A Series Engine

The car came fitted originally with an inline form of BMC’s A-series engine. At some point in this cars life the engine was replaced by a Morris Marina A series engine with the oil filter in a different place (and a different size: the marina block takes the same filter as the 1500 Triumph engine).

After perusing the Vizard ‘bible’ a cylinder head was bought from eBay for £25. It’s a big valve MG metro head: the 12G940 casting with the second largest valve sizes (the largest valves were reputedly prone to cracking between the valve seats) and double valve springs. This head was mildly ported as per Vizard (mainly cleaning up the valve seat castings and slight enlargement of the inlet and exhaust ports)

Note that this head came with ‘rimflo’ exhaust valves: designed to reduce back-flow into the exhaust for high valve overlaps. They also help with the flow at lower lifts (see the Vizard book). Notice the nice alloy rocker cover behind the head: looks nice, and also compresses the gasket more evenly than the pressed steel one.

At this point the inlet manifold was also enlarged to allow for the fitment of larger carburettors: specifically a pair of HIF-38 SU’s from a 1979 MGB. After much deliberation over needles (how is anyone supposed to work out what’s needed?) and application of the WinSU program (very useful), I just left the MGB needles in to see what happened. Turns out they’re perfect according to Minimaster rolling road at Penrith.

An adaptor plate was made to convert from the two vertically aligned bolts (for HS-2) to the two off-centre bolts used on the HIF-38 pattern.

The adapter plate can be seen here between the inlet manifold (dirty) and the carb spacer (black plastic):

A heat shield was also made to go between the carbs and the exhaust manifold, and the K&N’s were widened internally and had stub stacks fitted.

The car came to me with K&N filters and a long centre branch (LCB) exhaust manifold. After it passed its first MOT an old and tired RC40 silencer was fitted (was taken off a mini as it was too rusty!). This is fitted in the same place as the small silencer in the original system, and does away with the ‘across the back’ twin setup

The silencer only just fits, and is about half an inch off the fuel tank: a heatshield was made from stainless steel sheet for peace of mind; although the tank doesn’t seem to get too hot anyway. The proximity to the rear spring can be seen in this picture:

This silencer sounds fantastic and also makes the car feel quicker: may just be the effect of the ‘bum dyno’ but the engine seemed much freer revving with this and the LCB. When the link pipe eventually succumbed to the elements, a 1¾ inch link pipe was created to join the two together. This full setup gives a very good exhaust note and provides plenty flow for the engine.

Having been truly bitten by the terrible modifier disease, I started looking for other ways to boost the horsepower, and the topic of supercharging popped up. This is possibly one of the coolest way to get a 100HP midget (100HP at the wheels being the new target). So I purchased a supercharger thinking to manufacture my own manifolds and suchlike, and then have a 120HP (at the flywheel) Midget.

As the midget engine is naturally low compression (8.8:1), this lends itself to supercharging without resorting to double head gaskets and decompression plates.

The manifolds would not be too difficult to manufacture, as I was going for a suck through setup, and getting the thing to fit in the midget’s engine bay wouldn’t be too much of a problem, as the mini chaps have been fitting them to minis for a while now. A swift distributor mod (outlined in the moss installation instructions) and away we go.

The disadvantage is mainly that the poor old A-series is getting pretty stressed asking 120HP from it, and I would have always been a bit nervous of a grenading engine without an expensive and time costly engine rebuild for strength. After the second midget gearbox exploded, the realisation that a stronger 5 speed would be needed occurred. This was when the idea of the K-series popped up, and the amount of effort to make the A series strong enough and reliable enough to compete with even a 1.4 K was large. Another deciding factor was that there was a midget nearby (dad bought one as well…) with a poorly engine with low oil pressure, where my A-series could go and live happily as a present for the hours of welding and sitting in the pit that dad had done to get mine on the road.

A lot of research later, the supercharged A-series was dropped in favour of a K-series engine swap (see the K series section), the main reason being reliability.

So where are all the bits now?  Well the engine went into dad’s midget, and still is there, and the exhaust is still on the car.  The Vizard book reckons that the RC40 has no restriction up to 120bhp; the 1.4 K series makes 121bhp.