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Aftermarket pistons

IHRA · Engine

Aftermarket pistons

IHRA answers this part for 29 of its classes. 21 of those answers are permissions, with or without limits attached, and 8 are not. 8 are inferred from how the class is written rather than quoted from a rule naming this part.

Where it stands, class by class

29 classes, grouped by the answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.

Not permitted, not listed in the rules Our reading, not a rule we can quote at you. This class requires the craft to stay stock except where the rules allow otherwise, and this part is not on the list.

No rule, this is an open class Our reading, not a rule we can quote at you. This class carries no stock clause at all, so anything unlisted appears to be open. The rulebook does not say so in terms.

Legal, within limits 2 classes

Must retain the original compression ratio and profile, with no abrasive cleaning of the ports and piston weight within 25 per cent.

Legal, within limits 1 class

Must retain compression ratio, dome profile, skirt length, skirt shape, material type. Limits: max port chamfer 1 mm, max chamfer angle 30 degrees. · W.2.1

Legal, within limits 1 class

Must retain compression ratio, dome profile, skirt length and material type. Bead blast only, with no steel wool or Scotch-Brite. · AA.2.1

Legal, within limits 1 class

Boring is allowed provided the piston keeps its compression ratio, dome profile, skirt length and material type, and chambers are bead blasted only with no steel wool or Scotch-Brite. · N.2.1

Legal, within limits 1 class

Must retain original compression ratio, dome profile and material type. Boring and stroke modifications within displacement limits, and ports must not be abrasively cleaned. · Y.2.1

Legal, within limits 1 class

On four-stroke entries as Runabout GP2 at Y.2.1. On two-stroke entries the piston must keep its port timing, compression ratio, dome profile, skirt length and shape and material type, a non- conforming piston needs advance written approval, and weight stays within 25 per cent. · Z.3.1

Legal, within limits 1 class

Must retain the original compression ratio, dome profile, skirt length and material type, and the ports must not be abrasively cleaned, with piston weight within 25 per cent. · L.2.1

Legal, within limits 1 class

Must retain port timing, compression ratio, dome profile, skirt length and shape, material type. Non-conforming pistons need written permission. Limits: weight tolerance 25 per cent, max port chamfer 1 mm, max chamfer angle 30 degrees. · O.2.1

Legal, within limits 1 class

Must retain original port timing, dome profile, skirt length and shape, material type. Limits: weight tolerance 5 per cent, max port chamfer 1 mm, max chamfer angle 30 degrees. · U.2.1

Legal, within limits 1 class

Four-stroke entries: Limits: weight tolerance 25 per cent. BB.2.1 Two-stroke entries: Cylinders may be machined to accommodate girdle-system heads. Limits: weight tolerance 25 per cent. · BB.3.1

Legal, within limits 1 class

Boring and stroke modifications allowed within displacement limits. · X.2.1

Legal 1 class

Ring configuration may be changed. · T.2.1

Legal 1 class

Ring number, type, and placement may be modified. · S.2.1

No rule, this is an open class 1 class

No restriction in section CC, and CC.1 permits any modification it does not restrict.

Aftermarket pistons: if the rule your class applies reads differently to you, or the rulebook has changed since this was read, ask. We answer with the section we read it from, or that we have not read it. Ask a rules question.

Every IHRA class · where the rulebooks differ · signed checks on parts the shop sells.

Engine · two and four stroke · legal outright in 21 of 29

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