Temple for the tuners?

KR-1R · Post by **KR-1R** » Wed Jan 16, 2013 4:23 am

.
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doesnt a long rod increase the port-time area over the stroke?
(mathematical integration? of variable linear velocity in the stroke or sumting')
as well as reducing piston loading on the bore?

however
the '90 KX125 has a shorter barrel (maintaining the same 50.6mm stroke) than the KR so doesnt that indicate it has a shorter rod - 38PS = 70hp twin
or does it have deeper cases?

when I want to be confused I refer to the KiwiBiker misinformation thread "ESE's works engine tuner" and see whose swinging (Fritz, Jan, Wobbly)

http://www.youtube.com/watch?v=GZa_5k937hg

all the big guys swing there

JanBros · Post by **JanBros** » Wed Jan 16, 2013 8:02 am

KR-1R wrote:.
.
doesnt a long rod increase the port-time area over the stroke?
(mathematical integration? of variable linear velocity in the stroke or sumting')
as well as reducing piston loading on the bore?

I know a longer rod decreases piston-acceleration in TDC and BDC, so if the acceleration is slower, it means it spends more time there meaning your port-time increases

dave32 · Post by **dave32** » Wed Jan 16, 2013 2:18 pm

Great find thanks for posting

Only half way through it but i like the way these guys (Fritz and Jan) worked,apply logic and experiment,dont take anything for granted.
Shame GP's went 4stroke

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Im still lost on the "boost port" opening,my TZ opens as TSI says is the way to go,the KR (as stock doesnt),maybe due to one being developed for max performance and the other as a road bike,the lower main port allows for better idling and low down power?

TwoStroke Institute · Post by **TwoStroke Institute** » Thu Jan 17, 2013 2:37 am

mj43 wrote:In TSI's usual style unhelpful as ever. In the spirit of Frits Overmars an explaination would be useful. What Dan has posted seems perfectly reasonable.

Also have you decided whether 120mm rods are appropriate for a motor with a 50.6mm stroke?

I can't make anyone accept advice or answers, I can only offer the info. Frits is far smarter and has more time than me.
Might be 'reasonable' but it's not what happens in practice is it?
120mm rod I dunno but lets try it and find out, hmm maybe not the 120mm rod is only for a 24mm crank pin so have to settle for 118mm.

Difference between long and short rod port timing is minimal (a few deg either way) dwell at TDC longer ans shorter at BDC, slower down and faster up. Side thrust is way less but more torque either side of band is what you notice.

No more boost port Dave that's the Cport, then go round to B an A near the exhaust. The main exhaust opening first is just better all round, every manufacturer who has a triple port does it that way. Why would a sport bike be developed to idle well?

maccas · Post by **maccas** » Thu Jan 17, 2013 9:42 am

Dave meant the auxillary exhaust port Lozza not the c transfer port.

Have you converted a kr cylinder so that the main opens first? Do you havea dyno curve showing the results that you would be willing to share?

My cylinder with that porting arrangement made shit power and no bottom end compared to a stock cylinder.

Plus the curve goes up at a steeper incline due to the taller main port.

Dan

dave32 · Post by **dave32** » Thu Jan 17, 2013 1:55 pm

Ahh you know what i meant (exhaust boost ports)

,
Im just thinking out loud,a higher main exhaust port in most road going/sports 2 strokes usually results in LESS low down power,something thats needed on a road use engine.
The main port is open all the time and non variable on the KR,the sub/boost ports are closed to the exhaust duct until 8500rpm (there abouts) so if we just RAISED the main we will almost ceratainly lose low and possibly midrange power,taking into consideration the rest of the porting layout/ignition system etc i cant see it being a good idea to move the main any further up,unless the rest of the layout/port timing is radically altered.
I know what works on the aprilia GP engines (as Jan and Fritz have explained) but i dont think you can just take some of them ideas and apply them to ANY engine as the design is already set so you can only improve what your stuck with,make sense?

Im hoping someone can show me the error of my ways though.

