It seems that life is full of annoying little gaps. There’s the generation gap, the credibility gap and that annoying gap between David Letterman’s front teeth. For hot rodders, there’s also the gap between ring ends on each ring in each cylinder of your engine. The gap is there to allow you to install the ring on a piston, but it also serves as a wonderful path for cylinder pressure to escape from the combustion chamber. For years, engine builders and hot rodders have debated the relative merits of so-called “gapless” rings. Since we have never seen a definitive test of them, we decided to see for ourselves.
Bruce Walker at Childs & Albert offered to supply the parts necessary to find out if these rings really work as claimed. The premise was simple: Build a representative street engine, establish a power baseline, install C&A’s Zero Gap Second (ZGS) rings and then retest the engine. As you’ll see, the results were surprising.
Bob Lambeck offered to do the independent dyno testing, so our first objective was to build an engine. We started with a .030-over Chevrolet 350 that was treated to machine work by Jim Grubbs Motorsports (JGM), which has a reputation for precision machine work in the Southern California circle-track arena. JGM fitted the block with a set of Summers Brothers billet-steel four-bolt main caps and American Racing Products (ARP) studs supporting a Chevrolet 5130 steel crankshaft and a set of Childs & Albert 4340 forged-steel Super Stock 5.7-inch rods. JGM carefully torque-plate honed the engine and balanced the rotating assembly, including the C&A custom forged pistons. The pistons were designed to be used with a set of C&A Dura-Moly 1/16-inch first and second rings with a low-tension 3mm oil ring. The baseline test utilized a Dura-Moly ductile-iron moly-filled top ring with a cast-iron second ring. In the second test, the cast-iron second ring was replaced with the Zero Gap Tapered Face (ZGTF) second ring.
We wanted to really work the engine hard since this would be a test of cylinder leakage, and peak torque is where maximum cylinder pressure is generated. Since cylinder heads play a key part in this equation, we chose a set of aluminum Edelbrock Performer RPM street cylinder heads, which offer high-velocity 170cc intake ports that would deliver the torque. For valve timing, we chose a Competition Cams Dual Energy cam and valvetrain with 1.6 stainless-steel Pro Magnum rocker arms. We topped off the Mouse with a matching Edelbrock Performer RPM dual-plane intake along with a Holley 750-cfm double-pumper carb and a set of Hooker 1-5/8-inch headers.
The dyno-test procedure was a little out of the ordinary since we wanted to eliminate as many test variables as possible. The engine was first run 10 times to break in all of the new parts. Lambeck then performed three back-to-back runs that were averaged at each rpm point. As you can see from the baseline power numbers, the little small-block was no slouch. It produced 431 lbs-ft of torque at 4250 rpm and 414 horsepower at 6000 rpm while churning out over 400 lbs-ft between 3250 and 5250. That alone would have made an interesting story, but we were just getting started.
With the baseline completed, we replaced the iron second rings with the ZGTF rings. No other changes were made. Barely cooled off, the engine was returned to Lambeck’s dyno where 10 break-in and three final dyno pulls were performed, and the results were again averaged for each rpm point. As you can see, the addition of the C&A ZGTF rings produced a significant improvement in the entire torque curve, which surprised everyone except Walker, who said that he knew it would happen all along. Note that at 3750 rpm, the 355 picked up a stout 16 lbs-ft while averaging almost a 9-lbs-ft gain throughout the entire rpm band. You can feel that!
While the gains were impressive, we still needed to examine why they happened. Conventional wisdom says that increasing cylinder pressure will produce more power, since pressure is what makes torque. One way to increase cylinder pressure is to not allow it to escape past the end gap of a conventional ring. Tightening the ring end gap is dangerous because it can allow the ring ends to butt, instantly destroying the ring and piston. Theory also implies that you stand to gain more power at or below peak torque with less leakage because there is more time for cylinder pressure to leak past the rings at lower engine speeds. What was surprising in our test was that engine power improved above peak torque, given the fact that we tried very hard to seal the engine as efficiently as possible.
Unfortunately, there’s no free lunch with the ZGTF rings. As you might imagine, a ring of this complexity is more expensive to manufacture. The Childs & Albert ZGTF second rings combined with C&A’s Dura-Moly top and oil ring package are slightly more than twice as expensive as the Dura-Moly package with a cast-iron second ring. So the question comes down to what it always does: Is the power we found worth the extra money it costs? You decide. But for hot rodders, it’s an easy step to close the gap between your rings.
