FSE Fuel Pressure regulator The power boost valve Words and Rolling road data: Thierry Zoller Edited by Rob Bell Click here to return to standard FPR page

How does the FSE 'Power Boost Valve' work?

The FSE Power Boost Valve is an adjustable fuel pressure regulator (FPR) that replaces the original equipment FPR (The FPR is also known as a control valve or pressure relief valve). The FPR plays an important role in the maintenance of the fuel pressure to the fuel injectors. The electric fuel pump supplies fuel at a high pressure to the fuel rail and injectors at a rate that is surplus to requirement. The excess fuel is returned to the fuel tank when the pressure in the fuel rail exceeds the pre-set pressure in the FPR. Typically, the regulator is not adjustable (it isn't on the MG Rover fuel rail found on MPi K-series engines) and is pre-set to a 3.0 bar maximum pressure - with a tolerance of 0.2 bar. This is not, however, a fixed pressure, as there is also control of fuel pressure dictated by inlet manifold vacuum (inlet manifold vacuum increases when the throttle is opened and the engine speed accelerates, and is practically zero at engine idle). Thus, at idle, the FPR opens at a value 0.5 bar lower at approximately 2.5 bar. When accelerating quickly from standstill (increased inlet manifold vacuum), the fuel pressure increases at a proportional rate - retaining a relatively lean fuel mixture strength as required by E.E.C. emission regulations for new vehicles. However, the effect of the standard FPR can result in:

By comparison, the FSE FPR has an adjustable fuel pressure, effected by the movement of an adjustment screw on the crown of the unit. New Power Boost Valves are pre-set with a maximum fuel pressure of 2.5, 3.0 or 3.5 bar, depending on the vehicle in question. Moreover, rather like the original fuel pressure regulator, the fuel pressure is reduced by approximately 0.5 bar at idle. However, on acceleration from standstill, the Power Boost Valve fuel pressure will increase at 1.7 times the standard rate. This produces a much richer fuel mixture strength which will instantly, the makers claim, improve the driveability of your MG, providing:

The FSE is said to enhance engine performance on acceleration by enriching the mixture strength. At idle and on constant throttle/ cruise conditions the valve returns to a 'normal regulator function' - effectively mimicking the standard fuel pressure regulator, so presumably there is a minimal impact upon fuel economy of gently driven cars. And once set up, these mechanical units are considered maintenance free - effectively, 'fit and forget'.

Does the FSE 'Power Boost Valve' work?

FSE's claims are quite grand - but do they withstand scrutiny? Moreover, what is the ideal fuel pressure setting for the FPR? And what happens if you decide to 'crank it up a bit'? Good questions all - and this is something that Thierry Zoller decided to try and find out during what must have been one very long session at the rolling road!

Rolling Road Results:

Typically, up-rated fuel pressure regulators are fitted to and work best with cars that have upgrades to other parts of the engine, be that high flow air filters, improved exhaust manifolds, free-flowing back boxes etc. Given that the MGF Trophy 160 in question was more or less standard, a Green Twister air filter induction kit was first installed into the car in order to optimise intake breathing. The effect of installing a Green Twister airbox is shown in the data summary below. The technician controlling the rolling road session was also on a learning curve working with the mid-engine MGs at this time, and as a result he choose different gear changes at different intervals: for the AIR filter test he always changed to 5th at 60 km/h; with the FSE tests, he did so at 40 km/h ... As Thierry says: "donno about the consequences and if both are comparable?"

Phase one: testing the Green Twister induction kit

Summary of results : [Figures in black: metric; figures in red: imperial]

Air filter specification	Power (@ peak rpm)	Torque (@ peak rpm)	Click to enlarge power curves
Standard Trophy 160 airbox	114 kW @ 7060 rpm 153 bhp @ 7060 rpm	174 Nm @ 4750 rpm 128 lb.ft @ 4750 rpm
Green Twister induction kit	120 kW @ 6910 rpm 160 bhp @ 6910 rpm	177 Nm @ 3810 rpm 131 lb.ft @ 3810 rpm
Power curve opposite, we have Green Twister TOP and Airbox lower: [Note that FSE had NOT yet been fitted before the start of these tests]

The result is that Thierry's Green Twister installation resulted in a very impressive gain of 6 kW (7 bhp) power and 3 Nm (3lb.ft) torque. With the intake side of the engine 'optimised' for testing, it was time to move onto the next stage...

Phase two: testing the FSE power boost valve

Thierry: "We then put a manometer between the FSE and the Engine. We measured a max of 3.5 bar on the FSE. We then increased /decreased the fuel pressure relief valve and made a few more runs."
With FSE installed (in conjunction with Green Twister Induction kit):

The peak power output for 3.3 bar was 120 kW (161 bhp) @ ???? rpm*

Reducing the pressure from 3.5 bar to 3.2 bar produced an additional 3kW (5 bhp) power and 5 Nm (4 lb.ft) torque. *Unfortunately, there were no printed results from the intermediate pressure setting.

On the power curves one can see that the FSE evens out power/torque flat spots.
Thierry: "I altered the graphics to analyse them, I find the influence of the FSE on the Torque curve very interesting.
"Please take a look at curves on the power graph shown and let's compare them. The UPPER curve is the 3.2 bar curve, the lower curve is the 3.5 bar curve (the mechanic who originally installed the FSE for me clearly made an error - he should have set it up at 3.2 bar, but as we measured using a manometer the actually setting was 3.5 bar, hence the stink of fuel when driving)."

What is abundantly clear from Thierry's data is that increasing the FSE baseline setting from 3.2 bar has a significant and detrimental effect upon engine power - certainly on this standard (airfilter notwithstanding), Trophy 160. What is likely to be happening with the higher fuel pressure is that too much fuel is entering the engine, and as fuel has volume, it means that less air is able to enter at the same time. Result? Less fuel is burnt - which is bad for engine power, and it is certainly very bad for fuel economy and emissions as well.

Conclusions

A number of conclusions can be drawn from Thierry's data. First, and unrelated to the FSE, is that the Green Twister Airfilter appears to be an effective airfilter replacement for the Trophy 160. But really, that's a side issue to the main question here - and that is "does the FSE do what it's maker's claim?" The answer to that is somewhat clouded as there were no rolling road runs with the standard fuel pressure regulator - so unfortunately,  this is a question that will have to be answered at another date. Some encouragement can be taken from the fact that this Trophy is producing comfortable more than MG claimed for the model (Green filter plus FSE set at 3.2 bar, this is a 165Ps rather than a 160Ps vehicle) - but this can't be taken as an endorsement of the product.
Ironically, the clearest conclusion that can be made is regarding how not to set up the FSE: increasing the fuel pressure setting above 3.2 bar has clear detrimental effects upon engine power (practically 1 bhp lost for every 0.1 bar over 3.2!). Essentially what this means is that if you plan to install an FSE to your car, and it has a similar to standard specification, do not exceed 3.2 bar. Of course, whether Thierry would have seen an even greater power gain had he used less than 3.2 bar (what would happen at 3.0 bar for example?) remains an unanswered question... It would be interesting to find out!

Acknowledgements

I would like to thank Thierry Zoller very much for the supply of this fascinating information regarding the FSE - information that he hopes will be of benefit to those in the MG community considering similar modifications.