NA is Dead?

All too often on the web, you see guys talking about making big hp on cars through forced induction. Whether it’s a supercharger, turbo, twin charged, etc., there is always someone pushing the envelope here.  But what about good old fashioned NA power?  No boost, no having to inject various concoctions of combustible chemicals to be able to crank the timing – just plain ordinary air? I think it often gets left by the wayside.

I wanted to start a multipiece series on NA tuning, with particular emphasis on what to many people is the pinnacle of an NA setup – the Individual Throttle Body, or in web language, ITB. Let’s just get a basic understanding of what an ITB is and how it works.

As the name implies an Indivdual Throttle Body (ITB) means each cylinder has it’s own dedicated path for the air to reach the combustion chamber.  The bodies are linked together so that they open and close together, thus allowing the engine to ingest the air required for the combustion process.  There are several benefits that an ITB setup can have over a single throttle body.  First and foremost is cylinder balance.  With a single throttle body, you have little to no control over how much air is ingested into the the combustion chamber for each cylinder.  As a result, you end up with air reaching the combustion chambers in varying amounts, at various speeds, which can leave you with cylinders producing different power levels.  The amount this differs of course varies by the application.  With ITB’s there is no sharing of air.  Each cylinder is afforded unlimited air, and through tuning, the user can ensure that each cylinder is ingesting the exact same volume per air, at the exact same velocity. The second benefit is throttle response. With each cylinder now able to ingest it’s own dedicated stream of air, the combustion process starts quicker, and the engine responds faster to throttle inputs.  Furthermore, because you now have individual paths of air vs a large single path, the volume of air and the velocity that can be ingested into the engine as the throttle plate opens is often more than a single throttle body setup allows.  We’ll go into more detail on this last point in a future installment, as well as determining the right manifold design for a particular application, all with real world testing, graphs, videos and dynos!

As best I can tell, the first production car to use both ITB’s and fuel injection was the very rare BMW M1. This car was manufactured from 1978 to 1981, and used a combination of ITB’s and a mechanical fuel injection system developed by Kugelfischer and Bosch.  BMW still uses ITB’s today on their M series engines.

In the next installment, we’ll look more in depth into various ITB setups as well as design differences, etc. In the meantime, take a look and listen at this clip from Option Video from Japan of a tuned Acura with ITB’s.  If this doesn’t make you fall in love with an automobile, it’s pretty safe to assume you have no soul!