diff --git a/fuzzers/007-timing/Makefile b/fuzzers/007-timing/Makefile
index c164609e..2ec3a800 100644
--- a/fuzzers/007-timing/Makefile
+++ b/fuzzers/007-timing/Makefile
@@ -16,8 +16,12 @@ routing-bels/build/sdf:
 
 mergesdfs: bel/build/sdf.ok routing-bels/build/sdf
 	mkdir -p sdfs
-	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs $(SLICEM_SDFS) --site SLICEM --out sdfs/slicem.sdf
-	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs $(SLICEL_SDFS) --site SLICEL --out sdfs/slicel.sdf --json debu.json
+	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs $(SLICEM_SDFS) --site SLICEM --out routing-bels/build/precarry_slicem.sdf
+	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs $(SLICEL_SDFS) --site SLICEL --out routing-bels/build/precarry_slicel.sdf
+	python3 ${XRAY_UTILS_DIR}/carry4delays.py --input routing-bels/build/precarry_slicem.sdf --output routing-bels/build/carry4_slicem.sdf
+	python3 ${XRAY_UTILS_DIR}/carry4delays.py --input routing-bels/build/precarry_slicel.sdf --output routing-bels/build/carry4_slicel.sdf
+	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs routing-bels/build/precarry_slicem.sdf routing-bels/build/carry4_slicem.sdf --site SLICEM --out sdfs/slicem.sdf
+	python3 ${XRAY_UTILS_DIR}/sdfmerge.py --sdfs routing-bels/build/precarry_slicel.sdf routing-bels/build/carry4_slicel.sdf --site SLICEL --out sdfs/slicel.sdf --json debu.json
 	cp bel/build/*.sdf sdfs
 
 pushdb: mergesdfs
diff --git a/utils/carry4delays.py b/utils/carry4delays.py
new file mode 100755
index 00000000..dd4d7d56
--- /dev/null
+++ b/utils/carry4delays.py
@@ -0,0 +1,115 @@
+#!/usr/bin/env python3.6
+
+import sys, os, argparse
+from sdf_timing import sdfparse
+
+model_carry4 = {
+	'type'    : 'CARRY4',
+
+	'srcs' : { 'O5', '?X', '?X_LFF', '?X_LBOTH' },
+	'out'  : { 'CO0', 'CO1', 'CO2', 'CO3', 'O0', 'O1', 'O2', 'O3' },
+
+	'mux'  : '?CY0',
+
+	'pins' : {
+		'DI0' : { 'type' : 'A' },
+		'DI1' : { 'type' : 'B' },
+		'DI2' : { 'type' : 'C' },
+		'DI3' : { 'type' : 'D' },
+	},
+}
+
+def compute_delays(model, fin_name, fout_name):
+	data = ''
+	with open(fin_name, 'r') as f:
+		data = f.read()
+	sdf = sdfparse.parse(data)
+
+	keys = sdf['cells'][model['type']].keys()
+	if 'slicel'.upper() in keys:
+		sl = 'L'
+	elif 'slicem'.upper() in keys:
+		sl = 'M'
+	else:
+		print("Unknown slice type!")
+		return ;
+
+	nsdf = dict()
+	nsdf['header'] = sdf['header']
+	nsdf['cells']  = dict()
+	nsdf['cells']['ROUTING_BEL'] = dict()
+
+	for p in model['pins']:
+		pin = model['pins'][p]
+
+		outs = dict()
+		for o in model['out']:
+			outs[o] = []
+
+		res = []
+		cells = sdf['cells']
+
+		for src in model['srcs']:
+			source = src.replace('?', pin['type'])
+
+			_type = model['type'] + '_' + source
+
+			if _type in cells.keys():
+				cell = cells[_type]["SLICE" + sl.upper()]
+
+				for o in model['out']:
+					iopath = 'iopath_' + p + '_' + o
+
+					if iopath in cell.keys():
+						delay = cell[iopath]['delay_paths']['slow']['max']
+						outs[o].append(delay)
+
+		for src in outs:
+			s = sorted(outs[src])
+			for val in s:
+				res.append(val - s[0])
+
+		delay = round(max(res), 3)
+
+		muxname = str(model['mux'].replace('?', pin['type']))
+		rbel = nsdf['cells']['ROUTING_BEL']['SLICE' + sl.upper() + '/' + muxname] = dict()
+
+		iname = 'interconnect_' + pin['type'].lower() + 'x_' + str(p).lower()
+
+		rbel[iname] = dict()
+		rbel[iname]['is_absolute'] = True
+		rbel[iname]['to_pin_edge'] = None
+		rbel[iname]['from_pin_edge'] = None
+		rbel[iname]['from_pin']   = pin['type'].lower() + 'x'
+		rbel[iname]['to_pin'] = str(p).lower()
+		rbel[iname]['type'] = 'interconnect'
+		rbel[iname]['is_timing_check'] = False
+		rbel[iname]['is_timing_env'] = False
+
+		paths = rbel[iname]['delay_paths'] = dict()
+
+		paths['slow'] = dict()
+		paths['slow']['min'] = delay
+		paths['slow']['avg'] = None
+		paths['slow']['max'] = delay
+
+		paths['fast'] = dict()
+		paths['fast']['min'] = delay
+		paths['fast']['avg'] = None
+		paths['fast']['max'] = delay
+
+
+		# emit new sdfs
+		with open(fout_name, 'w') as f:
+			f.write(sdfparse.emit(nsdf))
+
+def main(argv):
+	parser = argparse.ArgumentParser(description='Tool for computing CARRY4 muxes delays')
+	parser.add_argument('--input', dest='inputfile', action='store', help='Input file')
+	parser.add_argument('--output', dest='outputfile', action='store', help='Output file')
+	args = parser.parse_args(argv[1:])
+
+	compute_delays(model_carry4, args.inputfile, args.outputfile)
+
+if __name__ == "__main__":
+	main(sys.argv)