MG Midget K Series Conversion 1 | Initial information: Introduction, Engines, Performance and Economy

January 23, 2012 at 9:37 PM

K Series Midgets are giant-killer sports-cars, combining traditional appeal with performance way beyond the maker's intention. In fact, the faster KSeries Midgets approach Porsche 911 levels of performance – but with exceptional economy and ease-in-use.

Any Midget can be upgraded to KSeries power, easily attaining Lotus Elise / Honda S2000 acceleration figures, but without the associated costs and most importantly retaining the car's character – the reason we became Midget enthusiasts in the first place.

Brief History

Unlike its contemporaries (the MGB Tourer and MGB GT), the MG Midget increased its performance over nearly 20 years of production through 4 engine upgrades: 948cc and 46 bhp, through 1098 (55/59 bhp), 1275 (65 bhp) and finally to 1498 with 65 bhp. In this manner, the car's abilities remained acceptable for the period. From the outset, enthusiasts modified their engines to improve performance - mainly through cylinder head, camshaft and carburation changes – better to exploit the fine handling and road-holding of the standard car.

In the early 1960s, the Healeys, the MG factory and some enterprising companies sought significant increases in performance through engine swaps, e.g. by installation of MGB power units (in the case of a factory racer) or by using a Coventry Climax FWE OHC alternative (Healey and Brabham); this advanced engine surely was the 'KSeries' of its time, being lightweight with OHC.

The factory couldn't stop the 3^rd party conversions – but would not sanction the Healey's Climax-engined car for sale, possibly because its performance exceeded that of all of its other sports cars in the MG and Austin-Healey range. Apart from a small number of Atlantis (Ford 1600) conversions, engine swaps were rare; most enthusiasts needing more performance chose conventional A-series upgrades.

Fast forward to the early 1990s: Rover has developed and is using an advanced, lightweight, twin-OHC, fuel-injected engine in its saloon cars - ideal for MG's agile and lightweight classic sports-car. By the end of the 1990s, two companies were providing converted cars and parts for home conversions: the KSeries Midget was born.

Can I Convert My Midget?

Any model of MG Midget can be used as the basis for a conversion. Some notes:

• MK-I Midgets are relatively rare; you might want to consider preserving your MK-I and converting a later car
• MK-IV 1500s have additional chassis strengthening that some believe advantageous.

Which Engine Can I Use?

All KSeries engines have the same major dimensions and weight, but it's suggested that the 1100cc version should be ignored (bhp for effort is not attractive). This leaves:

• 1400 SPi (single-point injection from e.g. Rover Metro)
• 1400 MPi (multi-point injection from Rover 25, Rover Metro GTa)/li>
• 1600 MPi (from MGF, Rover 25, ZR and ZS)
• 1800 MPi (from MGF, Freelander, Rover 25, ZR, ZS, 75)
• 1800 VVC (from MGF, ZR, ZS)
• 1.8T (from Rover 75T)

Notes:

• All engines have the same block size and weight; conversion effort is the same, apart from the 1.8T
• The VVC has additional height at front/driver's side (due to the VVC actuator); requires bonnet modification
• The 1.8T requires additional hardware to accommodate the turbo and inter-cooler; this is a challenge, given the available space; there are a couple of conversions underway, but I won't touch on the turbo conversion in this piece.

What Power and Torque Can I Expect?

In general terms, you can expect 5% more torque and 5-10% more peak power from your engine installed in a Midget based on free-flow exhaust and inlet configurations, and free of catalytic converter. With an after-market ECU, expect overall 10% more torque and 15-20% more power. For example:

What Performance Can I Expect?

The following performance figures have been calculated using a simulator, based on converting a standard 1275 (with notional 62 bhp DIN and 740 Kg weight); the conversions all have 5-spd boxes. You would need a strengthened transmission, suitable tyres to provide traction, and plenty of practice to replicate the following standing-start times (but the in-gear figures should be easily attained):

What Fuel Consumption Should I Expect?

As you might expect from a modern fuel-injected engine and 5 speed box, the fuel consumption is improved compared with the 'iron' engines: you should expect up to 40 mpg overall and up to 50 mpg touring – assuming your ECU is reasonably calibrated.

Anthony Cutler

Chartered engineer with MG Midget experience from June 1974. Now enjoying my 3rd MG Midget, a 1973 RWA, acquired end 1977. Converted to KSeries power in March 2002, it achieved class awards summer 2002 at Prescott and Curborough. With a high level of enthusiasm for these cars, especially the KSeries conversions, I was invited by the forward thinking Midget Register committee to be KSeries Registrar; this gives me a unique opportunity to encourage more conversions to use the wonderful MG-Rover KSeries engine and enjoy the company of other KSeries owners in conjunction with their remarkable cars.

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