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How to increase cr125 bottom end at home ?

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Is it possible i could do some free things to make my 2stroke have more bottom end on it at home ? I uploaded a picture to go with and I also heard drilling holes in the air box because the cr had a small air canal... I've heard a few things just wanna know what you guys think ?ImageUploadedByThumper Talk1378210341.155568.jpgto

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I have seen drilled holes in the airbox at my track, the cr's from year 2000+ are famous for a bog, all you can really do without buying anything is lean it out a tiny bit but don't do it very much or you'll hurt the engine

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Simply put, you will never get awesome bottom end from a CR125. It has potential to be a top end screamer with some mid range but that is about it. I have a YZ125 right now that is so much stronger than my CR125s; its eye opening at how weak the CR125 is.

 

Ive owned a 2001 and a 2002 CR125, and without a lot of internal engine work, you will never be happy. The air intake setup is restrictive on these bikes and they want more air than they can get. They really need higher compression, good gas, and a ported cylinder head.  Aftermarket reeds and exhaust wont do much to the CR125.

 

The way I see it, 2001 CR125s and 2001 CR250s are selling for prices that are really close to each other. Lets say 1300 for a CR125 and 1800-2000 for a CR250.  By the time you buy an exhaust ($300), reeds (130) larger rear sprocket (50), and cylinder head modifications ($200-600), you now have a CR125 that is still 'slower' than a CR250 and you will be spending the same, if not more, money than it would take to buy a stock CR250. This is why I own 2 CR250s now and not CR125s.

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Simply put, you will never get awesome bottom end from a CR125. It has potential to be a top end screamer with some mid range but that is about it. I have a YZ125 right now that is so much stronger than my CR125s; its eye opening at how weak the CR125 is.

 

Ive owned a 2001 and a 2002 CR125, and without a lot of internal engine work, you will never be happy. The air intake setup is restrictive on these bikes and they want more air than they can get. They really need higher compression, good gas, and a ported cylinder head.  Aftermarket reeds and exhaust wont do much to the CR125.

 

The way I see it, 2001 CR125s and 2001 CR250s are selling for prices that are really close to each other. Lets say 1300 for a CR125 and 1800-2000 for a CR250.  By the time you buy an exhaust ($300), reeds (130) larger rear sprocket (50), and cylinder head modifications ($200-600), you now have a CR125 that is still 'slower' than a CR250 and you will be spending the same, if not more, money than it would take to buy a stock CR250. This is why I own 2 CR250s now and not CR125s.

please do enlighten me, how does one "port a 2 stroke head" 

Edited by -oakley-
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please do enlighten me, how does one "port a 2 stroke head" 

 

Porting a 2 stroke head is a magical task that can be done in many ways to ultimately make more HP. It really is an art to determine what needs to be done to an individual cylinder head to increase horsepower that can be best used for a certain type of riding.

 

It involves removing any burrs or rough areas in the intake and exhaust ports and smoothing out areas to allow air to flow easier. You can change the port timing to allow the intake or exhaust ports to add or remove air/fuel sooner or later in the piston stroke. Changing the port timing will adjust the power curve either left or right on a X/Y graph (dyno chart). You can add bottom end power at the expense of less top end, or more mid/top end power with less bottom end grunt. You can also make the intake and exhaust ports larger by grinding away cylinder head material. Making the ports larger or changing their timing is the same concept as a 4 stroke camshaft with a longer duration or cam lobe height (opens the valves more, or leaves them open longer). It allows more time for air/fuel to enter or exit the cylinder. The more air/fuel you can move through the cylinder head, the more power the engine will make. However, the larger ports can decrease piston ring longevity and require top end rebuilds sooner.

Edited by Ilove2strokes

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The 01 CR125 was a turd. If you don't believe me, look it up. On any other year 125, you can make your bike have more bottom end by correcting the squish band using a flat glass plate covered with high grit sandpaper. Another mod that is geared towards low end is the reed spacer. I've never actually tried one, so take this with a grain of salt. Getting a pipe that is low end oriented like the FMF gnarly along with a silencer to match will also be a good option.

 

If all else fails, get a bigger rear sprocket or a smaller front. Your bike won't actually have more power down low, but it will feel like it.

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Getting a pipe that is low end oriented like the FMF gnarly along with a silencer to match will also be a good option.

 

Glad you brought that up.....   FMF does not make a gnarly pipe for the CR125! That is surprising to me. I have never seen a pipe designed to increase bottom end power for the CR125.  If anyone knows of one, I would like to know about it.

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Porting a 2 stroke head is a magical task that can be done in many ways to ultimately make more HP. It really is an art to determine what needs to be done to an individual cylinder head to increase horsepower that can be best used for a certain type of riding.

