increase HP on a 273

Good info guys. I believe Camcraft ground the original HP273 cams. The Isky E-4 is close to the factory HP cam. Not a split lift/duration but pretty impressive low end torque. (260/.425/108 deg.) I've been checking out cams on my Dyno program for some time now. A little more cam for the 273 helps a bit but more is not always better. More HP/less Torque at lower (usable) rpm. More lift and duration just makes it run more radical and requires a higher stall convertor and steeper rear gears to make it work. A dual plane intake improves low end torque but watch out for intakes made for 340/360's. The ports are too big and it won't help much. A 600-650 cfm carb is perfect, with vacuum secondaries for an .automatic. The biggest performance increase seems to be headers and free flowing exhaust. The 273 manifolds leave a lot to be desired for free flowing
exhaust. I don't believe you mentioned whether your 273 was a HP or not. The 10.5:1 compression makes a difference. If you have a 2 barrell motor and don't want to over haul it there's not much to do except shave the heads to increase compression. I am planning an overhaul on my hp273 this winter. Other than a bit bigger cam and some head porting it will be a stock rebuild using stock manifolds. The Dyno program figured 322 hp @6000 and 322 tq.@ 4500 rpm. I've tried all sorts of different combinations and this seems to be the best balance. Headers and low restriction exhaust bumped the numbers up over 350 hp and torque. So headers are important for performance. Good luck and keep us posted on your progress. toolmanmike