No, 8031 and 8086 are completely different MCUs. 8031 is microcontroler unit with 64K address space, 64K data space, 128 bytes internal data RAM and some integrated periferials like timers, ports, UARTs, 'interrupt controlers', some also with internal code ROM, EPROM or even FLASH ROM.
8086 is a microprocessor that has no integrated peripherials, but can access larger amount of memory (1M byte), has more computing power and is intended for more compute intense applications. 8086 is a predecessor of today popular i586. So you can see, what are target applications of this MCU.
Instruction sets are completely different, for the architecture is different. 8051 has 8 bit registers ACC, B, R0 ... R7, 16-bit DPTR, 8086 has 16 bit registers AX, BX, CX, DX, segment registers CS, DS, ES, SS, that some of them can also be used as 8-bit registers AH, AL, BH, BL...
8051 has also built in bit manipulation instructions (SETB, CLR, JBC, JB, JNB, ORL, ANL,...), 8086 has not, etc.
8051 target applications are small controllers, embeded systems. If you need more compute power, there are also available more powerful versions of say DALLAS 80C320, or even 16-bit devices like INTEL 251, that is downward compatible with 8051.

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