ESE's works engine tuner

[wobbly]

I have seen all manner of varying results from piston holes and Boyesens and floor ports etc etc.
But what I know now is that I can totally trust the result from the STA calculation made by EngMod.
The need for holes in the piston are totally dependent on the power ( read air flow requirement ) level being achieved.
For example the 400cc Banshee based cylinder from CPI does not need any holes at all until you approach 50 Hp ( crank ) per cylinder.
Under that and there is enough flow available thru the rising piston skirt area and Boyesens, over that and the extra flow inertia thru the reedblock
will work in concert with the piston cutouts to fill the case as is needed to make the extra power..
Things like the NS400 dont need big holes as the power level, thus bulk flow needed, is so low.

[SwePatrick]

I also think it´s depending on rpm.
The more rpm you want, the more easy you need to make it for the air to completely fill the crankhouse, even thou you have the same carb size.

[diesel62]

I have seen all manner of varying results from piston holes and Boyesens and floor ports etc etc.
But what I know now is that I can totally trust the result from the STA calculation made by EngMod.
The need for holes in the piston are totally dependent on the power ( read air flow requirement ) level being achieved.
For example the 400cc Banshee based cylinder from CPI does not need any holes at all until you approach 50 Hp ( crank ) per cylinder.
Under that and there is enough flow available thru the rising piston skirt area and Boyesens, over that and the extra flow inertia thru the reedblock
will work in concert with the piston cutouts to fill the case as is needed to make the extra power..
Things like the NS400 dont need big holes as the power level, thus bulk flow needed, is so low.

So why don't KZ2 have holes in their piston?

Sent from my SM-G900F using Tapatalk

[wax]

Thats interesting you say that wobbly. I am looking to get to about 90 out of the cylinder im using. I will maybe look at cutting the skirts up to start with in the mill.
It would make a more reliable piston and hey im interested in that. We are going to the world finials in havasu and the last thing i need is a damaged piston while i am over there.
My boysen ports are small compared to the ones shown before but the cpi are closer, I will look into making my boysen ports flow better. I also notich these cylinders have a large lump in the sides by the side of the reed block. I did read before where you were talking about flow from the side of the reed and I was thinking how this may effect it

[F5 Dave]

Jeez mate! What kind of cpi barrel is that?, certainly not a Cheetah.

[wobbly]

Not sure of the reason behind such a dumbarse question,but I will bite.
A KZ2 is a case reed setup, so no flow thru the piston at all.
And yes i have tried cutting a hole thru the boost port inner duct wall to align with a slot in the piston skirt.
This worked years ago on the original Rotax tandem twin, but the TM has a much better duct entry geometry, so no free lunch there.

[diesel62]

Not sure of the reason behind such a dumbarse question,but I will bite.
A KZ2 is a case reed setup, so no flow thru the piston at all.
And yes i have tried cutting a hole thru the boost port inner duct wall to align with a slot in the piston skirt.
This worked years ago on the original Rotax tandem twin, but the TM has a much better duct entry geometry, so no free lunch there.

Thanks that is where I was heading. Just didn't word correctly

Sent from my SM-P555 using Tapatalk

[peewee]

i wonder if anyone has done piston window tests on engines using methanol or nitro where there might be 2-4 times more fuel passing through the engine ?

[katinas]

I have seen all manner of varying results from piston holes and Boyesens and floor ports etc etc.
But what I know now is that I can totally trust the result from the STA calculation made by EngMod.
The need for holes in the piston are totally dependent on the power ( read air flow requirement ) level being achieved.
For example the 400cc Banshee based cylinder from CPI does not need any holes at all until you approach 50 Hp ( crank ) per cylinder.
Under that and there is enough flow available thru the rising piston skirt area and Boyesens, over that and the extra flow inertia thru the reedblock
will work in concert with the piston cutouts to fill the case as is needed to make the extra power..
Things like the NS400 dont need big holes as the power level, thus bulk flow needed, is so low.

Yes, std. NS 250/400 power level not very attractive, around 24 hp. from one cylinder on crank. Tuned versions around 30 hp. Bad thing is that this cylinders reeds house is very limited.
Some time ago, I write off this cylinders and bought TZ 250 DP4 01 02 ones for this engines, because studs mismatch with NS just 0,5 mm! And TZ barrels are very short from plane to plane, so it is possible to made 22-25mm spacer plate with big reed house. I prepare all things for this work, but suddenly, I don't know why, return to NS barrels, maybe because feels that not finished work from my racing days with Honda NS-250. I consciously restrict myself with this restricted barrels, and trying found something.

Honda NS 250 was my first Japanese motorcycle that, I bought in 1998 with Sugaya racing pipes. Engine was seized so I have no opportunity to try how it works. Prepare NS just for racing , but made some very big mistakes. It's pity, that was not two stroke man around to clear some things, at this time.
Made new pistons with holes, and modifying cylinders cooling with additional tube directly under exhaust duct (add photo of this old modified cylinder and piston), where Honda, for some unknowing reasons, left free space for air under ex duct .
The biggest mistake was compression, and this is very clear seen on piston dome and of course too much skimmed heads. Four big seize, nearly max speed, and one ended badly because of the rain, no time left to react. Later when I measured head volume, found 1:19 compression with RON 98!!! Until now I can't understand how I finished some of races, maybe additional cooling under duct help, and very rich mix. Remember, that speed was very similar to standard street Aprilia RS 250. But it was long time ago.

Maybe it's difficult to imagine, but the first Japanese motorcycle that I saw on the road in Lithuania, was around 1994, and this was Suzuki GSX-R 400

[F5 Dave]

Keep posting. I just love your passion.

[SwePatrick]

i wonder if anyone has done piston window tests on engines using methanol or nitro where there might be 2-4 times more fuel passing through the engine ?

My experiance was with methanol, i forgot to mention =)

[SwePatrick]

I also notich these cylinders have a large lump in the sides by the side of the reed block. I did read before where you were talking about flow from the side of the reed and I was thinking how this may effect it

This lump kills dead volume, good things happen =)

[acr]

Adding a 0.47mfd/200V cap across the trigger will create around 1*/1000 rpm retard.
So with around 6mm static I think it stared at 35* and by 10,000 it had 1.6mm = about 17*from memory
Thus the old pretty much straight line became a crude retarding unit, with extra mid advance for drive, and extra retard over the pipe for overev.

Wobbly is the cap an AC version or a DC cap and would a adjustable cap work to dail in the value needed

[peewee]

wob today im making new exh spigot. where it mates to the cylinder face is oval hole. do you maintain the oval shape through the spigot to the exit or you transition the oval into a round shape at the exit ?

[wobbly]

The cap I used was a Mylar ie DC type.
The value has to be fixed as you need to strobe the running system and create a reference set of marks to give you
the correct advance at one particular rpm.
On a TZ the original timing was 1.6mm and the original marks lined up at 10,000 rpm
The .47 on a TZ trigger worked the best, any bigger didnt retard any more /1000 and less gave less retard.
With the varying trigger inductance and static resistance of other model bikes, you would need to use s strobe on a variable rpm test bench like I did.

Re the add on spigot - yes transition from the oval port exit to the round header entry.