Using 400 SBC cylinder heads on a 305 engine
From Crankshaft Coalition Wiki
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Generally speaking domed pistons are not as efficient as a flat top design. But that may be the only option to get acceptable CR when using 76cc chamber heads on a 305. When the added cost and loss of efficiency of domed 305 pistons is considered, it may become apparent that using an all together different cylinder head would result in better performance potential at less cost. | Generally speaking domed pistons are not as efficient as a flat top design. But that may be the only option to get acceptable CR when using 76cc chamber heads on a 305. When the added cost and loss of efficiency of domed 305 pistons is considered, it may become apparent that using an all together different cylinder head would result in better performance potential at less cost. | ||
| − | Also be aware that the 1.94" intake is all the 305 bore will take without excessive valve shrouding. If the heads in question have 2.02" valves, they will not work on a 305 even if the intake valve clears the bore due to shrouding. | + | Also be aware that the 1.94" intake is all the 305 bore will take without excessive valve shrouding. If the heads in question have 2.02" valves, they will not work on a 305 even if the intake valve clears the bore due to shrouding. (If these are 338882 heads they may only have a 1.72" intake better measure) |
==Steam holes== | ==Steam holes== | ||
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==Bottom line== | ==Bottom line== | ||
By now, it's clear using 76cc heads on a 305 is '''not''' the hot ticket. All one could hope to gain is a marginally larger intake valve (1.94" vs. the 305's 1.84" intake). Everything else is the same or worse than the original heads, including the port flow. It has to be remembered that the 76cc "smog" heads are among the worst flowing SBC heads of all time. There are guys who like the 305 heads enough that they will rework them for use on a 350 SBC. These same guys would NEVER consider using the c/n 882 head, period- even on a 350, where it would make better compression than on the 305. | By now, it's clear using 76cc heads on a 305 is '''not''' the hot ticket. All one could hope to gain is a marginally larger intake valve (1.94" vs. the 305's 1.84" intake). Everything else is the same or worse than the original heads, including the port flow. It has to be remembered that the 76cc "smog" heads are among the worst flowing SBC heads of all time. There are guys who like the 305 heads enough that they will rework them for use on a 350 SBC. These same guys would NEVER consider using the c/n 882 head, period- even on a 350, where it would make better compression than on the 305. | ||
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| + | ==Compression ratio calculators== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html SCR] | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | {{Note1}} Some dynamic compression rtatio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate. | ||
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| + | {{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
| + | # Divide the intake duration by 2 | ||
| + | # Add the results to the lobe separation angle (LSA) | ||
| + | # Subtract any ground-in advance | ||
| + | # Subtract 180 | ||
| + | This result does not need to have any amount added to the IVC point, like the KB calculator calls for. | ||
==Resources== | ==Resources== | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:GM]] | [[Category:GM]] | ||
| + | [[Category:Cylinder head]] | ||
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