Max safe rpm for metrakit pr2

[Rwade]

I would like to the know the highest possible rpm it would be safe to run my metrakit pr2 block at. Im currently revin over 15,000 and the bike has lots of power i just need to know if it will last that long or if i would just have to change pistons rings etc sooner then usual.

Thanks for any info

 

[Dante'sZIP]

LET ER GOOO! LOL

 

[melf #50]

Maybe it can do 17,000 RPM and still not break down

there is not really a max to what a cilinder can do , there are guidelines....

if you can get a setup to run 16.000 rpm and not break down and score a higher (useably) amount of Hp's then your THE MAN off course

to be honiest , I think that it cannot be said what is safe and what is not , with these kind of rpm's /setups it is always a risk , 1 smalle error or part can destroy your engine.

so , only by endless testing you will know what will keep on running or when it will break down.

 

[tiba_karotsu]

you shouldn't be worried about the cilinder but the conrod, you should inspect your conrod after every race just to be safe, the crack only starts at the surface & it's always caused by too much tension.

one of the ways to prevent cracks from forming is to polish the surfaces of the conrod, the beam, big end & small end must be polished smooth so rough surfaces are eliminated, i have done this on our 2Fast crank & other conrods for 2takt & 4takt engines.

 

[roost]

I don't think there should be a problem, since the piston mean speed at 15000rpm is 19,6m/s. And that is not that high as it may appear. The 20m/s limit is tipical for racing applications. But you may go higher, since extreme racing engines run up to 25m/s, but they have engine lifes, before rebuild, measured in minutes.

 

[NickL]

What's the formula to calculate piston mean speed?

Ontopic: MK pr 2 is a high revin cylinder, put it at a dyno and you'll see where the power is

 

[roost]

It's
(STROKE / 1000) * 2 * (RPM / 60)

 

[Rwade]

Thanks everyone for the info

you shouldn't be worried about the cilinder but the conrod, you should inspect your conrod after every race just to be safe, the crack only starts at the surface & it's always caused by too much tension.

one of the ways to prevent cracks from forming is to polish the surfaces of the conrod, the beam, big end & small end must be polished smooth so rough surfaces are eliminated, i have done this on our 2Fast crank & other conrods for 2takt & 4takt engines.

Saturday ima gonna do a race simulation and if it doesn't do anything weird ill run it at 15,000 and above all the time. Metrakit block seem to be the most reliable to me. Im reving at 15,610 just to be clear and thats not on a real long straight it might peak higher i would love to run it at 16,000 power is nice and its still stock port timing i can imagine wat my ported block will run like at those rpms. Thanks guys ill let u know how it works out and see u saturday Dante bring yah damn leathers so u can ride it u stupid bastard. 15,000 and beyond its so much power with the 28 carb

 

[Dante'sZIP]

Saturday ima gonna do a race simulation and if it doesn't do anything weird ill run it at 15,000 and above all the time. Metrakit block seem to be the most reliable to me. Im reving at 15,610 just to be clear and thats not on a real long straight it might peak higher i would love to run it at 16,000 power is nice and its still stock port timing i can imagine wat my ported block will run like at those rpms. Thanks guys ill let u know how it works out and see u saturday Dante bring yah damn leathers so u can ride it u stupid bastard. 15,000 and beyond its so much power with the 28 carb

aye aye, fackin right...I will be there, in my saturday best.

 

[50cczip racer]

Hello Rwade
your scoot seems to go well at 15,000 rpm but if you try setting it up to run at 12,000 to 12,600 rpm ,adjust the ignition timing/rollers/pipe length to suit /try running a c16 manifold with the c20 pipe youll see a whole new side to the motor, forget tuning the pro race 2 its already too highly tuned try detuning it by decking the cylinder and adjust the cr and squish to suit if you want more power and huge amounts of torque this is the way forward and a tuning method never considered by most.your set up as it is should produce peak power at between 12,800 and 13,300 but will depend on how youve jetted,set ignition,set cylinder height etc.try finding the heaviest set of rollers it wil pull these revs on for best results and use a brand new torque spring before starting and as often as possible, the spring is most important dont chase lighter roller weights when the power starts to drop off after a few miles of use ,replace the spring first and adjust belt wear with shims to maintain full variation check this by marking pulley with permanent black marker and aligning lower belt width with end of variator centre bush

 

[Dante'sZIP]

Hello Rwade
your scoot seems to go well at 15,000 rpm but if you try setting it up to run at 12,000 to 12,600 rpm ,adjust the ignition timing/rollers/pipe length to suit /try running a c16 manifold with the c20 pipe youll see a whole new side to the motor, forget tuning the pro race 2 its already too highly tuned try detuning it by decking the cylinder and adjust the cr and squish to suit if you want more power and huge amounts of torque this is the way forward and a tuning method never considered by most.your set up as it is should produce peak power at between 12,800 and 13,300 but will depend on how youve jetted,set ignition,set cylinder height etc.try finding the heaviest set of rollers it wil pull these revs on for best results and use a brand new torque spring before starting and as often as possible, the spring is most important dont chase lighter roller weights when the power starts to drop off after a few miles of use ,replace the spring first and adjust belt wear with shims to maintain full variation check this by marking pulley with permanent black marker and aligning lower belt width with end of variator centre bush

That engine revs high and the pipe relies on high revs, ignition timing is set, why set it for lower revs, and we've already proven that it performs much better, higher?

