Has anyone tried theses turbo headers, I would not do the stainless version...let me know.
https://www.holley.com/products/exhaust/headers_and_exhaust_manifolds/all_headers/parts/12165FLT

 

I have. I bought two sets. As far as the collector and pipes they look good and fit my car perfect.

So far as the flanges go and the welding on the flanges, they are garbage. Right out of the box all four headers had severely warped flanges and holes in flange welds. They piled a ton of weld *inside* the ports. I tried to run one as is and there were so many leaks and they were warped like crazy (no way could belt sanding or milling "fix" them) I could barely spool. Finally after three passes it would not spool at all on the line.

I cut the flanges off one set and used some StainlessWorks flanges I had laying around. I bumped the FT header tubes out so I could slip the 1-7/8 stubs I put on my StainlessWorks high port flanges. I had to plug my straight across holes in the SW flanges because the head in line bolt holes leaked into them, but that was no big deal. I made .385" plugs on my lathe and tacked them in the unused flange holes.

I'm still getting data but I have a 3200lb car with a mid-frame cheater that fits 76mm compressor classes. I have a really tight converter because I run 28-30 psi boost in high gear. I generally spool to 4000 or so at 8-10 psi and bump in. I shift at 7650 RPM and run through the end about 8000 with a 4.10 gear and 28 tall radial tire if the track is tight enough.

Something like this:

T4 Borg 1.25 AR in a straight forward style header with up-pipe into the T4. 148+ MPH in 1/8th and 4.2 second spool. Pressure ratio 2.1 at 28 psi.

TiAL "T5" 1.45 AR V-band turbine FT out of box. Would not stage spool beyond 2 psi. Pressure ratio at 28 psi ~1.68

TiAL "T5" 1.17 AR V band FT out of box. 7 second spool to 6 psi boost. 141 MPH and 1.7 PR at 29 psi. Stopped working after three passes because of flange leaks.

TiAL "T5" 1.17 with new flanges on FT headers. No leaks. 5 second spool to 12+ psi. 151+MPH and 1.72 peak PR at 30 psi.

I'm going to get more data with the 1.45 A/R turbine housing now that I have good flanges.