For the 1969 model year the ZL1 option was offered featuring an all-aluminum big-block engine listed at gross, it propelled the ZL1 through the 1/4 mile in 12.1 seconds. The option cost $4,700 (the ZL1 was a $3,010 option that consisted of aluminum cylinder block and heads on top of the $1,032.15 L88 option). Though generally believed to deliver at least 100 hp (75 kW) more, this has been proved as only rumors, proper testing of the engine revealed closer to gross and net rating of only .