Carburetter Replacement Veritas-Nürburgring from 2x H4 standard to 3x H2 to increase hp

Veritas not only built successful racing-cars, but also produced interesting sports-cars at the beginning of the 50´s (Wikipedia:Veritas). Veritas racing-cars used their own engines, but the sports-cars used standard engines from other manufacturers that just happened to be available on the market. This was also the case as they used Zephyr engines produced by Ford. These robust, reliable 2,3liter, straight six cylinder engines were breathed by a single Zenith carb. These weren`t exactly highly powered and delivered a measly 65 hp.

At the beginning of the 50`s, Raymond Mays was a specialist in one-off jobs predominantly in the racing scene and helped Coventry Climax, Bristol and Armstrong-Siddley with their problems. The Metropolitan Police approached him, with a view to pep-up their fleet of standard Zephyr patrol-cars, as these weakly powered bangers had problems keeping up with the baddies.
A completely new aluminium cylinder-head with larger inlet-valves, two three-into-one exhaust manifolds and a one-piece inlet-manifold with two SU H4 cross-draught carbs (1,5 inch) were developed. This gave the engine a surprising 105 hp.

Here you can see the really inefficient gas-flow - the first and sixth cylinder were very badly fed. Sports-cars of the 30´s era also had a similar problem.
The only reasonable method to solve this problem was to convert the whole induction system to three separate carbs. The three more or less separate inlet ducts, each feeding two cylinders were ideal for this task.

The three inlet tracts were separated and new flanges for the carbs turned up. The inlet tracts were drilled horizontally and a jig made up to support all the parts as they were being welded. Three short, stubby tubes were also turned up as a base for the vacuum line.

To achieve optimal flow rates, H2 carbs were chosen. They have 1,25inch diameter ducts and the three of them have approximately the same throat diameter as two H4s – see following formula:

	Original Carburetter 2x H4	Replacement Carburetter 3x H2
diameter	d=25,4mm/“ x 1,5“ = 36,75mm	d=25,4mm/“ x 1,25“ = 31,75mm
radius	r=d/2=36,75mm/2 = 18,37mm	r=d/2=31,7mm/2=15,87mm
duct flowarea	A=πr²= 1059,61mm²	A=πr² = 790,83mm²
flowarea	D=1059,61mm² x 2 = 2119,22mm²	D=790,83mm² x 3 = 2372,49mm²
Compare	100%	2372,49mm²/2119,22mm²*100%=111,95%

The approximately 12% larger passage area is balanced by the constant-pressure operation of this carburetter series.

After final welding, the parts were fettled to shape and end-caps turned and also welded into place.
Finally the whole cylinder-head with the newly modified inlet-manifolds, were attached to a milling machine and the face-surfaces of the carbs were milled vertically. Aluminium tends to warp quite a lot during heat-treatment/welding and the jig could not garantee a plane surface. A vacuum line was produced out of copper piping with an extra outlet for the brake servo-unit and secured to the separate manifolds using turned, brass fittings. Finally choke- rods and throttle linkages were produced and fitted.

After several test-runs using various needles, the optimal mixture was achieved and smooth-running was the outcome with an estimated 115-120hp, nearly double that of the original, no doubt due to the extremely good gas-flow as the inlet-manifolds are basically directly in front of the inlet ducts.