 

It involves removing any burrs or rough areas in the intake and exhaust ports and smoothing out areas to allow air to flow easier. You can change the port timing to allow the intake or exhaust ports to add or remove air/fuel sooner or later in the piston stroke. Changing the port timing will adjust the power curve either left or right on a X/Y graph (dyno chart). You can add bottom end power at the expense of less top end, or more mid/top end power with less bottom end grunt. You can also make the intake and exhaust ports larger by grinding away cylinder head material. Making the ports larger or changing their timing is the same concept as a 4 stroke camshaft with a longer duration or cam lobe height (opens the valves more, or leaves them open longer). It allows more time for air/fuel to enter or exit the cylinder. The more air/fuel you can move through the cylinder head, the more power the engine will make. However, the larger ports can decrease piston ring longevity and require top end rebuilds sooner.

wow, so uhm, what would you think if i informed you that  your magical task you speak of, is you speaking out of your ass

2 stroke heads dont have ports.

 

The cylinder is the port, The head is a combustion chamber, and the only thing that can be done to it is increase or decrease the volume,

 

FAIL.

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wow, so uhm, what would you think if i informed you that  your magical task you speak of, is you speaking out of your ass

2 stroke heads dont have ports.

 

The cylinder is the port, The head is a combustion chamber, and the only thing that can be done to it is increase or decrease the volume,

 

FAIL.

HAHAHA thats all i got lol

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wow, so uhm, what would you think if i informed you that  your magical task you speak of, is you speaking out of your ass

2 stroke heads dont have ports.

 

The cylinder is the port, The head is a combustion chamber, and the only thing that can be done to it is increase or decrease the volume,

 

FAIL.

 

LOL.  I see what you did there.....  :thumbsup:   When I say cylinder head, I mean the CYLINDER in "Oakley's Terms".  Too much time working on cars..... same thing as people who call engines, motors....

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Glad you brought that up.....   FMF does not make a gnarly pipe for the CR125! That is surprising to me. I have never seen a pipe designed to increase bottom end power for the CR125.  If anyone knows of one, I would like to know about it.

 

aftermarket headers (expansion pipes) for your '01 CR125 are: fmf fatty, fmf sst, and pro circuit platinum... that all I could find

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Is it possible i could do some free things to make my 2stroke have more bottom end on it at home ? I uploaded a picture to go with and I also heard drilling holes in the air box because the cr had a small air canal... I've heard a few things just wanna know what you guys think ?attachicon.gifImageUploadedByThumper Talk1378210341.155568.jpgto

 

Drop a tooth on your front sprocket - I think your bike uses a 13T stock - drop to a 12T.  Costs about $8, but it makes a big difference.

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The head is a combustion chamber, and the only thing that can be done to it is increase or decrease the volume,

 

FAIL.

 

Careful when you tell someone that they are speaking out of their ass and then do the same :) Increasing or decreasing the size of the combustion chamber is not the only thing that can be done to a two stroke head. Modifying the squish band often requires the head to be machined/sanded down to get to the right tolerance. The size of the squish band helps to reduce detonation and control the flame front. The combustion chamber can also be reshaped to provide a more even flame front (yes, this is "technically" increasing/decreasing volume, but just a little more specific...)

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Procircuit and FMF are not the only pipe makers in the two stroke world either, check out DEP or PSI and they might have a pipe better matched to your needs. The Fatty is the best all around pipe and is geared towards mid-low to midrange power. The SST is a rev pipe designed to make peak power near the top of the rev range.

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Porting a 2 stroke head is a magical task that can be done in many ways to ultimately make more HP. It really is an art to determine what needs to be done to an individual cylinder head to increase horsepower that can be best used for a certain type of riding.

 

It involves removing any burrs or rough areas in the intake and exhaust ports and smoothing out areas to allow air to flow easier. You can change the port timing to allow the intake or exhaust ports to add or remove air/fuel sooner or later in the piston stroke. Changing the port timing will adjust the power curve either left or right on a X/Y graph (dyno chart). You can add bottom end power at the expense of less top end, or more mid/top end power with less bottom end grunt. You can also make the intake and exhaust ports larger by grinding away cylinder head material. Making the ports larger or changing their timing is the same concept as a 4 stroke camshaft with a longer duration or cam lobe height (opens the valves more, or leaves them open longer). It allows more time for air/fuel to enter or exit the cylinder. The more air/fuel you can move through the cylinder head, the more power the engine will make. However, the larger ports can decrease piston ring longevity and require top end rebuilds sooner.

 

 

wow, so uhm, what would you think if i informed you that  your magical task you speak of, is you speaking out of your ass

2 stroke heads dont have ports.

 

The cylinder is the port, The head is a combustion chamber, and the only thing that can be done to it is increase or decrease the volume,

 

FAIL.

 

 

 

I guess you can try what this guy did to a YZ250 http://motocrossactionmag.com/Main/News/HOW-TO-BUILD-THE-ULTIMATE-YAMAHA-YZ250-TWOSTROKE-I-8948.aspx

 

 

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