Cylinder head Information

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RPM - Ron's Precision Machine Santaquin Utah


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This page has information about how cylinder heads are machined and also about mira-cut & porting and cc combustion chambers.

When cylinder heads are brought in for machine work, eight basic things are done to re-build them. The first thing is to take the heads apart and clean them. Then either shot peen or glass bead them so they can be magnafluxed, in the case they are cast iron heads, or die checked, in the case they are aluminum, to check for cracks. They can also be pressure checked to see if there are any leaks from the water jacket. Next, new valve guides are installed and diamond honed to fit the valve stem. Next, the head or heads are 3-angle valve jobbed then the heads are surfaced in a machine to give the right RMS finish for proper head gasket seal. Installed height of the valves are measured to check valve spring pressure, and springs are either replaced or shims installed under valve springs to give correct seat pressure. Then open pressure and coil bind is checked to make sure the springs will work with the camshaft that is going to be installed in the engine. The heads are then cleaned again, then lubricated, then assembled with either re-faced valves or new valves, seals, shims, retainers, locks, etc.

If more performance is requested, or a higher lift than stock camshaft is going to be installed in the engine, then other machine work is required, to make sure all parts are compatible. For example: some camshafts require bigger valve springs, so the heads would have to be machined for bigger valve springs. Most stock cylinder heads have what is called a single spring or a single spring with a damper. If the new springs are a dual spring, then not only does the spring seat need to be machined bigger, but the valve guides also need to be machined to fit, and probably needs to be machined for positive type seals also, to clear the inner spring.

When stiffer (more valve spring pressure) springs are installed for high performance use, screw-in studs might be required so the stock pressed in stud won't pull out under higher spring loads and higher rpm.

If more horse power is your goal, then mira-cut and pocket porting might be one of your options. Mira-cut is a 3-step radius carbide cut system that machines a 90 degree cut down the side of the combustion chamber, radiused into a 15 degree angle, radiused into a 30 degree angle, radiused into a 45 degree (valve seat) angle, radiused into a 76 degree angle down into the valve pocket area. Then a pocket port is done with a carbide burr to hand shape the short side radius and bowl area to an exact shape. Then a sandpaper type cone is used to blend everything in. For every 1.4 CFM gain in cylinder head flow, there is a 1 horse power gain. Therefore, the more work that is done for better flow, the more horse power there is to be had.

After market cylinder heads usually flow more air, so naturally another option would be to buy better cylinder heads to start with, then mira-cut and pocket port them for even more gain!

To get the same compression in all cylinders, then you may want your heads cc'd. If you have really high compression; that is, over 11.0 to 1, then this becomes very important. The higher the compression, the more critical total volume becomes. Total volume is: deck height, gasket thickness, and cylinder head volume.

Currently R.P.M. sells several different brands of aftermarket cylinder heads for most of your needs, including World Product, Edelbrock, Dart, Trick Flow, Brodix, etc. R.P.M. also can fill most needs for stainless steel valves, springs, retainers, locks, screw-in studs, guide plates, p.c. seals, and all the machine work you may require to build your engine the way you want it done.


69 E. 580 N.
Santaquin, Utah 84655
1-801-754-5338 or Toll free 1-866-700-5877

Call toll free 1-866-700-5877 to purchase parts, or click e-mail or Order Form