diff --git a/racket/src/racket/src/port.c b/racket/src/racket/src/port.c
index 1e03860d1b..5f516f700e 100644
--- a/racket/src/racket/src/port.c
+++ b/racket/src/racket/src/port.c
@@ -3312,8 +3312,7 @@ static MZ_INLINE intptr_t get_one_byte(GC_CAN_IGNORE const char *who,
   return get_one_byte_slow(who, port, buffer, 0, 0);
 }
 
-int
-scheme_getc(Scheme_Object *port)
+int scheme_getc(Scheme_Object *port)
 {
   char s[MAX_UTF8_CHAR_BYTES];
   unsigned int r[1];
@@ -3362,7 +3361,7 @@ scheme_getc(Scheme_Object *port)
 }
 
 int
-scheme_get_byte(Scheme_Object *port)
+scheme_get_byte(Scheme_Object *port) XFORM_ASSERT_NO_CONVERSION
 {
   char s[1];
   int v;
@@ -4194,10 +4193,10 @@ int scheme_close_should_force_port_closed()
 
 /****************************** main output writer ******************************/
 
-intptr_t
-scheme_put_byte_string(const char *who, Scheme_Object *port,
-		       const char *str, intptr_t d, intptr_t len,
-		       int rarely_block)
+static intptr_t
+put_byte_string_slow(const char *who, Scheme_Object *port,
+                     const char *str, intptr_t d, intptr_t len,
+                     int rarely_block)
 {
   /* Unlike the main reader, the main writer is simple. It doesn't
      have to deal with peeks and specials, so it's a thin wrapper on
@@ -4262,6 +4261,32 @@ scheme_put_byte_string(const char *who, Scheme_Object *port,
   return oout;
 }
 
+intptr_t
+scheme_put_byte_string(GC_CAN_IGNORE const char *who, Scheme_Object *port,
+		       GC_CAN_IGNORE const char *str, intptr_t d, intptr_t len,
+		       int rarely_block)
+{
+  intptr_t out;
+
+  if (SCHEME_OUTPORTP(port)
+      && !((Scheme_Output_Port *)port)->closed
+      && (rarely_block != -1)
+      && (len == 1)
+      && !((Scheme_Output_Port *)port)->p.count_lines) {
+    Scheme_Output_Port *op = (Scheme_Output_Port *)port;
+    Scheme_Write_String_Fun ws;
+    ws = op->write_string_fun;
+    out = ws(op, str, d, 1, rarely_block, 0);
+    if (out) {
+      op->p.position += out;
+      return out;
+    } else if (rarely_block)
+      return 0;
+  }
+
+  return put_byte_string_slow(who, port, str, d, len, rarely_block);
+}
+
 void scheme_write_byte_string(const char *str, intptr_t len, Scheme_Object *port)
 {
   (void)scheme_put_byte_string("write-string", port, str, 0, len, 0);
@@ -6923,9 +6948,10 @@ static intptr_t fd_get_string_slow(Scheme_Input_Port *port,
 }
 
 static intptr_t fd_get_string(Scheme_Input_Port *port,
-			  char *buffer, intptr_t offset, intptr_t size,
-			  int nonblock,
-			  Scheme_Object *unless)
+                              char *buffer, intptr_t offset, intptr_t size,
+                              int nonblock,
+                              Scheme_Object *unless)
+  XFORM_ASSERT_NO_CONVERSION
 {
   Scheme_FD *fip;
   intptr_t bc;
@@ -8206,9 +8232,9 @@ static intptr_t flush_fd(Scheme_Output_Port *op,
 }
 
 static intptr_t
-fd_write_string(Scheme_Output_Port *port,
-		const char *str, intptr_t d, intptr_t len,
-		int rarely_block, int enable_break)
+fd_write_string_slow(Scheme_Output_Port *port,
+                     const char *str, intptr_t d, intptr_t len,
+                     int rarely_block, int enable_break)
 {
   /* Note: !flush => !rarely_block, !len => flush */
 
@@ -8280,6 +8306,30 @@ fd_write_string(Scheme_Output_Port *port,
   return len;
 }
 
+static intptr_t
+fd_write_string(Scheme_Output_Port *port,
+		const char *str, intptr_t d, intptr_t len,
+		int rarely_block, int enable_break)
+  XFORM_ASSERT_NO_CONVERSION
+{
+  Scheme_FD *fop;
+  intptr_t l;
+  int flush = (!len || rarely_block);
+
+  fop = (Scheme_FD *)port->port_data;
+
+  if (!flush && !fop->flushing && (fop->flush != MZ_FLUSH_ALWAYS)) {
+    l = MZPORT_FD_BUFFSIZE - fop->bufcount;
+    if (len <= l) {
+      memcpy(fop->buffer + fop->bufcount, str + d, len);
+      fop->bufcount += len;
+      return len;
+    }
+  }
+
+  return fd_write_string_slow(port, str, d, len, rarely_block, enable_break);
+}
+
 static void
 fd_close_output(Scheme_Output_Port *port)
 {
diff --git a/racket/src/racket/src/portfun.c b/racket/src/racket/src/portfun.c
index 94500aabfa..86d9ef9568 100644
--- a/racket/src/racket/src/portfun.c
+++ b/racket/src/racket/src/portfun.c
@@ -3112,9 +3112,24 @@ do_read_char(char *name, int argc, Scheme_Object *argv[], int peek, int spec, in
     return _scheme_make_char(ch);
 }
 
