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Ford Kent Pre Crossflow Tuning Guide

Ford Kent Pre-Crossflow Engine

This engine is easily determined from the Ford 'Crossflow' by the type of head since the carburettor and the exhaust are both on the right hand side of the engine.

The Pre-X/Flow, first fitted to the 107E Prefect and 105E Anglia in 1959, replaced the previous side-valve units and was initially available in sizes, 997, 1198, 1340 and eventually 1498cc. You’ll find them in Anglias, Mk1 and early Mk2 Cortinas, Corsairs and Classics. The small capacity engines - up to 1340cc had a three-bearing crank (hollow at first, but changed to a solid casting for later production engines) whereas the 1500 introduced in the Cortina (including the GT) had a five-bearing crank and is therefore most desirable.

1967 saw the introduction of the Mk2 Cortina and early versions had the most desirable Pre-X/Flow with proper engine seals rather than rope type seal. The 1500 Pre-X/Flow also provided the base for the Lotus Twin Cam, where selected blocks were bored to larger capacity. The Mk2 Cortina saw the L-block, which is cast with thicker walls and is ideal for large capacity Pre-X/Flows - it’s quite rare now though!
All engines except the 1500GT had a single choke carburettor - either Zenith or Solex whereas the GT had a 28/36 DCD Weber.

It is quite easy to tune a Pre-X/Flow to GT spec using either the GT carb or the twin choke from a X/Flow, which is slightly larger. GTs also had a tubular exhaust manifold plus a longer duration / higher lift cam, which is similar to a Kent Cams BCF1. You should see around 80bhp from this, a bit more with balancing.

The Pre-X/Flow suits the old Cosworth A-Series of cam profiles with their gentler ramp angles and lower lift compared to the X/Flow derived Kent Cams series, which are high-lift, low duration.

These engines are very sensitive to compression and you need to match the CR with the cam - the longer the duration, the more static compression you need. Therefore, you need to match the stage of head with cam combination. Plus, you need to check which head you have because there are many types - ideally, start with a 1500.

Pre-X/Flow heads can be modified but to special order only and all can be ordered with unleaded seats. At this point it’s best to uprate the standard rocker gear to steel since it is especially weak.

A Stage 1 on top of the GT / A2 cam should approach 100bhp with a twin choke, whereas an A3 cam with standard pistons, twin 40s and a 4-branch can push out 120bhp. You really need in excess of 10:1 with an A6, which really means forged pistons, a big valve head and ideally 11.5:1. We stock Accralite pistons for this combination in bore sizes of 82.5mm and 83.5mm. Most 1500 blocks will take this, meaning you should see 135-140bhp from 4000-7500 rpm. Combine this with Lotus 125E rods - again available from stock, plus 711M type mains caps - however, our steel ones make more economic sense since the block will need line boring to make them fit.

The induction needs swapping above 110-115bhp to a pair of 40 DCOEs, which are the ideal carburettor for this engine - larger chokes tend to slow the gas speed down too much. Around an A8 cam and the engine will be well past its 7500 rev limit with the aforementioned bottom end strengthening too. So, we stock a large range of steel components to suit such applications. The stronger Lotus crank will fit the Pre-X/Flow although the block will need relieving slightly to accomodate the larger counterbalance webs. Really this is racetrack only stuff, with power around 150bhp+ from 13:1, plus a big valve head and revs in excess of 8,000!