High compression question


42 replies to this topic
  • windaddiction

Posted January 15, 2007 - 06:43 PM

#21

lol my engien isnt pimped.... I was mearly stating that if your engine doesnt ping it should be ok with that octane of pump gas, that being said I ushally only use cheveron, no payless gas for me lol. Now on MY VTR I run 87 cuase that thing is lowwwwww compression compared to my WR

  • 250f92109

Posted January 15, 2007 - 06:44 PM

#22

Higher compression is typically associated with race motors that run cams with larger duration and more overlap which bleeds off compression. I have never built a race motor for a bike but can say that for cars it all depends on the cam you choose and your ignition timing whether it will ping or not.

You can always try a 50-50mix of race gas if you dont want to spend the $$ for straight race gas.

When you get it together please let us know how she runs. Since Yamaha doesnt have a wr525 yet, I might be making similar mods in the future.

  • David525

Posted January 15, 2007 - 07:20 PM

#23

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. Lower octane fuel ignites easier when compressed than higher octane. So in a high compression engine using lower octane fuels you will get compression detonation (pre-ignition = engine knock)

  • virus619

Posted January 15, 2007 - 08:39 PM

#24

Well, I have no idea how my simple question turned into a huge thing but thats a different story. I was just asking if moving to a 13 to 1 would require race gas, not because im a racer and absoutly need it, but because my bike is legal and its what I use to get around. Sure pump gas isn't the best, but everytime I want to go to the store or school, I don't wanna have to drive home and fill up with race gas thats just not practical. And I don't want my engine to knock because in my opinion high compression should use higer octane which would lead to why I asked the question in the first place. Just to make sure so I don't waste 150$ on a new piston, Switching to the high comp will require race gas correct?

  • trailordune

Posted January 15, 2007 - 09:15 PM

#25

91 or 92 octane pump fuel is allready borderline on these engines, especially at any altitude, so why risk it. You'll notice very little difference going 13:1.

  • Birdy426

Posted January 15, 2007 - 10:03 PM

#26

I can't comment on the 450s because I don't have one...I can comment aout the 426's though. Going from 12.5:1 (OEM) to 13.5:1 (Wiseco) made a HUGE difference on the rectal dyno. The bike pulled noticably stronger on the bottom, and maintained that edge all the way to bouncing off the rev limiter. With stock bore, hot cams, and proper jetting, it didn't even begin to ping or dingle on pump premium. Great mod just for the improvement in bottom end.

  • BIG HAL

Posted January 16, 2007 - 08:59 AM

#27

Well, I have no idea how my simple question turned into a huge thing but thats a different story. I was just asking if moving to a 13 to 1 would require race gas, not because im a racer and absoutly need it, but because my bike is legal and its what I use to get around. Sure pump gas isn't the best, but everytime I want to go to the store or school, I don't wanna have to drive home and fill up with race gas thats just not practical. And I don't want my engine to knock because in my opinion high compression should use higer octane which would lead to why I asked the question in the first place. Just to make sure so I don't waste 150$ on a new piston, Switching to the high comp will require race gas correct?


Your right.. Do NOT get That piston!! I can assure you that your bike is plenty fast and dependable now.. If you need a piston due to wear and lots of miles just go back stock.. Thats what I run and we race every single weekend in the off Road race series.. And I've even won the championship. So all i'm sayin is its a good combo that you have now. And on the long issue, We have people here that just want to here themselves talk and not speak from years of experience.. You dont need to talk about cam overlap,duration,bleed off, or any of that.. Most people dont even understand that nasa technical talk. Truth is that ALL the people that do go to the extreme of 13.1-14.1 big cams big carbs high power ignition systems will work on that bike every time they ride it.. It's very delicate and requires alot of attention. So ride your good WR and keep it the way it is and you'll have a fun time with it.. I'm sure it will go fast enough for you to get road rash anyway!! That is if you Crash it. Good luck dude and have fun.. BIG HAL!!

  • jnybbad1l40

Posted January 16, 2007 - 04:12 PM

#28

I have a 2003 wr450 with a high comp piston, ported head, hot cams and Vortex ignition and pretty much every other mod you can think of. I also have a 2006 WR450 stock except for the free mods exhaust and jetting. For the trail I like the 2006 because of the power band, easier to ride. For flat out fast power the 2003 is definately faster. I have gone head to head with a 2003 CRF450 and a KTM 525 and pulled them both and I out weight those riders by 50-60 pounds. It pulles so good I went down to a 46 tooth rear and it pulls hard. Its just peaky now, likes to rev.

