Parallel Twin Dragbikes

ONCE a very popular engine type in drag racing with endless Triumphs and Nortons, more often than not supercharged.
Currently the largest in action is 'The Beast' at nearly 2000cc, whilst in this country Tim Clark has a new engine of around 1400cc under development.

HOWEVER not all fast drag bikes have huge engines, witness Mick Hand's amazing 250cc Honda twin. Also let's not forget the many 500cc twins in the 8's including the late Dave Houghton.

SUPERLATIVES aren't enough to describe this bike; Mick Hand's 'Little David'.

Based on the 1960's Honda CB72 and 20 years in development, this bike still holds the 250cc world record at 9.8secs! Crankshaft was modified to 360° configuration and primary drive converted to gear rather than chain. This meant that the engine ran backwards of course. Not a problem to Mick who made his own 3 speed gearbox. Pistons, rods, cams and valves were all Mick's work too. Compression ratio was 6.5:1 and boost from the Marshal cabin blower over 30 p.s.i. Using 305cc barrels from the CB77, Mick recorded a 9.02 run. Mind blowing stuff.

I did see this bike once at Elvington when the lower picture was taken. The bike left one lasting impression on me and many other observers; the incredible noise such a small engine could make.

Photo 1 courtesy Jon Spoard.

DAVE Houghton bought this 500cc Triumph sprint bike in 1973 and over a long development period, refined it to the point where he ran an 8.87 - 161mph run at Santa Pod.
Based on a mid fifties 'Speed Twin' with Bewley 2 speed gearbox and Shorrocks blower, the bike weighed next to nothing. Not surprising considering he fitted a Yamaha FS1E moped front end, and the vestigial frame.

Painstaking development over 3 years resulted in a best time of 10.55 on straight methanol. Next he began to add nitro, refining the engine as he went along. From this point Dave was regularly in the record books. I was fortunate enough to see him many times at Elvington, though my photographic efforts weren't to good back then.

Note reversed cylinder head with minimal finning and extra studs holding plate over head. Shorrocks C75 mounted ahead of the crankcase with very short right angled manifold and SU carburettor. Float bowl is removed and fuel fed direct to main jet. What you can't see, is that he ran a total loss oil system to avoid contamination from the nitro. Scavenged oil being pumped into a catch tank. Minimal chassis appears to terminate ahead of blower.

Sadly Dave was killed shutting down from a 10.44 blast at Blyton during the 1991 George Brown Memorial Sprint.

No larger version of this image.

IS it something in the air in Sweden? Here is another team who decided to brew their own, the brothers Bengtsson, makers of the Bentec 2 speed transmission used on many fuel bikes.

The first pic is from 1993 again when the UEA Supertwins visited Avon Park. Since then the bike has acquired a new frame with detachable top tube. Noticeable also is how the final drive outrigger bearing support has been beefed up. I don't know whether the parallel twin engine is based on a couple of cylinders from a big V8 to allow easy sourcing of consumables or not. Though I know the first version had pushrod operated valves. The engine is a beautiful thing to behold, mostly carved from billet. I did ask one of the brothers if the crank was arranged 180° or 360° Triumph style but didn't get a conclusive answer.

GEORGE Laycock is a long time member of the National Association of Supertwins, and has always campaigned his Norton Commando in various guises. The bike has gradually evolved into what you see here, a blown methanol burning low 10 second runner. This despite the fact that George has kept the bike in a low state of tune for reliability.

The standard frame was sawn in half and the top tube extended to kick the front end out, whilst the swinging arm was replaced by a rigid and much stronger arrangement.

A Marshall cabin blower is neatly fitted above the gearbox which is a Bewley 3 speed unit. Clutch is modified Commando and for 2001 ignition is courtesy of a Joe Hunt type magneto grafted onto the timing cover. Compression ratio is reduced by use of a plate under the cylinder barrel.

I remember attending the World Records meeting at Elvington in the 70's when a team from Norton Villiers ran a Commando production racer. Over the 1/4 mile it ran a very low 11, and with raised gearing 143 mph in the flying 1/4. Stunning stuff, especially as these were the averages of runs in opposite directions.

Another bike from the ranks of 'NAST' (National Association of Supertwins).

Built by Tim Clark as 'Terminator' and developed to the point where the bike ran 8's, Tim then sold the bike to fellow club member Dave Witts. Tim is now working on a new bike based around half a Cosworth head and a capacity of around 1400cc.

Leaping onto a bike like this must be pretty daunting and Dave started from soft settings in 2001, finishing the season in the 9's together with the TF championship.

Engine is a 950cc Triumph based Nourish with reversed head, Roots type blower, and Hilborn injection running on nitro. Transmission is by slider clutch and 2 speed Bewley gearbox.