11/5/2020
Modified Racing Series
engine rule change for 2021
2021 Engine Rules Addendum
A. NASCAR Spec Engines must be sealed and meet all NASCAR specifications, this includes all carburetor specs.
B. All Aluminum Head Engines must use a NASCAR Legal Holly 390 CFM Model 4150 HP Series Carburetor with bridged boosters, boosters may be shortened to .500 inches, must meet Go & No-Go gauges.
*The exception to the above rule is the “Dart Budget Aluminum Head/Spec Engine Package” and the “Steel Head Engines” are allowed any size Holly Model 4150 HP Series Carburetor.
C. All Carburetors Must have booster’s safety wired.
D. Any Aluminum Head Engines will be allowed a single 2inch carburetor spacer only. There will be No stacking of carburetor spacers, as in two (2) into one (1).
E. Steel Engines must run a single 1inch carburetor spacer only. No stacking of carburetor spacers.
F. MRS Budget Spec Tri-Y Headers are allowed on all aluminum head engine packages.
Submitted By: William Doucette
