I was just wondering how much spark is typically added when going from swirl port heads to non-swirl heads. Perhaps a hard question to answer accurately, but I'm curious as to how much less timing the swirl-port heads require ...a ballpark figure. Thanks.

 

The factory used 6 deg more base advance on the non-swirl TPI heads than they did on the swirl TBI heads.

EDIT: GM did this because the swirl causes the flame to travel faster on the swirl-port heads, so not as much ignition advance was needed to make optimum power. That's according to the Chevy book, published by GM, on Chevy Powerfor v6s and v8s. GM also referred to the swirl port heads as being "fast burn" and efficient both from emissions and economy.

 

they had a diffrent cam profile though. It is really a mix of a lot of diffrent factors. basicly as the effeciancy of both air/fuel deliver and combustion chamber design, mixed with the atomization of the charge, will all effect timing.

 

Found out the hard way that 081s like 6* initial advance more than a stock TBI 305.

Not all TPI had the good cam though. Many had the TBI peanut cam with the only change being the TPI and 081s.