Im getting a new 50cc cylinder for my lads scooter as his is worn. Im not up grading to a 70cc due to legal reasons. I read that a high compression head can increase performance so what is it, are they any good and will it change the performance of a 50cc?
a higher compression squeezes a set amount of fuel and air mix to a certain ratio. BUT there can be problems when running a high compression, most of the time the standard unleaded fuel will pre detonate early due to the higher compression and it producing heat when its compressed, we call this knocking , its where the engine compresses the fuel before the piston reaches its very topdead center ready for the explosion and powering the piston down again. this early firing can caus ethe motor to fail, ie the crank/conrod due to huge stresses. to combat knocking most like race bike will run a race fuel with a higher ron rate, for your scooter its like only being able to fill up with bp ultimate or the likes a fuel with a higher ron that the standard 95 ( bp ultimate is around 97 ron so its less prone to pre ignition to higher compression ). the higher compression means you can sqeeze more fuel and air mix into the combustion chamber and set it off BUT only a certain amount to much fuel and air can lock the system or blow the engine up from extra stresses ie you pop the gaskets and the cylinder head as the bolts cannot compe with that added higher comression ration, but it also means more power. Visordown goes into some detail about compression ratios a good read http://www.visordown.com/features/workshop/understanding-compression-ratios
i would honestly say its not an ideal mod to run theres a lot more involved than just throwing on the new HC head. and youngsters will always have that devil on the shoulder saying " go on ragg it a little harder try and get 55mph not 50"
Thanks for the detailed response, much appreciated. Ill take the asvice and avoid it for my lads road scooter as he will probably just blow it up I reckon the racing cylinder set is a safer idea, cheers
a 50cc sport kit would be a better choice, can use the stock crank and just upjet the carb a fraction. once he has done the run in period, you could both then look at future upgrading like the variator to add a little extra pep via the roller weight setup and tune it to how he likes, ace on bottom end of the lights power, or eak out a few extra mph in the top end range . the sport kit just makes the porting a tad more agressive and lets you use that power a little better, more snappy response on throttle more bite mid range and a small kick just after mid range its also going to give a little more rpms to so it will rev out higher. speed wise maybe 50mph , but even 45mph will be a huge improvement over the 28-30mph a restricted bike has and up against a derestriced bike its going to have a little extra , for a 16yr old he will enjoy that scooter more if he rides safe and listens to dads wise old words
Dad originally stated he wouldn't be fitting a 70 kit for legal reasons. Surely fitting a 50cc sports kit or indeed any form of de - restriction that improves the performance of the scooter will have legal implications ??? Sent from my GT-I9195 using Tapatalk
The 70 kit would automatically mean he rides outside his licence. I understand but correct me if im wrong, that as long as its 50cc and he rides below 30mph then he is legal? The restrictors are in place to keep speed down and meet emissions regulations, the hp is not regulated on a 50cc? If he rides at over 30mph because the restrictions are removed then the insurance may look at it as modified but unless he crashes then the police are unlikely to strip it and check. If he crashes and the engine is checked then it is still a 50cc piston so all okay. Have i got that right? Sadly dads wise old words are given when he is pillion on my bike and sound like " Hold on and feel the torque on this! I know, if we crash now it'll hurt" Legal bike is vital so he doesnt lose his licence but a year of fun until he can get a bigger engine is important too.
Let's be honest; there probably aren't too many 16 year olds (or 47 year olds for that matter) that stick to the law with regards to a moped, there are plenty of 70 kits running around, exhausts with the restrictions removed etc etc. I'm pretty sure that once upon a time, and maybe it's still the case, mopeds had to have an upper speed limit of 45kmh by law ..... lots of us would be buggered if it is !!!! Sent from my GT-I9195 using Tapatalk
i have a high comp head on my tomos, the squish is a little harder is all, no noticeable differnce when riding or starting, it pinks a little bit on idle because of what tamiya said about pre-det.... but thats it....
