Any drawback to a Hi Comp piston?


15 replies to this topic
  • CanadianWR450

Posted October 14, 2009 - 01:42 PM

#1

Since I got to do a piston and stuff anyway, is there any draw back to a Hi Comp piston, with reliability, longevity, etc?

As for power/performance gains, where does it help, and what does it act like?

  • kiwisonfire

Posted October 14, 2009 - 01:46 PM

#2

Your bike will actually run a little bit hotter with the high comp, but its nothing to be concerned about and most high comp pistons are forged so they are last LONGER and are MORE reliable than stock cast pistons. You will see most power gains on the low end of the band but they add power everywhere. The ONLY drawback is it may become slightly harder to get the bike started, hot or cold. Hope this helps.

  • rcripper

Posted October 14, 2009 - 01:48 PM

#3

well depends on the high the compression ratio is before you have predetotion problems, typically a high comp piston will give you more power everywhere, i install a 08 pistion in my 06 yz250f and went up from i think 12.5-1 to 13.5-1 something like that and couldnt feel much diff, that was a oem piston change, aftermarkets make higher ratios, but you might have to mix race gas to prevent the predet..

  • kiwisonfire

Posted October 14, 2009 - 02:06 PM

#4

anything below 14:1 you can use 93 pump gas with no problem

  • pablo83

Posted October 14, 2009 - 02:36 PM

#5

Since I got to do a piston and stuff anyway, is there any draw back to a Hi Comp piston, with reliability, longevity, etc?

As for power/performance gains, where does it help, and what does it act like?


Your crank, tranny, and drive train will see more wear due to the higher power output, but the increased wear will be real minor. Your biggest worry is predetonation if you get the ratio too high. This can cause great amounts of damage.

  • tribalbc

Posted October 14, 2009 - 05:31 PM

#6

Since I got to do a piston and stuff anyway, is there any draw back to a Hi Comp piston, with reliability, longevity, etc?

As for power/performance gains, where does it help, and what does it act like?


You'll see more power in the low to mid with maybe a hair more on top.

The motor might run a hair hotter but if you end up using your clutch less than it will be cooler in the end. I weighed the pro's and cons and decided it was worth a go. I'll be your guniea next week.

The big question will be if it will run fine on pump with out predetonation.

  • CanadianWR450

Posted October 15, 2009 - 01:54 AM

#7

Thank's everyone....

I'll probably go this route over the winter with a slight increase in compression then..

  • GCannon

Posted October 15, 2009 - 07:48 AM

#8

Consider this:
Higher Compression piston by its self will create more heat and could cause detonation more easily. Many of the hi compression piston installations we have read about here have been done in conjunction with aftermarket cams. The increase in valve opening duration will actually bleed off compression by having the valves open for more time. I believe this is how a lot of the Hi compression piston installations get away without running pump gas.

Often a 50/50 mix of Race Gas and 92 Pump gas is all it takes but it is still a significant on going expense. it would depend on where and how you ride. If the way you handle your fuel is not a problem then it is most likley a great way to go.

Raising the cylinder pressure will work the rings harder so start with a good round bore with a good uniform finish.

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  • beezer

Posted October 15, 2009 - 12:19 PM

#9

I put a high compression piston in my 03 YZ450 and it got stronger everywhere but much more bottom. I use it on the ice and dirt track and rev the snot out of it. I haven't noticed any down side.

It may be a bit too snotty in the woods though. The bike becomes pretty abrupt. My WR450 with YZ cams is more than enough.

  • CanadianWR450

Posted October 15, 2009 - 12:34 PM

#10

Consider this:
Higher Compression piston by its self will create more heat and could cause detonation more easily. Many of the hi compression piston installations we have read about here have been done in conjunction with aftermarket cams. The increase in valve opening duration will actually bleed off compression by having the valves open for more time. I believe this is how a lot of the Hi compression piston installations get away without running pump gas.

