A new class of racing push mowers !! 4.5hp and fast

Hello im trying to create a new category of racing mowers. now before you jump to the conclusion that a 4.5 hp push mower is not fast then you are about to be surprised...But first a little history...
A local village to me here in France held an annual lawn mower race through the village.
I had never even been to a race, and being pestered to build a race mower, i decided just two weeks before the race to scratch build a racer.. I started by asking what the regulations were, and they replied that I could do anything to the mower to make it go faster and it was a pretty open field..
So I first looked at what mowers i had that could be used and quickly decided i didn't want to wreck my lawn mower so i would have to build one' and use a spare motor..but i had no spare big engine , just a load of 4.5 briggs push mowers and one honda 4.5 hp engine..
So i cut the middle of the deck out to have a support for the motor, and built a frame that would tale the "sub-frame" so that i could change the engine between briggs and honda by the common sub-frame mount with a rear engine configuration...i tested the briggs against the honda and found the honda a higher revving engine..i used the axles from a dead ride on mower that had good tyres and two lengths of box steel from another project i had, and knocked up a chassis and used the bonnet from a spare mower, i had to make a 90 deg turn for the gear lever linkage, and then tested to speed obtainable from either engine..the Honda came out tops when i had given it a dose of special engine oil additive.
the day of the race i turned up with my silly 4.5hp machine and was put in the first race against the biggest engine size mowers !! for the Le Mans style start, i was allowed to walk from a half distance rather than fun the 25 meters to the mower as i can't run. I have fibromalgia and suffer from chronic fatigue. you can watch the race on youtube.." chaze henri 2017 " and you will see the days event and races..Against all odds i beat them all..by having a machine that was lighter, as fast on the flat as the others and a LOT FASTER downhill and in ALL the CORNERS. The one and only corner that i had to brake for was a tight 90 deg turn at the back of the church..I was hitting that at 60 kph and broadsiding the mower to scrub of speed and down change to blast through the corner sideways at twice the speed anyone else could corner..the marshals were scared sh**les every lap by my approach speed...but it worked and I got a FIRST place win on my first ever race..
then later in the day i entered another race and got a third despite having been forced into some straw bales in an attempt to knock out the little 4.5hp early on...

So why am I posting this ? well they banned me from using the same machine this year as they have changed the regulations...so i can't beat them again !!! Worse i was building a bigger rear engined racer using a 13.5 hp engine and only found out about the changes half way through this years build...again it was not conform so that has been shelved for now...so what to do with a winning fast and very cheap to build racer ? everyone has a spare push mower engine.. and with a working front and rear axle from a ride on mower you can build a cheap but fun racer..no battery as its a hand pull start. I had even contacted oil additive supplier and they gave me a shed load of stuff for free, stickers, tee shirts, gloves even a big flag to show at the next race...
We will use the racer in our own races against the stopwatch three lap races in a field.. fastest person wins, so everyone has the same chance of being a winner...and it will still promote my sponsor !!!

So now that I have shown that a very cheap and easy to build rear engine'd racer can be so much fun I want everyone to see that and create a new category for racing or off roading a 4.5 hp pull start category..
I will share all the detail's of the racer, and all the pictures of the construction...

The class should be simple, and loosly resemble a F1 cace car configuration..
Motor has to be a pull start 4.5 hp engine, any make allowed..belt drive only.
The engine must be behind the driver and over the rear axle .
Fuel tank , exhaust, and carburettor must be attached to the engine or it's support.
Rear axle from a ride on mower with any tyre size on standard rims as per the axles original rims.
with a working brake on the rear axle
Front axle from a ride on mower. with front tyres from a ride on mower..
No batteries, or electric motors.
Protection from side impact, and some form of body covering the drivers legs.
Chassis can be hand built with ground clearance between 5cm, and 20cm
and basically safe, and no loose parts.

Even if this doesn't come about, you can still copy my design and build one for your own off road pleasure.. the 4.5 engine will produce a faire turn of speed,typically up to 50 kph on the flat. and it's finally going to be something usefull to build with all those push mower engines that are sitting on a rusting decks forgotten and abandoned behind the barn...

