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Thread: High Compression Piston

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    Talking High Compression Piston

    Howdy,

    I am working on powering up my low end. I have had a port and polish done to my bike which has given me a fun top end, but has robbed my bottom end. I want to know your though on WHICH high compression piston. If you have a high compression piston in your bike the reliability? cost to install? effect? etc?

    Thank you for your time and concern!

    V__853A(1).jpg

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    Racer Victork's Avatar
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    If you want more compression get a new head or have your head done for higher compression. Assuming you have a oem cylinder and its time for a new piston either go to the next piston size or hone the cylinder and put the same size new piston in

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    When I had my OEM cylinders ported and heads cut for squareness head gasket I used was an OEM 1985 Honda atc 250R gasket. It definitely raised compression but was also not to thin!

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    Racer kb250r's Avatar
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    Looking at that beautiful riding area in your photo seems you're mostly a trail rider and might have ended up with the wrong type port work for your riding application, maybe go to a cool head where you can change out the domes and have you 1 cut for higher compression and might help some but it's hard to get a good bottem end out of a cylinder that ported for top end. .In a two-stroke the compression is more in the dome/head I think a high compression piston is more of a four stroke deal .who did you have do your port work and set up your motor?
    Atc - 370r .6mill
    Atc - 370 4mill
    Trx - 431r puma

    "C-Leigh racing"

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    What pipe are you running?

    The exhaust system has more to do with power band shape than anything else that your can do to your engine!! With the right pipe you may be able to get more power everywhere with your current porting.

    Raising the compression lowers the Exhaust Gas Temperature. Lowering the EGT makes whatever pipe you are using act like a longer pipe. Raising the compression just takes RPM off the top and adds it to the lower RPM but the power average usually suffers when the pipe and porting are not optimally working together.

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    Thank you for all your help guys,

    The pipe is a shiny silver one

    It's a "Paul Turner Racing TRX Pipe" and in reality is not shiny at all. I know that it is a two part pipe (not including the silencer) and that at the joint of the two parts the o-ring is deteriorated, because my right leg has a moderate amount of oil on it after i ride. It might also be that I only have 1 of the 3 springs that should be there compressing the joint any more; or possibly its a combination of the o-ring or the missing springs to hold it together.

    Summary of potential problem at pipe joint:
    -Bad O-ring
    -1/3 springs
    -Both

    Thank you for your comments about the cool header. I am more familiar with 4-strokes so my first thought was a high compression piston, but am now looking at cool headers.

    I am interested in buying a cool header if you (anyone) have one.

    WP_20151026_002.jpg
    Last edited by New-To-This; 10-26-2015 at 03:01 PM. Reason: Add Picture

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    I bought the wheeler not knowing that it had been ported and polished (I am "New-To-This" get it?), so i don't know who it was done by. Once i had learned it had been ported and polished i asked the guy that i bought it from, but he didn't know.

    What I can tell you is that it takes maybe 300-500 more rpms to get my bike to move off the line (not racing just normal riding) than it takes my brothers bike (same bike/ no modifications), but once i hit about half throttle my power kicks in and the front of my bike doesn't come off the ground but starts to get a little light. My bikes top speed on sand is 62 mph.
    Last edited by New-To-This; 10-26-2015 at 01:55 PM. Reason: Additional Information

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    Racer StrokedAZ's Avatar
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    I'm not an expert by any means but the first thing I would address would be the exhaust just because it's the easiest. If it has a spot for 3 springs, 1 spring won't cut it IMO. Measure the spring u got and buy two more or measure the distance between the two hooks and minus 5mm. Use some rtv sealant when u put it together and the spooge will stay off you leg. 20 bucks will save many a pair of jeans lol. Good luck with your quad and welcome to the site.

