ESE's works engine tuner

[andreas]

The point, I think, is not that far fetched: Why not use a 180 front tire if it offered a substancial increase in grip-50% wider, it should more than well make up for a more cumbersome stearing that could be adapted by the riders and also the frame geometry.

[HenkS]

Would you mind telling us why "75% can't be good !" Henk?

Much to round and besides it does't look at all to the rouding of that blue and red example.
Peewee makes the drawing just right 75% of 64 mm is R48
100% R64, comes closer to that blue/red example.

[Frits Overmars]

What about those 75%, I did not read any reply on that. 75% can't be good !

Would you mind telling us why 75% can't be good Henk?

Much to round and besides it does't look at all to the rouding of that blue and red example.
Peewee makes the drawing just right 75% of 64 mm is R48. 100% R64, comes closer to that blue/red example.

If I understand you correctly, you say it can't be good because it doesn't look good. I think Peewee deserves a more substantiated reaction.

im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.

The port roof center radius of 75% of the bore is valid for a port width of 70% of the bore. For a 64 mm bore that means a port width of 44,8 mm, not 45,5 mm, and certainly not 51 mm, as shown in your drawing.
The FOS port shape concept was developed for port designing, not for template drawing. If you stretch chord widths to arc lengths, everything is pulled out of proportion and the radius percentages no longer apply.

In order to help Peewee out I briefly considered extending my port shape concept to be suitable for creating templates. But firstly, it's not really that simple, and secondly, I don't want to encourage the use of templates, not paper ones anyway. I never used one. At the end of the day you still have to work with the chord width of the port.

[TZ350]

2Stroke Stuffing.



Supercharged 50cc is Alive! Angry, Spitting Flames!

Looks like Alex has put the rotary exhaust valve project aside for the moment and has moved onto supercharging a more conventional 50.

[HenkS]

If I understand you correctly, you say it can't be good because it doesn't look good. I think Peewee deserves a more substantiated reaction.
The port roof center radius of 75% of the bore is valid for a port width of 70% of the bore. For a 64 mm bore that means a port width of 44,8 mm, not 45,5 mm, and certainly not 51 mm, as shown in your drawing.
The FOS port shape concept was developed for port designing, not for template drawing. If you stretch chord widths to arc lengths, everything is pulled out of proportion and the radius percentages no longer apply.

In order to help Peewee out I briefly considered extending my port shape concept to be suitable for creating templates. But firstly, it's not really that simple, and secondly, I don't want to encourage the use of templates, not paper ones anyway. I never used one. At the end of the day you still have to work with the chord width of the port.

Peewee, my translation of this answer is a little simpler,
Because everyone works like you with portmaps, so change that 75% as I wrote earlier to 100% and the problem is solved.
You actually see it quite easily, but if you calculate it, then that 100% is within 1% deviation. And that counts for every bore.
And mm to top of cilinder don't change between portmap and cordural .

[wobbly]

Husa , I have to disagree about bike tyre width not generating more grip , based purely on actual experience.
The Frepin TZ400 I built for Denis originally had a rear soft treaded 110/18 Avon as mandated by Post Classic Junior rules.
Later the swingarm was changed and an Avon AM23 soft 130/18 special construction rear was fitted , specifically designed to fit on the now way to narrow rim.
This generated so much rear grip the whole front end geometry , and the front tyre changed from a 90 to a 110 to get it to steer , and it dropped the Junior lap record at Hampton by nearly 2 secs.

Then the Aprilia Cup Bike with a RZ400 for Superlight in it , originally had a soft 150/17 rear tyre , this was changed to a soft 180/17 and again it needed huge changes in geometry to balance the grip levels.
Sure there will have been differing carcass construction etc , but absolutely the wider rear tyre generated way more corner grip, and it to broke the lap records at Hampton and Ruapuna.