Please take this post in a positive way, watch the video and email me for any more info you might require..
Colin MARTIN

oops im having trouble posting photos from my files!!! help !!

Very intereting. Are the engines ungoverned?

What's the pulley sizes from engine to transaxle? Or do you just connect the engine output crankshaft directly to the transaxle input with a centrifugal clutch? 4.5 hp engines are pretty rare here but a 3.5 Briggs are all over the place.

Pretty cool video. Wish they would do stuff like that around here. Those guys were going pretty fast too, and the spectators right along the track just like in the good old days lol. They should do a 24 hour one somewhere. That would be cool.

Hi everyone, yes the races are a lot of fun but they are changing the rules here and even trying to stop street racing with machines that are not taxed and insured !!! but that's an on going battle...they can easily move off road like you guys do it..
the 4.5hp racer has a tiny belt running to the axle drive pulley that is much smaller that original..and a spring loaded tension'er linked to the axle brake so one pedal disengages the clutch and then applies the brake..useful as you can't stall the engine when you brake or stop.. ill take some photos of the linkage and post them on here.. Most common engine over here is the 4.5 briggs easy start engine..they are fine for the job..i guess if you have an abundance of 3.5 hp engines then create a class for that size.. it will mean the top speed will be about the same but take longer to get up to speed. that calls for better driving to not let the speed drop... the engine is standard and using the original limiter...it's up to you how fast you dare have the engine turning..but that's racing.. even formula one cars blow engines from time to time...
also i will post the photos of the bigger version i was doing for this year, still rear engine'd and with a battery for the starter motor..but kept as light and low as possible...
it's amazing the difference in weight for the front axle, and different tyre sizes.. front axles can be solid billit or just tin and the weights varies between 12 and 25 kgs or so...again i can post some examples when i find the scales again..

and as for crowds lining the track ...ok if behind the barrier, but on my fast downhill run there is a left hander over a ridge in the pavement , and it's easier on the left, but as i aproached the turn on the first lap ( iwas in front) a lady ran from right to left across the reack in front of me.!!! i had to go wide around her and almost side slammed the wall....not funny...these events if done like this should sound a horn to advise the spectators that the race is starting, and not get caught out...
Please ask as many questions as you want i will reply to them all...
Colin

You clearly had an advantage in the corners with your substantially lower center of gravity.  I like the F1 styled chassis you built using a stock mower front and rear end.

thanks, yes the low C of G was a key in being able to keep the average speed high, by never braking for corners..except one on this particular course.. I was surprised to hear the 4.5 briggs easy start engine was not that common !! perhaps because the average house has either no lawn, or miles of grass and needs a ride on or two to cover all that area..
Im sure that will all the big parking lots, it would be easy to organise and mark out a nice miniature of a famous circuit and organise a race using a small mower engine..
The main think im trying to promote is a very cheap, simple, and not too technical format that anyone with some scrap mower parts and a welder can build a competitive racer that's not going to be so fast it's a life threatening sport but a lot of safe fun.. and i can tell you that the closer you are to the ground the higher the speed seems and the fun factor goes up.. like the stock mini bike racing for kids..of all ages, there should be no age restriction in this class...Im 65 and still very competitive.  
My latest project is very very different but still in the design stage. it will use a briggs big engine or possibly twin cylinder engine, but no wheels !!  I still have the mk2 racer to complete with it's rear engine, but that's on hold as i have a USA KPZ1000 police bike to do a final restoration before selling it this year..im taking more photos to post of the racer but here are a few other creations of mine..
A half size military land rover, that uses a lawnmower axle and engine, with a very modified briggs clutch, that would give enough power to climb slopes up to 45 deg ! despite it's 350 kgs weight  
and a Jules Verne inspired Bike..all a lot of fun to build and operate..

