ring end gap

[herbiehind]

how much more end gap is applied to hyper-eutectic pistons over stock? i was watching some show , probably horsepower and they said something about adding more for different pistons as they expand and contract differently and can lead to land fractures if done by stock gapping . thanks all .

[herbiehind]

got this from "racing articles" good info .
If a ring end gap is measured on the high side, you improve detonation tolerance in two ways. One, the engine will run longer under detonation before rings butt. Two, some leak down appears to benefit oil control by clearing the oil rings of oil build up. Clean, open oil rings are necessary to prevent from reaching the combustion chamber, which is also why we do not like gapless rings. A very small amount of chamber oil will cause detonation and produce significant horsepower loss. Top ring gaps can be increased 50% with hypereutectic pistons.

Ring Options of 1/16" or stock 5/64" are offered on most performance pistons. The 1/16" option reduces friction slightly and seals better above 6,500 RPM, while being considerably more expensive. Stock, (usually 5/64" compression rings), work well and help with the budget.

Piston to Bore Clearance for hypereutectic pistons were Dyno tested at wide open throttle with .0015", .0020", .0035" and .0045" piston to bore clearance. After 7-1/2 hours the pistons were examined and they all looked as new, except the tops had normal deposit color. Even with 320 degrees Fahrenheit oil temperature, the inside of the piston remained shiny silver and completely clean. Excessive clearance has been shown to be safe with hypereutectic pistons. Loose Hypereutectic pistons over .0020" do make noise. As they get up to temperature they still make noise because they have very restricted expansion rate and do not swell up in the bore. The Hypereutectic alloy not only expands 15% less, it insulates the skirts from combustion chamber heat. If the skirt stays cool piston expansion is drastically reduced. Running close clearances is beneficial to piston ring seal and ring life. A small short term HP improvement can be had by running additional piston clearance because friction is reduced. To obtain actual piston diameter, measure the piston from skirt to skirt level with the balance pad.

[Muad'Dib]

From what i understand this also depends on the location of the top ring. The pistons i bought didn't require a different ring gap for the top ring... they were all suppose to be the same. However different pistons may need additional gap for the top ring.

Research your pistons and or contact the manufacturer and get the recommendation for YOUR pistons.

[Retlaw01XJ]

x2 on the 'contact manufacturer' advise!

In general, the more heat the rings see, the larger the end gap should be.
I'm not aware of any recommendations that specify hyper pistons need more end gap.
Factory Jeep manual calls for 0.016", a little more for the second ring. Some like lots more on the second ring to prevent gas buildup between rings one and two...which can affect ring seal.

Lots of towing = little more gap.
Ring close to piston top = little more gap.
Nitrous = lots more gap.
Turbos = lots more gap!

If gap is too small, ring ends will butt together, rings get stuck in the bore, and it could rip the ring lands off the piston.... and that ain't good!

[woodjeep]

I'm pretty sure my hyperutectic pistons came with paperwork that said to increase the top ring gap by xx percent. The 2nd and 3rd rings remained at stock settings. 20 percent rings a bell but it was several years ago and can't remember exactly.

[Retlaw01XJ]

K-B recommends 0.0065" per inch of bore for their hypereutectic pistons, as the ring is very close to the top of the piston.
http://www.kb-silvolite.com/article.php ... ad&A_id=32

And 0.004" per inch of bore for their forged pistons.
http://www.kb-silvolite.com/assets/icon ... lation.pdf

Silv-o-lite hyper pistons call for 20-40% more end gap:
http://www.kb-silvolite.com/assets/silv ... lation.pdf

Sealed Power advertises their Hyper pistons as working with standard ring gaps. .... 0.004" per inch of bore.

What pistons are you using?

[herbiehind]

h802cps sealed power

[Retlaw01XJ]

h802cps sealed power

I work as an engineer and I generally make direct contact with the manufacturer's tech department for that kind of info....
Those are 'advertised' as working with stock end gaps.... 0.004" per inch = 0.016" for the top ring.
For a definitive answer, I'd suggest calling Federal Mogul 'technical inquiries' at
http://www.federalmogul.com/en/ContactUs/

Please post back with your results1

[herbiehind]

thanks for the linc. i will .

[Muad'Dib]

FWIW, i am running Speed Pro (aka Sealed Power or Federal Mogul) H825CP's and i contacted the manufacturer. They told me directly to use normal ring end gap on the top ring.


Again, dont go by what another manufacturer suggest's for pistons, nor go off of what your piston manufacturer says about different model pistons. All pistons are created differently; you should get this information specifically for your piston Manufacturer and part number. This is not the place to have incorrect information!