Stage I vs Stage II vs Stage III Heads
02-04-2003, 07:47 PM
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Stage I vs Stage II vs Stage III Heads I am curious as to what people think the differences are between the "Stages" of head modifications. Like, where do larger valves fit in? I guess this is like buying a "Premium" tire. No real documented mods to distinguish between the stages. Any opinions?
02-05-2003, 07:51 AM
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Re: Stage I vs Stage II vs Stage III Heads What Fenris said is mostly true --- the terminology differs from one supplier to the next. For example, CNC Performance Heads' Stage III's have stock-sized valves, and are specifically designed for use w/ the stock cam!
However, the general definition that I've seen from the major suppliers --- TEA, GTP, MTI, ARE, Absolute, etc. is as follows:
Stage 1 - stock valves, mild bowl work, ports just deburred or glass beaded.
Stage 1x - stock-sized swirl-polished valves, 4-angle valve job, glass beaded, ports opened up to 208-210 cc.
Stage 2 - over-sized valves (2.02" intakes) that will fit the original seats, extensive bowl & port work, 210-215 cc ports.
Stage 3 - 2.055" intakes on modified valve seats, extensive bowl & port work, 220+ cc ports.
All these heads can be milled for extra compression. Some suppliers go much bigger on port volume than others. The milder heads usually flow better at low lift #'s, not as high at .550"+, & have better velocity at low RPMs. The bigger heads flow better at high lift numbers, not as well at lower lifts.
These are generalities, and based on my personal observations only. The Director(s) of this UBB may (and often do) have differing opinions.
However, the general definition that I've seen from the major suppliers --- TEA, GTP, MTI, ARE, Absolute, etc. is as follows:
Stage 1 - stock valves, mild bowl work, ports just deburred or glass beaded.
Stage 1x - stock-sized swirl-polished valves, 4-angle valve job, glass beaded, ports opened up to 208-210 cc.
Stage 2 - over-sized valves (2.02" intakes) that will fit the original seats, extensive bowl & port work, 210-215 cc ports.
Stage 3 - 2.055" intakes on modified valve seats, extensive bowl & port work, 220+ cc ports.
All these heads can be milled for extra compression. Some suppliers go much bigger on port volume than others. The milder heads usually flow better at low lift #'s, not as high at .550"+, & have better velocity at low RPMs. The bigger heads flow better at high lift numbers, not as well at lower lifts.
These are generalities, and based on my personal observations only. The Director(s) of this UBB may (and often do) have differing opinions.
