Throttle Body Size Bayswater | Fuel Injection Bayswater

One of the questions I get asked quite a bit, is, "What throttle body size do I run on my engine?"

This comes down to, whether the engine's force fed or not, normally aspirated, and the size of the engine.

People love big throttle bodies, as big or even bigger than 90mm.  They will flow a lot of air.  But, if you're putting this on a 1300cc engine, anything more than about 25% throttle is useless, because, if you open that up more than 25%, it's not going to give you any more power.  

You've already got enough airflow for what the engine's requirements will be at about a quarter open.  So, if anything, it's going to send you backwards because, on a sharp acceleration, you get a big rush of air very quickly, and you have to accommodate that with fuel injection and ignition timing.  

You put a 90mm throttle on a big cubic inch V8, and that might be perfect for it.  So, assessing the size of throttle body size to the engine size is a very important aspect.

You may make power with a huge throttle body, but you may make it undrivable too, because, just remember, as I said, on a 1300cc engine from closed, to 25% open is equivalent to wide open throttle on a standard throttle.

So, that is the equivalent of moving the throttle peddle only 25%, and going from closed throttle, to effectively full throttle.  This is going to make the engine almost undrivable.