Building the ultimate cr125 engine

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9/12/2018 2:28 PM

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

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9/12/2018 3:50 PM

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

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9/12/2018 4:18 PM

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 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

So you are saying to build one with a 2005 to 2007 engine..?

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9/12/2018 4:23 PM

Depends on what your going for

If you already have an 05-07 - it may perform better than you'd expect vs transplanting a mid 90's engine and building that.

but - if you have a mid 90's engine - it CAN perform well too

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9/12/2018 7:12 PM

Put a ktm or yz 125 motor In and save your self a lot of time and money.

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9/12/2018 7:33 PM
Edited Date/Time: 9/12/2018 7:34 PM

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 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

What’s the weak link to the hpp? Power valve design, angled intake and air boot, short crank?

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9/13/2018 8:15 AM

Most power improvements over the years has come from scavenging gains, its these gains that pushed the aprilia to 55 hp out of 125cc when honda was in the gps at 45


This is too hard to accurately describe in a short time - and as Ive seen on a T shirt that sums up my experience in (not) understanding this - I can (try) to explain it for you, but I cant understand it for you

2 strokes are insanely complex despite their mechanical simplicity - with enough time and effort most engines can produce good power - but some of that time and effort may also include some welding/redesigning of a lot of variables - and sometimes its not worth the time or money to make one project good

The hpp powervalve sucks
Rod length is similar to yz - usable, angled intake isnt ideal but can work ok for mx application.

Im working on one fairly heavily soon - with a goal around 40hp. All new stock with 4 different pipes tested it was 30... will be some hmwk to make it happen.

If I figure it all out - ill post some details

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9/13/2018 1:48 PM
Edited Date/Time: 9/13/2018 1:49 PM

Well that's exactly where I'm at on my hpp 125. I love it but finding the competitive hp v cost/time debate is favouring another bike.
How much do TM144's Dyno at stock?

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9/13/2018 2:15 PM

Scotty Haynes has the port maps for the plano Honda set up. Problem is have the pipe. Performance factory he’s in Dallas.

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9/13/2018 3:38 PM

Jrewing wrote:

Well that's exactly where I'm at on my hpp 125. I love it but finding the competitive hp v cost/time debate is favouring another bike.
How much do TM144's Dyno at stock?

A lot more than the honda wink

We recently had the full PC team spec motor here at 33.5 or so on a 1991 If I remember right

It wouldn't be hard to be 35-36 - that's easy.

And the pipe thing - isn't too hard either - but to be where a modern ktm is at - would be nearly impossible

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9/13/2018 4:15 PM

Jrewing wrote:

Well that's exactly where I'm at on my hpp 125. I love it but finding the competitive hp v cost/time debate is favouring another bike.
How much do TM144's Dyno at stock?

Derek Harris wrote:

A lot more than the honda wink

We recently had the full PC team spec motor here at 33.5 or so on a 1991 If I remember right

It wouldn't be hard to be 35-36 - that's easy.

And the pipe thing - isn't too hard either - but to be where a modern ktm is at - would be nearly impossible

Well that's it. 35hp isn't going to pull my 84kg well enough against 65kg 250f riders. But I'm having fun trying.
Keen to follow your results with the modified CR project you're doing. Sounds like a lot of welding and devcon.

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9/13/2018 4:36 PM
Edited Date/Time: 9/13/2018 4:36 PM

Seems to be cheaper just put a ktm motor in it. Sadly I love Honda’s and that would be my next option. I just decided to go orange. Although, a ktm motor in a Honda frame would be the ultimate. Even today my 17’ 150 does not handle like a Honda cr 125.

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9/13/2018 5:15 PM

CrGuy2T wrote:

Seems to be cheaper just put a ktm motor in it. Sadly I love Honda’s and that would be my next option. I just decided to go orange. Although, a ktm motor in a Honda frame would be the ultimate. Even today my 17’ 150 does not handle like a Honda cr 125.

That's the other thing the Honda is my best handling bike I've had.

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9/13/2018 5:47 PM

Jrewing wrote:

That's the other thing the Honda is my best handling bike I've had.

If I ever build another Honda I would just put a 15 Ktm 150 motor in and be done. You will spend more money trying to get that cr motor “any configuration” you and still it be close to what a Ktm 150 has to off and stock at that.

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9/13/2018 7:05 PM

CrGuy2T wrote:

Seems to be cheaper just put a ktm motor in it. Sadly I love Honda’s and that would be my next option. I just decided to go orange. Although, a ktm motor in a Honda frame would be the ultimate. Even today my 17’ 150 does not handle like a Honda cr 125.

