Ted Eaton asked me to post the details of our recent discussions, regarding two of his articles, as well as my questions, regarding piston valve reliefs and metric rings.

While comparing the dyno sheets of two of Ted's engines/w very similar specs, I noticed that the "HP to the Cubic Inch" engine made 45.9 hp and 29.9 lb/ft more than the "Modified" engine. I asked Ted to explain why. Ted replied that the "HP" engine used metric rings. "I typically see 25-30 hp increase, when using metric rings." He also stated that the "HP" engine's static compression was 9.57:1 vs 8.75:1 for the "Modified" engine. When asked about oil consumption, ted replied, "No oil consumption or smoking issues with metric rings, but cylinder wall finish is critical. Modern technology requires modern machine work."

Regarding the need for piston valve reliefs, Ted replied, "You are generally safe up to 0.535" lift." "Changing lobe centerline or advancing/retarding cam can change valve/piston clearance." Bore size typically not a player, but notching cylinder edges when lift goes past 0.535 for iron heads, and for unshrouding intake valves on aluminum heads. 
Ted expects members, who have had experience with these issues, to chime in. 

Thin rings are one of the greatest advances in modern engine building. They help in 2 ways. 1 is reduced friction  If you ever assembled an engine with the old 3/32 rings and then remember how much force it takes to turn the assembled engine over.. The thin ring takes maybe 1/2 the force.  So that is one benefit.. the other is that thin rings conform to the cylinder wall much better and so provide better sealing of cylinder pressure. Like Ted said cylinder wall prep and tight tolerances on the piston grooves is important. That is 25 or 30  hp which is essentially free.

This metric rings topic is one that I know absolutely nothing about, but I am very interested in the concept in rebuilding my FYB 312 c.i. engine. Is there any written materials that explain all the how-to's and wherefores in using this technique? If so, how do I go about getting it? Thanks for any help!

All the current automobile manufacturers are using metric rings for their engines.  They has been in use for several decades.  The use of hydraulic roller camshafts, overhead camshafts, metric rings, synthetic engine oils, timing belts, electronic fuel injection, and catalytic converters, etc., all are part of getting less internal friction in the engine for better fuel economy, and performance.  If you order a set of pistons from JE, Diamond, Racetec, etc., they will ask you what ring package you desire for your build.  They are available in .8, 1.0, 1.2, 1.5, 2.0, 3.0 mm sizes on the top and second rings, with/without lateral gas ports, coatings, pin diameter/length, pin fitting, clips desired, etc..  The thinner the rings, the less the friction loss.  For street use, I personally would not go less than the 1.5/1.5/3.0 ring package.  Ted, or others will have their own preferences.  Joe-JDC

JDC

Do these pistons/rings like the cross-hatch cylinder surface finish or do they require something else? The cylinder surface was mentioned in the original post without saying what surface is needed, only that it is very important. 

how does the  molly rings with cylinder finished for molly rings. compare to the metric rings?. 3208 cat 8cyl diesel engines came with 2 ring pistons with molly rings. we found cheaper  3ring pistons with chrome top rings did not liv long, and lower output on dyne.

Metric rings aid in reducing cylinder wall friction and subsequently making more power by being both thinner and having less radial tension than the older and wider conventional ring sets.  The 1.5mm ring thickness is the equivalent of the older 1/16” wide racing rings but the metric rings also have less radial tension by lieu of not having as much radial depth as the older rings.  Hence less radial tension.  And then you can go even thinner with 0.8, 1.0, and 1.2 mm width rings.  While the 3.0 mm oil ring width is commonly used with the metric sized compression rings, 2.0 mm oil rings are also available.  And those oil rings are also available in less than standard tensions but caution needs to be applied there as the oil ring is a key player in controlling oil consumption.  While a moly ring is available in the 1.5 mm thickness, when going to the 1.2 and 1.0 mm rings, tool steel is the material of choice.
 
As mentioned earlier, cylinder wall finish does get critical when going with the thinner ring sets.  The thinner rings are susceptible to increased wear if using a single stone finish as is typical with the thicker rings.  While a the typical cross-hatch pattern is incorporated into the honing operation, a ‘plateau’ finish is necessary and it can take as many as three different honing stones to achieve this.
 
Adapting these rings to the older engines is typically done by making the new pistons with the appropriate ring groove widths and depths for those metric rings.  Another option is the use of spacers in the older designed pistons with wide ring width grooves that allows the metric rings to be used.  Not all old style ring widths will accommodate spacers for the metric rings.
 
If having to do a custom piston, then it’s relatively easy to have the piston manufacturer simply make the pistons where those pistons can use metric rings.  On my end, I order the rings first and once I know the widths and radial depths, that information is forwarded to the piston manufacturer when ordering the pistons.

Lorena, Texas (South of Waco)

I went to the thinner rings in my GMC years ago. I also use low tension oil rings and run a belt driven vacuum pump. Even with the long crankcase at my top rpm the engine has 9” of vacuum.
My son dirt car engine also uses a narrow pack but are advised to replace the rings more often due to the rpm and load the engine sees. We leak test the cylinders after every 3rd night of competition.

56 Vic, B'Ville 200 MPH Club Member, So Cal.