Chevy 305 engine
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==Intro== | ==Intro== | ||
| + | The 305 was introduced for 1976, to have a Chevrolet engine between the 250 and the 350. The small bore diameter of 3.736" limits breathing, which limits naturally-aspirated power, so this engine is much-maligned and shunned as a performance build. The primary appeal may branch from any combination of 3 common sources. The "underdog" appeal, already having one, and the success of the Ford 302 rival. | ||
| + | The 305 is plentiful, and easy to get for cheap. The build is about as cheap as the 350, but the power-per-dollar is always less. In practice, there seems little real advantage in gas mileage over the 350, but you may get less costly insurance rates. | ||
| + | Unless you already have a pre-'87 block, the '87-up is preferred, because of the cast-in provisions for the factory roller ( hydraulic ) lifters and the thrust plate for the cam. | ||
| + | Also, these later blocks tend to display far less bore wear, as most were EFI, which gives less fuel wash than even the computer-controlled Quadra-Jet carburetors. | ||
| + | With heads, the Vortec situation is a bit different from the 350. Vortec 350 heads had totally new intake ports, with raised short-turns and widened roofs. But the Vortec 305 heads were carried over, changing only the intake face for attachment of the Vortec MPEFI. Worse, the dreaded swirl-ports were also carried over into the Vortec configuration. | ||
| + | Swirl-port, pre-Vortec heads were used for all of the TBI 305s, and do not respond to porting and big valves. Don't even think it, it's been tried. | ||
| + | The best 305 heads have a casting number ending in '081. These were used with all '87 305s AFAIK, and all TPI 305s, '87-'92. These came with the same old 1.84" / 1.50" valve size, but with a slightly smaller ( 55 cc nominal ) more efficient combustion chamber. | ||
| + | The next most common 305 head for performance was the pre-'87 '416 heads. Nominally 58 cc combustion chambers, 1.84" / 1.50" valves. | ||
| + | These 2, as well as the '601s which I have few facts about, respond well to good porting, and 1.94" intake valves, if the machine shop does it right rather than doing it cheap. | ||
| + | A performance valve job for these heads, and for milled Vortec 350 heads, starts with ordering better valves: stainless steel, 1-piece, swirl-polished, undercut-stem. You can get all 16 for $70 plus shipping. Next is to have the shop put a 30-degree back-cut on them. Then have the seats cut with standard 30 / 45 / 60 angles, as far out on the valves as possible. Next is the bowl hog, a 75-degree cut that goes as deep as possible without hitting the guide boss, while simultaneously narrowing the 60-degree cut to about 0.050"-0.055" The de-shrouding sweeper cut really isn't worth it. If you're doing milled Vortec 350 heads, do 1.60" exhaust valves, it is worth it. | ||
| + | Porting. If you've done well on a junk head, then this is worth trying. Do taper all the guide bosses, except in the Vortec 350 intake ports. Ever so lightly, blend the 75-degree cuts into the ports, too. | ||
| + | Polishing the intake ports is not advised. Doing the chambers is good if you protect the seats. Doing the exhaust ports is great. Gasket-matching the ports isn't necessary, and for the exhausts it's not helpful, either. | ||
| + | If you are going to have a 305 block bored oversize, you may as well go right to "sixty" ( thousandths ), because the supply far exceeds the demand, and if you ever need a rebuild, you can replace the block cheaper than buying more pistons and getting the crankshaft re-balanced yet again. | ||
| + | For a 400-HP build with no nitrous, or a 500 HP build with mild nitrous, hypereutectic pistons are fine. If you anticipate boost, you may as well invest in forged, which are stocked in the common "thirty" oversize, but not "sixty". | ||
==Parts suppliers== | ==Parts suppliers== | ||
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