Chevy 305 engine
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There are a couple 305 heads that are marginally better than other 305 heads, the c/n | There are a couple 305 heads that are marginally better than other 305 heads, the c/n | ||
| − | ===Vortec | + | ===Vortec L30 5.0 L 305 head === |
| − | The L30 5.0 L | + | The casting number 12558059 Vortec L30 5.0 L head is quite a bit different than the L31 5.7 L Vortec heads. While the Vortec L31 5.7 L heads have a totally new intake port with a raised short-turn radius and raised roofs, the L30 5.0 L Vortec heads are 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. | 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. | ||
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===Swirl-inducing vane=== | ===Swirl-inducing vane=== | ||
| − | [[File:Tbi swirl port vane.jpg|thumb|left| | + | [[File:Tbi swirl port vane.jpg|thumb|left|300px|TBI swirl port vane]] |
<br style="clear:both"/> | <br style="clear:both"/> | ||
{| | {| | ||
| − | |[[file:305_VORTEC_SWIRL_RAMP_CN_059.jpg|thumb|center|305 Vortec L30 | + | |[[file:305_VORTEC_SWIRL_RAMP_CN_059.jpg|thumb|center|200px|305 Vortec L30 vane]] |
| − | |[[File:305 VORTEC CHAMBER CN 059.jpg|thumb|center|305 Vortec L30 casting number 12558059 chamber]] | + | |[[File:305 VORTEC CHAMBER CN 059.jpg|thumb|center|240px|305 Vortec L30 casting number 12558059 chamber]] |
| − | |[[File:L31 305 VORTEC HEAD CASTING ID.jpg|thumb|center|305 Vortec L30 casting ID | + | |[[File:L31 305 VORTEC HEAD CASTING ID.jpg|thumb|center|350px|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. | 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 | + | 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 1.84" x 1.50" valve sizes, but with a slightly smaller (55 cc nominal), more efficient combustion chamber. |
| − | The next most common 305 head for performance was the pre-'87 | + | The next most common 305 head for performance was the pre-'87 c/n 416 heads. Nominally 58 cc combustion chamber volume, 1.84" x 1.50" valves. These two heads, as well as the c/n 601 respond well to 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 degree 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, some use 1.60" exhaust valves. | |
| − | + | ||
| − | 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, | + | |
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. | 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. | ||
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