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Location:
Edmonton, Alberta, Canada
Registered:
October 2002
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 Why is an FMU no good for turbo?
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Fri, 07 November 2003 02:01
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I emailed Jackson Racing about using one of their FMU's for the turbocharged engine I'm working on. The email reply said "Sorry, our FMU will not work with a turbo". My knowledge of forced induction IS lacking, but I don't understand why it wouldn't work. An FMU is supposed to raise the fuel pressure by 5 PSI for every Pound of boost, correct? Then why would it make a difference whether the pressure came from a turbo or supercharger?
Somebody please explain what I'm misunderstanding.
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Location:
Brisbane
Registered:
May 2002
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 02:24
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WTF is a FMU?
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Location:
Edmonton, Alberta, Canada
Registered:
October 2002
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 02:38
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An FMU is a Fuel Management (something that starts with U). They usually sell them with supercharger kits like Paxton and Vortech. Its increases the fuel pressure by 5 PSI for every pound of boost so that you don't run lean under boost conditions but your fuel pressure stays normal when there's no boost pressure. Its basically a rising rate fuel pressure regulator.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 03:16
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get a malpassi rising rate fuel regulator
or better yet a standalone aftermarket ecu 
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Location:
Brisbane
Registered:
May 2002
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 06:31
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If FMU == RRFPR, then there's no reason it won't work in a turbocharged application.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 06:52
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it's a prety substitute for decent tuning. maybe they meant it will not work well??
by using the FMU (fuel management unit? or RRFPR, you are assuming that your fuel needs wil be matched by upping the fuel pressure by X-amount.
if you are running sayy, 10 lb's boost, that bumps up fuel pressure by 50psi.. can the fuel pump supply 90Psi? can the injectors handle that??
as Draven says, the only real solution for GOOD tuning is a reprogrammed ECU.
Cya, Stewart
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Location:
sydney
Registered:
April 2003
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 08:13
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it is a fuel management unit. i'll be using a vortech FMU in my turbo conversion probably, with a 10:1 disc. other people who turboed my camrys have used it with success.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: Why is an FMU no good for turbo?
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Fri, 07 November 2003 15:31
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the company probably told you that, 'cause they designed it for supercharged engines and never tested it for turbo engines (where the boost tends to climb faster)
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Location:
Edmonton, Alberta, Canada
Registered:
October 2002
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Re: Why is an FMU no good for turbo?
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Sat, 08 November 2003 06:17
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Yeah, I thought they said it
(A)because they don't deal with turbos, and, as Draven said, it wasn't tested on a turbo system
and/or
(B)they don't make a supercharger kit for the 4AGE and don't see me as a potential customer.
However, oldcorollas has a point with the fuel pressure being too high for the pump or injectors to keep up with. I don't know the math to figure out what size injectors would be needed to handle the volume of fuel it would require. I have heard of fuel pumps that put out bucketloads of pressure but I assume they would be huge $ race pumps. This one requires some more research.
I would love to go with a management system like the SDS but last time I checked, it was almost $2000 Canadian. Its a little out of my budget right now.
I got the FMU off ebay for $26 US, big difference. I know, I know, most of the time you get what you pay for. I just don't have enough to pay for the good stuff right now.
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Location:
Melbourne
Registered:
October 2003
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Re: Why is an FMU no good for turbo?
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Sat, 08 November 2003 08:39
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Just a suggestion, not knowing what a fmu is, but becuase
the boost generated by a supercharger is linear, then the fuel pressure could just go by some proportion.
ie, in a supercharger, boost is a linear function of RPM, so the fuel requirement of the engine increases (over the stock fuel curve) linearly..
In a turbo, you can have varying boost levels are varying RPM's. So is's possible the pressure increasue unit thinggy only has a 2d table in it, not a 3d table you'd need for varying boost levels..
Then again you can always try it. (if it was/is cheaper than a proper ECU)
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