A couple of weeks ago, I was getting some work done at HVE and asked Darryl whether or not the intake manifold is enlarged when they fit a BBTB as I had one installed some time ago. He told me that the Tib manifold unlike other models is already wider than the stock throttle body and hence enlarging it is unnecessary. Assuming always that max airflow was ones prerogative.

Does anyone know whether or not this is true?

 

At least here in the USA it is not true.

The Stock TB diameter we get is 52mm. Bored units are usually 58mm somtimes as big as 65mm.

The stock intake manifold opening is only 56mm, thus when going to a 58mm or larger TB, it is necessary to enlarge the IM.

One thing to keep in mind, the 52mm measurment is taken at the TB butterfly, the narrowest point in the TB. The TB is actually 60something MM going in, narrows down to 52mm at the butterfly, then enlarges back out to 56mm at the IM opening. So, depening on where one get's their measurments from, it numbers might vary from 60mm for a stock TB to 52mm for a stock unit. The important measurment is the narrowest opening, in the USA's case, 52mm.

 

to further random's post, it's also important that you don't have a "lip" where your tb bolts up the im. this creates unecessary turbulence, and can hinder air flow and decrease power. having the im port matched to the tb is definately a good idea.