They are targeting a speed of 130 mph (210 km/h).
That would easily beat the current record of 96.5 mph claimed by the fuel additive firm, Gold Eagle.
A first look at the machine – showing flames coming out of its exhaust – has been posted online.
Honda said it had taken on the project to promote its “sporty credentials”.
“The main engineering challenge stems from the need to retain the look of the lawnmower on which it is based, and the ability to still cut grass while achieving the speed and the handling characteristics required for this type of vehicle,” said Peter Crolla, team manager at Team Dynamics – Honda’s UK motor racing team partner – which is overseeing the project.
“To our knowledge, this has never been done before, certainly using this mower and engineer combination, and as such there are no previous learnings to draw upon.”
Top Gear Magazine said it had set a deadline of June 17 for the team to complete work on the machine.
The Japanese carmaker has upgraded one of its mowers by replacing its engine with one normally used in motorcycles.
A steering rack sourced from a Morris Minor car has been fitted to offer greater control, the mower’s seat has been lowered, the wheels and tyres have been substituted with those of a quad bike, and the metal part of the chassis that normally holds the blades has been replaced with a glass fibre equivalent to make it lighter.
The alterations have forced the engineers to rethink how the machine cuts grass.
The original model featured metal blades, but they had to be removed as the engineers found it too complicated to connect them to the new engine.
Instead the machine now houses two electric motors with lengths of brake cable attached to them. These will spin round at about 4,000 rotations per minute to cut lawns down to size.
The team believes that, when complete, the machine should be able to accelerate from 0-60 mph in about four seconds
“There’s no scientific reason why we asked Honda to build this,” said Piers Ward, senior road tester at Top Gear Magazine.
“The grass needed mowing and everything on the market seemed a bit slow. Why take an hour to mow a football pitch when you can do it in five minutes?”
In fact, racing lawnmowers at high speeds is not a new phenomenon.
The British Lawn Mower Racing Association traces its origins back to a West Sussex competition involving 80 of the machines in 1973.
Over the years, famous names including Formula 1 winner Sir Stirling Moss, Le Mans champion Derek Bell and the actor Oliver Reed have taken part in its events.
However, the organization said Top Gear’s mower would not be able to compete in July’s World Championships because of strict limits on the amount of modifications entrants can make to their motors and mower bodies.
“After all the work that’s been done to the machine, it isn’t really a mower as such anymore,” said Mark Robinson a member of the BLMRA’s committee.
“Mower racing is not all about power – handling is an important aspect too – and in fact we think our machines would still be relatively competitive against Honda’s model on a tight track.
“But we’ll still be watching Top Gear’s progress with interest.”
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