SMT8-FT TECHNICAL MANUAL

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Support for your SMT8-FT Unit.

TUNING

The SMT8-FT can tune :

  • The fuel injectors
  • An analog signal (or AFR signal)
  • An Ignition (Crank) signal

 

Only one process or all of the above may be applicable to you!

 

 

FUEL TUNING

 

This is the process of changing the amount of fuel your engine gets with the same amount of air. Some or most engines run a closed loop system : it measures the exhaust fumes and adjusts the fuel accordingly. Changing the fuel with the FT will  not help in this instance : whatever fuel you put in extra, the stock ECU will take out again because it upsets the exhaust gas. However, and this is important, most closed loop systems stop operating at approximately 2500 RPM.

 

You have to try it!

 

Most modern engines have a short and long term fuel control loop strategy. This may affect you in a couple of days. This can be found out with an OBD scanner. If you have problems with the fuel tuning you need to look at Lambda Tuning or Analog Tuning to supplement (or affect) the fuel tuning.

 

 

LAMBDA TUNING

 

This is the process by which you change the exhaust gas reading (Lambda) in order to fool the stock ecu in to doing the right thing. There are two ways to look at it :

 

You put more fuel in by other means, and tune the Lambda signal down (leaner) to hide the fact that the ACTUAL mixture is rich.

 

You make the lambda signal LEANER as it actually is, and the stock ECU puts more fuel in to compensate for it. Of course this method can only adjust by a predefined amount, so you may have to use both methods anyhow.

 

 

ANALOG TUNING

 

This is a process by which an analogue signal is tampered with in order to prevent  the stock ECU from knowing what you have done to the engine. Example : You have increased the manifold pressure and your AMP sensor tops out. Route the AMP sensor signal through the SMT8-FT and limit it. Example : You can get more fuel into the engine when you fool the MAF sensor. There are  many more examples of analogue tuning. However, the SMT8-FT has only one analogue channel. More analogue channels can be found on different SMT8 products.

 

 

IGNITION TUNING

 

Ignition tuning is only recommended on engines with no knock sensors, and only in absolute required circumstances. It is a little tricky to say the least, but otherwise very rewarding if you use good grade fuel. In this method you intercept the crank  position sensor signal and play it back to the stock ECU a little later (retard) or a little early (advance). Most people ask : How is advance possible? It is a little complicated. The unit learns the wheel pattern and then can anticipate the next coming signal ahead of time.

 

 

FUEL MAP ENTRIES AND THEIR EFFECT

 

When tuning with the LetRipp II a positive number adds and a negative number subtracts fuel as a percentage of the ECU injection length. Example : Entry of 5, adds 5% fuel. The stock injection length can be displayed as well as the injector utilization.

 

 

AFR, POWER AND FUEL ECONOMY

 

The AFR (Air Fuel Ratio) is one of the most important measurements in tuning fuel. The SMT8-FT can measure the signal from a narrow band lambda sensor and interpret it in AFR or Lambda.

 

AFR and Lambda are often used interchangeably. 1.00 Lambda = 14.7 AFR.
Here are some important AFR numbers :

14.7 AFR = Normal Operation
13.2 - 13.8 AFR = Maximum Power
12.2 AFR = Maximum Power for Supercharged or Turbocharged Engines
15.5 AFR = Lean, point of Minimum Fuel Consumption


Modern engine technology can change the AFR numbers to a certain degree, but the principle remains : you can run the engine LEAN, but not on full power.
Another way of looking at it - if you want strong horses, you'll need to feed them.