Nike (NKE) had the highest return in August 1986 by a large-cap US stock, returning 85.5%.

ASSET	MONTH	% RETURN
Nike (NKE)	August 1986	85.45%
Shell PLC ADR (SHEL)	August 1986	40.43%
Imperial Oil (IMO)	August 1986	31.59%
Parker-Hannifin (PH)	August 1986	31.49%
Gold Fields Ltd ADR (GFI)	August 1986	30.59%
Occidental Petroleum (OXY)	August 1986	27.18%
Jefferies Financial (JEF)	August 1986	26.91%
Autodesk (ADSK)	August 1986	26.85%
Micron Technology (MU)	August 1986	26.58%
Carpenter Technology (CRS)	August 1986	26.17%
Intel (INTC)	August 1986	26%
Toyota Motor Corporation ADR (TM)	August 1986	25.95%
Essential Utilities (WTRG)	August 1986	25.39%
Advanced Micro Devices (AMD)	August 1986	25%
SEI Investments (SEIC)	August 1986	24.14%
Chevron (CVX)	August 1986	24.11%
Halliburton (HAL)	August 1986	23.1%
Honda Motor Co Ltd ADR (HMC)	August 1986	22.63%
Cooper Companies (COO)	August 1986	22.58%
ConocoPhillips (COP)	August 1986	22.38%
Koninklijke Philips NV ADR (PHG)	August 1986	22.15%
Loews (L)	August 1986	21.05%
Hecla Mining (HL)	August 1986	20.55%
CACI International (CACI)	August 1986	20%
Applied Materials (AMAT)	August 1986	19.43%

Large-cap stocks are treated as having a market cap of $10B+.