I mostly want to upgrade to a 58mm from my 52mm for the snappier throttle response.
With bigger throttle blades/bores, it takes less pedal to allow a given amount of air to flow through, providing a "touchier" gas pedal.

 

Just an FYI, BBK makes the TB for Edelbrock

 

If you do a little math, things don't look so good for the stock 48mm throttle body.

Just to give you an example. Let's take a 350 ci motor turning 6500 rpm. We'll assume 85% VE.

350x6500x.85/3456 = 560 cfm

You can calculate air speed (feet/sec) through a given section area pretty easily.

cfm/area x 2.4 or (1/60÷1/144)

Each throttle bore covers half the engine demand so (580/2 = 280)

280/2.81 x 2.4 = 239 fps

General rule of thumb states that anything over 240 fps will cost you power so you might assume we're safe?

What about the throttle shaft?

If the shaft is 5/16" in diameter, then our new section area is 2.22 in^2

280/2.22 x 2.4 = 303 fps

Take the stock LS1 75mm in comparison, calculate area minus the shaft (5/16"??) and you get this

553/5.928 x 2.4 = 224 fps

Not hard to see that you could see some gains in going 52-58 or even monoblade with better heads/cam/exhaust, better VE and higher rpm.

-Mindgame

 

Not trying to nit-pick or anything, but doesn't that equal 290?

 

Yep, that's because I had 560 in the head (from our previous equation) and just hit the wrong key.

So it all works out in the end.

Thanks for keeping me on my toes... I went through this pretty quick so feel free to bring any errors to my attention.

-Mindgame

 

Hell, I guess if I would have been paying attention, I would have noticed that!

 

Some companies may be that way, but not all. I port and sell them on ebay and have had nothing but positive feedback. None of my throttle body blades stick and the blades seal very tightly. I've actually have had a few people trade in their BBK 58mms for a ported 52mm of mine and said that it fixed the sticky throttle and idle problems. There are some companies that don't put sealed roller bearings in and they may have the problems that you stated above.

I just wanted to point out that not all are this way.