AS has already been said, ALL L67'* REQUIRE PREMIUM GAS! If you have an L67 it requires premium gas. If you run lower grade gas you will only hurt performance and gas mileage. Now if you were to put on a larger pulley so it runs less boost, install an intercooler and keep the same size pulley on or not go with one that is much smaller, or you put on a more effiecient blower, then you may be able to run regular gas with no detonation, and you will still get decent gas mileage, but that would be some $$$ that you had to fork out for those mods, so it wouldn't be worth it. For instance, now that we have put ~$7000 into the engine of the GTP we could run 87 octane gas on the street with no detonation with a 3.0 or 2.9 pulley. But running that size of a pulley would cost us a ~20hp loss, we would get worse gas mileage, and we spent $7000 to be able to do it, so what is the point in doing it. Nothing buy 92 or higher goes in the SSEi, and nothing but 93 or higher goes in the GTP, we like to keep our engines running good.
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!