Power Boost Valve fitted - power & torque down

[House]

Just picked my '96 Griff 500 up from a tuning company after service and some minor upgrades. Following a rolling road session last year (max power 259bhp@4951 rpm/torque 300lbft@4k rpm) it was suggested I had the standard Fuel Pressure Regulator replaced with a power boost valve as this would allow greater degree of control over fuel delivery. I've also had the injectors ultrasonically cleaned (now improved and more consistent pressure as a result) and a K&N air filter fitted (the old foam one was heavily clogged with dirt/oil). The latest rolling road figures now showing max power 254bhp@5200rpm/torque 295lbft@4krpm. The garage is saying whilst peak power/torque down slightly, the mid-range is up but this doesn't appear to be right as, comparing the two graphs, the curves are almost identical except for the lower figures on the latest run. I noticed on the invoice the power boost valve is for a 3.9i Chimera (https://www.carperformanceuk.co.uk/350i-power-boost-valves-pr-20871.html).

Appreciate in the real world I'm not going to notice the differences in power/torque here but can't help thinking I could have saved best part of £600 and left the car as it was! Is the power boost valve the problem here i.e. correct part for the engine? Whilst the garage isn't a TVR/V8 specialist they seemed to know what they were doing. Anyone else had one fitted with similar results?

[900T-R]

I think FSE uses the term 'Power Boost Valve' only for their 1.7:1 rising ratio fuel pressure regulators - which are fine for use with the old flapper type Lucas injection but not with the CUX14 hotwire system as on Griffs and Chims (which sort of have the same WOT enrichment feature 'built in' electronically) - what you want for these cars is a 1:1 ratio adjustable fuel pressure regulator which FSE also do.

[chrispitman]

As said with a 1:7 instead for the 1:1 it will also be overfueling, under 3500rpm the lucas uses the lambdas to adjust fuel but after 3500rpm they don't so unless the ecu has been mapped with th 1:7 reg it will be overfueling.

[GreenV8S]

House said:

Just picked my '96 Griff 500 up from a tuning company after service and some minor upgrades. Following a rolling road session last year (max power 259bhp@4951 rpm/torque 300lbft@4k rpm) it was suggested I had the standard Fuel Pressure Regulator replaced with a power boost valve as this would allow greater degree of control over fuel delivery. I've also had the injectors ultrasonically cleaned (now improved and more consistent pressure as a result) and a K&N air filter fitted (the old foam one was heavily clogged with dirt/oil). The latest rolling road figures now showing max power 254bhp@5200rpm/torque 295lbft@4krpm. The garage is saying whilst peak power/torque down slightly, the mid-range is up but this doesn't appear to be right as, comparing the two graphs, the curves are almost identical except for the lower figures on the latest run. I noticed on the invoice the power boost valve is for a 3.9i Chimera (https://www.carperformanceuk.co.uk/350i-power-boost-valves-pr-20871.html).

Appreciate in the real world I'm not going to notice the differences in power/torque here but can't help thinking I could have saved best part of £600 and left the car as it was! Is the power boost valve the problem here i.e. correct part for the engine? Whilst the garage isn't a TVR/V8 specialist they seemed to know what they were doing. Anyone else had one fitted with similar results?

If you want a bit more power then next year when your K&N filter needs replacing you could upgrade it to a good high flow foam filter. These are easily cleaned and re-oiled and will last as long as the car lasts. Ask your 'tuning' company, they can probably find an old dirty one kicking around at the back of their workshop which they would let you have for a fair price.

The rising rate fuel pressure regulator will have effed up the fuelling, depending how they're set it it will either be lean on part throttle or rich on full throttle. If they are people who are trustworthy to run your car on the rolling road then they should also be monitoring the air/fuel ratio (among other stuff) and it would be immediately obvious that the car was over-fuelling.

PS £600 to clean the injectors and fit a new FPR and air filter seems rather excessive to me.

Edited by GreenV8S on Sunday 26th July 13:11

[House]

Thanks for the comments. Sounds like my best bet would be to have the standard regulator re-fitted and get car set up on this basis. Presume the 1:1 adjustable fuel pressure regulator, such as sold by Sytec, not going to acheive anything unless I get re-map as well? Appreciate help.

[GreenV8S]

A 1:1 fuel pressure regulator is what you want. The "1:1" means that as the manifold pressure goes up by 1 psi, the fuel pressure goes up by the same 1 psi. This means the pressure drop across the injectors is constant, and the ECU is mapped to suit this.

Aftermarket adjustable is fine as long as you set it accurately, but an ordinary standard fixed one is all you need.