The latest tuning development from Forge is so simple – and so effective – that it might just become a default fitment for forced induction tuners everywhere. We popped along to the company’s Gloucestershire HQ to watch it being fitted to a scene favourite – the venerable Subaru WRX.
No matter which field of endeavour you work in, every now and then, a product comes along that truly changes the game. It doesn’t have to be expensive or complicated like the mobile phone or microwave. In fact, it could be something as simple as a paperclip or a Biro. But once, you’ve seen it, you wonder why nobody thought of it before.
Can I put it to you then, that we are perhaps witnessing that moment right now? What you see before you is a small, relatively simple, yet utterly ingenious development from Forge Motorsport that might very well become a de rigueur fitment under the bonnet of every turbocharged car over the next few years. Good job they’ve patented it them, really…
Dump Valves – The Problem
Dump valves, Blow-off valves, call them what you will, but hopefully, we’re all reasonably familiar with the concept these components as a safe way of allowing excess boost to escape harmlessly when off-throttle, and holding the boost system tightly in check when mashing it into the carpet. Excess boost vents either to the atmosphere, with its familiar metallic sneeze, or for those that prefer their journey to sound a little more subtle, back to the low pressure side of the turbo circuit, depending on the type of valve you run.
On cars with low or factory boost pressures, the spring or diaphragm inside these valves only has to be a fairly weak affair. This allows the valve to move quickly and freely, but with the downside that the valve is useless on a tuned or high-boost car. That lack of resistance simply won’t be able to keep the valve gas-tight as the boost pressure increases.
For tuners, the solution to that problem has been simple for many years now, simply up the spring rate inside the valve (diaphragms tend not be up to the job on tuned vehicles) to allow it to cope with the higher internal pressures created by the tuning process. This keeps the valve shut under load, but with the downside that response time is reduced thanks to the spring being stiffer and therefore physically harder to compress.The fitment of the stronger spring can also limit the opening of the valve which restricts the volume of air it can flow.For this reason, most quality valves come with either a choice of springs or some kind of internal pre-load adjustment, in order to allow the tuner or owner to set the internal spring pressure to match their boost settings.
But this brings us onto to our next problem. Thanks to the plethora of sophisticated ECU software out there, these days, many cars also have some kind of easily-switchable throttle maps. On systems like EcuTek, where moving between throttle and boost maps can be as simple as clicking and flicking your cruise control switch, how on earth can a dump valve spring be perfectly set for your ‘everyday’ 1.0 bar map, but also work perfectly for your drag strip ‘all-out’ 1.4 bar mental mapping? Put simply, it can’t… so up until now, all dump valves had to be set to some sort of compromise to be a jack of all trades and master of none.
If only there was a way to make the dump valves spring operation completely independent of the spring pressure inside. A way to allow its function to work perfectly at any boost level. Clearly concerned by this very same problem, Forge’s technicians beavered away to find a solution. What they came up with is called the Intake Pressure Compensation Valve (or IPCV for short)… and it’s really rather clever.
The Science Bit
What makes the IPCV valve ingenious is that it re-routes the various high and low pressure feeds through a clever internal piston system (see diagram). When the throttle is opened and the car is accelerating, boost pressure generated by the turbocharger will ensure that whichever dump valve or recirculation valve you have fitted will be kept sealed. As no boost is now being lost through the intercooler (which can usually be anywhere between 1-3 psi of boost drop) the pressure acting on top of the piston of your dump valve is precisely equal to that underneath it. The result? Only a relatively weak spring is required to keep it operating, which means response times can be kept quick and throttle response is immediate.
Because dump valve springs usually have to compensate for the pressure drop across the intercooler, and this problem is now no longer an issue, the dump valve can now be run with a very weak spring. In fact, during testing, Forge has actually been able to make this system work with no spring in the dump valve at all!
When the throttle is snapped shut either to change gear, or on over-run, the vacuum created by the engine opens up the dump valve and allows the air to either recirculate back around the turbo (in the case of a recirculation valve) or straight back out to the atmosphere.
Put simply, what these means, is that even on a fire-breathing 1200 bhp GT-R, the dump valves now only require a very weak spring to operate perfectly with no boost loss, allowing them to open more responsively on partial throttle, improving performance in every gear – and at whatever revs you care to use. Best of all, this principle works as well on a bone-stock Subaru WRX as it does on a Drag-spec Evo. Boost levels simply don’t affect this part of the equation any more.
Fitting It Up
Keen to see how it worked in practice, we joined Forge’s development engineer Dom Hensley, the man who came up with concept of the IPCV, as he fitted one to his own WRX Wagon. Standard apart from an EcuTek remap and a cat-back exhaust, this car is a great representation of the ‘real-world’ tuning scene. Although the IPCV will work brilliantly with any stock dump valve, in this case, Dom was also going to fit one of Forge’s much loved ‘vent to atmosphere’ dump valves to add a little drama to his daily commute. Well, there’s nothing like that sound to liven up rush hour, is there?
The Forge VTA dump valve was very easy to fit, bolting directly to the intercooler flanges, exactly as per the OEM version. The recirculation side was simply plugged, the bolts tightened, and that’s it. Normally, at this point, the original vacuum line would be re-attached to the new valve, but on this fitment, this was left off to allow the new IPCV to be fitted.
The IPCV kit comes with everything needed to fit any turbocharged car, including the valve itself, all brackets, new race-quality silicone vacuum lines, joiners and T-pieces – and even a series of different sized stubs to ensure a perfect fit on your factory boost and vacuum lines. Not half bad for the all-in kit price of around £80!
Once a suitable bracket had been chosen and fitted from the kit and the valve bolted to a suitable spot (we didn’t forget to leave room for the bonnet to shut) it was a relatively simple case of routing the new silicone pipes to their new homes. The kit came with a generous length, so by laying it over where it needed to run, cutting carefully, and then fitting with the connectors and T-pieces provided, it was the job of mere minutes. Once we had checked that everything was tight, and the new hoses were neatly cable-tied in place,we hit the local highway for a road test.
On a car like a mildly tuned WRX, we didn’t expect the difference to be earth shattering, but it was apparent that the new dump valve, which had been fitted with Forge’s softer ‘green’ spring, was now very crisp and positive in its action compared to the relatively lethargic action of the stock valve. By way of comparison, we also tried circumventing the new IPCV and running the dump valve with factory-style vacuum routing, and you can genuinely feeling a difference between the two, with the car having just a little more response through the gears with the new IPCV system fitted. Obviously, the further up the tuning food chain you go, the bigger this difference will become, as you will be able to run a much softer and responsive dump valve spring on a car that simply would have not been able to cope with it before. In short, this is a revolutionary little mod, for a very sensible amount of money. Best of all, it is going to work on every Japanese turbocharged car out there, irrespective of its output or price. Expect to see a lot of these under bonnets at shows and race meetings over the next few years!
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