Thread: Want 300hp out of chevy 305...?

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OK, I'll jump in here and give you my two cents worth, even though I normally would advise against trying to build horsepower with a 305.....

Bore the block 0.030" and use Keith Black #KB143 hypereutectic pistons with a 5 cc valve relief notch. Pay close attention to their recommended piston to bore clearance and ring end clearance.

Cut the block deck so that the pistons pop up out of the bore by 0.006" at TDC.

Use World Castings iron heads #042650-1 assembled with springs for 0.560" lift. These heads are designed for use with the 305 block, using 1.94"/1.50" valves and 58 cc chambers. Bolt 'em on with Fel-Pro #1003 head gaskets, 0.041" compressed thickness. With the pistons popping up 0.006" and the 0.041" gaskets, your squish will measure 0.035" and allow you to run on premium pump gas with the calculated 9.94:1 static compression ratio.

Use an Edelbrock Performer Air-Gap intake #2601 (not the RPM model) and a 600 cfm carb such as the Edelbrock #1405 manual choke model. Manual chokes work every time and are bulletproof.

Use a cam with somewhere around 225* duration @ 0.050" such as a Crower #278H or Comp #XE268H or Crane #284H12 or Isky #270/280 Mega Hydraulic or Summit #SUM-K1104.

Use 1 5/8" headers with no larger than 2 1/4" pipes.

That's how I'd build one for 300 hp. I'd also make provision for offset dowels in the cam gear to play with advancing and retarding the cam by as much as 8 degrees either way (or use an edelbrock Hex-a-just #7331 timing chain set for plus or minus 6* using a hex key). Use 12* ignition lead at the crank and 22* centrifugal lead all in by 3,200 rpm's. I'd also use a 2,200 to 2,500 rpm stall converter to get up on the cam right away.

If I were building a 350, I'd go with Chevy 37's suggestion of the Vortec heads, but on the 305, I'd use the World heads because of the cost of modifying the Vortecs to use a cam with enough lift to make the 305 work. Vortecs are limited to about 0.430" lift as manufactured unless you opt for the modified heads or modify them yourself. The intake runners on the World heads will be more 305-friendly also.