Often a 50/50 mix of Race Gas and 92 Pump gas is all it takes but it is still a significant on going expense. it would depend on where and how you ride. If the way you handle your fuel is not a problem then it is most likley a great way to go.

Raising the cylinder pressure will work the rings harder so start with a good round bore with a good uniform finish.



I already have stage 1 Hotcams,and FMF PowerCore Ti, along with all free mods, and JD jetting, fuel screw, etc. Cam's only have about 2,500 KM's on them.

When I do this, it will be with a brand new cylinder or a newly replated cylinder. rings, etc... I also will be going only "1 step up" so to speak in compression, 13:1 range I imagine.

Bike is a 04, Canadian bike, with mods listed above, and it already is pretty snotty, but I like snotty. Snotty is fun...lol...:bonk: ..as long as your not actually running real races/enduro's, HS that is, which I'm not...I just go out and have fun (call me Bubba, because when it comes to "skills", I have none!).

I mostly run pretty open stuff,like 4-wheeler trails, and old fire roads, and snowmobile trails in the summer with 14/51 sprockets (14/50 is stock), but switching to 13/48 for next season.

I am NOT going to run race gas though, and do not want detonation.....

  • thatraptorguy

Posted October 15, 2009 - 12:43 PM

#11

I already have stage 1 Hotcams,and FMF PowerCore Ti, along with all free mods, and JD jetting, fuel screw, etc. Cam's only have about 2,500 KM's on them.

When I do this, it will be with a brand new cylinder or a newly replated cylinder. rings, etc... I also will be going only "1 step up" so to speak in compression, 13:1 range I imagine.

Bike is a 04, Canadian bike, with mods listed above, and it already is pretty snotty, but I like snotty. Snotty is fun...lol...:bonk: ..as long as your not actually running real races/enduro's, HS that is, which I'm not...I just go out and have fun (call me Bubba, because when it comes to "skills", I have none!).

I mostly run pretty open stuff,like 4-wheeler trails, and old fire roads, and snowmobile trails in the summer with 14/51 sprockets (14/50 is stock), but switching to 13/48 for next season.

I am NOT going to run race gas though, and do not want detonation.....

what cam did you end up putting in both exhaust and intake or just one of them???and how much did you have to change your jetting once you put them in

  • CanadianWR450

Posted October 15, 2009 - 01:01 PM

#12

I put both in...
I'm afraid I can't help you a whole bunch on your jetting question, because, I did the cam's, FMF, and JD Jetting all at once....

I called up JD, told him what I had in my bike, along with my temps, altitude, etc, and he advised me to follow his instruction sheet for the YZ instead of the WR, and that's what I did. The only difference between the jetting for the JD kit between the YZ and WR is 1 clip position richer for the YZ on the needle.

No complaints at all, I could probably lean it out that one clip position on the needle in the hottest part of summer....but for all season use (spring, summer, fall), I'd say it's pretty much bang on,unless I want to start tweaking the jetting every month to have it "perfect" all the time.

The only reason I say that is because I was out Monday in 10 degree Celsius temps, and the thing was freaking hauling the mail! It still runs GREAT even in 30 degree celsius temps, no flat spots, no "burpling", crisp throttle response, and crisp exhaust.....

  • thatraptorguy

Posted October 15, 2009 - 02:08 PM

#13

I put both in...
I'm afraid I can't help you a whole bunch on your jetting question, because, I did the cam's, FMF, and JD Jetting all at once....

I called up JD, told him what I had in my bike, along with my temps, altitude, etc, and he advised me to follow his instruction sheet for the YZ instead of the WR, and that's what I did. The only difference between the jetting for the JD kit between the YZ and WR is 1 clip position richer for the YZ on the needle.

No complaints at all, I could probably lean it out that one clip position on the needle in the hottest part of summer....but for all season use (spring, summer, fall), I'd say it's pretty much bang on,unless I want to start tweaking the jetting every month to have it "perfect" all the time.