By the way the cutter drive clutch , sorry brake clutch, is a common part to get worn and fail. there is a no replacement clutch plate policy from the manufacturer as ones repaired often fail again after little time, and that's because the top and back plates the clutch and brake faces respectivly, would be worn and have lost their grippy surface treatment. also the plate it's self if over heated by slipping will loose all it's hardness, and the center splines will wear and fail.. so these clutches re a costly repair, having to pay hundreds of dollares for a replacement unit...However they are fantastic for all your off road mower projects as firstly that can be modified to be mounted higher up on the engine shaft. and provide a clutch and secondary brake, for your upgraded macking.. the cork is from wine bottle corks, cote de rhone and bordeaux being popular ( joke) cut to a thickness of 4.5mm and bonded with a hard two part resine glue, sanded flat, and a spacer fitted. it's easy to do and if anyone is interested ill post a full set of instructions and photos..This modified clutch, will give excellent power grip, and a bigger pulley drive to your rear axle..much better than a belt tension clutch.

This is a clutch that would ordinarily be found on a push mower.  It allows you to stop the blade but keep the engine running?  Kinda rare these days over here.  Most I see have the blade bolted right to the crank.  The engine only runs if the operator is gripping the handle.

Okay that half size military land rover is one of the most amazing builds I've seen.  You need to start a thread on that with detailed pictures please.

My friend and I are adapting a peerless 900 series and a Briggs 5.5 pressure washer engine to a go kart we have. These pushmower engines are dime a dozen here. Lotta clones and Briggs. I’ve been itching for something to find some way to torture test these engines and compare real world power

OK time for some answers. sorry they are all in here together but im a tad busy but still want to reply to all the comments...so far...

Ok i was asked if the small engines have a guvnor. yes they do but it's an air guvnor..under to ventilated top cover of the small engines, where the pull start handle cord is stored, there is a colombe of air sucked in from this high point ( where there is the least dust) and it get thrown out horizontally through the fins around the flywheel, and ducted over the cylinder fins. the govnor is a blade about 2 inches high and 4 inches long and curved so it fits close to the flywheel fins. as the engine speeds up this plastic blade gets blown outward away from the flywheel...it is linked to the carburettor that has a very basic full open or shut movement, that is regulated by the govnor..so to rev higher, the easiest way is to remove the top cover ( 3 screws) and cut a slot in the blade. this is so you can tape over the slot if you over did the reducing of the blade surface..also a slot in the middle of the blade is easier to control the amount of extra rpm's rather than lobbing off the end of the blade and finding it won't do anything to slow the engine and it will all end in tears !!
By the way i didn't do any rpm modification to the little honda engine as it was turning pretty fast anyway and on the downhill sections it was being forced to rev it's little nuts off anyway...

The picture of the clutch with the cork sections is the type used on a lot of the briggs engines, from 12 hp to 16 hp and they cost a fortune to replace..it's directly attached to the crankshaft, and has a smaller pulley above that drives the drive wheels, the clutch is for the blades...there are several different types, but it's basically the same inside. the pulley can be welded, or mounted on three pins, and you can modify these very easily..i will do a video on them one day...but i have many photos that also show the mods...they are of course very useful as a drive clutch, rather than a belt tensioner. and this is what i used on the half size landrover.. it has enough power to climb up a set of ramps at 45 deg !!! and the weight of the landrover and me equal 450 kgs...nearly half a ton !!! trust me they are excellent when modified..

and the small push mowers with drive, have a simple tensionner for the belt to provide forward motion..some have the actual gearbox that drives both wheels, rotate slightly to tension the belt..

Latest news, i dusted off the little race mower and it started 2nd pull, but then wouldn't rev so some crap had settled in the tank and blocked a jet..so i had to remove the tailfin, to get at the carb to clean it..other wise it was a engine dismount (thats also very fast) to get to the carb...a flaw in ln my design.. unbelievably it is still running of the tank of fuel i filled for the race !!! i raced in two races, coming first in one and third in the other one. winning the top prise and had some racing about in the garden afterwards before being put away for the next race season and it never got re fueled again...

more pictures on the way, and please keep those questions coming in...

A couple more pictures of that clutch mod and the cutaway drawing of the clutch assy modified..

Yeah not seeing any pictures