ok its gray derestriction is the speed, ie instead of 28mph your removing a restriction in the motors drive to allow it to stretch its legs, thats kinda illegal , if your hooning around like a total idiot mr policeman is going to be called and your bike looked at. capacity is no more then 3.1cu in stock barrels. if mr police man spots you and follows you and your tucked down behind the bars topping 35.2mph he is in his right mind to pull you over, if your topping 40mph and the limit for road is 40mph he aints so stupid and knows your bikes been tinkered with he may pull you over and if he had a bad day throw the book at you. its a risk the rider takes for being more safer on the roads these days ( its an unfair law in my eyes and many others to ) 50cc sport kit now this is the gray bit. the 50cc sport kit is still a 3.1 cubic inch capacity there aint no change , the change happens to be that the ports have been moddified, ie they are set more agressive on timing , exhaust and inlet will be slightly higher and wider so they stay open for a tad longer in the draw cycle allowing more gas to escape and a bigger charge to come into the engine, BUT capacity is still 3.1cubic inches. a 50cc sport kit may just have a 50cc stamp on it OR it may have wording like SPORT, that sport word give the game away to a moddified cylinder , otherwise they would have to rip apart the motor get out the guages and measure the ports one by one , and compare them to a stock bone cylinder but still again its only 3.1 cubic inches and is legal as in that respect its the timing of the ports thats made it a better more revvy motor and added a extra 0.5hp to it. 28mph is unsafe, any rider that has a full licence will even tell you they were scared riding on a restricted scooter on a main A road because of that super slow speed of travel. its the flow of traffic, your traveling at 28mph and cars are coming up behind you at 50mph +. if your hit from behind thats it game over. mopeds can ride on a dual carragie way, 28mph V 70mph its a no brainer if your hit 0% chance of living through the impact , yet mopeds that are restricted are so called fine on the dual carrage way ( in the govs eyes ) , the problem is EU directives. us bikers would rather see a 16yr old on a unrestricted 50cc that can near enough keep up with A-B road speeds (40 -45mph) your a lot more safe being able to keep up with traffic flow and cars are not able to force you into kerb riding ( they bully you over because your to slow for the flow of traffic) and its why we always say to new riders stand your ground and do not ride in the kerb side . Before 2001 the eu directive was 31 mph, in 2001 they changed it to 28mph, and in the 70s there was no eu directive, the FS1E was the fastest 50cc around stock legal at around 40mph
You could always go for either a sport 50cc kit or maybe even the stage 6 street race 70cc if it's available for your bike. It's a 70cc but the cylinder is stamped 49cc so unless they tear the engine down and measure the piston they won't be able to find out
you misunderstand the law.. the limit is 50cc AND a power limit, your engine is on that power limit RESTRICTED, its also an mph limit.. so your allowed 3.4bhp at 27mph with NO MORE than 50cc... so if your breeaking one, its just as illegal.. now, high comp head does fuck all unless you have the requirement to run higher octain fuel.. you dont, your port timing is lazy, its stock. buy a kit, or accept how your bike is stock. there is NO legal way to make a MOPED faster in the UK
heres how it works. your stock 50cc in the uk produces around 3.1 to 3.4hp at a capacity of 49.99cc . thats a restricted moped that travels no faster than 28-30mph. remove variator = its illegal , the moped now goes above the legal 28mph its certified for. fit a sports pipe leave variator restricted = its illegal, you have upped the HP by around 0.5hp even this tiny amount of power now puts your bike as a motorcycle because its above a certain kw/h output . BUT there is a way to run a sport pipe legal and thats NOT TO derestrict it or to have it restricted via a cone inside the manifold end so it hinders exhaust gas flow and chokes the motor, but even then you may still find your illegal due to it being a sport pipe. even your bog standard exhaust can be made illegal by removing the restriction put in place, be ait a little washer / cone welded in the manifold , or a small leach pipe from the manifold pipe, or even cutting open the pipe and removing baffles and likes. play with port timings with a dremmel = yep thats illegal to, you have changed the kw/h power output ie the bike will produce a higher horsepower. fit a 50cc sport kit, but its 50cc still the same bore and stroke, = yep its illegal its not the size that counts here its the power output your sport jug produces more hp because of the agressive port timing thats added basic if you mess with the 50cc stock restricted scooter it becomes illegal if it produces more horsepower - goes faster than 28mph , the only way to stay legal is not touch it, so if your exhaust blows you replace it with a stock factory oem second hand job , variator wears you replace it but make sure its restricted by use of a wedding band ring on the slide boss. is there any way to make a 50cc faster / more powerful and stay legal = YES, move to a country where 50cc's are not restricted , some countrys in asia you can buy a 50cc and it will do 40-50mph as there is not law on restrictions for mopeds, some USA countrys have no law on restrictions of 50cc to , but if your in scotland - england - wales - ire your all restricted to 28mph and a max kw/h limit
