I have a 84 z28 305. i have2.5in flowmaster 40seriesexhaust system on it now with the stock manifold and looking to put headers on it. What would be the best size for maximum performace?I located a set of 1 5/8in. headers and 1 1/2in. headers for a good price. Would either of those be a good set i believe the small one is hookerand the largerdynaflow?

 

To the best of my knowledge you won't see a real performance gain over the larger header on a 305. Since I'm assuming you'll be sticking with a Y-pipe exhaust, your exhaust will give you whatever little backpressure you may need.

 

The 1 5/8 should work pretty good...if your looking for power tho save your money that you spend on parts and get a 350 and rebuild it. Trust me its worth it.

 

he could go with the larger size for now, and when the time comes to replace the engine, hes already got a set of headers. thats my philosophy

 

with a stock 305 im not sure if having 1 3/4" exhaust would provide enough backpressure to work the valves correctly. Stick with 15/8" or less.