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  R.J.V tuning


R.J.V motor engineering, perhaps more famously known for their Mini creations? Personally speaking, I'd never heard of the company, so I was quite shocked when I read they had carried out several different stages of tuning on the BMC 1100. In the kit you got a replacement exhaust system, exchange cylinder head and special inlet manifold to take a progressive-choke Solex carburettor, all fitted for 73 14s.

The R.J.V Morris 1100. Externally the same as a standard, but the tricks packed away inside make the difference.

The exchanged cylinder heads were modified by Nerus, you may remember that Nerus carried out the tuning on the Austin 1100 Supremo. Combustion chambers and ports were reshaped and polished, with larger inlet valves fitted. Stronger valve springs allow much higher crankshaft speeds before valve bounce and the compression ratio is raised from the standard 8.5:1 to 9.3:1. All Combustion chambers were measured and machined to be identical, for smooth idling and even low speed running. Nerus call this their stage II cylinder head. Also available was the Stage III Nerus head, which has larger exhaust valves as well as the bigger inlet valves used in the Stage II, and double valve springs. The Stage III looses a little torque at low revs, but accelerating through the gears, and especially above 3,000 r.p.m, the Stage III's extra power boosts performance.

The progressive-choke PAIA Solex carburettor is familiar, as it was also used on a conversion carried out by Mangoletsi. The Solex carburettor works in this way: at low crankshaft speeds only the first choke is in use, but as gas speed through the venturi increases and reaches a predetermined value, a diaphragm opens the second throttle, provided the driver takes up the extra pressure on the accelerator. This uses more petrol, but I'm informed that it gives the extra punch when needed for maximum acceleration or top speed. A light spring within the operating lever has a delaying effect, preventing the second butterfly from opening too abruptly if the throttle is suddenly banged open.

The advantages behind this carburettor are ease of tuning, economy and low cost in relation to the price of an alternative twin carburettor set-up. A Special inlet manifold was used on the 1100, cast in aluminium and including a tapered baffle in the mixing chamber it ensures that both pairs of cylinders receive an equal charge, whether one or both chokes are opening. The manifold had a water jacket over it using the feed pipe from engine to heater.

The round top of the carburettor can be seen quite clearly in this shot. Space was an issue between the bonnet and the top of the carburettor. Maybe another option would have been to use the 1500 bonnet?

The downside, the space between the top of the carburettor and the bonnet is limiting, and the use of the small pancake type air filter is a must. Moving onto the exhaust, the efficiency is greatly improved by a three branch manifold which blends the exhaust of nos. 1 and 4 cylinders first, joined by the combined pipe for nos. 2 and 3, after a straight section. R.J.V recommended that a large bore exhaust pipe be used with the manifold.


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