 

[50cczip racer]

ive built the same motor myself pr2 and c20 combo and im sharing the experience of over 2 weeks on my dyno developing and track testing and numerous rebuilds and specification changes to C.R./squish/port duration/pipe lengthh/ign timing/fuels ,yes the motor will produce power at 15,000 but its at the tail end of the power curve and well past peak,i regularly find that the transmission has a sweet area that it likes to work in with a specific roller weight and torque spring and thats what youve probably found?is it digital or analogue ignition/digital requires very fine set up when your shifting peak power rpm about ive ran up to 1.5mm different from 1 pipe to another and low comp to hi comp settings,Does Rwade still use the hebo variator,there really bad,i threw mine away.Try sticking it on a dyno and locking out the variator to see where true peak power revs are at then fine tune the transmission to work best with it,it will run a lot more powerful and safer at the lower rpm and at 15,000rpm+ cranks dont last long so if it lets go it will probably take the rest of the motor with it

 

[Dante'sZIP]

ive built the same motor myself pr2 and c20 combo and im sharing the experience of over 2 weeks on my dyno developing and track testing and numerous rebuilds and specification changes to C.R./squish/port duration/pipe lengthh/ign timing/fuels ,yes the motor will produce power at 15,000 but its at the tail end of the power curve and well past peak,i regularly find that the transmission has a sweet area that it likes to work in with a specific roller weight and torque spring and thats what youve probably found?is it digital or analogue ignition/digital requires very fine set up when your shifting peak power rpm about ive ran up to 1.5mm different from 1 pipe to another and low comp to hi comp settings,Does Rwade still use the hebo variator,there really bad,i threw mine away.Try sticking it on a dyno and locking out the variator to see where true peak power revs are at then fine tune the transmission to work best with it,it will run a lot more powerful and safer at the lower rpm and at 15,000rpm+ cranks dont last long so if it lets go it will probably take the rest of the motor with it

I see, thanks for explaining..

 

[Rwade]

its never ever bin under 14,000

the bike made little if any seriouse power under 14,000 it was slow as hell at 12,890. The higher i reved it yes the more power i got my gear ratio is the stock one 13.06:1. So it will rev vry high and be peaky im trying to get the most out of it before i use gears. Unless i get it running the same speed as the other bikes without gear. The bike has always reved smooth and showed nice signs of any failure. I could try to run the bike at low rpm the timing has been retarded and compression raised. But still it makin massive power up high. Thanks for the info Daryl if this setup dont work out ill definetly have u to fall back on. But im one to try different things and ive only gained power and speed since the start. We will see how it handles it though i got extra casings, crank block and clutch just incase.

Thanks everyone

Rev her to the moon if she comes back send her the fuck again

 

[Speed]

Metrakit

Rwade,
Hope to see you on saturday. I'll tell you if your bike is running. I'll bring the radar gun set up with me. My theroy is to rev. the motor to what you have your port timmings set at. For example, you can purchase the Gram Bell 2t tuning book which has a guide line that compares rpm with port timmings because nobody has a dyno down here, nor does anybody have the experence to know how to work it properly.

Note: Think you can take the Super Scooter 70cc championship this season?

Speed

 

[Rwade]

hope to be there saturday myself

Rwade,
Hope to see you on saturday. I'll tell you if your bike is running. I'll bring the radar gun set up with me. My theroy is to rev. the motor to what you have your port timmings set at. For example, you can purchase the Gram Bell 2t tuning book which has a guide line that compares rpm with port timmings because nobody has a dyno down here, nor does anybody have the experence to know how to work it properly.

Note: Think you can take the Super Scooter 70cc championship this season?

Speed

Speed i might be gettin sent to school for 2 months of theory so thats a hell no and anyway i aint got the experience for that. I just hope to give a good showin and maybe try and get up front a few times if i can. My theory is to rev also ive seen nothing but positive results but we will see when i tare down how everything looks.
It still got the stock gearwheels in her and i aint got no real factory parts so its pretty good far as im concerned long as i aint 10 mph down like when i started. Oh wats the status on the hebo 50 racing kit i cleaned up my c20. Ill be seeing u soon though for some other stuff as i want to have a second motor before the season starts. Later doggy GLC go like cunt peace

 

[Rwade]

hey everyone bike ran great at 16,880 had so much power but my stage 6 28 mm carb had matel filings or somthing in it and it blockin the fuel flow. But for the most part it ran really fast ive never felt so much power. any guesses on how long the crank wil last ?

 

[rydah]

just keep fresh gas and good oil in your bike.

 

[Rwade]

Tiba anyone else

just keep fresh gas and good oil in your bike.

When do u think it would be a good point to change the crank i wanna have a spare motor or two to spread the wear and tear out. If i can run the engine like this all season i will there so much power and speed. Also im gonna take your advise on polishing the connecting rod but i will have about 3 cranks just wonderin if thats enough for a whole season of racing about 4 or 5 months 2 or 3 races a month 20 minutes races 2 each sunday somtimes 3

 

[tiba_karotsu]

yes a spare motor would be a good idea to spread the load, an engine can only take so much abuse before it gives out. polishing the conrod isn't a solution to wear & tear it is just a preventive measure against stress cracks from forming on the surface of the conrod.

just use the best oil you can find & you'll be fine (not that amsoil crap).