I plan on installing the ZZ4 conversion kit in my '84 Z28 and wanted to know if the SLP headers are the way to go? Also, what size should I get, the 1 5/8 or the 1 3/4?

 

Yep, I've got SLP headers on mine and they're great. Which ones to get depends on your plans for the car. If you're a street driver, get 1 5/8". If you're a racer, get 1 3/4". If you're gonna put in a larger cam, get 1 3/4".

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I plan on putting bigger valves in the heads or putting different heads on but that won't be until probably until next year. What would be the difference between the 1 5/8 and the 1 3/4 on the stock ZZ4 and then when the engine is modified?

 

Dont bother with bigger valves in the ZZ4 heads, its not worth it.

I dont think anyone has done a dyno comparison between SLP 1 5/8" headers, and SLP 1 3/4" headers. I switched on mine but I did a lot of other mods at the same time. SLP recommends 1 3/4" headers for a 350 or larger engine, and 1 5/8" for a 305 engine. If you've got plans for different heads and cam next year, get 1 3/4" headers now. You wont lose anything now, and you'll gain more after you swap.