That's quite interesting to know, perhaps something I'd consider trying myself.

It will allow the Rail to run at 136Bar

So if you have a map which request 130bar it wont keep fluctuating as much around the 127-132 bar it would be more consistent around 132-134 bar. In theory.

Looking at the Logs being posted it seems to do this and more. So can only help make it smoother if nothing else. Smooth is good (as i always tell the wife )

However your going to need a map that asks for that pressure

A positive or negative fuel pressure deviation wont give any more fuel unless stock injectors are at their max allowed duty cycle. It will just correct injector opening time so that the fuel mass required is reached.

The only benefit I can see is if you're totally maxing out your injectors and/or your HPFP. 5bar more pressure wont give much better spray, so air/fuel swirl in combustion chamber (better swirl gives better torque) isnt improved much.

ECU calculates fueling by calculating the fuel mass required for the air mass entering the combustion chamber. If it detects deviation from setpoint values, it corrects the injector opening time to keep the fuel mass constant. So if your fuel pressure deviates by lets say +10%, it opens the injectors about 3-4% less.

Just based on those logs, I dont believe you get much gains from that mod, but I'm going to test it when I have a spare second, just to be sure.

It will allow the Rail to run at 136Bar

So if you have a map which request 130bar it wont keep fluctuating as much around the 127-132 bar it would be more consistent around 132-134 bar. In theory.

Looking at the Logs being posted it seems to do this and more. So can only help make it smoother if nothing else. Smooth is good (as i always tell the wife )

However your going to need a map that asks for that pressure

Are you going to give this a punt Carl....since you've swapped pretty much every other sensor and valve?

It would be good to see some before and after dyno plots with this as the rail pressure figures are a bit of a 'surrogate endpoint' for true performance gains. I have been looking at this for a while but have been a bit put off by the lack of dyno info and JKM's comment that I mentioned earlier (albeit with respect to a K04 car with S3 injectors). I may still do it as one point in the O.P. was that some stock valves can be weak and I have a suspicion of this on my car.

Edited 24 November, 201015 yr by muckipup

A positive or negative fuel pressure deviation wont give any more fuel unless stock injectors are at their max allowed duty cycle. It will just correct injector opening time so that the fuel mass required is reached.

The only benefit I can see is if you're totally maxing out your injectors and/or your HPFP. 5bar more pressure wont give much better spray, so air/fuel swirl in combustion chamber (better swirl gives better torque) isnt improved much.

ECU calculates fueling by calculating the fuel mass required for the air mass entering the combustion chamber. If it detects deviation from setpoint values, it corrects the injector opening time to keep the fuel mass constant. So if your fuel pressure deviates by lets say +10%, it opens the injectors about 3-4% less.

Just based on those logs, I dont believe you get much gains from that mod, but I'm going to test it when I have a spare second, just to be sure.

Our messages crossed Mikko but I wanted to say that I found a post from a 'techie' on another forum saying very much the same thing. I can't find it now but I printed it off so will share it when I get home

Are you going to give this a punt Carl....since you've swapped pretty much every other sensor and valve?

It would be good to see some before and after dyno plots with this as the rail pressure figures are a bit of a 'surrogate endpoint' for true performance gains. I have been looking at this for a while but have been a bit put off by the lack of dyno info and JKM's comment that I mentioned earlier (albeit with respect to a K04 car with S3 injectors). I may still do it as one point in the O.P. was that some stock valves can be weak and I have a suspicion of this on my car.

I might aswell for £30.

I'll be severely pi55ed of :swearing: if it turns out it this solves it as it would have saved me around £1k in parts and about £400 in fuel

I might aswell for £30.

I'll be severely pi55ed of :swearing: if it turns out it this solves it as it would have saved me around £1k in parts and about £400 in fuel

I guess it's more about the hassle of getting at it with all the obstruction of the inlet manifold rather than the cost of the part. The guys that have done it have either taken the manifold to bits or have managed with bent spanners and similar home-modified tools. I think the guy on the Mk5 forum is going to post up his version of a 'How to' guide.

Yeah ive read that as well.

To be honest im only going to do it out of curiosity. As the rail pressure is fine, within tolerances and the requested is being met i can't see it making a difference.

I doubt it's going to suddenly give me 15+ bhp

As promised, here is the link to the page that I found a while back where a 6 bar drop in actual rail pressure is being discussed:

Fuel Cut with APR HPFP

Of interest is the responses from Mike@APR although he says "a 6 bar deviation will not cause a large enough change in injector on-time to result in any issues", I guess it does not go as far to say a deviation to the positive of a few bar (from a RS4 valve) would not be beneficial to a greater or less extent.