no limitation for 8i ( 8.1.6 and above).
Certain OS might have a filesystem limiation of 2gb.
any 32 bit os cannot have a file more than 2GB.
even in those cases there are workarounds.
You can use unix pipes 
or
use FILESIZE paramter in EXP, to create multiple export dump files , of predermined size.

exp scott/tiger FILE = dat1.dmp, dat2.dmp, dat3.dmp FILESIZE=2048

quoting docs
FILE
Default: expdat.dmp

Specifies the names of the export files. The default extension is .dmp, but you can specify any extension. Because Export supports multiple export files (see the parameter FILESIZE), you can specify multiple filenames to be used. For example:

exp scott/tiger FILE = dat1.dmp, dat2.dmp, dat3.dmp FILESIZE=2048

When Export reaches the value you have specified for the maximum FILESIZE, Export stops writing to the current file, opens another export file with the next name specified by the FILE parameter, and continues until complete or the maximum value of FILESIZE is again reached. If you do not specify sufficient export filenames to complete the export, Export will prompt you to provide additional filenames.

FILESIZE
Default: Data is written to one file until the maximum size, as specified in Table 1-3, is reached.

Export supports writing to multiple export files, and Import can read from multiple export files. If you specify a value (byte limit) for the FILESIZE parameter, Export will write only the number of bytes you specify to each dump file.

When the amount of data Export must write exceeds the maximum value you specified for FILESIZE, it will get the name of the next export file from the FILE parameter (see FILE for more information) or, if it has used all the names specified in the FILE parameter, it will prompt you to provide a new export filename. If you do not specify a value for FILESIZE (note that a value of 0 is equivalent to not specifying FILESIZE), then Export will write to only one file, regardless of the number of files specified in the FILE parameter.

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Note: 
If the space requirements of your export file exceed the available disk space, Export will abort, and you will have to repeat the Export after making sufficient disk space available.

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The FILESIZE parameter has a maximum value equal to the maximum value that can be stored in 64 bits.

Table 1-3 shows that the maximum size for dump files depends on the operating system you are using and on the release of the Oracle database server that you are using.

Table 1-3  Maximum Size for Dump Files
Operating System Release of Oracle Server Maximum Size 
Any
 Prior to 8.1.5
 2 gigabytes
 
32-bit
 8.1.5
 2 gigabytes
 
64-bit
 8.1.5 and later
 Unlimited
 
32-bit with 32-bit files
 Any
 2 gigabytes
 
32-bit with 64-bit files
 8.1.6 and later
 Unlimited
 

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Note: 
The maximum value that can be stored in a file is dependent on your operating system. You should verify this maximum value in your Oracle operating system-specific documentation before specifying FILESIZE. You should also ensure that the file size you specify for Export is supported on the system on which Import will run.

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The FILESIZE value can also be specified as a number followed by KB (number of kilobytes). For example, FILESIZE=2KB is the same as FILESIZE=2048. Similarly, MB specifies megabytes (1024 * 1024) and GB specifies gigabytes (1024**3). B remains the shorthand for bytes; the number is not multiplied to obtain the final file size (FILESIZE=2048B is the same as FILESIZE=2048).