting to atmosphere (your ECU delivers too much fuel because the re-circulated air is gone) coats the bores of your cylinders and eventually this will cause your piston rings to fail due to lack of proper lubrication. The other concern is unburnt fuel gets dumped in your CAT which then overheats, melts and blows your turbo through excess back pressure.
Convert your car from a MAF to a MAP system and you can happily run a BOV without any problems, because the MAP sensor sees the pressure drop from VTA and adjusts the fuel delivery accordingly.
BOV on a MAF system doesn't work properly - period.
A modern engine management system, ie the Bosch Me unit fitted to 1.8T's has "adaptive" learning on the fuel, ignition and airflow side.
Because Me is a Torque based structure it's calculation of engine torque verses driver demand is critical to the driveability of the car and it's performance / durability.
When you fit a "leak" in the intake system (open circuit valve) the original calibration of the MAF sensor to manifold and cylinder filling modeling will not corespond. However due to the 20% allowance in the long term adaptive values the ECU will relearn you engine and "leak"
At idle the inlet model calculated airflow will exceed the MAF meters measured output, and depending on the state of your particular components - ie MAF ageing / contamination, throttle plate leakage, Fuel tank purge vapour concentration this may, or may not push the adaptive to it's 20% limit. If it hits the limit the ME unit will run in FMEM mode (Failure mode and effects management) causing reduced system efficiency. The Me unit will use the switching signal from the lambda sensor to return fuelling to lambda 1, storing the correction as a map agaisnt airflow. and add this correction to the fueling calc when operating at non closed loop conditions, ie WOT, fuel injector reenstatment (after overrun shut off, traction control intervention etc.) Now depending on how you drive and how sensative you are this may or may not be felt by the driver during certain manovevers. The throttle plate position will also learn the new airflow to maintain control of idle speed, but you may notice poor engine load rejection, ie turn on the aircon and the engine speed varries etc. or engine speed flares on starts or when operating PAS when parking.
However in all cases this will result in "incorrect" fueling. Now by "incorrect" i mean, not as the manufacturer intended. A post MAF leak will cause rich operation initially, but the adaptives will pull fuel out and become negative. This tends to cause a rich to lean spike on tip outs and other throttle transient. Now it is extremely diffucult for an untrained observer to spot these effects as they occur mainly on throttle transients, when the average drive may not notice. Therefore you could say "why do i care?". Well, any AFR excursion from the intended fuelling set by the manufacturer will result in non-standard engine operation. because of the adaptives this is unlikely to cause immediate engine problems, but over the course of time will change things like catalyst ageing, exhaust and turbo charger valve durability etc. Manufactures spend millions accruing miles on development fleets so hopefully the customers don't get landed with big bills as time goes on, and with most modern cars life'd at 150k miles (min design life) this is a big task.
It is unlikely that this will result in any performance loss, as at WOT the system is open loop, but you may see the result of an open circuit valve oas over fueling on gear changes etc. (a tell tail puff of black smoke is what you can see, a 1200 degC Catalyst is what you can't see, as excess fuel when injection reenstates and excess air from overrun shut off period combine in cat)
Now as you can see this is a seriously complicated subject and i haven't even mentioned the dreaded EOBD or OBDII words yet. Typically Bosch Me units have approximately 9000 calibratable parameters (constants, maps etc) and an engine calibration program will take a team of 8 calibration engineers 18 months to do the basic mapping and OBD validation. These days it's no problem to do the basic fuel and spark mapping, maybe 4 weeks on a midlimit engine on a dyno, but the diagnostics and emmisions devs takes years.
Moral or the story, before you start playing with something you don't understand, find someone who does!(And not just thinks they do!)
(for anyone thinking, "hey what makes me such an "expert" on this subject?" then i'd better mention the last 10 years i've spent as a senior calibration engineer at Cosworth and Prodrive!)
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whitter45
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Registered: 15th Nov 02
Location: Norton
User status: Offline
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can be done but will fail eventually
Best thing for the VAGs is to reloacte the DV - much better and one of the better mods I did
Also I have a forge DV but still with the spring not piston thus can shim the DV for better response
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Stu_22
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Registered: 25th Mar 02
Location: Luton
User status: Offline
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Same situation as me and other Mk3 Supra owners.
I have just got a piggy back ECU the ditches the Air flow meter and uses the MAP sensor ans speed density of the air flow
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