-static Scheme_Object *
-read_char (int argc, Scheme_Object *argv[])
+static Scheme_Object *read_char_fast(Scheme_Object *port) XFORM_ASSERT_NO_CONVERSION
 {
+  int ch;
+  
+  ch = scheme_getc(port);
+  
+  if (ch == EOF)
+    return scheme_eof;
+  else
+    return _scheme_make_char(ch);
+}
+
+static Scheme_Object *
+read_char (int argc, Scheme_Object *argv[]) XFORM_ASSERT_NO_CONVERSION
+{
+  if (argc && SCHEME_INPUT_PORTP(argv[0]))
+    return read_char_fast(argv[0]);
+
   return do_read_char("read-char", argc, argv, 0, 0, 0);
 }
 
@@ -3136,9 +3151,24 @@ peek_char_spec (int argc, Scheme_Object *argv[])
   return do_read_char("peek-char-or-special", argc, argv, 1, 1, 0);
 }
 
-static Scheme_Object *
-read_byte (int argc, Scheme_Object *argv[])
+static Scheme_Object *read_byte_fast(Scheme_Object *port) XFORM_ASSERT_NO_CONVERSION
 {
+  int ch;
+  
+  ch = scheme_get_byte(port);
+  
+  if (ch == EOF)
+    return scheme_eof;
+  else
+    return scheme_make_integer(ch);
+}
+
+static Scheme_Object *
+read_byte (int argc, Scheme_Object *argv[]) XFORM_ASSERT_NO_CONVERSION
+{
+  if (argc && SCHEME_INPUT_PORTP(argv[0]))
+    return read_byte_fast(argv[0]);
+  
   return do_read_char("read-byte", argc, argv, 0, 0, 1);
 }
 
@@ -4107,13 +4137,13 @@ newline (int argc, Scheme_Object *argv[])
 }
 
 static Scheme_Object *
-write_byte (int argc, Scheme_Object *argv[])
+write_byte_slow (int argc, Scheme_Object *argv[])
 {
   Scheme_Object *port;
   int v;
   unsigned char buffer[1];
 
-  if (argc && !SCHEME_INTP(argv[0]))
+  if (!SCHEME_INTP(argv[0]))
     scheme_wrong_contract("write-byte", "byte?", 0, argc, argv);
   v = SCHEME_INT_VAL(argv[0]);
   if ((v < 0) || (v > 255))
@@ -4136,14 +4166,31 @@ write_byte (int argc, Scheme_Object *argv[])
 }
 
 static Scheme_Object *
-write_char (int argc, Scheme_Object *argv[])
+write_byte (int argc, GC_CAN_IGNORE Scheme_Object *argv[]) XFORM_ASSERT_NO_CONVERSION
+{
+  if (SCHEME_INTP(argv[0])
+      && (SCHEME_INT_VAL(argv[0]) >= 0)
+      && (SCHEME_INT_VAL(argv[0]) <= 255)
+      && SCHEME_OUTPUT_PORTP(argv[1])) {
+    char buffer[1];
+    buffer[0] = SCHEME_INT_VAL(argv[0]);
+    scheme_put_byte_string("write-byte", argv[1],
+                           buffer, 0, 1,
+                           0);
+    return scheme_void;
+  } else
+    return write_byte_slow(argc, argv);
+}
+
+static Scheme_Object *
+write_char_slow (int argc, Scheme_Object *argv[])
 {
   Scheme_Object *port;
   unsigned char buffer[MAX_UTF8_CHAR_BYTES];
   unsigned int ubuffer[1];
   int len;
 
-  if (argc && !SCHEME_CHARP(argv[0]))
+  if (!SCHEME_CHARP(argv[0]))
     scheme_wrong_contract("write-char", "char?", 0, argc, argv);
   if (argc > 1) {
     if (!SCHEME_OUTPUT_PORTP(argv[1]))
@@ -4162,6 +4209,23 @@ write_char (int argc, Scheme_Object *argv[])
   return scheme_void;
 }
 
+static Scheme_Object *
+write_char (int argc, GC_CAN_IGNORE Scheme_Object *argv[]) XFORM_ASSERT_NO_CONVERSION
+{
+  if (argc
+      && SCHEME_CHARP(argv[0])
+      && (SCHEME_CHAR_VAL(argv[0]) < 128)
+      && SCHEME_OUTPUT_PORTP(argv[1])) {
+    char buffer[1];
+    buffer[0] = SCHEME_CHAR_VAL(argv[0]);
+    scheme_put_byte_string("write-char", argv[1],
+                           buffer, 0, 1,
+                           0);
+    return scheme_void;
+  } else
+    return write_char_slow(argc, argv);
+}
+
 static Scheme_Object *port_read_handler(int argc, Scheme_Object *argv[])
 {
   Scheme_Input_Port *ip;