CHRIS_D

I'm having my sti5 remapped in a couple of months. I phoned the mapper today to pay my deposit and had a v.quick chat about what was needed, explained mods etc inc the Forge VTA DV currently fitted

Was advised to remove the VTA dump valve and fit a recirculating one instead prior to the remap.

Now the mapper is a well reputed one so im not doubting his advice in anyway at all, however just to satisfy my curiosity why would / should i remove and replace the VTA for a recirc for the remap.

BTW I'm after a technical answer here in relation to my curiosity, not the usual 'it sounds stupid' answers

chris

CHRIS_D

anyone ?

stevebt

iTrader: (8)

had my car mapped twice with a blitz VTA dump valve and have had no problems,
i was told that by using a VTA it might confuse the maff signal as its mapped on how much air to use and the VTA dump valve changes that( or something along that lines) anyway as i said mine is fine

Pitzi

Similar problem here, but this one is the recirculating one....... http://bbs.scoobynet.co.uk/showthrea...86#post3186886

greasemonkey

Erm, because they sound stupid, and make your engine run worse!

More seriously/technically though, the Subaru ECU calculates the air:fuel ratio under boost by measuring the amount of air that flows into the car via a mass-airflow sensor (the dreaded MAF sensor) in the early part of the induction tract.

Recirculating dumpvalves allow air to pass from the pressurised side of the inlet tract back into the turbo inlet, and thus the MAF values remain correct at all times.

If you use an atmospheric dumpvalve, dumped air is vented out of the system, and so, the fuelling values calculated by the ECU on lift-off and (for a short period) will be wrong. The overfuelling that results can cause popping and banging as unburnt fuel ignites in the exhaust, but can also cause bore wash and subsequent oil contamination, both of which can cause premature engine wear.

greasemonkey

Should have added that, in response to the question posed in the header of your first post, namely "VTA dump valves and re-map - are they / arnt they compatible ?", the answer is that vent to atmosphere dumpvalves aren't properly compatible with any MAF based Subaru ECU, remapped or not.

CHRIS_D

thanks for the reply GM

have since replaced VTA BOV with OE item and have also had a PM from Bob Rawle giving more or less the same answer and advice

Anyone want a Forge VTA BOV ?

chris

RB5_245

Actually I do!

You have a pm, or will have if i can figure the damn thing out!

Dave

CHRIS_D

dave you have a pm back mate

sold the vta already