ok will this work or will it be "too" free flowing, rb road race headers to a custom 2.5in pipe back to a magnaflow 3in inlet with a 4in outlet...anyway let me know what you think...this will be on a stock 81 12a till i have my engine rebuilt and (monster)streetported but thats still a while away, thanks

 

There's no such thing as "too free-flowing". However, that setup will be loud as ****!

Use the RB r/r headers to a collector merged into 2.5" pipe with as long a presilencer as you can find/fit in the middle. Keep the 2.5" piping size consistent with the muffler in/out. If you want it quiet, use as big and "volumnous" Magnaflow at the end as you can fit. That setup should work well with a future big streetport as well

 

yes, keep it 2.5" all the way.