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Old 09-19-2011, 12:35 AM   #1
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Default Injector Q's

Hey Everyone had a Few Q's about my injectors and ECU Capability.

I started with purchasing the http://www.bellengineering.net/produ...roducts_id=242
Now i know the stock ECU can only handle about 335cc injectors what can this one handle?
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Old 09-19-2011, 02:25 AM   #2
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I am confused... what can what handle?
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Old 09-19-2011, 02:44 AM   #3
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The FMU... What injectors can it handle?
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Old 09-19-2011, 02:53 AM   #4
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But... you still have the stock ECU.
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Old 09-19-2011, 03:55 AM   #5
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The FMU adjusts fuel pressure with boost, turning [email protected] injectors into [email protected]* injectors. So it has nothing to do with injectors directly. It can only go so high though, so larger injectors are required. You can only go to about 335 until the stock ecu can't idle them.

You won't be changing the idle settings, so the ecu still thinks it has 235(?)cc injectors, instead of the 335. This is 42% more fuel, so idle will be VERY rich. Any richer And it will stall. Hence the rough 335 limit.

*not real figures.
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Old 09-19-2011, 04:02 AM   #6
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Quote:
Originally Posted by Dylan O56 View Post
The FMU... What injectors can it handle?
The BEGI Adjustable Rising Rate Fuel Pressure Regulator (ARRFP not FMU...get your acronyms right NOOB!) can "handle" any size injectors you can stuff in the intake manifold...however your stock ECU probably won't be able to handle any injector over 300cc. The ARRFP is just a dumb, adjustable, pressure sensing device that increases fuel pressure X% for every Ylbs of boost.

FMUs/ARRFPs, "auxilary" fuel pumps, MSD ignition retards, O2 clamps et al are all just bullshit, bandaid approaches to engine/fuel management that will cause you nothing but grief and aggravation! I can guarantee that you will NEVER get your car to run smoothly from idle to full boost at WOT without hesitation and inconsistent fuel air ratios. If you want to turbocharge your Miata, do yourself a big favor and build/buy and install a Megasquirt system and practice your tuning skills on your stock NA motor before installing a turbo system.

If you shop smart and/or DIY build the Megaquirt you won't spend much more money than buying the all "bandaids" (aux fuel pump, ARRFP, boost retard & O2 clamp all add up quickly) and you'll have a very robust tuning system. You'll also need a wideband 02 setup....don't believe all the bs info BEGI provides with their ARRFPRs for tuning "with fuel pressure". Been there, done that, doesn't work consistently and a wideband readout of 14.0 AFR @ 8lbs of boost @ WOT isn't safe even if you are blasting 100psi of fuel pressure into stock injectors.

Just my .02.....but I think I can claim the dubious honor of "Bandaid King" with over 43K miles on a factory rebuilt Aerodyne (original puked on me in 3k miles due to prior owner's reliance of BEGI "tuning guidelines") BEGI 8psi intercooled "bandaid special"! It's ugly, please don't replicate what I've suffered with!
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Old 09-19-2011, 04:05 AM   #7
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OP, what I'm trying to get at is, you still have the stock ECU. Until you upgrade your ECU you are still limited when it comes to injector size.

Although if your goal is to run low boost, 3XXcc injectors will be fine with bandaids. You still need a wide band though.

Honestly you should just get a MS from the start.
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Old 09-19-2011, 10:42 AM   #8
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Dylon,

https://www.miataturbo.net/useful-saved-posts-8/diy-faq-all-your-answers-one-big-post-10821/

Here you must go.


Quote:
Originally Posted by Myself
Adjustable fuel pressure regulator

The turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.

SO...when you add boost to your Miata you typically need extra fuel flow through your injectors. Why? Because injectors are typically rated in cc/min at 43.5psi of fuel. Which can be converted into how much HP each can handle. By raising the fuel pressure in the rail, you effectively increase the HP capabilities of your injectors. In a nutshell, raising the fuel pressure raises the cc's of an injector! Get it? **Section 3**

An APFR or FMU are ideal alternatives to expensive ECU modifications. This is accomplished by using the manifold vacuum/pressure to drive the fuel pressure up as the boost rises.

The BEGi standard rising-rate regulators are designed to increase fuel pressure and fuel flow in a fuel injection system by augmenting the factory fuel pressure regulator. These regulators must be used in conjunction with a factory regulator, which provides the base fuel pressure (the fuel pressure at fuel rail during idle conditions). The amount of fuel pressure rise can be adjusted by adjusting a screw on the side of the unit.

Sources:

Bell Engineering



The Vortech FMU (standard on the GReddy kit) works in the same principal however the amount of fuel pressure rise is determined by a disc and cannot be changed on the fly. Recalibration kits can be bought for cheap however they require the disassembly of the unit to change the ratio.



Sources:

Vortech Superchargers





To determine the amount of fuel you can supply with your AFPR or FMU follow this calculation:

Fuel pressure @ rail = Rise x boost + idle pressure


Example: 10 x 5 + 50 = 100psi

So with a ratio of 10:1 (10psi of fuel for every 1psi of boost) you can supply 100psi of fuel to your injectors when boosting 5psi. If you don’t plan on adjusting your boost levels often the simple static disc FMU unit can be had for cheaper than an adjustable unit. However, with the added benefit of being able to easily supply your injectors with the right amount of fuel by the turn of screw adjustments they are worth the extra cost.



-Note- Larger injectors, Intercooler, etc., can change the desired fuel levels. Hoever, most do not recommend over 100-110psi of fuel at the rail in boost. *At this point it's time to think about larger injectors that can handle higher HP ratings at 100psi of fuel in the rail. The stock ecu can handle a -+ 20-30% injector. So the fueling with the stock ecu can only go so far. If you feel you're going to breach this point, then EMS should be considered.



*SEE SECTION 3 ON FUEL INJECTORS



Installation is Easy! Pic



Hard Line -> Front of Fuel Rail -> OEM FPR -> OFFSET Fitting of FMU -> CENTER fitting of FMU -> Return Line
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