48MM vs 52MM or 58MM Throttle Body

[ChuckG]

I'm wondering: at 103k miles (with a rebuilt motor), if my TB needs to be rebuilt. I hear they're iffy after 80k and I am having to kick down the throttle more than I'd like.

Given I have heads, a mild cam, and cat-back exhaust, will I actually gain anything from a larger throttle body, or is that all just hype?

I found a guy who offers an OEM TB rebuilt and bored to 52MM for $189 outright. Seems fair, but is it? Is it big enough for my setup?

[928stech]

The key to pumping more air through the engine is to make sure you are able to push it out. I have seen folks spend a boat load on the engine, without looking at the exhaust, and it doesn't work out for them. I believe the mix for a good streetable engine is that the exhaust should be 90% of the inlet volume. If the car is just for top end runs you throw that number out, and run wide open....be cool

[ChuckG]

Well, I do have the Cat-back, a high-flow Cat and a cam with 284/270 464 lift....

If nothing else, I'm sure the original TB is tired. GM made stuff then out of spit and shit. I worked for them in the 80s--that's why I always bought Fords.....

[c4c5specialist]

HI there,

Remember, the larger the throttle body, the more it supports higher RPM horsepower.

The SMALLER the diameter, the more it will support low rpm torque.

Allthebest, c4c5

[ChuckG]

That's a good point. I would like to move the power band up a bit. A lot of the low-end torque just goes up in smoke, but the car really huffs and puffs at 4500.

I know the runners keep things kinda that way too, so I'm slow to change them. Besides, they're not wear items. I really think my TB is worn out since I've corrected every other possible reason for my poor idle.

I've decided on the 52MM. Not far off stock and won't require any work on the plenum. For whatever reason, Chevy engineers made the plenum 52MM and the TB only 48MM. Maybe CAFE, maybe EPA, but they did make the upgrade easier.

[ChuckG]

Got the 52MM throttle body installed. WOW! Does the car breath better! No more feeling like it's gasping for air at 3500 RPM!

Still looks stock as all get out, but runs way better. I'm told the ECM has to relearn a lot, but so far, I can feel a difference.