what are?

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samueljon
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what are?

Post by samueljon » 15 Apr 2011 04:04 pm

the advantages of running a fuel pressure regulator on a f7p engine?

does it just help you control what pressure the fuel is at the injectors?
in which case how do you know what pressure you should be running?

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Chris_C
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Re: what are?

Post by Chris_C » 15 Apr 2011 07:13 pm

You need an FPR on it to work... do you mean an adjustable one?
'89(G) 340 GLE B172k
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Ex:
'89(F) 340 GL F7R (ex B172k) - Fake -> SBKV 300 Runner Up 08, 12; '91(H) 340 GL B14.4E - Kar; '88(F) 360 GLT B200E - Jet -> BKV 300 Runner Up 09; '89(G) 360 GLT B200E - Beast

samueljon
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Re: what are?

Post by samueljon » 15 Apr 2011 11:22 pm

Would they not all be adjustable? Or are there ones set at certain pressures?

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Chris_C
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Re: what are?

Post by Chris_C » 16 Apr 2011 10:58 am

The F7x fuel rail has a fuel pressure regulator fitted into the end of it, it's what makes sure the fuel is always at the right pressure the injectors are expecting rather than fluctuating with the fuel pump.

You can buy adjustable regulators that let you change that pressure on the rail, so when the injector opens for x time, it lets more fuel through as it's at a higher pressure. To my mind, that's a horrific bodge that's no better than the power resistor of justice :lol:
'89(G) 340 GLE B172k
'03 S60 D5 SE, '91 (J) MX5, 1954 Cyclemaster
Ex:
'89(F) 340 GL F7R (ex B172k) - Fake -> SBKV 300 Runner Up 08, 12; '91(H) 340 GL B14.4E - Kar; '88(F) 360 GLT B200E - Jet -> BKV 300 Runner Up 09; '89(G) 360 GLT B200E - Beast

samueljon
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Re: what are?

Post by samueljon » 16 Apr 2011 04:57 pm

i just wondered what the pros and cons where :) so really you could just run what ever pump as it will be limited on the rail itself?

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Chris_C
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Re: what are?

Post by Chris_C » 16 Apr 2011 07:21 pm

I'm not too sure on this tbh, I'd like to say yes but I don't understand whether the reg lets everything above 3 bars worth (lets say) pass through, or whether it just lets 20% past. Both numbers pulled out my backside but hopefully you get what I mean ;) I run a larger pump than most and can't notice anything between my F7R and Speedy's when we've had them side by side, we both run the same map too.
'89(G) 340 GLE B172k
'03 S60 D5 SE, '91 (J) MX5, 1954 Cyclemaster
Ex:
'89(F) 340 GL F7R (ex B172k) - Fake -> SBKV 300 Runner Up 08, 12; '91(H) 340 GL B14.4E - Kar; '88(F) 360 GLT B200E - Jet -> BKV 300 Runner Up 09; '89(G) 360 GLT B200E - Beast

zombeh
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Re: what are?

Post by zombeh » 17 Apr 2011 01:10 pm

Chris_C wrote:I'm not too sure on this tbh
All fuel pressure regs work roughly the same, there's a valve that allows fuel to flow back to the tank, and a spring keeping it shut. The preload on the spring sets the fuel pressure, typically this is set by shims, most aftermarket regulators are adjustable so have a screw instead of shims so you can adjust the preload.

So if the spring is set at 3 bar then any pressure above that will force the valve open by hopefully enough to bleed that pressure off back down to 3 bar. If you have a massively powerful pump and too small a hole in the regulator valve to allow the fuel back to the tank then that'll restrict the flow of fuel and the pressure will rise. It's the quality of the spring and the size and shape of the hole that are the important factors in whether it works properly or not.

If your pressure reg is a bit shit and you stick a massive high flow high pressure pump on it then you may not get the pressure you expect all the time.

So to answer the original question, the advantage of running a fuel pressure regulator returning to the tank on an NA engine is that it's cheaper and easier than building a magic box full of pixies* to control the pump to give the right amount of fuel all the time. (on turbocharged engines that would read "cheaper and MUCH easier" as the pump controller would have to adjust not only for the amount of fuel you're using but also for the boost pressure trying to force it back into the fuel rail, whereas with a simple mechanical regulator you just run a hose from the inlet manifold to the spring side of the valve)

*Pixies should perhaps read "electronics"

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