    Sent from my Galaxy S5
    86 TRX 250R

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    Racer StrokedAZ's Avatar
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    Also your pipe is a high Rev pipe. If your porting is geared toward the pipe there will not be much "bottom end" left for ya, just saying. You can't have both on a stock cylinder unfortunately. If u want both you gotta go bigger 💸💸

    Sent from my Galaxy S5
    86 TRX 250R

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    Racer kb250r's Avatar
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    When you get time to do a little research on jetting, pipes, and different porting to get a better understanding of a two-stroke engines and that will help you better narrow down your problem and make adjustments to your liking.. Be sure to make sure your motor is physically sound before you can start to address or correct any issues not to your liking.. Correct Compression, jetting, no air leaks, Ect ..just my opinion...

    Ps there is a chance there has not been any porting done on the cylinder at all Old salesman trick tell people is "port and polished"and they want it more because they think it's faster. Just a heads up so there could be room for improvement in that area as well.. Good luck
    Atc - 370r .6mill
    Atc - 370 4mill
    Trx - 431r puma

    "C-Leigh racing"

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    http://www.atvsource.com/articles/pr...r_dyno_run.htm

    This site was informative in regards to the 250R and different pipes.

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    Quote Originally Posted by New-To-This View Post
    http://www.atvsource.com/articles/pr...r_dyno_run.htm

    This site was informative in regards to the 250R and different pipes.
    Divide the torque numbers by 2 and multiply the RPM by 2 to get the actual torque and RPMs correct. This is what happens when the dyno operator is asleep while testing and not paying attention to what he is doing.

    I would not make ANY pipe purchasing decisions based upon what you see in this series of test. I do not think that the dyno operator had much experience testing two strokes. The reason the torque numbers are wrong is because he had the dyno tach set to measure RPM for a 4 stroke. There is not any point in running a stock cylinder engine over 10,000 RPM in the field or on the dyno to the point to where the power has dropped to the 5 to 10 hp range. You will never run a stock engine to this high of an RPM in any gear but 1st gear or when missing a shift.

    It would have been a lot more informative if he had started taking measurements at lower RPMs rather than waiting until the engine was in the 5000 to 6000 RPM range to start recording data. The dyno was also reading low because he added an idler wheel to support the right rear wheel of an ATV on a motorcycle dyno. The dynojet software cannot be modified to add the moment of inertia of the idler support wheel to produce more accurate power numbers. Add about 2 to 4 hp to the numbers to get the numbers obtained on other Dynojet dynos.

    The series of dyno test and the curves presented were all relative to each other on stock ports but when used on various porting combinations most of the shapes of the curves will drastically change.
    Last edited by Jerry Hall; 10-27-2015 at 06:55 PM.

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    Pro-X broken1's Avatar
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    Quote Originally Posted by StrokedAZ View Post
    Also your pipe is a high Rev pipe. If your porting is geared toward the pipe there will not be much "bottom end" left for ya, just saying. You can't have both on a stock cylinder unfortunately. If u want both you gotta go bigger ����

    Sent from my Galaxy S5
    Looks like he's got the "trx race" pipe not the hi-rev.
    overkill is an often underrated achievement

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    Racer StrokedAZ's Avatar
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    Quote Originally Posted by broken1 View Post
    Looks like he's got the "trx race" pipe not the hi-rev.
    You are correct, I misread. Is the race pipe more of a mx/midrange pipe then?

    Sent from my Galaxy S5
    86 TRX 250R

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    Pro-X broken1's Avatar
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    Ya the trx race is a mid range pipe. Never tried one out but I have a PT hi-rev, it's a good dune pipe but would suck for trails or woods.... New-To-This what carb is on your R? It looks nice by the way.
    overkill is an often underrated achievement

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    I think it's the stock carb. I have seen it on 4/5 250r's that i have seen is why i think that it is the stock one. And thank you think she's pretty aswell.

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    I have the stock exhaust for the bike and am working on re-installing it. I want to see if the stock exhaust will give me a more linear power band.

    I had about 1/16 of an inch of carbon build up in the paul turner pipe and plan on roasting the pipe over a fire to try and burn it out.

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    The pipe needs to be heated until it is red to make the carbon flake off. Even after high heat the surface needs to be brushed to make it clean like a new pipe on the inside.

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    I have switched out my paul turner "TRX Race" pipe for the stock exhaust and my bike is much better.

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