Fuel pressure reg mounting

[Marcus Miller]

will depend somewhat on jetting, but I'm under 3 Psi in my pro7.

Marcus (Pressure regulator mounted to shock tower)

[Andy Bettencourt]

Can't speak to the carbs but I think a couple hours on the dyno would be worth you while. On 2nd gen cars, we have optimized anywhere from 38 to 52lbs - depending on the car...weird I know but trial and error will yeild the best results for your own application.

We mount on the drivers-side inner strut tower.

AB

[bldn10]

Andy, this issue has come up before but I do not recall ever seeing a consensus. W/ you being a power that be and all, and using an after market regulator, what is your opinion? The question is whether the GCR allows you to modify or remove the stock regulator on a 2nd Gen. if you use an after market one. It don't say it. One person even suggested a custom fuel rail. How can that be legal? I realize that the stock regulator needs to be eliminated for the new one to work properly, and that the rules allow an after market one, but IMO that does not mean you can mess w/ the stock one. How is Flat Out dealing w/ this?

[Andy Bettencourt]

"Power that be"... How about 'tiny voice in the distance'...

Here is how I look at it:

The configuration of the S4 cars (injectors, CPU, etc) is such that they seem to like higher FP than stock. An in-line FPR will override the stock one so no mods are neccessary to get to where you need to be.

The S5 cars are different IMHO. We have seen the most power at LOWER FP that stock, so you must disable the stock FPR in order to make the aftermarket unit effective.

And I know you know all of this...so to answer your question:

If protested based on the literal wording of the GCR, I would defend myself by arguing that since an aftermarket FPR is allowed, it is inferred that the stock one may be disabled. I would point to the brake proportioning valve allowance as supporting evidence. It doesn't say you can disable the stock unit, so the limited effect a aftermarket BPV would have makes it illogical to think it can't be disabled.

As far as fuel rails, etc...some people take very liberal interpretation of the 'fuel lines are free" allowance - not us - we see them as two distinct pieces but I could see someone arguing it.

All of this is IMHO of course. Agree - disagree? Miller? Darin? Gulick? Amy?

AB

[lateapex911]

"Inferring" ...is logical, but, the old "It doesn't say you can.." thing comes into play.

I bet the rulesmakers need a little clarification on that one....

[Eagle7]

Originally posted by Andy Bettencourt@Sep 29 2005, 02:27 PM
... since an aftermarket FPR is allowed, it is inferred that the stock one may be disabled. ... As far as fuel rails, etc...some people take very liberal interpretation of the 'fuel lines are free" allowance - not us - we see them as two distinct pieces but I could see someone arguing it.

[snapback]61471[/snapback]

I look at this as "if it says you can, you bloody well can" (haven't heard that in a while). Since the S5 FPR is integral with one of the fuel rails, you have to modify that fuel rail in some way if you are disabling the FPR. But you can't modify it in such a way that it performs an illegal function.

[bldn10]

"Relative" power.

"The configuration of the S4 cars (injectors, CPU, etc) is such that they seem to like higher FP than stock. An in-line FPR will override the stock one so no mods are neccessary to get to where you need to be.

The S5 cars are different IMHO. We have seen the most power at LOWER FP that stock, so you must disable the stock FPR in order to make the aftermarket unit effective."

Oh Lord, now I'm confused. I thought the stock FPR operated by bleeding off pressure through the return line. Thus, if you boost pressure upstream and leave the stock FPR in place, it will bleed off that increased pressure. Conversely, if the upstream pressure is reduced, the stock FPR will never come into play. I.e. I understand exactly opposite of what you describe. You are more apt to be right but why?

"I would defend myself by arguing that since an aftermarket FPR is allowed, it is inferred that the stock one may be disabled."

Geez, that opens up a whole lot of options, doesn't it?

"I would point to the brake proportioning valve allowance as supporting evidence. It doesn't say you can disable the stock unit, so the limited effect a aftermarket BPV would have makes it illogical to think it can't be disabled."

To my knowledge I've never had a car w/ the BPV disabled. How can you tell?

[Eagle7]

Think of it like a garden hose with a hole (think injector) in it, but the end open (think return line). The water system (think fuel pump) can deliver lots of pressure, but with the end of the hose open, there's lots of flow but very little pressure in the hose, and not much leaks out the hole. You put your thumb (think pressure regulator) over the end of the hose - the pressure goes up and lots more water squirts out the hole. Your thumb isn't strong enough to withstand all the pressure the water system can deliver, so water starts streaming past it, increasing the return line flow and limiting the pressure at the hole. You put both thumbs on the end of the hose (think additional FPR) - now two thumbs are stronger than one so you can build up more pressure before the water streams past it. But your second thumb doesn't make the first one weaker, so it can't reduce the pressure at the hole.

The only reasonable location to plumb an additional FPR is in the return line after the injectors, and it can only increase the FP, not reduce it.