Looking at the the two dyno runs there is a noticeable dip in power that occurs from 2750 to 3250 rpm. I wonder if this is related to the inablity of the fuel pump to provide sufficient pressure/ flow for the requested demand.
The Pump used is a CP4.1 with a single barrel .The designation R35 refers to the capacity of the pump. The pumps have various size pistons and different strokes to alter the capacity.
Inside the HPFP - TDIClub Forums
If you look at the pump on a 3.0 V6 they use a cp4.2 rated at R65 nearly twice the capacity for only 240bhp.
The pump used in the VRS is used across many other engines in the VAG range from the 1.6 through to the 2.0 engines.
It's in the interest of the manufacturers to size the pump at a level that just does the job. Larger capacity pumps take more power to run so impacting fuel economy etc.
With this kind of tuning box they rely on upping the pump pressure to get more fuel flow. If the car currently calls for 1700 bar when running flat out and you want 10% more power you need more pressure If you raise the pressure to 1870 bar that will give you roughly 10% more fuel but obviuosly there is a limit to how much pressure you want to ask for.
This tuning box uses a second channel to massage the boost signal to produce some more boost to try and keep the AFR reasonable and the EGT's down as well as looking after the DPF a bit but at the end of the day it's fuel that gives power so when there is talk of 30% improvements you know thats never going to happen with this kind of box as the fuel pressure would have to be off the scale.
You can get large improvements in the mid range performance with big gains in fuel pressure and boost over what the car would normally have and this can be seen in the dyno plots.
I agree that the final run on the shark dyno at 220bhp sounds plausible. Going from 184bhp to 220bhp would be a 17 % improvement and going from say 1700 bar that would mean the pump pressure would be around 2050 bar. 1700 / 0.83 = 2048.
The CP4 pump is designed for 2000 bar max .
The reason I asked about pump pressure is there is a big issue with these pumps in the USA, probably related to the poor quality of their diesel and the money saving approach that is taken with these pumps that are no where near as reliable as the old school CP1 , CP3 pumps.
These boxes have a place in the tuning world but I don't think it's for out and out performance. On a remap if you want more fuel you probably will increase the pump pressure a little but most of the gains come from injecting for longer. It's the pressure the pump is generating that wears them out not the volume of fuel it's flowing.
Karl.
