302 head porting

[chargd72]

So I've done lots of research and reading on porting heads.  I have a set of '302' cast (swirl port) heads and I'm going to to match the runners to fit my air gap manifold.  While I'm in there, I figured I would do some extra porting to further enhance the performance.  However, I found no info on porting the bowls of these heads and I'm concerned with loosing the 'swirl' aspect. 

I've found that the swirl technology is simply from the air moving more aggressively toward the cylinder wall (see pic below).  But no one mentions how to modify these correctly. 

Is it better to leave the bowls untouched to keep the 'swirl'? 

[alcusswhen]

The basic shape of the port creates the swirl effect. That basic shape of the port should not change when ported, it should just get a little bigger and smoother. In effect allowing more air to enter faster creating even more swirl.

[Challenger340]

Some thoughts(IMO)
The Bowls purpose in life, is to transition the Airstream from the port, to a "rounder" shape in preparation to exit the "round" Valve Seat.
Increasing the Bowl "Volume" above the Valve, generally speaking, provides "time", due to the greater Volume, for the Airflow to slow down(while filling all areas equally of the said "greater Volume"), to then provide more equal flow around the Valve.
The swirl heads will invariably provide the greatest flow to come crashing out beside the plug anyways, enhancing the Bowl will only provide more "everywhere", including "swirl".

Making the Bowls "rounder", and removing the ridge above the Valve seat by blending it into the wall only HELPS !

This is an Old 340 "J" Head, but hopefully this gives you the idea of a "rounder" Bowl shape above the Valve  ?
Even with the J Heads, this 340 made 391hp with the Blueprint "resto" Cam from Comp Cams at 9.5:1 CR., Stock Factory Intake & Thermoquad Carb, 1 5/8" headers.

[elacruze]

^ Well said!

I'll try to make sense without writing a thesis-

'swirl' doesn't make power in any significant amount. Swirl does improve emissions and resistance to detonation. Swirl only adds power when it can be improved _after_ port airflow is maximized. Poor swirl plus good squish is a better combination than good swirl and no squish.

Another way to restate Challenger340's post is that increasing bowl volume slows airflow velocity, which allows the air to turn the corner to the valve easier.

My self-imposed rule is limit myself to 'cleanup' unless a flow bench is used-and I don't own a flowbench so that means I don't do anything more than remove edges and rough spots, and port match to about 3/4". Increasing volume anywhere without measuring changes guarantees only that you'll breathe iron dust, not that you'll get a faster motor.

[chargd72]

Some great info guys!  This helps a ton. 

So would it be smart to stay away from a carbide bit so I don't go nuts on them?