Cylinder Head Theory
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I created this page to include a thread from the forum that really gets into the heart of the matter of head flow. It was commented on by at least two professional head gurus and is information that should not be allowed to get away. Please read through this thread to get a better understanding of combinations and head flow..... | I created this page to include a thread from the forum that really gets into the heart of the matter of head flow. It was commented on by at least two professional head gurus and is information that should not be allowed to get away. Please read through this thread to get a better understanding of combinations and head flow..... | ||
http://www.hotrodders.com/forum/matching-profiler-heads-my-engine-356417.html | http://www.hotrodders.com/forum/matching-profiler-heads-my-engine-356417.html | ||
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| + | I will add tutorials to this article from time to time. This one deals with cc-ing the heads.... | ||
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| + | Unless they have been in your possession since they were cast at the foundry, you have no idea what the actual volume of the combustion chambers is or what has been done to them by those who owned them before you. Even if you have owned them since new and had been told what the chambers poured, factory tolerances could be 3-4 cc's off. They could also have been angle milled, so you will want to find that out before you go any farther with this project. This angle milling operation changes the angle of reference between the surface of the cylinder head and the valve centerline to aid flow into the cylinder and raise the static compression ratio, it's an old hot rod trick.....here is a small block Chevy example..... | ||
| + | http://image.hotrod.com/f/10203945+w660+h440+cr1/ctrp_0312_02_z%2Bcylinder_head%2Bangle_milling.jpg | ||
| + | If the heads have been angle milled, the intake manifold must be angle milled too, to match up and effect a seal. If the angles of the heads and the manifold do not match, the gaskets will not seal up and the motor can pull oily crankcase vapors into the cylinder on the intake stroke. This is what happens sometimes when fellows find oily spark plugs and blame it on valve seals. No amount of spraying a combustible product around the motor will detect a vacuum leak at the manifold/head interface if the gap is on the underside. | ||
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| + | Here's a cheapo cc kit that will suffice....if you're careful, you should be able to keep the results of your pour within one cc and that's close enough for our purposes. | ||
| + | http://www.ebay.com/itm/Cylinder-Head-CC-Kit-for-measuring-combustion-chambers-/300993449341?rmvSB=true&rmvSB=true | ||
| + | If you want to invest in a better tool that is precise down to 0.2 cc's, you can buy a kit like this that will require less refilling during the pours. | ||
| + | http://www.summitracing.com/parts/sum-911581/overview/ | ||
| + | Use rubbing alcohol and food coloring from your local grocery so you can see the meniscus of the column, red, green or blue, your choice..... | ||
| + | http://en.wikipedia.org/wiki/Meniscus | ||
| + | https://www.youtube.com/watch?v=V7V40ZWNgCo | ||
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| + | Once you have nailed down the volumes of your combustion chambers, you can do your buddy's chambers for 30 bucks for a pair of heads and recoup your investment plus earn a little gas money on the second and subsequent sets that you do for other fellows. Don't just do one chamber, do them all so you can be sure that the heads were not mis-registered when the faces were cut at the factory, resulting in different volumes on the same head. | ||
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| + | You can also pour the intake and exhaust runners the same way. For the intake runners, lay the head on its side with the intake ports facing up. Put a little Vaseline on an intake valve stem and valve face where it seats in the head to prevent leaks, grease the intake port and place the plexiglas over the intake port the same way you did for measuring the combustion chambers. When you've done the intakes, turn the head over so that the exhaust ports face up and repeat the process with Vaseline on the exhaust valve face and stem. It won't take a whole lot of Vaseline on the valve stems, just a light coat. You just want to prevent the alcohol from leaking between the valve stem and the valve guide. If you put too much on, the glob that results will skew your results and make the runners smaller by the volume of the glob. If you pour the chambers, intake runners and exhaust runners and record the results, you will be armed with information that will help you to know what to do next. Choosing the proper cam for a street motor requires that you know the actual static compression ratio of the motor and to do that, you need to know the exact volume of the chambers. | ||
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