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What are the advantages of Throttle bodies?


perksy

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If the three parameters of engine performance can be summarised as flexibility, economy and power, it is easy to set up carbs to provide two of the three and very difficult to get all three. Any competently set up throttle body installation should achieve all three without any problem at all.

With the number of experts in carb tuning on the decline you might be struggling to get carbs set up to get the best out of them. Setting up carbs requires experience and patience because the changes take time to implement (you need to change jets, etc.). The adjustments interact with each other and each adjustment has an effect at more than one area in the engine's range of revs and load.

With throttle body injection and a decent ECU, each point in the engine's range of load and speed can be adjusted individually and without affecting other areas. Adjusting the "MAP" which defines the fuel required at various engine speeds and loads requires only a few key presses on a Laptop connected to your ECU. The results may be seen instantly without even stopping the engine.

Comparing reasonably well set up examples of each on the same engine, throttle bodies will typically produce a little more peak power (say 5%), much better flexibility in "off-cam" areas such as low speed torque delivery and much better fuel consumption.

Carbs are cheaper than a traditional throttle body set-up of aftermarket throttle bodies and ECU and arguably simpler due to the reduced amount of wiring and simpler fuel system. Many enthusiasts are now fitting throttle bodies from bike engines, however. These can represent a significant saving when compared to the cost of aftermarket throttle bodies.

If your engine's age is Post-August 1995 at SVA time you will need to pass a catalyst emissions test so this might dictate the need for injection since only fuel injection will provide the precise control of the mixture required for a catalytic converter to function.

Throttle body injection systems often use a device called a "Lambda sensor" in the exhaust system. This samples the exhaust gases and feeds back a measurement of the ratio of air to fuel to the ECU in order that it may adjust the fuel delivery to compensate for variations in the mixture. Such devices are normally necessary to maintain the accurate mixtures required by catalytic converters.

Most Lambda sensors used in catalytic converter installations are of the "narrow band" type. They are only capable of measuring the mixture when it is close to the chemically correct "stoichiometric" ratio of 14.7 parts of air to 1 part of fuel. Engines require much richer mixtures than the stoichiometric ratio under heavy load so in such installations the Lambda sensor is only active and controlling the mixture when cruising at constant speed.

The rarer "Wide band" Lambda sensors are able to measure the ratio of air to fuel over the full range of engine operating conditions. For this reason they can be used to correct the mixture when under full load. Wideband lambda sensors are a useful tool for the enthusiast for tuning fuel injected and carburretor engines and can even make a visit to a rolling road unnecessary.

Kevin

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