Afterthought,i think any engine thats developed for road use (KR1) is a compromise (it has to be ),it has to IDLE,start easily,put up with trundling along in a high gear etc etc,if your developing or designing an race engine none of that really applies.
what other triple exhaust port design on any road engine produces better more useable power than the KR1,i cant think of any as it is the best (in standard form there is performance wise
Dave

TwoStroke Institute · Post by **TwoStroke Institute** » Fri Jan 18, 2013 3:27 am

maccas wrote:Dave meant the auxillary exhaust port Lozza not the c transfer port.

Have you converted a kr cylinder so that the main opens first? Do you havea dyno curve showing the results that you would be willing to share?

My cylinder with that porting arrangement made shit power and no bottom end compared to a stock cylinder.

Plus the curve goes up at a steeper incline due to the taller main port.

Dan

I would have to get permission from the dyno owner first. In every case when I've done that the owner hasn't put it back or asked for it to be put back the way it was. It is a not a matter of just raisng the main port, when you do it properly, you get more and a better spread of power. I certain I've explain what I do on here(where you posted all the port rubs)

TwoStroke Institute · Post by **TwoStroke Institute** » Fri Jan 18, 2013 3:50 am

dave32 wrote:Ahh you know what i meant (exhaust boost ports) ,
Im just thinking out loud,a higher main exhaust port in most road going/sports 2 strokes usually results in LESS low down power,something thats needed on a road use engine.
The main port is open all the time and non variable on the KR,the sub/boost ports are closed to the exhaust duct until 8500rpm (there abouts) so if we just RAISED the main we will almost ceratainly lose low and possibly midrange power,taking into consideration the rest of the porting layout/ignition system etc i cant see it being a good idea to move the main any further up,unless the rest of the layout/port timing is radically altered.
I know what works on the aprilia GP engines (as Jan and Fritz have explained) but i dont think you can just take some of them ideas and apply them to ANY engine as the design is already set so you can only improve what your stuck with,make sense?
Im hoping someone can show me the error of my ways though.
Afterthought,i think any engine thats developed for road use (KR1) is a compromise (it has to be ),it has to IDLE,start easily,put up with trundling along in a high gear etc etc,if your developing or designing an race engine none of that really applies.
what other triple exhaust port design on any road engine produces better more useable power than the KR1,i cant think of any as it is the best (in standard form there is performance wise
Dave

As above, lower the cylinder, so the subs sit where the man previously was, then raise the main up to where the subs first opened. Not radical at all, lets you fix the transfers as well.
Go back and read Pit Lane carefully about what happens with the roof of the main.
More Blowdown =more HP.You CAN take any of the apsects of the Aprilia engine and apply it to any 2 stroke and IT WORKS. I've applied to 70cc chainsaw engines and air cooled 125 VMX engines. The KTM50cc cylinder is a direct copy of the Aprilia cylinder, with 22HP regularly pumped out of them. To get a genuine 50HP at the wheel from a 125 needs every trick in the book.
The 250 2T were all developed as race bikes that would be ridden on the road(win on Sunday sell on Monday), where did I put that Virago 250 race kit?

KR-1 has a 10,500 peak opposed to the rest of the 250's with 11,500 which is always going to make a better road engine. TZR has a triple port and the most restriced cylinder has great potential.
The pipe has the biggest influence on peak rpm not the exhaust port. In a kart that has peak at 13,000 with over rev to 14,200 we open the exhaust at 86deg ATDC has a short fat pipe to help it rev.

Top-shaggy · Post by **Top-shaggy** » Fri Jan 18, 2013 9:03 am

TwoStroke Institute wrote:...
You CAN take any of the apsects of the Aprilia engine and apply it to any 2 stroke and IT WORKS. I've applied to 70cc chainsaw engines and air cooled 125 VMX engines. The KTM50cc cylinder is a direct copy of the Aprilia cylinder, with 22HP regularly pumped out of them. To get a genuine 50HP at the wheel from a 125 needs every trick in the book.

Sorry to invade this excellent discussion but I would still like to know how this will work with the AR125 disc valve engine especially in respect of the exhaust port matching that of the Aprilia.. The discussion on this TSI ended a year ago when I sent you a barrel and piston to look at. Hope you have found a way to upgrade the barrel etc ? Please let me know.

