Several years ago, we had the chief LS1 engineer at our local corvette club meeting and the same question was asked of him. Both ported and polished. As I recall, he mentioned the polished would help increase throttle response but a ported on a stock engine would not help anything. The firmware in the PCM is hard set for certain air flow characteristics and the programable portion of the PCM allows for adjustments of different engine configurations (5.3,5.7,6.0 etc). According to him increasing the diameter would decrease (slightly) the velocity of the air flow and a PCM adjustment would have to be made to optimize any change. He also mentioned as you added changes--external and internal--the HP advantages of going to a larger TB could help significantly, especially with increase cubes or H & C.

 

Well sounds like porting the throttle body would be beneficial to the OP then.

 

Would probably be more beneficial to switch intakes (TBSS or NNBS) and get a 90mm TB.

Costs more though.

 

what is the big benifit of the 90 mm? i would then have to buy a new peice to connect my intake right? no biggie. jw

 

To play devil's advocate a little bit, how is the increased air flow through a ported stock TB any different than the increased air flow through a 90mm TB and intake. Yes, the intakes are different, but I think we all know that the TBSS intake flows better.

As Scott said, a gas engine is basically an air pump. More air in usually equates to more power if you adjust the fuel accordingly. That is the key. You can't just open it all up and not adjust the fuel, cause then what's the point.

 

the world may never know. never. seriously. we are all fucked. its ruined. oh god

 

If its causing a restriction then yea porting will help. My engine with the stock 350 throttle body would probably pull 5-8 inches of vacuum at WOT if not more because its too small to flow the air the engine needs. Even with a 454 throttle body I currently see about 4-5 inches of vacuum at WOT since the hot cam swap but I think that is due to the air intake setup or possibly the dual plane intake. Long story short if you aren't pulling vacuum at WOT then technically you don't need to port it.

 

Just to answer your question, a 90mm TB is much bigger than a 78mm TB no matter how much you port it. That is the real difference. The better flowing intake is of course a nice bonus!

 

Ok, yeah i know, that's a true statement, but not what I was getting at.

Folks were bemoaning a ported stock TB saying the increased airflow is decreasing the velocity to a point that power was lost. How can one state such a claim and then share in the almost universal support for the large 90mm TB with intake when it obviously makes its gains from an increase in air flow which would, by their own theory, realize a decrease in air velocity from the large inlet size and intake.

 

Wheatley did a live tune and a live retune on my truck with the ported TB on both times, so I am assuming he adjusted the fuel curve accordingly for the increased airflow. It might just be that the stock TB flows plenty for a stock or lightly modded 5.3.