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Old 10-17-2008, 02:21 PM   #21
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It'd all come down to the flow and the real world losses. Has anyone measured this on a stock system? Measure it at 100 cc's, 500, 750, 1000 dot dot dot. You may find the losses become significant at 200 hp, you may very well find them at stock levels (in which case it's likely taken care of in the fuel map, as a change in VE even though of course it's ridiculous), but it might be a 2% loss in pressure at 75 gallons per second. :-)

If someone's measured it, I'd love to see it. I wouldn't put that set up on without knowing what the drop was, and it's easy to measure.

So why not regulate at the far end of the rail like the NA cars?
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Old 10-17-2008, 02:32 PM   #22
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Quote:
Originally Posted by AbeFM View Post
It'd all come down to the flow and the real world losses. Has anyone measured this on a stock system? Measure it at 100 cc's, 500, 750, 1000 dot dot dot. You may find the losses become significant at 200 hp, you may very well find them at stock levels (in which case it's likely taken care of in the fuel map, as a change in VE even though of course it's ridiculous), but it might be a 2% loss in pressure at 75 gallons per second. :-)

If someone's measured it, I'd love to see it. I wouldn't put that set up on without knowing what the drop was, and it's easy to measure.

So why not regulate at the far end of the rail like the NA cars?
A stock 99' will not hold fuel pressure above ~5500 RPMs. POPSTOY on miata.net has done extensive measuring and found even a 190 HP won't keep fuel pressure from falling on a stock 99' fuel system. He found that a 255 HP would keep fuel from falling on a stock stystem w/ stock injectors. My stock 99' lost fuel pressure after 5K. New stock fuel pump didn't fix it. I still loose fuel pressure at high loads.

Regardless of what the measurements are, it's silly to have a returnless setup on a boosted car where fuel is "so important" that people buy 200 dollar fuel rails just to minimize a "possible" pressure difference between each injector. Yet all these 99's are running around loosing who knows how much at load. Rail fuel pressure is a function of many variables.

Gotta go to D.E.
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Old 10-18-2008, 03:26 AM   #23
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Ok then, i'm sold - if someone has actually found it to be an issue, and it's more than just theory, I'm in.

I don't know if I'll go through the trouble yet, but soon. the pumps aren't all that expensive, though I think the lines and whatnot start to add up!
-Abe.
P.S. It's "Diffy Qs"
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Old 10-18-2008, 04:34 AM   #24
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Super high fuel pressures and direct injection is absolutely the future. I've also been looking at running a Speed3 fuel pump and having my block tapped for injectors. And no, I'm not kidding.
I'm not convinced. The MS3/6 Community seems to have a strange battle (from what little I've seen of it) with gaining extra fuel for higher levels of boost. The Factory MS6 fuel pump operates at like 1200psi with a maximum of something like 2000psi, and an 'upgraded' pump is around $700.00.

I have to admit though, my formal education on electronic fuel injection systems is well over ten years old and at that point DI was more of a theory for emissions than anything else..
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