The only reason I say that is because I was out Monday in 10 degree Celsius temps, and the thing was freaking hauling the mail! It still runs GREAT even in 30 degree celsius temps, no flat spots, no "burpling", crisp throttle response, and crisp exhaust.....

how much of a power differance did you notice all around....i know sometimes with cams you'll lose power down low or up high

  • CanadianWR450

Posted October 15, 2009 - 02:39 PM

#14

Doing it all at once was a huge difference. Didn't seem to notice any loss anywhere, even bottom end seemed stronger, but very hard to keep it reving low, you need throttle control because the thing hits the rev limiter so fast it's scary, and it now has quite a MX'ish "hit" to it.
I run the FMF with out the spark arrestor, but if you DO run the spark arrestor, it mellows out the hit some, and makes the power delivery a bit more "manageable", and I put it in if I know I'm going to be doing really nasty single track, or traction is really going to be a issue (which is almost never for me)

By far the biggest gains were in the mid and top end, it hit's hard and fast in the middle, and just keeps pulling until the rev limiter.
I'm almost positive they also changed the head a bit in 05 (along with some other things, like cam's and such I believe..) to "smooth" the "hit" out of the WR 450's to make them more "woods friendly" (mine is a 04)

A riding buddy of mine who has a 08 KLX 450 was pretty shocked by it when he tried it out and said " It just keeps pulling!!".
He's a hard core nasty single track kinda guy though, and it didn't suit his riding style/conditions at all, but he did like it better with the spark arrestor in the pipe. It's much more "snotty" then his KLX though. Not saying his KLX didn't have power, just COMPLETELY different power delivery, way more linear, and electric motor like (very deceiving actually...lol).

It all depends on what you want. If your in to nasty gnarly technical riding, or HS, things like that, this set up probably isn't what you want.

If your into desert, open stuff, 4-wheeler trails, fire roads, etc and just go out to have fun, throw roost, and looking more for a YZ'ish power delivery (keeping in mind you still have the FWW, Wide ratio tranny, and extra weight), then it's great!

  • thatraptorguy

Posted October 15, 2009 - 05:10 PM

#15

Doing it all at once was a huge difference. Didn't seem to notice any loss anywhere, even bottom end seemed stronger, but very hard to keep it reving low, you need throttle control because the thing hits the rev limiter so fast it's scary, and it now has quite a MX'ish "hit" to it.
I run the FMF with out the spark arrestor, but if you DO run the spark arrestor, it mellows out the hit some, and makes the power delivery a bit more "manageable", and I put it in if I know I'm going to be doing really nasty single track, or traction is really going to be a issue (which is almost never for me)

By far the biggest gains were in the mid and top end, it hit's hard and fast in the middle, and just keeps pulling until the rev limiter.
I'm almost positive they also changed the head a bit in 05 (along with some other things, like cam's and such I believe..) to "smooth" the "hit" out of the WR 450's to make them more "woods friendly" (mine is a 04)

A riding buddy of mine who has a 08 KLX 450 was pretty shocked by it when he tried it out and said " It just keeps pulling!!".
He's a hard core nasty single track kinda guy though, and it didn't suit his riding style/conditions at all, but he did like it better with the spark arrestor in the pipe. It's much more "snotty" then his KLX though. Not saying his KLX didn't have power, just COMPLETELY different power delivery, way more linear, and electric motor like (very deceiving actually...lol).

It all depends on what you want. If your in to nasty gnarly technical riding, or HS, things like that, this set up probably isn't what you want.

If your into desert, open stuff, 4-wheeler trails, fire roads, etc and just go out to have fun, throw roost, and looking more for a YZ'ish power delivery (keeping in mind you still have the FWW, Wide ratio tranny, and extra weight), then it's great!

well this winter its going through the supermoto process so itll be strictly street used......so isnt that the kinda power im looking for??

  • CanadianWR450

Posted October 15, 2009 - 05:37 PM

#16

For the street, yup, I would say it would be damn fun!




 
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