Period IV, Formula One and Two

Eligibility cut-off: Limited to machines built prior to Dec. 31st, 1985, no updating beyond this year. Expressly prohibited model: 1982 TZ250H (YPVS)

This class will comprise of two sub-groups:
Formula - 1

  • Unlimited displacement air-cooled four-strokes, steel frames.
  • 750cc two-strokes, steel frames.
Formula - 2
  • 650cc 4 stroke air cooled maximum
  • 275cc 2-stroke liquid cooled maximum
  • 500cc 2 stroke air cooled maximum
Maximum displacements above do not include permissible overbore of 5% over class limit.

Rules applicable to Period IV, Formula One and Two
i. Engine: Internal modification limited only to period type. Normal induction (no forced/ram air). Powervalves not allowed in Formula 2
ii. Chassis: Original or period aftermarket frame. Frame bracing ok if done in period and workmanlike manner. Monoshock and monoshock conversion OK. Conventional front forks of period construction and size. Period brake systems/components only.
iii. Wheels: Min. diameter. 18" Max. front width WM4 (2.5) Max rear width WM6 (3.5) Treaded tires only. We suggest testing* of cast wheels in F - 2 and require testing* with written certification for F - 1. When using cast wheels if you have any questions about their safety or structural integrity we suggest you have them tested*.
iv. Bodywork: aftermarket allowed, period styles and materials only
v. Fuel: Gasoline only, pump or commercially available race fuel (no methanol, etc.)
vi. Number Plates: White plates with black numbers with a 1" wide florescent green border for F -1 or a 1" wide florescent red border for F -2
vii. Liquid cooled machines must run water only flush system completely.  No antifreeze allowed, waterwetter allowed.
viii.  Carburetors: Round, Sand sand-cast CR's, Die-Cast CR's and flat slide carburetors allowed.
viii.   Rider eligibility / qualifications: All period 4 riders must show written proof of one of the following:

  1.  A current Expert license 
  2.  An Expert license within 5 years of expiration. 
  3.  Show successful completion of an Advanced Race school on a Period 4 machine or comparable performance machine.
*Testing Criteria:   FP I (Florescent Penetrant Inspection) per MIL - STD 6866, Type I, Method A, Level II  Acceptance: no cracks allowed, all over.  If parts are painted, they will have to be stripped to be inspected.   If parts are coated (i.e. anodize, HAE, black oxide, etc.) parts do NOT have to be stripped to be inspected.  It would be best if you could put part numbers and description on wheels so that could be put on written certificate.  Wheels should be retested every 5 years and immediate retesting upon visible marks on wheel(s) from a crash.  Testing can be done at local Non Destructive Testing  Labs.  Names & addresses of  labs located in the eastern U. S. and Canada are available upon request. 

Table of Contents (click on any item to view that page)
Names and Addresses
Class Overview
Bumping
Rule Changes
Championship Points
General Rules
Early Vintage & Pre '65
Screaming 50's
Grand Prix (Period I)
Supervintage (Period II)
Middleweight (Period III)
Period IV
Formula RD
Formula CB350
Sidecars
American Twins

Last Updated: 2/28/06