Engine tuning-Standalone vs Piggyback ecu - Performance DIY by DIY Guru

Performance DIY by DIY Guru

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Standalone ecu vs a piggy back computer
(I think it is physically possible to write a 500 page book on this so I will try to be brief and cut out as much of the fat as possible – stick to the essentials… hopefully)
So your car is boosted from the factory, or your car has been equipped with aftermarket boost or you have an n/a car and are planning on boosting whatever the case, you are interested in buying an aftermarket computer but you are a little confused, its o.k we have all been there, most of us still are (including me – the blind leading the blind in this article ? ) So which ecu is best for you?  This umbrella question encompasses a whole host of other questions all of which I will try to address
First we should understand how and what engine parameters your ecu takes in to determine the tune of your car.  There are three main parameters (maps) when tuning your car:
1.) Fuel  (A/F Ratio)
2.) Cam angle  *note*
3.) Ignition timing

*note*  When I talk about cam angle, I will be referring to today’s newer cars with variable cam timing…

O.K. so your car uses these three parameters to build a “map” or tune for your vehicle.

Next let’s explain what a standalone ecu and piggy back ecu are and what they can and can’t do.

Stand Alone ECU
There are many different types of stand alone ecu’s that all encompass their own unique features, to many to talk about, so I will try to stick to the roots of the equipment.
A stand alone ecu is an ecu that is separate from your cars stock ecu (in most cases, Hondata would be an exception).  A standalone ecu lets you build new ignition cam angle and ignition maps for your car, starting from scratch.  This is the main difference between a piggy back and standalone and also the most important so I think I’ll leave it at that.

Piggy back ECU and or A/F Controller
Again, like the standalone ecu, there are many different types of piggy backs with their own unique functions.  A piggy back ecu or a/f controller takes signals from your sensors and modifies them to trick your ecu into reading a different value.
Ok.  So which ecu is for you.  Once having a fairly in depth idea (more then the knowledge base that this article provided) of how your ecu builds maps and how a piggy back and standalone ecu work the answer should become quite obvious.
If you have a n/a car and you are planning on boosting it, there really is only one reasonable choice.  A stand alone ecu.  This is because a naturally aspirated cars ecu is programmed for a na engine.  The main concern is your ignition timing.  An na tuned car (i.e your stock car) will have ignition maps that are way to advanced for a boosted application causing detonation, which is detrimental to your engine.
Well doesn’t a a/f controller and piggy back computer control ignition timing?
Yes but not effectively.  An a/f controller takes readings from your maf/map sensor and alters them trick your ecu into reading a different signal.  And since all your maps are tied in together, your maf/map sensor signal also will move where your ecu reads its ignition timing on the map.  your maf/map is not only used to maintain air/fuel, but its also used by the ecu to determine load, and load is used for determining timing advance, this has the side effect of fooling the ecu into advancing timing beyond what is safe.  These readings will also effect where your cam angle is, which more then likely will not be at the optimal angle for your boosted application.
Newer piggy backs like the e-manage ultimate can control your ignition timing separately from your airflow readings, but there are still catches.  You are able to change ignition timing maps but the e-manage simply changes the output signal the ecu sends to the coils.  The problem is the ignition timing numbers are not always consistent with the changes you make to the load sensor, whether its your map, or maf sensor. So you are guessing the timing numbers. The stock ecu also has multiple maps it can run for different conditions so you are not always consistent with the tune.
A stand alone ecu lets you build, from scratch, completely new ignition timing maps and fuel maps and cam angle maps. Optimal for your boosted application so you can run a safer tune that will make more power.
A car that has come from the factory already has optimal ignition timing maps and there for really only needs a a/f controller or a piggy back that can compensate in a relatively small window range. Unless you plan on drastically changing your stock boosted air flow characteristics, a piggy back will suit you just fine.  

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