Building the ultimate cr125 engine

Jrewing
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Jrewing 4/8/2019 4:31am
4/8/2019 4:31am
Jrewing wrote:
Tm runs T ports!! You’d have thought 3 port exhaust was superior and they’d run that?
Derek Harris wrote:
They do for kart engines But at the power it has production - exceeding that of the ktm (or about on par with new 19) I...
They do for kart engines

But at the power it has production - exceeding that of the ktm (or about on par with new 19) I think they don't want the headache of the powervalve complexity...

The transfers are fantastic - and obviously where the power comes from vs a yz or ktm
What’s the shape of the exhaust port to exhaust spigot like?
Derek Harris 4/8/2019 1:28pm
4/8/2019 1:28pm
Jrewing wrote:
Tm runs T ports!! You’d have thought 3 port exhaust was superior and they’d run that?
Derek Harris wrote:
They do for kart engines But at the power it has production - exceeding that of the ktm (or about on par with new 19) I...
They do for kart engines

But at the power it has production - exceeding that of the ktm (or about on par with new 19) I think they don't want the headache of the powervalve complexity...

The transfers are fantastic - and obviously where the power comes from vs a yz or ktm
Jrewing wrote:
What’s the shape of the exhaust port to exhaust spigot like?
Like a yz/rm t port motor

Jrewing
Profile picture for user Jrewing
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AU
Jrewing 4/8/2019 6:01pm
4/8/2019 6:01pm
Derek Harris wrote:
They do for kart engines But at the power it has production - exceeding that of the ktm (or about on par with new 19) I...
They do for kart engines

But at the power it has production - exceeding that of the ktm (or about on par with new 19) I think they don't want the headache of the powervalve complexity...

The transfers are fantastic - and obviously where the power comes from vs a yz or ktm
Jrewing wrote:
What’s the shape of the exhaust port to exhaust spigot like?
Derek Harris wrote:
Like a yz/rm t port motor

Interesting that it has the power of a KTM when KTM go to so much effort CNC’ing the exhaust port.

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Derek Harris 4/8/2019 7:18pm
4/8/2019 7:18pm
Jrewing wrote:
What’s the shape of the exhaust port to exhaust spigot like?
Derek Harris wrote:
Like a yz/rm t port motor

Jrewing wrote:
Interesting that it has the power of a KTM when KTM go to so much effort CNC’ing the exhaust port.
They CNC a small part where bore and exhaust valve meet. If you got a "good one" of the 18's it was same as the 19
profeshenal125 4/5/2022 5:41am
4/5/2022 5:41am
Derek Harris wrote:
While the mid 90's engine have a strong reputation - I think people would be surprised just how good the 05-07 can be We are working...
While the mid 90's engine have a strong reputation - I think people would be surprised just how good the 05-07 can be

We are working on a full works build 97 - custom mapped hpi to suit
But the base cylinder and engine in all stock, rebuilt form - only produced 30 hp on my dyno, it was quite sad vs modern engines
I have a 05 engine to drop in a 04 chassis. What are the secrets to getting a quick responding strong and wide mid range pulling into the top end engine ? Thx
2
cz511atk604
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6/14/2022
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Palmdale, CA US
cz511atk604 6/14/2022 10:16pm
6/14/2022 10:16pm
Tassari reed block,pro cir porting & head ,jd jet kit& dial a jet kit,pro cir pipe & shorty sil,gearing ,race gas,hpp 32.1, German piston kit every 7 hrs,hold it wide open ! Oh add 2 mm header flange
1
mark911
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Ashville, OH US
mark911 6/16/2022 9:49am
6/16/2022 9:49am
Nobody really knows how a two stroke works (the multi physics from air box to exhaust tip). Even the most sophisticated finite element multi-physics simulation programs can't even figure it out, otherwise, everyone would be making similar numbers. The real trend setters (in motoGP) spent literally thousands of hours experimenting with different theories going through hundred of cylinders/heads, fuel systems, exhaust, resonating air boxes, and all sorts of crazy ideas just to gain a few tens of a HP (at 15-19,000 rpm) and it's always a compromise. You rarely, if ever, gain across the board. And these were guys that did this at the factory level 24/7. They'll be the first to admit that simple cut and try is the only real way they made advances and that's probably still true even today, and that takes time and resources.
There is antidotal evidence (if this then that) that truly experienced tuners use, but 90% of the time they don't know why so it's not always transferable from engine to engine. So it's hit and miss.

EFI is a good step forward but direct injection would be much better. Maybe another 5 years.
2

Pit Row

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