I had a few and mine never pinged even on regular gas but they were for sure under powered and tuning them, even to stock standards is big improvement over unturned but until you do get it tuned . I would run premium just to be safe, I always did. Only reason I knew it didn't ping on regular is what was left in the tank after the swap and test driving it and buttoning it all up..
A PI motor doesn't need premium. Only if you get it tuned for Premium is it worthwhile. It's a low compression motor, runs fine on 87 with a good tune.
If you don't tune it, and run it off a bone stock MN-12 ECU, it's going to run poorly. By running poorly, that doesn't necessarily mean it's going to ping a lot, or backfire, etc, but it's going to at the very least leave a lot on the table unused, and if you're not going to bother to tune it, why put a better motor between the fenders in the first place?
A tune isn't horribly expensive, and not that complicated for the good tuners to get a bone stock motor running properly in your car. You can get an SCT for cheap on Ebay, a tune is $100. It's well worth it, just do it. All that effort just to run at 3/4 or 2/3 of the potential? No thanks.
97 Thunderbird LX (The GT Bird)
2003 Explorer WAP block with Modular Head Shop "street ported" heads and Stage 2 PI NA cams, 75mm Accufab throttle body, C&L upper intake plenum, Kooks 1.75" primary/3" collector headers, 2.5" full exhaust with mid mount Magnaflow dual in/out muffler, 24lb/hr injectors, 80mm MAF, Tuning from Don @ www.lasotaracing.com
, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels with 35mm offset, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.