As far as gas, I run VP Ult 4 in the 2003 and 2006 as it lets the motor run cooler and cleaner. I have run pump gas in my 2003 and can feel the diff. Most likly because its jetted for VP. I have never heard detonation though. If I did I have 10 diff ignition curves to adjust for the fuel and riding conditions.

Lastly I can say that my 2003 has started easy everytime I have started it. Even better than my 2006. It has been built raced and rode hard for two years with just normal maintenance and One top end check which showed no excessive wear. I believe if you are meticulous with the build use quality lubricants and break the motor in right there is no reliability issues with cams and a high comp piston.

Just my experience, good luck.

  • j753301

Posted January 16, 2007 - 04:53 PM

#29

big hal i think you are taking what im saying wrong.if you can get away with running 93 in a 12 to 1 motor it will probably run better than if you run vp in it,as long as the jetting is right.i really think you should obtain fron coming on here an insulting people before you even know what i do or how much experience i have.and if people want to run a 13 to 1 piston on the street for a daily driver they will.i do and love it.so what if i have to do valve adjustments and oil changes more often.the power increase is worth it.even doing the top end every couple years isnt a big deal.so please just chill out..:lol:

  • virus619

Posted January 16, 2007 - 05:12 PM

#30

Nobody has had any problem with running high test in a 13 to 1. The only thing im worried about is a knock, I don't really want to do valves more often but the harder you ride a bike usally the more you have to adjust it. I have some experiance but not as much as some people here which is why I am asking before I make a stupid decision. Thanks guys :lol:

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  • BIG HAL

Posted January 17, 2007 - 05:39 AM

#31

big hal i think you are taking what im saying wrong.if you can get away with running 93 in a 12 to 1 motor it will probably run better than if you run vp in it,as long as the jetting is right.i really think you should obtain fron coming on here an insulting people before you even know what i do or how much experience i have.and if people want to run a 13 to 1 piston on the street for a daily driver they will.i do and love it.so what if i have to do valve adjustments and oil changes more often.the power increase is worth it.even doing the top end every couple years isnt a big deal.so please just chill out..:lol:


Dude I'm cool!! Just tryin to give the Virus guy a hand on the subject.. I've been racin cars,motocycles,gocarts, since 79 maybe before you were born, Not to offend you... But I'm not sure where you read or learned that trying to get away with the pump gas in a race motor running as rich as you can and not detonate? You will have to run richer with a lighter fuel. The KEY is to run as LEAN as you can with quality FUEL on the borderline of melting down ,detonating, or whatever you want to call it, The horsepower is surely not going to come from 87 octane gas from Chevron. Sure you can build a motor for the 87 I'm not sayin that you cant... Dang I'm just ramblin... Dude like I said Why do you try and steer people away from a quality fuel that will produce MORE horsepower and stability..Lead is the key for the valves.. Is the end of the muffler black or grey? I really love workin on motors and bikes and I really like to share my experience with ya'll, sometimes I really get involved so dont take it as I'm mad I'm just stating the facts from what I've been through in my motor days.. Jetting is an easy thing replacing parts are easy too.. The hard thing is payin fer it!!! Over and over and over... I have no problems anymore cause like ya'll are doin now, I've learned some years ago. Good luck,, 50/50 race fuel pump gas will always be better than straight 93. That really is'nt 93.. Motor octane on premium pump gas is really 89.. race fuel has saved my motors many times... And I've even melted a few down too... Darn Nitrous.. The higher the compression the hotter the cylinder!! Hey Virus good luck and P.M. me if you need more advice.. See Ya!!! BIG HAL...

  • ncmountainman

Posted January 17, 2007 - 07:00 AM

#32

NASA talk....pimped out motor.....sounds like the low tech redneck approach has worked well fer ya champ:thumbsup: i had a conversation with rick petersen a while back and he is of the same school of thinking.... that you can get more with less. he mentioned trying up to 17:1 on a 4 stroke(can't remember which motor) but gained little. his kits (most of them) actually run less comp than stock for a broader more useable power. like big hal i race offroad and am about the same size as him,i'm sure he fights the same heat issues i do. raising comp will make for easier flameout,more heat,harder starting...not exactly a offroad racers dream. now for natural terrain MX or desert i could see it.
sorry about the lowtech redneck dig hal,just had to:busted:

