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Post by sublunacy on Jan 20, 2016 21:28:42 GMT -5
the street race cylinder is a good choice but i would enlarge the outlet to atleast 20mm. that is a good cylinder that is limited to 19mm outlet for the sport pipes. i think a 1mm boost in size would wake it up nicely. no need to change anything else.
aswell as a non hpc crank. ask me why if you want.
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Post by PIG on Jan 21, 2016 0:34:32 GMT -5
i like how you did that. if you get the correct primary compression and cylinder combo it will make 10ft/lbs at 10000rpm. if you get it wrong like an mk1 racig cyl plus a hpc crank it will be shit and make 8ft/lbs at 11000. How are you getting these numbers? |
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Post by sublunacy on Jan 21, 2016 11:43:44 GMT -5
i like looking at dynos and port maps/ port heights etc. i have a keen memory for such things. did i say something wrong?
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Post by sublunacy on Jan 21, 2016 12:11:31 GMT -5
if your using a streetrace cyl plus a forrace4 the dyno is easy to find. the streetrace is timed pretty high but the outlet is likely 19mm. thats the only thing holding it back from being upper midrace. exhaust port area does not change much between cylinders because there is no room to make them wider.
the exhaust manifold is 24mm and the cylinder outlet is 19mm. with such an offset it will be better to atleast match the carb to the outlet if nothing else. then if the cyl needs air it can get it and last along time. does that make sense?
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Post by 190mech on Jan 21, 2016 12:54:05 GMT -5
What about the stepped exhaust port on the road racing Honda rs125 and Aprillia rsa125??
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Post by PIG on Jan 21, 2016 13:06:16 GMT -5
i like looking at dynos and port maps/ port heights etc. i have a keen memory for such things. did i say something wrong? No you said nothing wrong. It's you list these numbers like its a matter of fact. One person could set up a combination of parts one way, and another person could set up the same parts and have different results. There's to many variables to be able to say "x" parts will give everyone the same results. Weather, different climate, altitude, dyno's etc etc, all affect these numbers. Also, what crank are you using that can handle rpms that are in the 11,000+ rpm range that are not HPC or full circle cranks? Everything that I'm familiar with that can handle the big rpms is HPC. |
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Post by sublunacy on Jan 21, 2016 14:42:58 GMT -5
What about the stepped exhaust port on the road racing Honda rs125 and Aprillia rsa125?? if you are asking about powervalves on the exhaust port it has pros and cons but it stands out as easiest thing to change and get a longer powerband and an increase in hp with no loss of torque. there is other ways to do it but its a comprimise between engineering and simplicity. |
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Post by sublunacy on Jan 21, 2016 15:30:35 GMT -5
old tech was to increase the primary compression. this no longer applys to modern exhausts. the primary compression nowadays only needs minor adjustment from a sport cylinder up to full race cyl and beyond.
these are loop scavenged engines meaning the pipe is king and everything else just supports it.
a full circle crank is needed when the tranfer ports open much earlier on the downstroke.remember the piston is not yet at bdc.
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A FULL CIRCLE CRANK WILL EXPERIENCE MASSIVE INEFFICIENCY WHEN THE OUTGOING GASES PUSH TO HARD FOR THE RETURNING PULSE. MEANING YOU LOSE TO MUCH INTAKE CHARGE OUT THE EXHAUST.
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Post by sublunacy on Jan 21, 2016 15:49:38 GMT -5
i dont want to sound like a know it all cause i could use a couple months more to think about everything. i feel like my comprehension of port area and port timing and blowdown is still slightly limited so far. BUT primary compression i understand well.
the discussion is arbitrary when case volume and port maps and dynos are in reach.
the primary compression thing needs to be evaluated as a DYNO result. the point is to build torque and rpm not one or the other.
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Post by Lucass2T on Jan 21, 2016 18:20:58 GMT -5
Honda rs and aprilia rsa don't have powervalves.
Edit: aprilia rsa (backside rotary valved) does....TM racing KZ engines don't.
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Post by 190mech on Jan 21, 2016 19:20:58 GMT -5
Here we are thread jacking again!As of today,primary compression needs to be as low as possible as the exhaust is the key to pulling the mixture through,even into the exhaust port and then pushed back into the cylinder before the exhaust port closes..This only works well if the setup has ample transfer ducts,pointed in the right direction with an induction system that'll feed all this crazy nanosecond happening...If we are working with 60's technology(like lots of scoots),then its "polish that turd till it shines!".. A bit on the RS125 step here; www.bonavolta.ch/hobby/en/moto/rs125r.htm |
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Post by PIG on Jan 21, 2016 19:42:11 GMT -5
I matched up the transfers and boost ports and cleaned up some rough casting marks these cases have. Nothing really special, but every little bit helps. With a gasket on you can see what needs to go  Marked out and ready to cut  Matched up  All cleaned up, and cranks installed.  |
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Post by sublunacy on Jan 21, 2016 19:59:31 GMT -5
the primary compression balances the length of the powerband only.
the only way to tell for sure is the output. if it pukes power all at once- the primary compression is to low. if it takes to long to reach peak torque and hp- the primary compression is to high.
when primary compression is to high- it is very inefficient as alot of intake charge gets wasted by the limited strength of the returning pulse.
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what does this mean for us that are building engines.? dont mess wth a good thing. malossi for example-----
the 70cc sport is optimum for 8ft/lbs at 8000rpm with a non hpc crank.
the 70cc mhr/mhr team is optimum for 12ft/lbs at 12000rpm with a hpc crank.
malossi does not do midrace period. the transfers are identicle in size between the two cyls. the tranfer height changed alot so an hpc crank is needed for the mhr cyl to return the balance to the primary compression.
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based on these two examples/ logicaly you should expect a midrace cylinder to make 10ft/lbs at 10000rpm.
can this be done? ABSOLUTLY YES-
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Post by 190mech on Jan 21, 2016 20:00:59 GMT -5
Lookin' Good!!  |
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Post by PIG on Jan 22, 2016 15:00:07 GMT -5
What do you guys think, ditch the autolube or keep it? I'm guessing this set up will run in the 11,000-11,500rpm range. To me that's the upper limits of these little pumps. But I'm no expert when it comes to these pumps so what do you guys figure?
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