103mm TB on a factory LS3 manifold - what's it worth? Definitive dyno results inside

[acammer]

Hey folks - happy Cinco de Mayo. At GPI we get asked about porting factory LS3/L99 manifolds out to accept a 103mm throttle body pretty frequently. We don't offer that service because we've always thought it doesn't actually help add any significant power, but we've never truly put it to the test. Last month we went ahead and did test this. The bottom line, for the guys that don't wanna read, is that the 103mm throttle body is worth NOTHING on the stock manifold.

If you're into the details, have a look. I've got it summarized in a video on my YouTube as well.

https://gwatneyperformance.com/103mm...ow-much-power/

[morepowerjoe]

Very nice test. I've been wondering about the exact same thing. I would have thought that it would have picked up something but I guess the dyno doesn't lie. Thanks for the info as always, I'm sure everyone is very grateful for you guys.

[acammer]

Originally Posted by morepowerjoe

Very nice test. I've been wondering about the exact same thing. I would have thought that it would have picked up something but I guess the dyno doesn't lie. Thanks for the info as always, I'm sure everyone is very grateful for you guys.

Yea - it's a test a lot of us have always talked about, but I've never seen done and documented. I wish we had more time to mess with stuff like this - we definitely are always trying to gather more information.

I'm pretty sure the restriction is just the manifold itself, and the throat specifically. If you look at the opening, especially once it's ported out, you can see that predominately the roof, but then also the sides of the throat all neck down right behind the throttle body flange, and I'm pretty confident that negates any sort of flow you can add right there at the throttle body.

[Chris49066SS]

Don't people usually remark on improved throttle response as being one of the draws of the TB upgrade? Personally I haven't noticed any substantial improvement in throttle response, but mine doesn't have the stock manifold either and also had the heads ported, so I don't have apples to apples comparison or anything, and just have the 102. Good write up!

[acammer]

Originally Posted by Chris49066SS

Don't people usually remark on improved throttle response as being one of the draws of the TB upgrade? Personally I haven't noticed any substantial improvement in throttle response, but mine doesn't have the stock manifold either and also had the heads ported, so I don't have apples to apples comparison or anything, and just have the 102. Good write up!

So, yes - porting an OEM throttle body is not really about gains much in terms of actual flow - the purpose is mostly to kill the ledge behind the blade opening, to improve response when you crack the throttle. You could accomplish that with a 102, but that's a much more costly way to achieve the same result.