PRV Testing

[boostin20v]

Anyone tested various pressure PRV with software that the tuner claims will adapt for an upgraded PRV of 150 bar or higher? RS4 PRV is out...rated pressure is too low, and the rest on the market are 155 (APR) or higher in the 165/175 bar range. If the software adapts...would a higher breaking point for the valve always mean more fuel in the motor and thus more power? Software already requires S3 injectors and HPFP upgrade.

If the pressure supported by the PRV largely doesn't matter, than going for the lowest cost unit above the software threshold would make the most sense whereas if each pressure increase the PRV supports will output a bit more power than buying largest would be better.

thoughts?

[Brillo]

You need to match the PRV with your particular tune. Basically, your tune should not call for higher rail pressure than the relief pressure of the PRV. The ECU controls the rail fuel pressure by controlling the amount of fuel allowed into the HPFP via the Pressure Regulator Valve (N276), not to be confused with the PRV which is purely a mechanical relief valve. Certainly, higher pressure in the fuel rail is capable of delivering more fuel charge to the cylinder, and higher volume fuel injectors may work better with higher fuel rail pressure.

I'm sure you realize the stock HPFP peters out at higher boost pressures at higher RPMs, so you'll need to invest in a higher volume HPFP.

[EvolutionArmory]

^^^ This.

The PRV doesn’t control jack. All it does it take a dump if rail pressure exceeds its rating. Requested fuel pressure is all ECU controlled and the PRV has nothing to do with how much fuel pressure is requested.

My tune asks for 130 bar so I run the RS4 PRV. Swapping to a 155 valve won’t change the rail pressure for example. It only asks for a max 130 bar. You want a PRV rated a few bar more than requested and going much higher than that nets you absolutely nothing.

[boostin20v]

As stated injectors and HPFP were already part of the mix, and how the PRV isn't in question...but thanks for stating that again.

The tuner claims that any PRV above 150bar will work and the tune will adapt. long and short....cheapest PRV I can get my hands on above 150bar will be fine, thanks

[EvolutionArmory]

Sounds like your tuner doesn’t understand how the PRV works. The PRV only reacts to pressure above what it is rated for. There’s no adapting to anything. The valve is “dumb”. If your tune asks for 130 bar, get a 136. If it asks for 140 bar, get a 155. The only important thing is you get a valve that is rated higher than what your tuner sets requested fuel pressure to so it doesn’t dump fuel due to the odd fuel spike slightly over requested. He sets requested fuel, not the valve.

[i3oricua]

The tune won't adapt but the tuner will write the tune according to your limitations. If you have a 500 bar PRV and your tuner sees your mods and only asks for 130 bar of fuel pressure then the PRV won't do anything. If the tuner writes the tune for 550 bar of fuel pressure then when at wide open throttle (WOT) the ecu requests 550 the PRV will "crack" and dump fuel and the engine/car will experience fuel cuts or hesitation. You're on the right track of understanding but I don't think you explained your understanding of it well. I used exaggerated numbers to make the explanation clearer....at least I hope it was clearer. Sounds right in my head.

Now, the tuner may want raise your power levels then it will require more fuel and in this case higher rail pressure. A large consideration is the life of your cam follower and can your LPFP also keep up with the demand of the fuel request. Anyways, another discussion for another day.

[aluthman]

As stated above, the tune will not adapt on its own to a higher prv. The tune can be adjusted for one, but that requires changes by the tuner. The fuel rail pressure is controlled by the n276 to the pressure set via a table in the tune. The values in that table can be raised if you have a prv to aupport it, but nothing is “adapting” to it by itself.