A brief history of attempts to design reliable XPAG/XPEG Twin Cam engines

M.G. had a brief flirtation with a double overhead camshaft engine in the MGA Twin Cam. Introduced in 1957 and intended as the competition version of the MGA, the new engine had teething problems, amongst which was an alarming propensity to melt pistons! The culprit was found to be the 10:1 compression ratio so it was reduced to 8:1. However, due no doubt to prospective customers’ concerns about reliability, sales of “the competition version” were not very good, accounting for a fraction of the 100,000 or so MGAs produced, and it may well have been an expensive lesson for the Factory.

Prior to the introduction of the MGA Twin Cam, there were four known private (as opposed to the Factory) initiatives aimed at perfecting an XPAG based twin cam engine. The driving imperative for the first, the Uihlein Twin Cam was to build a car which would restore the competitiveness of the XPAG in racing against European machinery (The OSCA, Maseratis and others) in the 1.5 litre class.

The Uihlein Twin-Cam

The 1953 issue of Speed Age featured on its front cover the David V. Uihlein Special with the banner headline “Uihlein’s 130 mph MG”.

Under the sleek aluminium body built on a modified TD chassis there was an XPAG (TD bottom end) with a hemispherical combustion chamber head with dual overhead camshafts. This engine was said to produce 90 b.h.p.
The design and construction had taken two years but on its initial testing at a sports car event in Illinois the Special was reported to have retired with minor mechanical trouble.

Uihlein’s ambition to go into commercial production with the engine modifications was never realised for it seems that the car’s performance was disappointing. Against this background the project was allowed to ‘wither on the vine’ albeit Uihlein, who was an avid collector of antique automobiles, is reported to have kept the car in his collection.

He died in 2010.

The Runyan Twin Cam

Dale Runyan was another M.G. aficionado who had designs on making an XPAG twin cam engine available to T-Series owners. Runyan realised that development of such an engine would be an expensive business so he formed an association with Norman Timbs and William Zimmerman; these two gentlemen were known to Runyan through his upholstery business, Timbs being chief engineer of Halibrand Engineering and Zimmerman being the pattern maker for Meyer- Drake-Offenhauser.

Development from first drawings to prototype took just over 5 years and the engine was featured in an article in Hot Rod magazine in March 1956.

According to the article, the engine produced 80 b.h.p. at 5,000 r.p.m. on a dynamometer and a potential 110 b.h.p. was thought possible at 6,500 r.p.m. using larger carbs.

For whatever reason, the engine was never run again and it was destined to become an exhibit.

A possible explanation for not proceeding with the project might have been that after 20 minutes running time on the dyno the engine suffered a failure and there was a reluctance to throw good money after bad, especially now that the MGA was in production.

The engine, together with all drawings, patterns, tooling and spare castings was sold to Louis Schulte, who, three decades later entrusted the lot on loan to Carl Cederstrand.

And there the story ends… or rather, it has had new life breathed into it – but that’s a story still to be told…

The Ken Miles Twin Cam

This engine was built using one of the Factory 1500 competition blocks made for the EX179 record attempt in 1954. According to Road & Track magazine, it was designed and built by Ken Miles a notable West Coast racer who campaigned his TD based Specials (‘R1’ and ‘R2’ – ‘The Flying Shingle’) with great success in the mid-fifties. The twin cam engine had been fitted for the 1956 racing season but it ran a rod bearing (no.3) and caught fire during testing.

The engine ‘went to ground’ for twenty years but was discovered in 1977 in a hangar near Los Angeles airport. It was purchased by Chris Nowlan, who was Moss Motors Product Development Manager at the time.
The engine changed hands again when Chris Nowlan sold it to Don Martine. At the time both Chris and Don tried to persuade the then current owner of ‘R2’ to purchase the engine so that it could be re-united with the car, but without success.

Don then sourced a period racing chassis to house the engine and purchased an ex-race TC chassis.

The car which is described as ‘1947 MGTC DOHC Race Car’ on Don Martine’s website martineinnmotorsports.com was restored in the 1980s using a body made from small steel tubing with an aluminium skin attached by cap screws.

It had some notable racing successes in the 1980s and this DOHC/XPAG has proved to be the most reliable of the four attempts to design a twin cam XPAG/XPEG. The intention is to race it again.

The Puma Twin Cam

PUMA, an acronym for Purdy-Mueller Associates, was the name given to this head. It was built by two Southern California men, Rudy Mueller and Hatton Purdy (PUMA = PUrdy Mueller Associates. They may well have seen the Speed Age article about “Uihlein’s 130 mph MG” and probably thought that they could also manufacture a twin cam head for the XPAG/XPEG. Rudy was a pattern maker by trade and his ‘shop’ worked on Offenhauser engine parts. Hatton was a machinist with some racing experience. The plan was to fit the engine to a TD, race it, to prove its credentials and then (as Uihlein had wanted to do) market the head commercially. Unfortunately, it didn’t work out because the casting alloy was porous and water leaked into no. 4 cylinder. Only one engine was produced.

This engine was acquired by Lawrie Alexander in 1983 and was fitted to his TD Special (chassis no. TD6183) only to find that it leaked water just about everywhere! The cracks and pin-holes in the casting were welded up and the engine re- installed.

The car was taken on a 3,000 plus ‘test drive’ to the 1984 GoF in Victoria, British Columbia. It was reported to have run well, albeit when climbing steep hills the oil in the head flooded the rear valves, with the result that much smoke was emitted out the back.

The engine was then removed from TD6183 and some modifications carried out (notably the fitment of an external rear oil return to overcome the flooding of the rear valves). It was then fitted to Lawrie’s race car and entered in the Historic Races at Monterey. Unfortunately, the engine ran a con rod bearing and overheated, cracking the head.

Attempts to have the head welded were unsuccessful – no further work was done on the engine.

It was acquired by Chris Nowlan and has since crossed ‘the pond’ and is now in the UK.

Ed’s Note: I’ve put this article together using various sources and to the best of my knowledge it records reasonably accurately the separate attempts to develop a twin cam XPAG/XPEG engine. However, if anybody out there has any further information (or has corrections to make) I’d be pleased to hear from them at jj(at)octagon.fsbusiness.co.uk {substitute @ for (at)}.

My reference to “a story still to be told” regarding the Runyan Twin Cam is work in progress (for me) and I hope to be able to bring this to fruition in the not too distant future.

One thought on “A brief history of attempts to design reliable XPAG/XPEG Twin Cam engines

  1. Erik van Hardeveld says:

    In 2015 dutchman Jan Roelofs fitted a modified Alfa Romeo 1300 twincam cylinderhead to a modified XPAW Wolseley engine.

    Because I wanted a crossflow cylinderhead for my XPAG-engined MG TA special he produced a prototype cfhead first. This head is now running well on my car, and sofar an extra batch of 6 crossflow cylinderheads has been made of which 3 are sold.

    It is his intention to finish the engine with the twincam head soon. If there is demand, he may also produce these.
    Pictures (and more information if wanted) of both cylinderheads are available.

    November 2017,

    Erik van Hardeveld
    [email protected]

Comments are closed.