So I've been researching some performance upgrades for my 5.9 and a common one seems to be 52mm throttle bodies.

What is confusing to me though, is how can people report an increase in performance when the stock throttle body flows 635cfm(source: hughes) but the stock intake manifold only flows 180cfm(source: allpar intake shootout) and the stock heads only flow 199cfm (source: mopar action magazine)?

 

Throttle body is total flow, Manifold, and head flow is for ONE cylinder/runner.

Consider, the engine is just a giant air pump. It 'displaces' 360 cubic inches of air per two revolutions. So, about .21 cubic feet. Figure a redline of 5500 RPM, and that works out to max flow of 577.5 CFM. Well below what the 52mm throttle body supplies.

Of course, that's figuring 100% volumetric efficiency, which these engines don't even come close to. I think if you get 75-80%, you are doing really well.

 

O ok, I never thought about the cfm ratings of the manifold and heads being for one cylinder. Thanks for that.

With your calculation though, wouldn't the stock throttle body be more than sufficient and thus upgrades wouldn't provide any performance advantage?

 

You don't get any more horsepower really, but, you do get better throttle response.

 

I could see that, for equal throttle pedal movement you're letting in more air.

 

I've been debating getting a 50mm for my 5.2 for years. Just can't get convinced that $250 will be worth it.

 

It won't be....

 

But it will help (slightly) if you remove your TB, round-off (radius or blending) the incoming edge and polish the throat up a bit.


And, its free!

 

250 seems way too much to spend. It seemed a little more able to rev, maybe.

What happened to dakrt?? he used to sell the ported ones on ebay for 100 bucks. That was a bit more tolerable.

There is a guy selling some on ebay for 200. Still a bit high if you asked me.

 

I loved my 52mm but it also was on top of a hughes airgap.