It was so long ago I had to go looking for the thread
viewtopic.php?t=7744&postdays=0&postorder=asc&start=15

mj43 · Post by **mj43** » Fri Jan 18, 2013 12:35 pm

TwoStroke Institute wrote: As above, lower the cylinder, so the subs sit where the man previously was, then raise the main up to where the subs first opened. Not radical at all, lets you fix the transfers as well.

That means dropping the barrel by 1mm and lifting the main exhaust port by 2mm. Based on what has been said it would be better to get some longer rods on your crank and then lift the barrel appropriately. This has two benefits a) it stops you weakening the barrel as shortening will mean it will crack. b) longer rods appear to be the way to go for added performance

For rods 109mm KDX200/220 or I suspect that Banshee 110mm rods will work. Both move you closer to the rod length/stroke ratio that Jan Thiel indicates seems to be the sweet spot.

By effectively dropping the barrel you will reduce your transfer port timing so they will need raising to get you back to stock.

You will also have a problem with the bottom of the port not aligning with the piston. Frits Overmars mentioned that this was important as it contributes to flow staying attached to the piston at BDC and helps piston cooling.

dave32 · Post by **dave32** » Fri Jan 18, 2013 2:15 pm

So am i right in assuming the PIPE design and PORTING layout is what restricts the KR to 10,500rpm and nothing to do with the ignition curve (which always seem to be variable from bike to bike)?
So if we lower the cylinder and raise the ports to bring them back to where they were in relation to opening/closing points (with increased duration) then bringing the main above the subs by a small amount (1mm max) will increase the HP or PEAK rpm?
What do we do about having the piston crown sitting below the exhaust port at BDC?
Cheers

mj43 · Post by **mj43** » Fri Jan 18, 2013 2:47 pm

Dave if the cylinder is lowered the crown will sit above the bottom of the exhaust port. It already does so by about 2mm this will just increase it to 3mm.

dave32 · Post by **dave32** » Sat Jan 19, 2013 12:21 am

Yes your right of course it will

TwoStroke Institute · Post by **TwoStroke Institute** » Sun Jan 20, 2013 2:14 am

Top-shaggy wrote:
Sorry to invade this excellent discussion but I would still like to know how this will work with the AR125 disc valve engine especially in respect of the exhaust port matching that of the Aprilia.. The discussion on this TSI ended a year ago when I sent you a barrel and piston to look at. Hope you have found a way to upgrade the barrel etc ? Please let me know.

It was so long ago I had to go looking for the thread
viewtopic.php?t=7744&postdays=0&postorder=asc&start=15

I managed to get a very close approximation of the RSA cylinder into the humble AR barrel

The complete cast iron cylinder was a road block I didn't expect, it's out at my mates who has the proper cast iron welding rods and heaps of experience in welding cast iron. I'll prod him on Monday(price you pay for getting things done for free eh).Should have a nice upgrade regarding this disc too but more on that later..........

MJ if you raise the barrel with a spacer and use a longer rod,the port timing will still be basicaly the same, I did say "fix the transfers" and check what "stucco verde" is

I'm thinking the barrel is cracking because of that tiny radius where the pad meets the cylinder. I will be making a large gusset to go from outside the pad to the cylinder in a big radius. Only been saying since 09 that a longer rod is beneficial.
Dave if the pipe is the same peak rpm should be the same.

mj43 · Post by **mj43** » Sun Jan 20, 2013 8:01 am

TwoStroke Institute wrote: MJ if you raise the barrel with a spacer and use a longer rod,the port timing will still be basicaly the same, I did say "fix the transfers" and check what "stucco verde" is
I'm thinking the barrel is cracking because of that tiny radius where the pad meets the cylinder. I will be making a large gusset to go from outside the pad to the cylinder in a big radius. Only been saying since 09 that a longer rod is beneficial......

3mm longer KDX200/220 rod and a 2mm spacer has exactly the same effect as lowering the barrel by 1mm with the benefits I mentioned earlier. I just happen to have a crank like that

and may try testing your theory but I would like to see that dyno curve first and do a bit more reading before I possibly waste a set of barrels.

"stucco verde" for those that haven't read the Pitlane thread is the name for the filler used at Aprilia. What would be useful is info on where to buy it.

On cracking I agree that is part of the problem but as soon as you weld you distort the barrel and end up skimming the bottom of the barrel to get it flat again.