Jrewing wrote:

That's the other thing the Honda is my best handling bike I've had.

CrGuy2T wrote:

If I ever build another Honda I would just put a 15 Ktm 150 motor in and be done. You will spend more money trying to get that cr motor “any configuration” you and still it be close to what a Ktm 150 has to off and stock at that.

Makes sense.

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9/13/2018 7:48 PM

Jrewing wrote:

Makes sense.

I actually have a like new ktm 200sx motor on the bench. My wheels are now turning!

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9/13/2018 8:36 PM

Now you're talking!!

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9/13/2018 10:15 PM

KTM Honda 125 hybrid actually has been already done:

https://thumpertalk.com/forums/topic/1176376-the-ultimate-cr-125-af/

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9/15/2018 11:08 AM

CrGuy2T wrote:

If I ever build another Honda I would just put a 15 Ktm 150 motor in and be done. You will spend more money trying to get that cr motor “any configuration” you and still it be close to what a Ktm 150 has to off and stock at that.

Jrewing wrote:

Makes sense.

CrGuy2T wrote:

I actually have a like new ktm 200sx motor on the bench. My wheels are now turning!

the new 150 with minor work will outrun a 200 with significant work...

Just my thoughts.

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9/15/2018 11:38 AM

Derek Harris wrote:

the new 150 with minor work will outrun a 200 with significant work...

Just my thoughts.

The torque on the 200 is amazing. I don’t see that ever happening with a 150 motor maybe more top end I can see as the 20” is old technology. I would like to stroke my new 150 motor and see how that would work out. I kinda wish ktm would kept it a bore and a stroke.

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9/15/2018 11:47 AM

CrGuy2T wrote:

I actually have a like new ktm 200sx motor on the bench. My wheels are now turning!

Derek Harris wrote:

the new 150 with minor work will outrun a 200 with significant work...

Just my thoughts.

CrGuy2T wrote:

The torque on the 200 is amazing. I don’t see that ever happening with a 150 motor maybe more top end I can see as the 20” is old technology. I would like to stroke my new 150 motor and see how that would work out. I kinda wish ktm would kept it a bore and a stroke.

It's the pipe - not the engine

build a longer pipe for the 150 - and you will shift the rpm range the same way

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9/15/2018 2:08 PM

Do you do custom pipes?

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9/15/2018 2:41 PM

I picked up a 1995 cr125 complete engine today
What is the best mods to to this engine ....?

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9/15/2018 8:04 PM

Webby130 wrote:

I picked up a 1995 cr125 complete engine today
What is the best mods to to this engine ....?

a competent builder, lots of cash - and a wait time.

In your neck of the woods:

https://twostrokeperformance.com.au/

does great work

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9/16/2018 12:39 PM

Back in '93-94 I know the HPP factory Honda 125's were a hair over 40hp. Light years ahead of the others here in America. The amount of grinding and putty involved was pretty intense. I saw one of Henry's '94 cylinders and it was a work of art.

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9/16/2018 1:51 PM

DynoDan22 wrote:

Back in '93-94 I know the HPP factory Honda 125's were a hair over 40hp. Light years ahead of the others here in America. The amount of grinding and putty involved was pretty intense. I saw one of Henry's '94 cylinders and it was a work of art.

Did they run powervalves

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9/16/2018 8:22 PM

Yes. Fully functional HPP system.

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9/16/2018 9:47 PM

DynoDan22 wrote:

Back in '93-94 I know the HPP factory Honda 125's were a hair over 40hp. Light years ahead of the others here in America. The amount of grinding and putty involved was pretty intense. I saw one of Henry's '94 cylinders and it was a work of art.

quite the improvement from the peak bikes in 91-92 then

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9/16/2018 11:43 PM

The mugwn cylinders are supposed to run very well. Never seen a set up one dynoed but Nino in Switzerland says his 125 runs as well as the ktms

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9/17/2018 6:38 AM

Derek, Yes. I think Mitch was around 35-36hp back then. The hardest thing when comparing HP numbers is figuring out what dyno the bike was run on and what correction factor was used. The difference between a Dynojet and a Superflow is pretty significant. Cliff White did some amazing things on those HPP valve 125's. They did machine all new power valve guides (taller) and EDM in taller bosses so they could raise the exhaust port significantly. if you raised the stock exhaust port that high on a stock cylinder, it would pass over the top of the valve guide and basically make the powervalve non-functional. I did see the dyno graphs and the torque was impressive.

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