S5 upper fuel rail & aftermarket FPR

Eagle7

Eagle7

New member
S5 intake manifold. Upper (secondary) fuel rail has an integral fuel pressure regulator. In order to use an aftermarket fuel pressure regulator, I need to remove this one. It's not clear to me that it's feasible to (easily) modify this rail to remove the FPR. Plan B is to make a new rail from universal fuel rail stock - should be legal because it's a fuel line. BTW, AN fittings and SS lines are part of the plan. Am I on the right track?

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
If you are not comfortable doing the mod to the fuel rail yourself. ISC Racing (iscracing dot net) will do it for you for $35, which is what I did. Then just plumb in an adjustable fpr.

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction
 
Can you describe what they did to it? I'm pretty comfortable trying most anything. Its knowing what/how to try that eludes me. Ideally, I'd like to eliminate the FPR and the nipples on each end, adding AN-6 fittings directly into each end.

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
Basically all they do is cut off the stock FPR and weld the end shut and powder coat. This approach still uses high pressure rubbber fuel line rather than AN fittings and flex metal lines.

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction
 
Marty, personally I don't care but I don't think a fuel rail is a fuel line, and you cannot build a new one. I even question that the FPR can be removed. I don't know what ISC does w/ it but if it's gutted/disabled no one would ever know but, still, it's not a mod that is specifically allowed. If it prevents an aftermarket pump and regulator from working properly I can see how the argument could be made that the mods are part of the legal pump/regulator installation but that may be stretching it.

How does that thing work? Does it bleed off pressure at a predetermined level? Does it matter if the vacuum/? line is removed and left uncapped? My used SS car has the FPR still there but the fitting is open. It does not have an aftermarket regulator. Aside from the rules, is there power to be gained in all this?

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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
"Fuel line(s) may be replaced, relocated, and given additional protection."
"An external fuel pump pressure regulator may be installed."

Not sure if I've got this exactly right, but "if it says you can, you bloody well can". It's not possible to use an external fuel pressure regulator with the stock unmodified fuel rail. If there was, I would do it. So now what we're discussing is the extent of modification allowed. Since I don't see any restriction in the GCR on that modification, I'm very confident that I can do it any way I want, as long as I don't also provide with it some prohibited feature. Golley, all we're talking about is a tube that carries fuel for a couple inches, and the entire fuel delivery system to and from it is nearly unrestricted in size, materials, capacity, etc.

The reason I need an external FPR is to adjust my mixture. I ran pretty lean last summer, and it may have contributed to my blown engine. Now if I had a MoTeC...
smile.gif


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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
"Fuel line(s) may be replaced, relocated, and given additional protection."

Given. But I don't think that rule is applicable because the rail simply is not a fuel line w/i the meaning of the rule. The underlying purpose of the fuel line rule is safety - not performance.

"An external fuel pump pressure regulator may be installed."

Given. But that's all it says; it absolutely does not say that you can make any other mods. If it meant what you say, it would include the words, "and any stock regulator may be removed or disabled if necessary."

"Not sure if I've got this exactly right, but "if it says you can, you bloody well can".

It don't say it.

"It's not possible to use an external fuel pressure regulator with the stock unmodified fuel rail. If there was, I would do it. So now what we're discussing is the extent of modification allowed."

Maybe w/ other cars it is possible, and we are just stuck. Happens all the time. Or whoever drafted the rule did not realize that the stock FPR needed to be replaced. This may be a good case for a rule clarification. Why don't you include it on the other thread re rule changes.

"Since I don't see any restriction in the GCR on that modification,"

Marty, you know very well that is not how the GCR is read! :-)

"I'm very confident that I can do it any way I want, as long as I don't also provide with it some prohibited feature."

I wouldn't be.

"Golley, all we're talking about is a tube that carries fuel for a couple inches, and the entire fuel delivery system to and from it is nearly unrestricted in size, materials, capacity, etc."

Good logic but the GCR is not logical. For example , the air intake after the AFM is just a tube that carries air for just a foot or so, and forward of the AFM is (mostly) unrestricted but you cannot mess w/ the tube aft of the AFM. Same reasoning you are using.

Just find a way to disable the thing.

Does no one know how the stock FPR works?





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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
I'm not a rotary guru, but according to Alldata, the entire assy you describe is considered the "fuel pressure regulator" and is what you get if you order one.
the rule states "adjustable fuel pressure regulators are permitted". End of story-remove your stock "regulator" and install your fabricated adjustable one. And PS: if you really need to be anal, as long as your goal is to run higher than stock fuel pressure, you can daisy chain the higher setting regulator on the return line.
edit: the quote is from the 03 GCR-is the language now different?

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phil hunt

[This message has been edited by pfcs (edited February 04, 2005).]
 
Originally posted by bldn10:
"Fuel line(s) may be replaced, relocated, and given additional protection."

Given. But I don't think that rule is applicable because the rail simply is not a fuel line w/i the meaning of the rule. The underlying purpose of the fuel line rule is safety - not performance.
Click to expand...
I'll grant you this this might be a stretch, but I'm not sure that it isn't valid.

"An external fuel pump pressure regulator may be installed."

