I have a ZZ4 (355hp stock was a 208/221 dur -.480/.510 lift cam & SMALL 168cc heads and crappy intake).

Reviews: "The aluminum heads are basically the same as late-'80s L98 Corvette heads; the dual-pattern hydraulic roller cam is lazy; and the low-profile intake manifold, although it offers ample hood clearance, just doesn't flow the air." Hot Rod Magazine.

I replaced the heads with 195cc Trick Flow heads, an RPM manifold, and a 230/235 dur. - .530 lift cam. I'm assuming 400-420HP (+/-)

So... if I'm 85% street/freeway...and 15% strip... which will suit me better? 1 5/8" or 1 3/4"?
I will (when this needs rebuilt....could be years from now) be turning this into a 383 but the use will be the same (85% street 15% strip).
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I would just go with the 1 3/4" headers. Might as well make sure everything is ready for you to go bigger. Especially with what you have going on with it right now you still might as well go bigger.

 

i would go with the 1 5/8. since it will be an engine with its revs primarily kept under 4k, the smaller diameter will keep the exhaust velocity higher at the lower revs, thus improving the low end power. yes, it will drop off about 10 peak hp, but it will perform better in the rpm range you will be using it in. when you do eventually go to a 383, that would be the best time then to go up to 1 3/4