Spec me a fast road setup for my runner 125 sp

you require a fast accwelerating bike with around 80mph? you need no port work ATALL, good case work will warrent a gear up and top speeds of 90+ easily. your spec unported would probably be more than what you was expecting but if changing the crank the flow work is prittymuch silly to not do.

long stroke cranks up piston speed, internal port modification reduces life/drivability. id sudgest a stock 172 with your spec and a modded case, MAYBE enlarged transfer feeds but again, for what you want of the bike that spec is more than adiquate

dyno figures are exactly that, figures worked out through an equasion of torque worked out from an equasion of kw generated by a static motor. dyno's ALL need setting up frequently to keep them anywhere close to accurate and an engine people would belive to be 25bhp (tested at psn/pm/twa/whitton or the more common places) read WAY above that of ACTUAL bhp to a wheel.... altering tyre pressure or load on a machine can increase or decrease power, but as i say a "so called" 25bhp bike can read anytrhing from 17 up to 33 in this or any country, there for comparesen purpous mostly. not definitive power delivery, need a road recording device to see POWER on the ROAD wiht YOU on the bike, thats AL that matters.

the fastest bike at iow was 22.6bhp (port work equal to that of a 34bhp psn cylinder WITH a long stroke) tested on jb's portable dyno. the avarage bolt on bike (23-24 ish bhp consistant at psn (sent a few up now neer identical 23/24's), 25mm,172,pm59) was around 16bhp.... explain that. dyno's tell tails, i couldent care what they say. aslong as it reads flat steady power and your faster than the bike next to you.

the most bikes on the road will have is every bolt on part, even then its wasting money as the pipe carb and cylinder are the only performance enhancing parts, everything else is just bullshit bar a few fractions of a second to 60 quicker, so havign a full bolt on and a little flow work means its gonna be faster than any other professional build engine.

god damn i got into that one a bit

 

m8, get an engine done or read a book..... i prittymuch just told you what needs done to get what you asked for.

case work is case work, port work is port work.. NO port work is ANY good for a road bike. even a slight topuch means long distances (more than 10 miles) are TOTALLY out the question unless its once in a while... wouldent rag a crosser at full throttle down the road would you.
case work and the bolt ons would make you a happy man. anymore and your exceeding your requirements of the vehicle and ruining any use other than "ye its fast init" down the local. gear up wont kill accel with a good build/flow work and see 90+.


why is it you let people klnow theres more and they want it, but reliable, and able to thrash it for miles, and never repair it...

you want somthing reliable buy a bike and leave it alone... want somthing wacky you can ride for miles but still scares you then get all the bolt ons and the case done, want a bike you really cant run for more than 20 mins have the internals ported


a race engine is a race engine, a road engine is a road engine. you CANT have everything. there is NO such thing as reliable big power. there IS however reliable flow'd engines munching up 10,000 miles, in one go if you so wish (stopping for fuel obv)

 

forget stroker crank and billit head.. pointless on a road bike (strokers require port work to use on a road and have higher piston speeds/wear out quicker in other words, high comp heads are to regain lost compression from porting, again useless on a road bike)

bolt on's, stock head, case flow with or without transfer feed enlargment (takes lots of time so labour go's up by a fair few hours) will see happy happy times.. can always add more to this.

transfer feeds are a little up in the air. can flow well without enlarging these, but get slightly better when you enlarge them, also it means you can forget about it for future mods as its already done, problem is the time it takes... i wont do a case wih transfer feed enlargment for less than 200 as it takes easily 2 days to get the case/barrel matched and maxed.

think about how mad you intend to go, if you dont mind it being a bit of fun eventually.. if you do want to USE this bike as a vehicle not a hobby id just go flow, stock transfer feed, bolt on's and leave it at that rep[lacing bits as they go.

its all down to USE of the engine not the whims of the owner as explained you let people know what the deal is, they want big power, they get the bike, exceed its desighn brief then WINGE when it breaks... then it gets branded unreliable.. an engine is reliable as you build it if you KEEP TO THE LIMITATIONS OF THE SPEC. with or wihtout feeds done you will be able to ride it as you would any other 172. it will be faster, it will accelerate harder, it will live just as long.


the main considderation is how your gonna use the engine, longest distances, typical mialage a year and most of all how much money you have, not only to build it, but to replace parts to KEEP it reliable

the ammoun t of times ive heard lazy ass people with ported bikes claming unreliability is silly... if it starts first time and gets 5 miles up the road befor it overheats its reliable, just not fit for perpous. like i say, cant have everything so find the balance as you say.. i recon this ly's in the wallet now as spec is prittymuch decided

 

not a prob... not only you im helping afterall (well, thats if anyone looks at threads they didnt write themselves these days)

 

no, people who throw on a cdi with a 172, 25mm carb and no gear up thinking there bike will somhow go 100 is whats known for blowing engines up.
rev limiter is there for a reason, never exceed gearing via rpm, this is the cause for any cdi related explosion.... why do you think they have a limiter with short gearing? its not ment to exceed the speed limit!! (learner legal, bearly 70 is more than enough for overtaking and the like,)

so ye, more horror story's drummed up by a million so say engine builders blowing engines and blaming parts

 

left my job, more free time, alot less stressed (still get the idiots giving the bigman chat via pm/facebook mind you) but ye trying to keep hold of my little head