6G Celicas Forums

is it neccesary to have an FCD for a 5sfte?i was reading the mr2 forums and they was saying it is needed... but ive nvr heard of ne1 here using one...i am building my motor from top 2 bottom and plan on a LOT of boost.

A FCD is different on a 5sfe than it is on a 3sgte.

A 3sgte uses an airflow meter to determine how to fuel the engine. It uses the MAP sensor for things like fuel cut.
A 5sfe uses the map sensor to determine how to fuel the engine. It also uses it for things like fuel cut.

Fuel cut happens somewhere around 4.7 volts coming to the ECU from the MAP sensor
on a regular 1 bar map sensor (installed on a stock 5sfe) 4.7 volts happens at around ~2psi. So just around 2psi the ECU will go into fuel cut.

What most 5sf't'e guys do is switch up to a 2 bar map sensor with bigger injectors.
Like i said earlier, the 5sfe uses the map sensor for fueling so when you switch to a 2bar map sensor you have to compensate for this change with larger injectors, otherwise hte engine will not be fueled correctly.

On the 2 bar sensor, 4.7 volts happens somewhere around 12-14psi... depending on your altitude, the exact temperature ...etc (alot of factors affect exactly where fuel cut happens but it's around tha t psi level).
Since most 5sfe users won't run more than 10-12 psi then they don't need a fuel cut defender, because their fuel cut is usually higher than the boost they choose to run on a daily basis.

Furthermore, the ideal injector to use with a 2bar sensor for a typical sized turbo is around 360-400 cc injectors.
Most of hte recent 5sfe turbo conversions are using 450 cc injectors off the RX7. These injectors are larger than needed so most people will have to add negative corrections on the SAFC or Emanage to make the air fuel ratio perfect at full throttle. What the negative corrections does is make 4.7 volts happen at an even higher boost level (a -10% correction will add 1.5 to 2psi to your fuel cut, putting it around 14 to 16psi) ...

So with the 2 bar map sensor and 450cc injectors and an SAFC / Emanage dyno tune most people will not need a fuel cut defender because fuel cut will be at a boost level higher than they need and it will be a good safety feature to have fuel cut at 14-16psi if you're running at 10-12psi setup.

Everything before here applies to most 5sf't'es ... End of part 1
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Part 2: Crazy boost:

A 5sfe with the right parts can be built to make 3sgte like hp in the 300-400 crank hp range.
This will take some mods like head porting, valve work, cams, intake and exhaust manifold work, the right combination of internals and compression ratio, and last but most importantly the CORRECT sized turbo.

A modded 5sfe making peak power (in normally aspirated version) at 6400 rpms rather than 5400 rpms will be able to make around 360-380 hp at around 19psi.
To fuel this kind of a monster you have a few fuel options but the easiest would be something like this:

3 bar map sensor
four 540cc main injectors
Emanage ultimate for tuning

The 3 bar map sensor means 4.7 volts happens around 21 psi.
The 540cc's will match the 3 bar map
and you won't need a FCD.

The problem with using that big an injector is that it may not idle cleanly at 700. So this kind of setup would go well with a cam that will idle at around 1000 rpms, especially if you can use the emanage to move your redline to 7000 rpms or so ...