Project S4: Forge Motorsport Blow-off valve

Turbocharged cars, like my Audi S4, have blow off valves (BOV’s), often called dump valves, fitted to them. They prevent compressor surge “loading,” by allowing compressed air to vent to atmosphere (or be re-circulated), to reduce wear on the turbocharger and engine.
Nine times out of ten, manufacturers use horrible, cheap plastic BOV’s, which might do the job OK, but don’t offer the same turbocharger protection and surge control as uprated, metal units sold by aftermarket tuning companies. Nor do the OE plastic units last as long as the tougher, more advanced units.
In the past, I have fitted BOV’s from, with great results. NEVER ‘dump valves’ that dump the air to atmosphere, that emit high street “pssssu” hissing sound, I might add: Way too chavy for me, and my S4. I like the re-circulating versions, and Forge Motorsport (01452-380999) have a fabulous range of all BOV’s on offer – including their FMDV006 Fast Road Closed Loop Diverter Valve, with Adjustable Vacuum Connection units.
They cost £99.78 each, excluding VAT, and are suitable for all VAG 1.8T engines (single BOV) & Porsche 911/996 Turbo, Cayenne Twin Turbo and all VAG 2.7-litre Twin Turbo engines, as my 2.7-litre V6 £30V bi-turbo S4 is fitted with, which require two BOV’s.
The Forge BOV’s are manufactured from billet aluminium and are a re-circulating diverter valve system – which dumps the charge-air back into the air intake system. This keeps external hissing noises to a minimum.
As well as being made to last longer, the higher clamping load of the valve maintains boost pressure and quickens throttle response, by reducing turbocharger lag when you are off the throttle.
Fitting, up at Dave Green’s brilliant Henstead Motorsport (01502-714177), was easy as pie. Ten minutes: Remove the cover, un-screw the two connection clips, pull the OE valves out… bin them… then clip in the new, shiny, black anodised Forge Motorsport units. Done!
The effects are not dramatic: But they are most definitely noticeable… with a considerable decline in turbocharger lag (even on small twin turbos like on the S4) between throttle applications, and a matched increase in throttle response. There is a little increase in boost noises too – in a nice way, as you can hear the boost circulating through the inlet system, at full chat.
No hiss. No fuss. No need to replace… and a marked improvement in throttle response and overall performance. Another tuning result for Project S4, thanks to Forge Motorsport, and Dave at Henstead Motorsport. Result.