FMU, Boost Compensated regulator, 1:1, 6:1 Whaaa?

[donpearsall]

Since I have been running turbo bikes the last 5 years, I should already know this. But can anyone tell me the difference and applications between a Fuel Management Unit, and a boost compensated fuel pressure regulator? I ask because I have seen posts saying one turbo system uses FMU, another that one uses a boost compensated Pressure Regulator. Some posts say they run a 1:1 regulator, others say they run a 6:1 and others say they run 12:1. How do I choose which is right?
I am building a Kawasaki ZX10 with used turbo parts and homemade plenum. What is the correct pressure regulator to use for about 0-10 pounds boost? I will have a power commander running the injectors.
Thanks in advance for the turbo 101 lessons.
Don

[maj]

Don
 the names for fuel regulators vary somewhat but essentially they are all doing a similar thing
the 1:1 is straight boost compensating.
So your effective fuel pressure remains constant,  and you would use one of these if you had a boost referenced engine management system and injectors big enough to cover the fuel requirements of your engine
anything more than 1:1 is a rising rate regulator and can be 1.2:1 and up to 12:1
the common use bell style FMU is about 6:1 , esp on the current stg 1 turbo kits there a cheap way to get extra fuel out of a small injector and also not need a boost reference ecu .like a PC3 with throttle position based mapping

for street use with no sustained load the fmu works ok but for anything more serious a boost referenced engine manager either secondary controller,piggy back or standalone with supporting fuel system would be preferred  .

[Jonny Hotnuts]

Don, this is just my opinion but I would do a secondary setup.

To run 10# you will likely need bigger injectors on your primarys if you dont run secondaries and often times can lead to low RPM tuning issues. (*some may argue this)

Secondaries allow your bike to run off its OEM computer-injectors-fuel pressure until boost comes on and additional fuel is added by the secondary injectors.

All the turbo mapping can be done on the secondary fuel controller.

It will also give the ability to run more boost in the future without having to upgrade.

~JH

[Chris Horoho]

to give another option
i honestly prefer the standalone setup
they can run as good as stock on big injectors and are much more tunable
and not all of them are expensive
the one i will be running isnt as much in cost as the others and is proving to be as tunable and almost as good as the high dollar ones
and all the things you need in just one box not 2-5 boxes to do the same thing

[Rex Schimmer]

Don,
The amount of fuel that goes through the injector is dependent on the pressure differential across the injector, i.e. the difference between the injector fuel pressure and the air pressure in the inlet of the engine. If you use a good fuel pressure regulator, 1:1 ratio, and reference it to the engine inlet by connecting the back side of the control diaphragm, good regulators will typically have a 1/8 NPT port on the cover for the diaphragm, the regulator will automatically change the fuel pressure as the inlet tract pressure changes. This allows the injector to operate at the same differential pressure all the time. Varying differential pressure across the injector can provide fuel flows that vary in a non linear way which can present a tunning challenge. If your injector is working close to its max rated flow for the power you are making at a specific differential pressure and you decrease that differential, by increasing manifold pressure, you may not be able to hold the injector open long enough to get the required fuel to the engine. Obviously you can run a big injector and then tune the engine on a dyno and compensate for the change in differential pressure by holding the injector open longer but in my opinion using a good 1:1 fuel regulator with the control side referenced to the manifold pressure makes the easiest and most reliable system.

Rex

[DanBadger]

The low-rpm and idle tuning issues JH was eluding to are caused by the minimum open-close cycle of an injector.  A HUGE injector sprays enough fuel, even when opened for the minimum duty cycle, to run rich when there is no load and low RPM.  For this reason, for higher fuel demands it often makes sense to run stock or moderate primary injectors, and a secondary set of injectors controlled with something like the injector controller sold by 034 Motorsports.  This allows you to keep good idle and low-RPM performance, without risking an injector-maxing lean condition up in the power band in boost.  I am not sufficiently familiar with the fuel system on your bike to make any sort of an educated recommendation, but as a general rule, it is more expensive to buy an FMU and little-guy stuff now and upgrade to the big buy stuff in a year or two than it is to only build your fuel system once to a higher level.  Also, if you are building your own plenum, you can build in the injector bungs and fuel rail now and not have to engineer twice.

Good luck!

[Chris Horoho]

we have a few bikes idling like stockers with 750 cc injectors set at 80-90psi idle fuel pressure
its all in the controller(standalone) and its ability to get the injectors to pulse right
i personally have a set of ID 1000 injectors (1000cc injectors)
there are a few who have had ID 2200 (2000cc injectors) to idle like a stock bike

[John Burk]

Don
If you don't mind replacing your fuel injection you could talk to Airflow Performance in Spartanburg SC . They make mechanical fuel injection controlled by a mass airflow signal and fuel pressure in a range of sizes and work over a range of fuel supply pressure . Mine uses port nozzles . Many air racers use AP injection to work with altitude changes .