Ford Kent Crossflow Tuning Guide
This engine was introduced in the Ford Mk2 Cortina and differs from the earlier units by having the carb on the left and the exhaust on the right - hence, ‘crossflow.’
They also varied from Pre-X/Flows in that the combustion chamber was shifted from the head to the bowl of the piston and were know as BIP engines (Bowl In Piston). Early heads also feature a small combustion chamber in the head too.
Early blocks bore the casting marks 681F and capacities you’ll find are, 940, 1098, 1298 and 1599. You’ll find a X/Flow fitted to Mk1/2 Escorts, Mk2/3 Cortinas, Mk1/2 Capris plus late Transits. Most cars came with a single choke Ford IV carb although the 1.3 and 1.6 GT models had a 32/36 DGV Weber twin choke.
1970 saw the big change to the thicker-walled 711M block with square mains caps, large diameter followers, wider cam lobes and modified crank seal. Also, the head was now completely flat.
There are two main capacities of 711M, determined by block height - the 1600 is 7/16" taller and you can see the difference between it and the 1300 by the space between the water pump and head. Also, the 1300 has 711M 6015 AA cast in the side whereas the 1600 ends in BA.
The engine was also fitted to 1.3 and 1.6 Mk1 Fiestas in the 80’s with a 771M casting. These feature no side engine mounts plus a shortened water pump and timing chain/crank area.
The final versions, OHV, HCS and Endura are similar but shorter versions and share very few if any inter-changeable parts and reverted back to the original pre-X/flow design of a three bearing crank.
Kents are quite easy to tune to GT spec, which usually means the biggest capacity block, slightly bigger valves (usually taken care of with a performance head), GT cam/A1, free flow exhaust and twin choke Weber - you should see around 80-90bhp. Switch to a Kent BCF2 or a 224 and you’ll be approaching 110bhp. For all builds we would recommend ARP rod bolts and replacement of the front pulley for a one piece steel item. The valve train should be strengthened with steel posts, spacers and rocker shaft to cope with the additional stresses caused by high lift cams, HD valve springs and higher revs. A double timing chain kit should also be fitted for the same reasons. Performance heads are available in both iron and brand new aluminium and all can be ordered with unleaded seats.
You can use the old Cosworth A-series cam profiles too, which are long duration and lower lift. However the current Kent Cams, high lift and short duration type are friendlier on emissions with less lobe overlap resulting in reduced un-burnt fuel down the exhaust.
Add a stage 2 head and Kent 224 and you’ll be pushing 115bhp although the favourite X/Flow cam is the 234 for 118-120bhp. You should get this with a re-jetted twin choke although twin 40 DCOE Webers would be better. This is an all round great cam and engine spec for the road.
A 244 cam and stage 3 head results in 135-145bhp, although, these figures are best achieved with a recommended maximum 83.5mm bore and forged Accralite pistons, giving 1700cc. There is a cheaper option in that the compression can be raised using modified 1300 pistons in the 1600 engine, giving a ratio of around 10.3:1. Capacity is easily increased with cast pistons available up to +0.090" oversize which will give 1696cc.
40 DCOEs tend to be on their maximum choke sizes at this stage so many switch to 45s. However this does result in lower gas speed and less low down torque, which is important on the road.
All side draughts need a side exit distributor cap (available for Lucas and Bosch distributors) to clear the inlet manifold and for convenience it’s best to fit an electronic ignition kit such as an Aldon Ignitor or Lumenition. For a complete ignition solution, our constant energy, non-vacuum modified Bosch distributor and coil kit is ideal for most modified engines.
This is about as far as you want to go on the road since you’ll be stretching the 7500-8000rpm limit of the crank. After this and you’ll ideally need steel components, which we have a superb range including cranks, rods, flywheels and forged pistons. To complement these we also have full-race spec heads to take the Kent as far as possible on the race track - currently that’s about 185bhp+.