Just like title says what size header primaries would y’all suggest for 1200+ Flywheel hp 427ci. 4.5L whipple pro street style application? Getting ready to pull the trigger on some ARH headers. Thanks for any input in advance.

2” primary’s will give you more power everywhere. I run the ARH 2” and I’m at 715ish flywheel. I’d go at least 2” if I were you, maybe even 2 1/8”. Can you fit a 3 1/2 collector/exhaust?

I’m leaning hard to 2” and I’m pretty sure I can fit 3 1/2 collectors. It’s going in a 85 Monte and ARH says they can do the g body 2” primary with 3 1/2 collector but unsure how well they fit and how much ground clearance they provide.

Minimum 2 inch, probably could go bigger.

Those guys at ARH are artists. I’ve seen a couple C6 Vetts (crazy tight engine bay) with ARH 2 1/8” primary’s. I don’t feel that fitment (space) with a 2 1/8” primary is as tough as getting to the spark plugs with a primary that big, although it’s possible.

Was waiting on response from engine builder, so apparently engine was dynoed with 1 7/8 stepped to 2” within 7” of flange. Thinking that may be a good option as well now just have to get with ARH about availability in my setup I guess. Maybe a stepped header will provide a little more plug wire clearance also.

lol yeah right!