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{{youcanedit}} ==Overview== Basic details and suggestions on hotrodding the SBC 305 (5.0 L) engine. ==Introduction== The 305 SBC engine was introduced in 1976 to have a Chevrolet engine smaller (and supposedly more economical to use) than the SBC 350, yet having adequate torque for the same applications that used the SBC 350. ==Cost== The 305 is cheap and plentiful. The cost to rebuild is about the same as the 350 but piston selection isn't as good as for the 350 and there is a definite lack of aftermarket support for cylinder heads. Regardless of the cost to rebuild the 305, the power-per-dollar is less for the 305 than the 350. In practice, there seems little real advantage in gas mileage over the 350, but you may get less costly insurance rates. ==Design considerations== The 305 engine is much-maligned and shunned as a performance build, mainly due to its small bore diameter of 3.736" which limits breathing. Limited breathing also limits naturally-aspirated power potential. The primary appeal of the 305 may be due to its "underdog" appeal, or simply because that's what is on hand at the time. Unless you already have a pre-'87 block, the '87-up block is preferred because of the one piece rear main seal, and the cast-in provisions for the factory hydraulic roller lifters and thrust plate for the cam. Also, these later blocks tend to display far less bore wear from carb-related fuel washing of the cylinders, as most were EFI. ==Cylinder heads== ===Pre Vortec heads=== Generally, the 305 heads were akin to 350 heads except they had smaller intake valves (1.72" or 1.84", depending on the application), as well as a smaller combustion chamber as mentioned above. There are a couple 305 heads that are marginally better than other 305 heads, the c/n ===Vortec heads=== The L30 5.0 L Vortec head is quite a bit different than the L31 5.7 L Vortec head. While the Vortec L31 5.7 L heads had a totally new intake port with a raised short-turn radius and raised roofs, the L30 5.0 L Vortec heads were somewhat of a carry over. The L30 Vortec heads use the same intake bolt pattern as the L31 5.7 L Vortec heads, but share few other similarities with them. The 305 Vortec heads have a spark plug location similar to the swirl port head, and a similar combustion chamber shape as well. The chamber volume is less than the 5.7 L heads, just like any other 305 vs. 350 head. This is to keep the compression where it need to be. While the 305 Vortec head has a swirl vane in the intake port, it is much smaller than what's seen in the 5.7 L swirl port heads like the c/n 191 and 193. ===Swirl-inducing vane=== [[File:Tbi swirl port vane.jpg|thumb|left|350px|TBI swirl port vane.]] <br style="clear:both"/> {| |[[file:305_VORTEC_SWIRL_RAMP_CN_059.jpg|thumb|center|305 Vortec L30 casting number 12558059.]] |[[File:305 VORTEC CHAMBER CN 059.jpg|thumb|center|305 Vortec L30 casting number 12558059 chamber]] |[[File:L31 305 VORTEC HEAD CASTING ID.jpg|thumb|center|305 Vortec L30 casting ID.]] |} 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, always bore to the next smallest oversize. If you can get away with a 0.020" overbore, all the better. Use the same guidelines as you would for a SBC 350 for selecting the type of piston. Cast are fine for engines that won't see nitrous or boost, forged if it will. There are those who say using cast pistons and nitrous/boost is acceptable. And it is- providing the tune is spot on and the engine never sees detonation. If it does, the cast pistons will be the first thing to fail, and when they go they usually damage the bore and possibly the cylinder head as well. ==305 intakes== 1986-back heads use a "regular" intake 1987-'95 heads use straight center bolts 1996-'02 heads use the Vortec bolt pattern ==Parts suppliers== ==Resources== *[http://outintheshop.com/faq/casting/castings2.html SBC head casting number go-to site] *[http://web.archive.org/web/20080518030656/http://www.mortec.com/ MorTec archived] ==References== *[[Building a Chevy 305 engine]] *[http://www.hioutput.com/tech/343hp/343hp.html "Lunati's 343 hp 305 Build-up"] *[http://www.popularhotrodding.com/enginemasters/articles/chevrolet/0667_phrs_305_chevy_engine_blocks/viewall.html "150 HP for a 305 Chevy Engine - Hate Me: Add 150 HP to the Chevy No One Likes"] [[Category:Engine]]

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