Car performance improvement is very minimum but increase performaance in battery life, brightness of head lights & ICE performances; all the above due to better efficientcy in alternator charging during high alternator drain(multi-task) at lower rpm range(espeacially Auto cars) ie on 'D' gear in traffic jam, wipers on, head lights on, brake lights on & ICE also on full blast. Your existing standard alternator will not be able to churn the juice for your requirements at 700 to 800rpm, this extreame stress will kill your 60 to 70amp OEM alternator faster than normal.