IJSBA · Engine
Legal broadly, but the closed-list classes impose geometry and weight constraints.
This page is IJSBA only, and the bodies do not agree. The same part under IHRA and UIM. Which one applies to you is decided by whoever sanctions the race you enter.
20 classes, grouped where the same rule gives the same answer rather than listed one by one, because an answer that holds for a class usually holds for every class that borrows its rules.
Legal, with conditions 3 classes
Permitted, subject to the limits IJSBA applies to every class, namely the sound ceiling, the hull repair tolerance, and the intake grate and sponson dimensions.
Legal, with conditions 2 classes
Must retain OEM compression ratio, dome profile, skirt length/shape and material type; weight within +/-25.00% of OEM. Non-conforming skirt shapes only with written IJSBA approval.
Legal, with conditions 1 class
Within +/-25.00% of OE weight; original port timing, compression ratio, dome profile and skirt retained.
Legal, with conditions 1 class
Replacement piston assemblies must keep the original compression ratio, dome profile, skirt length and shape and material, and this class states no weight tolerance and no approval route for a non-conforming skirt. · FSKL.3.1
Legal, with conditions 1 class
Must also retain original PORT TIMING. +/-25.00% weight.
Legal, with conditions 1 class
Must retain original port timing, dome profile, skirt length/shape and material type, and weigh within +/-5.00% of OEM. Note this is 5%, tighter than the 25% used elsewhere.
Legal, with conditions 1 class
+/-25.00% weight, OEM compression/dome/skirt retained.
Legal, with conditions 1 class
Non-OEM-replica pistons require written IJSBA approval. · RAL.3.3
Legal 7 classes
Engines may be bored and aftermarket piston assemblies are allowed, with displacement kept within the class limit.
Legal 1 class
Aftermarket piston assemblies. · SKSS.3.5
Legal 1 class
Pistons may be aftermarket under the four-stroke engine clause, which sets no weight or profile limit on them. · RSS.3.2
Aftermarket piston assemblies: 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 IJSBA class · where the rulebooks differ · checks on parts the shop sells · how this site reads a rulebook.
Engine · two and four stroke · legal in 20 of 20 answered, 11 with conditions