[peewee]

Peewee, my translation of this answer is a little simpler,
Because everyone works like you with portmaps, so change that 75% as I wrote earlier to 100% and the problem is solved.
You actually see it quite easily, but if you calculate it, then that 100% is within 1% deviation. And that counts for every bore.
And mm to top of cilinder don't change between portmap and cordural .

thnks henk i like a simple answer

[husaberg]

Husa , I have to disagree about bike tyre width not generating more grip , based purely on actual experience.
The Frepin TZ400 I built for Denis originally had a rear soft treaded 110/18 Avon as mandated by Post Classic Junior rules.
Later the swingarm was changed and an Avon AM23 soft 130/18 special construction rear was fitted , specifically designed to fit on the now way to narrow rim.
This generated so much rear grip the whole front end geometry , and the front tyre changed from a 90 to a 110 to get it to steer , and it dropped the Junior lap record at Hampton by nearly 2 secs.

Then the Aprilia Cup Bike with a RZ400 for Superlight in it , originally had a soft 150/17 rear tyre , this was changed to a soft 180/17 and again it needed huge changes in geometry to balance the grip levels.
Sure there will have been differing carcass construction etc , but absolutely the wider rear tyre generated way more corner grip, and it to broke the lap records at Hampton and Ruapuna.

Hi I am not sure i said that?
Was that something Kevin Said or in the question to Kevin?
i thought Kevin said pretty much what you had said? which was what i said rather clumsily
I said the simple physic's of the sliding object in an equation doesn't take into account all the variables or words to that effect.

[F5 Dave]

Great so we are back to where we hopefully started. Friction is all very well, but rubber in shear deforms as it tries to smear itself on the concrete, if only just a little, and bites into all the little irregularities.

[TZ350]

2Stroke Stuffing.



Ever more promising. I am looking forward to seeing some data from a couple of good runs with the supercharged setup.

[ken seeber]

OK fellas, feel rewarded.

Give yourselves a pat on the back for all those tuning tips, STAs, RADs, exhaust temps, port staggers, jetting etc etc that you have been giving to Wobbly over the years.

Look closely at the pic.

[lodgernz]

OK fellas, feel rewarded.

Give yourselves a pat on the back for all those tuning tips, STAs, RADs, exhaust temps, port staggers, jetting etc etc that you have been giving to Wobbly over the years.

Look closely at the pic.

I manned the recovery quad on the qualifying day, and those guys were just flying. Well done Wobbly!

[wobbly]

Thanks Ken and Lodger , the guy in 3rd place has a Wobbly sticker as well.
The author forgot to mention Mat is a 10 times National Champ , getting the double digit was the goal in the weekend.
He isnt as old nor as good looking as me , but 2 little kids and a business taking over much of my engine building work probably means he wont contest any more - sad really as he is one
of the best kart peddlers I have ever seen or tuned for.

Edit , be real interesting the see what happens this weekend at the World Cup in LeMans , the factory TM will have some of the new homologation legal parts on board that next years KZ R2 will have.

[HenkS]

thnks henk i like a simple answer

Unnecessarily complicating is also a way.
The red/blue example is very misleading, because nowhere does it say that the 75% cordural should be measured.
Everyone I meet on the internet works with portmaps and applies that 75% to a portmaps.
And mm to the top of the cylinder are therefore also the best to check, so certainly templates are possible.

And not unimportant to know that that 75/100% is also just an approximation.
I have seen successful examples that had a radius of over 200% and were also wider than that 70% and had still not suffered any damage after years. Good gate edge rounding is a condition here.

[wobbly]

Frits makes the assumption we all know the measurements are chordal , its like trying to convince a cop the 100 sign on the side of the road you thought were mph as opposed to kmh.
And he has tried to give a guide for all bore sizes , we all know small bores down at 40mm are a special case and will tolerate more than 70% with ease , but anything with R200 and more than 70% would have
to have huge corner rads , but then its already well departed from anything approaching the mechanically possible " optimal " Blowdown geometry.