25 replies to this topic

[Wiggy]

Now, I realise that the modern 'S' kits provide one, but my JCG converted MPi doesn't.

Has anyone ever taken a well driving, problem free MPi S, and done a before and after power run to see if one is necessary/beneficial? Or at least a gas analysis?

Ive had a read of as many threads as I can about them, and some people say it did wonders for the way the car drives. Mine drives perfectly though.

But it's possible that fitting one just masked an existing problem? Tired or partially blocked injectors? Tired standard FPR? Dodgy O2 sensor? I don't know, just surmising.

Does anyone has any views or evidence on
the subject?

[Bat]

Hi,

Well it it depends on whether the car was mapped for one if you're comparing what has and hasn't got one fitted.

There's more than one type of adjustable fpr there's a standard 1:1, there's the rising rate or power boost valve and the 2:1 race valve. 

Obviously the mpi engines run out of injector window as more fuel is required for mods to the engines air flow, so to get more fuel in during the window you use more fuel pressure.

Cheers 

[Wiggy]

Ta for the reply.

My MPi isn't mapped, and it's not possible to 'map it' as far as I know. The MEMS2J is very sophisticated.

I understand that if the engine is running out of fuel, the ECU will try to compensate by increasing the pulse duration. This has its own problems because of the siamese ports. But a FPR set to a higher level is bypassing the ECU and injecting fuel at a greater rate than it realises. Thus fooling the ECU.

My question is; is it beneficial?.... Is it needed?

[Bat]

Hi,

What do JCG do to the engine then, surely the map must be altered to increase the fuelling for whatever they did or is it just done with the FPR?

Cheers 

[hazpalmer14]

Hi,

What do JCG do to the engine then, surely the map must be altered to increase the fuelling for whatever they did or is it just done with the FPR?

Cheers 

 

The ECU can self adjust to an extent. WIth more air flowing into the engine the ECU senses this through its various sensors and in turn adds more fuel. You can tune the engines to an extent but only within the ECUs limitations and then to get more you would have to go to something like megasquirt etc

[Bat]

Hi,

It only self adjusts when in closed loop mode the rest of the time it refers to the the map as its only a narrow band sensor.

Cheers 

[Wiggy]

Just to be clear. The ECU is totally standard with these conversions.

The injector pulse width is controlled by the ECU. By increasing the fuel pressure, you're increasing the amount of fuel injected within the fixed pulse.

I'm not really a fan of the idea in principle, but I'd love to know of the actual benefits. If any.

[Shep76S]

On my 96 Spi JC's fitted a resistive link in the coolant circuit so the fuel was richer

[Wiggy]

On my 96 Spi JC's fitted a resistive link in the coolant circuit so the fuel was richer

Never heard of that before! Not sure I like the idea of that....

[Sprocket]

The correct FSE power boost valve fitted to the S Works engines is what is called a rising rate valve. What this means is the differential fuel pressure rises as the manifold pressure rises. This is slightly different to the normal FSE pressure regulator or the standard fuel regulator for that matter, where the differential fuel pressure remains fairly consistent as the manifold pressure rises.

The reason this type of valve is used, is to increase the AFR in open loop high load engine conditions where more fuel produces more power. The A Series 5 port engines like fueling around 12.5:1 and produce power there rather than loose it. Most OEM engines of the period are only tuned to low 13's AFR high load conditions, so increasing the fuel pressure in this region increases the fuel delivered, decreases the AFR and in theory increases the engine power (other modifications dependant)

[Wiggy]

Ok nice. That gives me some background knowledge, which is most helpful. But why was it not always standard with the S Works package?

I get the theory behind it, but does it actually increase power with the S Works cars? There doesn't seem to be concrete evidence of such.

[Bat]

Hi,

If the ECU is unchanged and it cannot sense an increase in airflow as there's no MAF, then the only thing that can richen the mixture when the engine is modified is the FPR as Sprocket has stated. 

Was there 2 different S works packages?

I can't see a power boost valve giving you much unless there's a shortage of fuel in your current setup?

As is well known tuning a modern engine doesn't give massive gains, unless you make massive changes and that's made more difficult with Siamese ports.

Cheers 

[drs]

my jcg s5 has a "up rated" fpr, i am very sure its not the std mpi one.  my s5 came direct from jcg in 97, i am the only owner!

 

it not the same as the mini sport large thing.

 

are you sure yours is std?, they have the same size ish!

 

paul

[minifreek1]

I had a FSE 'Power Boost Valve' on my X20XEV powered Vectra, and it made absolutely no difference whatsoever to the power then engine produced. Was always consistantly 140BHP (rolling roaded). The reason as it was explained to me was that because of a closed loop system (using MAF sensors, Lambda sensors etc....) the ECU would only allow so much fuel into the chambers, if the fuel pressure was increased, then ECU would see it and cut back to amount of fuel it needed to run.

[viz139]

How close to the limit do Rover injectors run. If you improve the induction system, K&N filter , larger throttle body ,high lift rockers and larger valves is it possible to deliver more air than than the injectors can deliver at max pulse at standard fuel pressure. The ECU cannot control the amount of air entering the engine it just delivers the amount of petrol needed to maintain the AFR. Maybe the higher fuel pressure ( or larger injector) is needed to overcome this limit.