| |
Q - Does anyone know the formula for converting CC to HP and HP to BHP.
JF - Posted 12 Oct 09 |
_ |
A 7hp Vire engine is 269cc. Vire bore 70mm, stroke 70mm, compression 6.5:1 at 3200 rpm.
The formula to get cc is, bore x stroke x 0.7854 x bore = cc
70x70x.7854x70 =269cc
But if the compression is raised to 9:1rpm 4500 you have a 12Hp engine.
You need all the facts to get the answer. Put engine on Dyno. |
|
| |
Q - What is the legal position when fitting a sidecar to a motorcycle?
Do you have to notify DVLA, insurance company, etc?
Can you MOT bike then fit chair or does it need to be MOT'd when fitted?
Any info would be great. KM - Posted 22 Nov 09
|
_ |
You must inform all of the parties concerened even if you change the colour of the paint. You should MOT after the sidecar is fitted, as DVLA log book is changed.
Any alteration will make your insurance nill and void if you you do not inform them. Be Safe in this present age of P/C.
Hope you have fitted a side car before as it is not as easy as you think. You have to alter the gearing , spokes, chain, tyres, get the proper toe in to side car wheel and toe to bike which has to be checked every outing and even on outing. Then you have to go on a Charles Atlas body building course to drive the damed thing any distance and to get it out of the garage Good fun though. I used to drive with a bath on my one, and when it was taken off it was used as a hedge trimmer. The hedge usually finished up between the bike and the sidecar wheel . Get the weight wrong and you will be driving on the bikes wheels while trying to get back on to the three wheels, or if it is too heavy you will rip the rear wheel off the bike, or you can just be a woosie and drive at 30 mph max and have some fun
Good luck.
JF |
|
| |
The taxation of vehicles in the UK began circa 1637 with Hackney carriages in London. Come 1747 this was extended to include all forms of horse drawn carriages plus, in1770, mechanically propelled vehicles (intended for steam powered vehicles). In 1861 the Locomotive Act controlled taxation of all vehicles on British roads being administered by local county offices. This resulted in councils issuing their own licences and, if you needed to go into a different county, you were required to pay that council's tax too ! At typically 2 guineas per annum a go (£2.10p or £2-2s-0d in old money) it could be very expensive. This annual licence was a certificate, rectangular in shape, bearing the name and address of the owner, description of the carriage (eg carriage drawn by four horses), the county of issue, the amount paid and expiry date.
The first legislation referring to motorcars specifically was the Motor Car Act 1903 which laid down a registration fee of £1pa for cars and 5s (25p)pa for motorcycles and again this was administered by the county councils who continued to do so up until 1974. By 1910 a sliding scale of duty of £1 per Horse Power per annum was introduced on cars. The HP formula used was set by the RAC and based on (DxD xN) divided by 2.5 where D = diameter of cylinder and N = number of cylinders. Obviously the manufacturers of the engines quickly realised that by having a narrow bore with a long stroke you would be in a lower tax bracket. Hence long stroke engines became the norm with the HP calculation bearing little resemblance to reality – something like a third of its true output.
The Motor Vehicle Acts of 1919 and 1920, amongst many things, introduced in 1921the Tax Disc still in use today and switched motorcycle taxation to weight and wheels parameters (taking into account sidecars). I believe there were three weight limits of upto 174lbs, 175 – 199lbs and 200lbs +. A solo in the highest bracket would cost £3 pa (more if a sidecar was attached) with the 175-199lbs lightweight class at 30s (£1.50)pa which in 1931 was extended to 224lbs.
Looking at Motorcycle manufacturers brochures of the 1920's by circa 1926 most of them had discarded the HP in favour of engine capacity in cubic centimetres although HP was still quoted but on a slightly more realistic capacity basis, eg 2.5hp = 250cc, 3.5hp = 350cc, 4.5hp = 500cc , 6/7 hp = 680cc.
I'm uncertain as to exactly when the road fund licence for motorcycles changed from wheels and weight to engine capacity but this was probably in 1948 when the RAC hp rating was dropped for a flat rate of £10 pa per car. Since then we have had motor cycles taxed on engine capacity bands.
Hope this is of use to you and if anybody knows anything different from the above I would be very grateful for their input. GH - Posted 1st Nov 09 |
- |
Reply to G/H Hi thank you for that interesting info.
I have been given the data on a 7 HP two stroke engine, year 1975, from the manufacturer service book, the cc is 269.
To calculate the cc - (bore) 70 mm x (stroke) 70mm x 0.7845 x (bore) 70mm = 267cc. For a standard engine.
Interesting info: - The above engine 7 hp = rpm 3200 compression 6.5.1 gives 7hp
If the engine is altered to rpm 4.500 compression 9.1 that gives you 12 hp
Conclusion the same engine altered can give a different hp. So you must put it on a dyno machine to get the modern BHP.
The problem was that I required a carburettor for a 7hp two stroke but did not know the cc
So who has a carburettor for a 250cc two stroke?
Bore 25mm, 46mm distance between studs holes on flange. JF |
|
