This injector is the first stage high performance injector for the Mack E7 VMAC I & VMAC II engines built between 1991-1997. This injector provides between 10-15 percent increase for the 1991-1993 E7 300, approximately a 5 percent increase for the 1991-'93 E7 350 and 400, a 30 percent increase for the '94-'97 E7 300, and approximately a 15 percent increase for the '94-97 E7 325 and 350. On their own, these level one injectors provide substantial performance improvments, but when they are used with the Bixxton-Mack the performance is improved dramatically. These are reman injectors requiring that old cores be returned. CORE CHARGE: A core charge of $150.00/injector will be applied to your credit card account, if the old cores are returned within 30 days, you will get credit. Feel free to call our parts department at 800-891-8038 with any questions.