Nippon Racing Pistons FAQ Page
Frequently asked questions and specifications for Nippon Racing piston sets..
Clearances:
All Nippon Racing Pistons will use OEM clearances.
Piston to wall clearance (PTW) should be set at .0013 the same as the Honda recommended clearance. For instance if you are using a 81.5mm B-Series Nippon Racing piston You will need to make sure that your cylinder is exactly 81.5 mm to achieve proper piston to wall clearance.
If it is oversized beyond the designated size of the piston set you are trying to install your ring gaps will be off.
Valve clearance. All Nippon Racing piston sets have deeper cut valve pockets. This is to accommodate larger camshafts, generally up to stage 3.
We still recommend double checking all clearances when building your engine. If your head or block has been milled, cut or resurfaced several times and you are unable to achieve proper clearance. We recommend running a thicker head gasket. .050 is generally sufficient.
Ring gaps:
When choosing the best ring gap for your engine you must consider several important factors, such as Boost, NA, engine use (Drag, Road Racing, Circle track or street) or fuel used. Many customers believe that they must follow OEM Honda specs and that is not always correct for your application or build. Always use OEM gaps if you are using OEM pistons and original Honda rings. Every ring Manufacturer generally has their own recommended gap sizes. (Note) Turbo gap specs listed below are stated at approximately 20 PSI of boost or less. For more that 20 PSI of boost add .001” more gap to the First and Second ring for every additional 8 PSI of boost.
HASTINGS 2C SERIES HIGH TENSION RINGS
TURBO TOP .018”-.020” SECOND .022-.024”
NATURALLY ASPIRATED TOP .016”-.018” SECOND .020”-.022”
STREET USE: USE THE SAME AS NATURALLY ASPIRATED BUT CLOSEST TO THE SMALLEST NUMBER
DO NOT TOUCH OIL CONTROL RING OR RAILS
HASTINGS SNH / NPR GNH SERIES
TURBO TOP .017”-.019” SECOND .021-.023”
NATURALLY ASPIRATED TOP .014”-.016” SECOND .018”-.020”
STREET USE: USE THE SAME AS NATURALLY ASPIRATED BUT CLOSEST TO THE SMALLEST NUMBER
DO NOT TOUCH OIL CONTROL RING OR RAILS
NPR SW SERIES
TURBO TOP .017”-.019” SECOND .020-.028”
NATURALLY ASPIRATED TOP .016”-.018” SECOND .020”-.030”
DO NOT TOUCH OIL CONTROL RING OR RAILS
STREET USE: USE THE SAME AS NATURALLY ASPIRATED BUT CLOSEST TO THE SMALLEST NUMBER
If you are unsure of what your specific needs require, please contact us with your specific engine use and fuel you will be using for a custom ring gap recommendation.
Note: If you are unable to achieve specifications. Please check your bore size and Piston to Wall Clearance. Typically that would mean that sizing is off. The bore was cut too large or the cylinder is either worn or out of round.As indicated above your PTW Clearance should be .0013 .
Compression ratios:
All Nippon Racing pistons use OEM specifications and compression ratios. Unlike many aftermarket forged pistons. Nippon racing Pistons are classified by an OEM specification. IE: PR4/ PR3/ P30/ P73/ PCT/ P72 for B series. PG6/ PM6/ P29/ Vitara for D series. PRB / PRC/ RL5/ RRC for K series. These are examples that you would use to reference in order to calculate compression.
Some common compression ratio estimates are noted on each given piston set. However for a more specific calculation. Or for any estimates not already listed. Please use the following external link to calculate compression based on your build:
http://www.zealautowerks.com
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