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?
cdoggy81
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cdoggy81 4/8/2019 5:36am
4/8/2019 5:36am
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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
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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
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cz511atk604
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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
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mark911
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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.
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Roberdj3
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Roberdj3 1/7/2025 7:34am
1/7/2025 7:34am
Webby130 wrote:
Hi all I’m looking to build a power house cr125 engine. But I’m unsure we’re to start with what year engine Or what year bottomend to...
Hi all I’m looking to build a power house cr125 engine.
But I’m unsure we’re to start with what year engine
Or what year bottomend to topend I have been told a couple different ways to go.

First idea is
1996 cr125 bottomend with the 1996 cylinder
But usinging the 1998 cr125 power valves

Second idea
98 motor with Six speed box wider transfer ports standard than the earlier models and tune cylinder send it to Steve clithero
With an hpi ignition 37mm carb

Any comment I will read and take not of what the best idea is to get the most power out of a cr125 engine

The 1992 barrel had the most aggressive porting so id start with that.

1998 power valves had a better sealing design. Very hard to get though.

Messico or spes exhaust makes a massive difference. There is a European guy called Nino who has tested every single pipe and he recommends messico as the best.

He also bores the carb out the 38mm.and puts a stronger power valve spring in to compensate for the bigger carb delaying the power higher in the revs.

1997 ignition has the most advance curve And gives the bike more snap.

 

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cz511atk604
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cz511atk604 1/8/2025 3:29am
1/8/2025 3:29am

MIss & a Hit  Thousand s of cyl & heads                         2 yrs In R&D testing the Newly designed Honda cr125 engine package slated for production  1/2 years qthe Japanese 125 2 stroke Engineer's working 3 Shifts 24 hrs a day along side a wall of workers grinding on blank cylinders Strict Deadlines are followed  Decisions & choices finalized on no less than 4 different cyl head ported combos  they choose the Newly developed engine package most likely to increase raceable hp each year  On a 4 yr production run  

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cz511atk604
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cz511atk604 1/10/2025 6:43am
1/10/2025 6:43am

The 2nd eng package 98

 it's all there, order the billet exhaust flange and Euro Messico Pipe/Silencer There's your Power house, I like 6 gears,V force intake ,Power Now wing and lite weight alum friction plates. Electric water pump,vortex igniter adj mapping , Hot Wire spark wire ,38 mm Kehein pkw /stic carb ,Carrillo rod & stroked balanced  crank,2 mm bore =140cc ,Wiesco Lite piston.  Use only the 97 ignition with 97 crank it's in the  tapering fit.  add a old school boost bottle  and Micro Nitrous Burst .   

MX 88 kg twin pipe CRR150r rotary induc fi 2x2 stroke 

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