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Old 01-02-2007, 08:47 PM   #1
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Default FMU modification

I wanted togive this concept its own thread thread. Appologies to the op of the other thread which I/we jacked pretty good.

Corky Bell told me before going to such extremes, I should tee off the check valve line and run a second check valve. I'll give it a shot tomorrow if I have time. Got an insanly complex, insanly high value project I'm building a bid for.
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Old 01-02-2007, 09:35 PM   #2
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are you doing this with a vortech style fmu or begi?
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Old 01-02-2007, 09:43 PM   #3
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this would apply only to the BEGi units. including the rebadged BEGi units like cartech.
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Old 01-02-2007, 10:20 PM   #4
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I was going to install a needle valve on the fitting on my vortech fmu today. but it ended up tapping the wrong size so it didn't fit... I gotta figure out what size thread it is (i thought 10/32) and try again with another fitting...hopefully I can make myself a BEGi unit....just without being able to adjust my 0 ~hg pressure.
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Old 01-02-2007, 10:29 PM   #5
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Quote:
Originally Posted by braineack View Post
I was going to install a needle valve on the fitting on my vortech fmu today. but it ended up tapping the wrong size so it didn't fit... I gotta figure out what size thread it is (i thought 10/32) and try again with another fitting...hopefully I can make myself a BEGi unit....just without being able to adjust my 0 ~hg pressure.
Very cool. You have an o2 clamp, so I woudnt sweat the overall pressure adjust too much. Though having both would be the best.

Another option is to tee the fitting you add and put the needle valve on one end and a ball n spring mbc on the other. That would give you adjustable rise and give you the ability to set a maximum fuel pressure.

Let's see how it works out.
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Old 01-02-2007, 10:32 PM   #6
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i think my stock fuel pump will do a good job of giving me a maximum fuel pressure of about 75-80 psi
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Old 01-02-2007, 10:35 PM   #7
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Quote:
Originally Posted by adbradley View Post
i think my stock fuel pump will do a good job of giving me a maximum fuel pressure of about 75-80 psi
I think you'd be real lucky to get 75+ psi out of it under load. I was good with my stock pump to around 160 or so rwhp. Switching it for the 190lph hp gave me a ton more fuel to work with.
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Old 01-02-2007, 11:40 PM   #8
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the funny thing is, is I'm too lazy to buy a BEGi rebuild kit and just run an adjustable FMU.
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Old 01-03-2007, 08:04 AM   #9
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If you send the BEGi unit to BEGi, they'll rebuild it for you for only the cost of the rebuild kit. Seems like the way to go.
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Old 01-03-2007, 08:24 AM   #10
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atlanta stop making sence over there!
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Old 01-03-2007, 09:35 AM   #11
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yeah I know that....but then i'd have to put it in a box and mail it....
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Old 01-03-2007, 09:42 AM   #12
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Yeah, and the effort involved with that is astronomical!
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Old 01-03-2007, 02:52 PM   #13
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I picked up a check valve from Advanced Auto at lunch (it was next to Zaxby's so it was a no brainer). They had a 2 port check valve, so no tee was needed. Inital impressions are very positive.

Before the mod, my lc/xd would report boost afrs quickly going to 10:1-10.5:1, and usually going to 9:1-9.5 at high rpm full boost.

After the mod, the gauge is showing boost afrs around 11.5:1 until around 6000 or 6500 rpm, where it will richen to around 10.5:1.

Transistion to boost seems unhcanged. Response at low boost is much snappier. The car feels more powerful from 2-6 psi.

I'm happy with this cheap mod, though the clutch is starting to complain. It's starting to slip more, and when hot chatter when engaging 1st from a stop.

Cost of mod: $6.32 with tax. Recommended highly to everyone running the BEGi FMU.

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Old 01-03-2007, 03:03 PM   #14
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Nice work. Something more to play with when I finally get my setup going.
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Old 01-03-2007, 03:05 PM   #15
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I again hit a snag in my mod....I tapped the fitting with the correct size, but when I was tightening the needle valve down, I for some reason cranked down on it and stripped the threads....so I won't have results untill tomorrow afternoon...

Ben, take a pic of the entire setup....I visualized it differently

*edit* i get it now.
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Old 01-03-2007, 03:34 PM   #16
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Simple concept. The needle valve vents boost to atmosphere, but does so through a check valve. Otherwise there would be a vac leak through the fmu while running below positive manifold pressure. If the check valve is too restrictive to allow boost to escape, it negates the adjustability of the needle valve. When I was on the dyno, I didn't understand why the needle valve had so little effect on lowering my fuel pressures. Well, the needle was working fine, but the check valve in line after the needle valve was the restriction. Now there are 2 check valves installed after the needle, and parallel to each other. So the needle valve is now allowed to vent boost to atmosphere without restriction.

This is a very good mod. Not only does it result in more power, but it also is good for economy :gay: . So it will actually end up paying for itself.

I haven't cut the vac hose to length or secured anything yet.

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Old 01-03-2007, 03:38 PM   #17
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So running no check valve would accomplish the same thing, ignoring the vacuum leak?

I'm not sure I get why adding an additional path and valve helps.
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Old 01-03-2007, 03:41 PM   #18
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man, on the dyno I could make Brad run at 60psi or 120psi at 12psi, with the tiniest little turn of the ****.


Are you running a restrictor on the vacuum line?

when you described what Corky said to do I was thinking this (see image)

But it makes sense to just open up the breather line to help relieve more pressure out of the fmu so the needle valve can work more effiecently.

Last edited by Braineack; 10-02-2007 at 04:01 PM.
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Old 01-03-2007, 03:59 PM   #19
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Quote:
Originally Posted by jayc72 View Post
So running no check valve would accomplish the same thing, ignoring the vacuum leak?

I'm not sure I get why adding an additional path and valve helps.
You don't want to run without the check valve. There is the vac leak to deal with, but also the car will return to lower fuel pressures under vac more quickly with the check valve compared to without.

The mod works becuae the needle valve in the FMU is capable of bleeding more air than the original check valve could freely flow. The additional valve and additional path to bleed pressure to atmosphere keeps up better with the needle valve, and results in less pressure in the FMU and a slower increase in Fuel Pressure with boost.

This was not my idea. Corky suggested it before going buckwild with the second needle valve behind a pressure relief, as was my original plan.
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Old 01-03-2007, 04:10 PM   #20
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I know the vac leak is a bad idea

I get it now. And this is why I'm buying a link
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