tuning a single cylinder 4 stroke

[steven_191]

im thinking of getting a ktm lc4 640 engine. at 55hp (which is probably enough) i might want a bit more for a project.

my question is, is tuning a single 4stroke engine the same as you would go about tuning a 4cylinder engine?

im hoping to get a bit more power due to the fact i want a 'naked' style and with zero aerodynamics may need some more grunt, depending on the end weight and what its like to ride. which i wont know until i finish.

also the ktm engine apparently vibrates alot. am i wrong in thinking a well sorted balance shaft should sort that out??

[Frost]

It's different in that the gearing tends to use the engine in a different way. Singles tend to be about maximising torque over peak power. When riding the thing you'll notice you can usually go faster by just changing up a gear rather than revving it to the limiter. But otherwise the things done to tune one are the same.
I rode a KTM 660 SMC, that vibrated a lot more than my SRX 600.

Look into Supermono racing, they tend to nick big KTM singles and stick them in a 250 frame. They get 80+bhp out of some of the motors, but i don't think you should be aiming for that unless your pockets are deep and your wallet fat.

One difference is that changing pistons and boring the engine out are a lot more plausible when you've only got to do it to the one cylinder.

[G]

[steven_191]

so would the aim for more torque be better than more horse power be sensible?

im slightly expecting this to want to wheelie.

my plans are, cagiva mito frame, aprillian rs125 swing arm to suite the chain on the right hand side, ktm lce 640 engine. i may even use the rs125 frame but that depends. its just that i have the cagiva frame and apparently they are good.

the mito and rs125 are competing bikes in terms of lightweight 2 stroke 125cc road bikes and theyre both quick so using that swing arm wont alter too many characteristics. but with the extra power and espcially torque i think it might want to wheelie quite easy. but thats a problem to adress in the future.

[steven_191]

[G]

It'll probably be less likely to wheelie than in it's original frame - as you'll have a lower centre of gravity.

[steven_191]

how much though? im not sure ive even heard of husaberg?

and it depends how much needs spending all in. im not planning on tuning anything to start with. just a thought as theres a big difference between one and four cylinders.

[chris-red]

Husaberg AKA Husabang

My mate had a supermoto one, it needed an oil change every 1.5 hours IIRC. He said his was about 70bhp from a 650.
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[G]

The thing is, unless you're going for a racing class, you choose a single cylinder bike for road use because you like the lack of power generally.

Don't know specific costs for tuning and will depend on how much you get done, but on average I'd say people are at the least in to four figures.

Husaberg is owned by KTM - their bikes are similar to the EXC range KTM has, but they go bigger while still keeping light weight.
As I say, 750cc kits are available and used for desert racing in north America, where you're staying at pretty high speeds.

[hmmmnz]

ktm is only really taken a foot hold in the uk in the last 5 years,
but here in nz they have been the best selling bike (offroad) for the last 10 years atleast,

there are loads of tuning options,
mostly involving cam changes, carb upgrades, and porting
there is bigbore kits available but you'' only get a few extra cc so basically no one ever uses them,

if you keep up with maintainance they last a fair while, and rebuilds are nice and easy
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[Tristan.]

[G]

Sorry, yes the calculation is power=(torque*revs)/5252 ; my apologies.

Anyway, the point was that they were directly related, so more torque=more power. And yes, I do realise he was using the Jeremy Clarksons 'torqs' thing.

[steven_191]

i would like to lose weight off the bike but really that would cost more than it would be worth to do.

i would aim for better flow and more efficient combustion and utilising the cam and displacement to its potential. not too sure about the carb because from my own research changing the carb isnt always that worthwhile. just the 'right' choice.

and the way i normally view these things is, if KTM thought the carb was shit, why would they put in into a mass produced bike? and this bike sells fairly well and i havent read about the carbs not doing their job right.

it'll be more a case of getting a decent mixture in the the combustion chamber and getting it ready for combustion. considering its only got about 9 inches or so of travel from the carb to the valves, thats why i say the 'right' choice of carb.

ive still got to buy an engine yet though

[stevo as b4]

How about get an engine of your choice and get it fitted into the frame and everything sorted like mountings, chain alignment, fuel and lubrication systems plumbed in etc, before you start to worry about wanting more than the 50/55bhp that your thinking of.

I know of people who have spent ££££'s building a tuned or specially modified and or frankenstein car engine, and then not had or being able to afford a suitable car to stick it into. It's just pointless to spend lots of money and time on a trick or special tuned engine, if all your going to have at the end of the day is an engine and thats it?

[binge]

[steven_191]

I wasn't planning on doing it before it was all working. I said earlier I wouldn't know until I finished and rode it to see what it's like. I was more interested in wheather the tuning approach to a single was the same as an engine with more cylinders.

[G]

[steven_191]

Buying a faster bike is definitely not as much fun.

[G]

Ah, I thought you were making the bike primarily for riding, not for the sake of building and spending money; fair enough then :p.

[tahrey]

[G]

Yes, this old argument it would seem . If you read my later post, you will note I DID post the correct formula.

So, what you're saying, is that you want torque spread across a wide range of rpm, going to a high rpm.
So, what shall we call this concept, hmmm, maybe 'quarop'? Hmmm, doesn't sound right, how about, err, 'power'. Yes that sounds quite good!

Having torque figures alone tells you nothing. I could present you with a bike engine that has 1000NM of torque spread across 4/5th it's rev range. But the output shaft is spinning at .1-1rpm. Throw in some sensible gearing and suddenly you've got very little force at the rear wheel.

So we can see that 'torque across the rev range' actually means very little.
To be useful, it needs to be qualified with rpm too. When you include RPM, you are then describing power, not torque.

With RPM/Power you can get a good of the gearing you CAN run. This gives you an idea of the likely force at the rear wheel.