I recently had one of the two factory cats break up inside and I replaced them with 2 new Catco high flow cats. Since replacing the cats my times have been right on and even better BUT Ive lost 2-3 MPH in the 1/8th and 4-5 MPH in the 1/4. Only thing different from my best run of 13.63 @ 99 MPH (78.16 MPH in the 1/8th) is the Catco cats. I ran tonight, went 13.521 on a 1.77 60ft (75.65 MPH 1/8th) and I ran my normal 94.97 MPH in the 1/4. Anyone else have similar results with Catco?? Anyone have any kinda opinions as to why I lost that much MPH across the board? Any info or opinions would be appreciated....

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1992 Z28 L98:
bolt-ons, 2k stall conv, shift kit and cooler and various other mods.
Best ET: 13.521 on a 1.770 60ft.

 

Heres my thought, You might of had you car tuned to run great with your old cats, witch were probably cloged or on there way out, so there was more back pressure,So with the new one on less back pressure so you might need to fine tune your fuel pressure or timing or something minor?

 

Thats something I was thinking about, Im still running stock everything fuel wise and Im planning to port the plenum and when I do add new injectors and an adj FPR so maybe with a lil adjusting that MPH will come back, maybe its just leaning out but Ill be honest Im far from a mechanic so its just a guess thats why I figured Id ask here and see what kinda of responses I get, thanks again....