Given. But that's all it says; it absolutely does not say that you can make any other mods. If it meant what you say, it would include the words, "and any stock regulator may be removed or disabled if necessary."
Click to expand...
We may have to differ on this. I say that removing the stock FPR is part of installing an external one, and the modifications required to do this are part of what's permitted. No specific restrictions are placed on how these modifications are to be performed, so if the modification is clearly for that purpose and doesn't provide a prohibited function I believe it to be legal.
"Not sure if I've got this exactly right, but "if it says you can, you bloody well can".

It don't say it.
Click to expand...
No, but many of the rules nerds that hang out here do.
"Since I don't see any restriction in the GCR on that modification,"

Marty, you know very well that is not how the GCR is read! :-)
Click to expand...
Actually, in the context of my argument stated above, that's exactly how I understand it to be read. I certainly could be wrong.

"Golley, all we're talking about is a tube that carries fuel for a couple inches, and the entire fuel delivery system to and from it is nearly unrestricted in size, materials, capacity, etc."

Good logic but the GCR is not logical. For example , the air intake after the AFM is just a tube that carries air for just a foot or so, and forward of the AFM is (mostly) unrestricted but you cannot mess w/ the tube aft of the AFM. Same reasoning you are using.
Click to expand...
Well, maybe a cousin, but not the same. The GCR is pretty clear that modifications forward of the AFM are allowed, but past the AFM are not. Here we're talking about the method of carrying out a specifically allowed modification in an area that the GCR is silent about.
<font face=\"Verdana, Arial\" size=\"2\">Just find a way to disable the thing.</font>
Click to expand...
Evidently if I sent it to ISC they would remove it. I really don't know how to disable it without removing it.
<font face=\"Verdana, Arial\" size=\"2\">Does no one know how the stock FPR works?</font>
Click to expand...
You're talking about what the vacuum line does? I wasn't sure so I didn't answer.

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
Originally posted by pfcs:
edit: the quote is from the 03 GCR-is the language now different?
Click to expand...
You quoted 17.1.4.D.1.a.6.
I quoted 17.1.4.D.1.b.
Looks like no changes here to me.

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
Originally posted by C. Ludwig:
Is it time to start racing yet?
Click to expand...
Well, at least today it's not -10 degrees. And the snow is only about a foot deep. We're getting close.

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
"according to Alldata, the entire assy you describe is considered the "fuel pressure regulator" and is what you get if you order one."

I don't even know who Alldata is but Mazda calls it a Fuel Distributor (S), S meaning secondary. The parts catalogue for 89-91 engines does not list anything called a fuel pressure regulator. That term is used w/ regard to the earlier 13B's but it is a separate, removable part. On the primary rail I have seen it referred to as a Pulsation Damper. Now, you are right, if for some reason you concluded that the regulator was bad and you tried to order a new one, you would get the entire Fuel Distributor. But I think this does poke a hole in your reasoning, Phil.

Yes, Marty, how does the FPR work? Does it make any difference if that line is attached to wherever it originally went, is capped, or is left open? Does it limit pressure to 40 lbs. or what? Is there power to be gained from more pressure? Doesn't the ECU cut back on injector duty cycle if it senses you are putting the fuel through under higher pressure? In other words, isn't the ECU going to compensate for either higher or lower pressure by decreasing or increasing the duty cycles - nixing any attempt by us to change the mixture w/ fuel pressure? I don't know; I'm trying learn something here. :-)

Marty, come to Memphis 3/19-20 and you can race then.


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Bill Denton
87/89 ITS RX-7
02 Audi TT225QC
95 Tahoe
Memphis
 
The stock FPR controls the pressure in the secondary fuel rail by allowing just enough fuel to return to the tank so the pressure remains constant. The two fuel rails are plumbed in series, so the primary rail has roughly that same pressure. The pulsation damper doesn't enter into the pressure regulation picture, except to "smooth out" the pulses from the injectors firing. By the way, the S4 pulsation damper is a huge fire hazard (it leaks) - the general advice for the street crowd is to remove it.

The vacuum line alters the pressure setting, but I'm not sure how it's supposed to be controlled or exactly what the result is.

If I put an external pressure regulator in series with the stock regulator, I expect that I would get weird results - I'm not going to test that scenario.

The ECU doesn't operate in feedback mode at wide open throttle - it uses preset maps to determine injector duty cycle. The only way that I know to change the WOT mixture is to change the ECU maps (nobody seems to know how to do this with the stock ECU), or change the fuel pressure.

Thanks for the invite to Memphis, but I doubt my car will be together by then, and it's more of a tow than I'm up for right now.

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Marty Doane
ITS RX-7 #13
CenDiv WMR
 
back to back mustang dyno runs on my car with a well used motor produced the following results. I had 21 races/track days including a 3 hour enduro and 440 miles at Mosport on 2 consecutive days. There was 1 hour cool down between 1st and 2nd run and 30 minute cool down between 2nd and 3rd.)
1st run stock fpr, rail and injectors. 160.1hp/125.1tq
2nd run stock fpr removed and an adjustable FPR and stock injectors @38 psi 169.0hp/129.6tq
3rd run same as 2 but adjustable fpr set @49psi 170.9hp/131.2tq

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Jamie Kekeisen
86 ITS RX-7 NER
92 325IS under construction
 
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