  • BIG HAL

Posted January 17, 2007 - 10:19 AM

#33

NASA talk....pimped out motor.....sounds like the low tech redneck approach has worked well fer ya champ:thumbsup: i had a conversation with rick petersen a while back and he is of the same school of thinking.... that you can get more with less. he mentioned trying up to 17:1 on a 4 stroke(can't remember which motor) but gained little. his kits (most of them) actually run less comp than stock for a broader more useable power. like big hal i race offroad and am about the same size as him,i'm sure he fights the same heat issues i do. raising comp will make for easier flameout,more heat,harder starting...not exactly a offroad racers dream. now for natural terrain MX or desert i could see it.
sorry about the lowtech redneck dig hal,just had to:busted:


LOL!! Yeah I was just using some terms that maybe the youngsters might understand!!! PIMPED LOL!!! I too am from Cali.. Huntington Beach that is.. Back on topic Virus guy was going to use his WR to drive on the street most of the time... I was just saying NO to 13.1!!! LOL!!!! See ya on some other threads.. Mountain Dude!!! LOL!!!

  • virus619

Posted January 17, 2007 - 04:28 PM

#34

Thanks for all of your responses guys. I know that if I were to switch to the high comp that I should run race gas. Its not that race gas cost more $, its just that its hard to get, well I can't get it at the pump. And Im probley gonna say that 93 straight isn't gonna work so well in a 13 to 1. But with that aside, I trying to make my wr more into a supermoto or a street bike. Its ok lots of people tell me im stupid. Any advice on what mods I should do to make it more street friendly?

  • ncmountainman

Posted January 18, 2007 - 09:58 AM

#35

your best bet would be to go with a stage 2 hotcam for more top end and get a exhaust that will compliment the top also. 14/47 or maybe even 15 depending how fast ya wanna go. better brakes(larger rotor frnt,good pads etc) lower the suspension etc:thumbsup:

  • virus619

Posted January 18, 2007 - 04:08 PM

#36

your best bet would be to go with a stage 2 hotcam for more top end and get a exhaust that will compliment the top also. 14/47 or maybe even 15 depending how fast ya wanna go. better brakes(larger rotor frnt,good pads etc) lower the suspension etc:thumbsup:


Thanks I was thinking alot about the gearing but I heard lowering it to much can destroy it. One of my friends told me if you make tge gearing alot lower then the stock it will kill your tranny? Im not sure if this is true but I think it is. Am I right?

  • Oasis_Flame

Posted January 19, 2007 - 12:33 PM

#37

619
Been running a 13.5 to 1 for four years, not a single problem and great power. Don't let these arm chair mechs scramble your brain. Buy the piston and run pump gas just hang-on tighter to the bars. :lol:

  • BIG HAL

Posted January 19, 2007 - 01:14 PM

#38

619
Been running a 13.5 to 1 for four years, not a single problem and great power. Don't let these arm chair mechs scramble your brain. Buy the piston and run pump gas just hang-on tighter to the bars. :lol:


4 Years.. WOW It's about 10.1 by now!!! Still runs? Besides the arm chair thing.. HMMM LOL!!! Pump gas wont work... Flamer.. Especialy in the hot summer..

  • virus619

Posted January 19, 2007 - 08:23 PM

#39

Ive heard 2 different stories, some people way that the 13 to 1 will work on 93 and other say no way. Honsestly the damage is not worth the extra horsepower in my mind, that is if it will cause damage? Im confused. :lol:

  • BIG HAL

Posted January 20, 2007 - 05:26 AM

#40

Ive heard 2 different stories, some people way that the 13 to 1 will work on 93 and other say no way. Honsestly the damage is not worth the extra horsepower in my mind, that is if it will cause damage? Im confused. :lol:


Well, yeah it will.. Detonate, run hot, wear out faster.. If the factory thought it would be a better bike they would've ran that piston. Why do you think they did'nt.. Cause they would have to run it so rich for pump gas so it wont detonate. Just go ahead and do it and getcha a barrel of race fuel and mix it 50.50 when you fill up.. Your good to go.. That barrel will last a couple months its only 350.00 shoot it might last you 6 months. Maybe even a year.. Why are you so against running the right fuel? If your so concerned about doing the right thing cause you cant afford it then go back stock... I've told you all I can on this subject and that should be enough, make your decision and follow through with it, let me know how it works. Good Luck




 
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