2" primary headers loss vs. 2 1/8

[C8OZ]

I have a set of 6376 Hooker adjustable headers, the 2" version of the 6375 (2.125).
Any idea how much power I'm leaving on the table with the 2" primaries?

I'd like for the build to live quite a while, so I'm okay bringing the peak RPM down some.

These are for a 4.375 x 4.375 Tunnel Port, single Holley 4500, 13.5:1-ish and E85.
Shooting for 3400 pound max, 4-speed, 29" tire, weekend 1/8 mile car, not a max effort racer.

The rest of the specs are tbd, as it's still early. I just hate to take hammer to car and pipes in mockup if these need to stay on the shelf for a smaller CI build.

[chilly460]

What kind of power do you anticipate making, I've seen tests between 2" and 2 1/8" on a 700hp BBC and the bigger headers were 5hp better.

[C8OZ]

I'd like it to go mid-sixes 1/8-mile and live. I haven't done that with an FE, so I'm making some guesses. But 700 ballpark is my goal depending on how much weight I can drop.

[Stangman]

Not a hairy difference. Not enough to loose sleep over.

[gt350hr]

  Might not show at all. 2" used to be THE size to use.

[frnkeore]

Does anyone make a stepped, 2 - 2 1/8 header. That might be interesting.

[thatdarncat]

REF Unlimited will make step headers, custom sized.

[C8OZ]

Thanks guys.
A slow project gives me plenty of time to start questioning parts choices. I'll plan on putting the 6376 to use.

I've read that a third version of the Hooker adjustable was stepped 1 7/8, 2, 2 1/8, but I've never seen a set.

[Posi67]

I think my 390 would prefer the 6376 headers given it's smaller size but these haven't been made in years. All I ever had/have are 6375's and they seem to not hurt performance no matter the cubic inch. I doubt you'll see any difference with your combo. I'm fairly certain the Hooker Race 1 7/8" which I've never seen either were not a step header. Seems the jury is still out on any real benefit on step tubes anyway. Now Hooker doesn't make any of them for some reason.

REF makes some good headers but apparently nothing out of the ordinary. A guy at the track today said he (or no one else for that matter) would build Headers for a 66/67 FE Fairlane with a rear sump pan. He ended up making his own.

[475fetoploader]

Here’s my REF 1 7/8 headers, had jet hot coat them. They’re for a 67 Fairlane, he was a pretty cool guy to talk with. His opinion was I could shove quite a bit of power through 1 7/8. We shall see.

[475fetoploader]

Try again with photo

[475fetoploader]

Ugh

[C8OZ]

Everything I've seen from REF looks top notch. I like that those collectors angle inboard where the Hooker is straight back.

[Falcon67]

I'm making 575 in a 393C with 1 7/8" tubes so IMHO go with what fits.  You'd not know the difference. 

[Joe-JDC]

I made 561/595 with 1 5/8"-1 3/4" stepped FPA on my 375 CI Y Block.  Fits '55 Thunderbird. Same headers made over 600 hp on a different engine.  There are a lot of dyno tests that prove the stepped headers work if you actually do back to back testing.  REF is a race header, but he designs them for specific chassis, so they fit SE and SS cars classes as well as street.   Joe-JDC