Using 400 SBC cylinder heads on a 305 engine
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| − | + | ==Can c/n 338882 SBC 400 heads be used on a SBC 305 engine?== | |
| + | You can- but with proviso's. The info provided here will hopefully help in the decision making process. | ||
| + | ==Compression ratio concerns== | ||
| + | Swapping out a set of ~58cc chamber heads for a set of 76cc heads will significantly reduce the compression ratio. The 305 SBC came with 58cc nominal chamber volume heads for the most part. Using a 76cc nominal chamber volume head such as the casting number 338882 will reduce the compression ratio by about 1.75:1. This means that special attention will need to be paid to what the static/dynamic compression ratio is going to be when using the 76cc chamber 400 heads on the 305. | ||
| − | + | ==Milling the heads== | |
| + | Unless the heads are milled a lot and/or domed 305 pistons are used, the CR is likely to be very low- too low to support a cam with much [[]] duration at 0.050" lift]. There is a limit to how much can be milled from a set of heads before the deck becomes too thin or the cooling passage by the spark plug gets into the fire ring of the head gasket. Even angle milling might not be enough. | ||
| − | + | If milling is going to be attempted, first zero deck the block. Then plan on using the tightest quench that's safe. From there the exact amount of chamber reduction can be calculated. A [http://www.wheelspin.net/calc/calc2.html compression calculator] comes in handy for this. | |
| − | + | ==Domed pistons== | |
| + | 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 effeciency 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. | 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. | ||
| + | ==Steam holes== | ||
| + | [[File:Steamholes400.jpg|thumb|400px|Correct angle of intake side steam holes. These holes are larger than those found on factory heads]] | ||
The main difference in any 400 cid small block head compared to any other small block head is the "steam holes" between the combustion chambers, due to the 400 block having siamesed cylinders (meaning they are physically connected to each other due to the bore size being as large as it is and the design being a part of the structure necessary for durability of the engine block) and the usual coolant passages not having the normal small block engine designed flow characteristics. | The main difference in any 400 cid small block head compared to any other small block head is the "steam holes" between the combustion chambers, due to the 400 block having siamesed cylinders (meaning they are physically connected to each other due to the bore size being as large as it is and the design being a part of the structure necessary for durability of the engine block) and the usual coolant passages not having the normal small block engine designed flow characteristics. | ||
| − | The 400 heads with the steam holes can be | + | The 400 heads with the steam holes can be used on other blocks without problem by using a 350 head gasket. Non-400 heads can be properly installed on the 400 block by simply laying a correct 400 head gasket with steam holes on the head and drilling the steam holes in the non-400 head. This can be done by hand if attention is paid to angling the drill bit on the 3 holes on the intake side towards the exhaust side of the head. Drill the 3 remaining holes straight down, 90 degrees to the deck. This can also be done by using a drill press. |
| − | A | + | There are quite a few builders who claim the holes are not needed on an engione that will see "normal" duty, i.e. not idled for extended periods like a delivery truck, for example. Among them is [http://www.speedtalk.com/forum/viewtopic.php?f=1&t=30647&p=363026&hilit=steam+holes Joe Sherman] (of Joe Sherman Racing) who says, "I have built hundreds of 400 engines, WITHOUT the steam holes, and never had a problem. Guys used to send me their heads for me to drill the holes, becaused I only charged 80 dollars to do the job, but I never did it for my own stuff." |
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| + | ==Resources== | ||
| + | A tutorial with pictures can be found [http://www.gregsengine.com/converting-350-heads-to-400.html HERE]. | ||
[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Undeveloped articles]] | [[Category:Undeveloped articles]] | ||
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