I've got a 52mm on mine and have a couple decent sized turbos on the car. A 52mm throttle body will fit w/o modifications on a LT4 manifold for sure and I think it'll fit on a LT1. Someone will have to get the calipers out and take some measurements though.

I'm not too concerned w/ the throttle body size since it's a FI setup. I'll take the money I would've spent on a 58 and spend it on the fuel system or suspension.

 

could i port my 52mm to a 54mm or 58mm throttlebody?

 

Velocity is only part of the equation. Pressure is the other. You trade pressure for velocity. the mass flow rate over a nozzle or orfice is the same before and after which is equal to the density of air * crossectional area * Velocity... so your making trade offs.


Total energy shouldn't change much either and if it does its happening at the area with the smaller cross sectional area where velocity is high and friction is really working against you.

Am I right Mike? I don't know much about fluids outside thermodynamics.

 

Factory made the TB small because I think they didn't care to go any bigger. WIth a stock car with manifolds, at WOT you're at full atmospheric pressure in the intake in most cases, it's when you add headers/some head work and cam that you notice your manifold pressure is at a vacume, but stock it's fine.

I always believed that the TB has nothing to do with increasing velocity of the air, it's like saying your K&N airbox is too big which decreases velocity. The importance of this only happens in the intake port just before it enters the cylinder, and it happens when the piston is going down and the intake starts opening. What happens at the TB don't matter, that part should just be big enough to keep enough air in your intake for your engine, having vacume in the intake while at WOT, may only disturb the proper function of how the air speeds up in the intake port.

Anyways just woke up, you get the idea, but this is all for NA, for boost I honestly think the bigger the better, no need to worry about velocity when the air is being showed in.

 

Most people may not realize that performance is NOT the only thing that goes into the design of an engine. I'd bet my turbocharger that GM used the 48 mm 2-barrel TB on the LT1's for cost reasons alone. This is very similar to the TPI throttle body designed in the early/mid '80's. It's cheap to have your supplier continue to supply a product they're already tooled up to make.

Mike