[scottj]

IMCA is a circle track sanctioning body. A motor built to IMCA specifications will vary by class and engine brand. Here's an example of IMCA dirt Late Model engine rules:

24. IMCA SPEC ENGINE RULES:
(A) Steel blocks only.
(B) Maximum 361 c.i. (GM), 362 c.i. (Ford) 364 c.i. (Chrysler). Minimum four-inch bore. Minimum stroke: GM – 3.48 inch, Ford – 3.40 inch, Chrysler – 3.313 inch.
(C) Maximum compression – 10.5 to 1, checked at any time with Whistler. No tolerance.
(D) Brodix/IMCA spec cylinder heads only. No grinding, polishing or altering of any kind. No use of any substance that may change or alter shape or size of ports, runners or combustion chambers. Only alteration allowed to heads are for push rod clearance and to install shaft rocker system. Maximum valve sizes are 2.08 intake and 1.600 exhaust. Valve seats and guides to remain as manufactured and in as-cast positions. Minimum combustion chamber size to be 62 cc volume. Valve angle to remain as manufactured. Approved cylinder heads as follows:
• General Motors (i.e. small block Chevrolet) – Brodix # 46 221
• Ford Motor Company (i.e. small block Windsor) Brodix #46 223
• Chrysler Corporation – Mopar – Brodix #46 222
(E) No modification to intake manifolds, must be used as produced by manufacturer. All engines must run unaltered one inch carburetor spacer – Flow Design part #FD7060. Maximum 0.100-inch thickness gaskets only, one on top and one on bottom of spacer. List of approved intakes as follows:
• General Motors – Brodix #HV100946
• Ford Motor Company -Edelbrock #2981 or 2980 (351) or #2921 (302)
• Chrysler Corporation- Edelbrock #2915
(F) Camshafts may be of roller, flat tappet or mushroom design.
(G) Crankshafts and connecting rods must be steel. One inch inspection hole required in pan – no obstructions to crank and rods. If obstructions are present, must remove pan for inspection.
(H) Flat top pistons only.