High compression question


42 replies to this topic
  • virus619

Posted January 13, 2007 - 08:56 PM

#1

Hi, I was thinking of buying a high compression piston for my wr450 2003. The standard compresstion is 12 to 1 i think ( correct me if I am wrong). I was thinking of switching to a vertex high comp 13 to 1 piston, If I make this switch to the 13 to 1, will I have to use race gas, I don't mind using high test but I don't want to have to buy race gas every time I want to fill up.

  • BIG HAL

Posted January 14, 2007 - 05:56 AM

#2

Hi, I was thinking of buying a high compression piston for my wr450 2003. The standard compresstion is 12 to 1 i think ( correct me if I am wrong). I was thinking of switching to a vertex high comp 13 to 1 piston, If I make this switch to the 13 to 1, will I have to use race gas, I don't mind using high test but I don't want to have to buy race gas every time I want to fill up.


I tried it I have an 03 WR 450 and I weigh 290 Did'nt do anything for my power in fact took away from the top end. I went back stock and pulls great.... This is not like a car engine higher is not better.. Stock is awesome You shold be using race fuel now just like EVERYONE!!! Pump gas is TRASH its the lowest quality in the world... It's made for low compression fuel injected emmission controlled CARS!! If you need more power for you!! Then I suggest A CR 500.. If not then just go back with a Wiseco ultralight stock compression good luck.. Oh yeah and some cams might help go with the YZF 450 cams...

  • j753301

Posted January 14, 2007 - 10:10 AM

#3

i will have to dissagree big hal, going up on compression will give you more power everywhere in the rev range.it must not have been jetted correctly or maybe the timing on the cam was off or something,i do this for a living so im not talking from no experience here.going up on compression is the only way to gain everywhere.

  • virus619

Posted January 14, 2007 - 10:41 AM

#4

Yea, thats what I thought, I was planing to do it at the same time that I put in some new hotcams. But will I have to use race gas or can I still just use high test?

  • j753301

Posted January 14, 2007 - 10:49 AM

#5

it really depends on the bike,a fellow tech has a klx650 bored to 700 and a je 13 to 1 piston with just about 70 horse and he uses 93 octane with no problems.so i would give it a try at least you may be able to get away with it.

  • virus619

Posted January 14, 2007 - 10:52 AM

#6

ok, Thanks for the info:thumbsup:

  • windaddiction

Posted January 14, 2007 - 11:25 AM

#7

correct me if im wrong but for the most power, you should run the lowest octance you can get without pinging.

  • j753301

Posted January 14, 2007 - 11:34 AM

#8

exactly

  • windaddiction

Posted January 14, 2007 - 11:46 AM

#9

I'm running 91 with no prob, bike is jetted and free moded.. dynoed it at 49.8 HP too!

  • WR450_Mike

Posted January 14, 2007 - 05:37 PM

#10

you should be running 91 octane stock. The Owners Service Manual recommends 95 octane unleaded fuel (page 1-24). You won't find that at the local pump. So it would make sense that if you go to 13:1 compression, you should run even higher octane then that. The results of not running higher octane would be the higher probability of detonation. The fuel igniting before the ignition fires. This results in two flame paths coliding with each other and thats what makes the awful noise, and can cause severe damage.

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  • toyota_mdt_tech

Posted January 14, 2007 - 08:18 PM

#11

Your 2003 has 12.5:1. It will create more power, it will make more noise. But it does require higher octane fuel.

  • toyota_mdt_tech

Posted January 14, 2007 - 08:24 PM

#12

it really depends on the bike,a fellow tech has a klx650 bored to 700 and a je 13 to 1 piston with just about 70 horse and he uses 93 octane with no problems.so i would give it a try at least you may be able to get away with it.


Agreed. There is "mechanical compression ratio" and this is the number you see, and then, there is "effective cylinder pressure" which takes into consideration, valve lift, opening, duration, overlap etc. Basically, this squeeze doesnt take place until the last vavle has closed. So mechanically, compression ratio can be high, but squeeze can be lower. Now if you dont change anything except the higher compression piston, you will also raise squeeze. And a larger bore will also raise compression. As compression ratio is "the area above the picton at TDC vs BDC, and with the oversized bore, the area above the piston at BDC will increase, while area at TDC doesnt, effectivly raising compression ratio too. Most late model cars now come with a compressio ratio of 10.5 and 11:1, doing this while running regular gas because of variable valve timing.

  • virus619

Posted January 14, 2007 - 10:03 PM

#13

Ok, so i should just stay with the normal comp then. My bike is street legal and I wanna be able to fill up at the pump so if going up to the 13 requires race gas then im not gonna do it. I always fill it up with high test anyway.

  • BIG HAL

Posted January 15, 2007 - 07:12 AM

#14

exactly


If you do this for a livin then you should know NOT to run the lowest octane you can!!! How long ya been doin it? And did you know that the fuel we use for the cars is not worth a darn!!! If ya'll are just trying to save money than maybe you need to get into fishin!!! This is crazy if you really think that!!! Race fuel has additives that keep the cylinder temp down and this creates MORE horsepower period... I've been doin it since 1980.. High compression causes problems for the bike.. It will NOT last as long as stock!!! Stock.. The word is not the same as using stock for a car!!! Like your ford truck is stock... put compression on it and it will run great cause it has 8.1 compression. These bikes come out of the factory race ready, but most of you dont race, so why do you want to go all out and pimp these motors out? Can you handle the power all the way through and stay WFO through the whole race? We race every series TCCRA,TORN,WORCS,TORCS,STORM,PRO CIRCUIT, And All the other mx series I do NOT see but maybe 10% of people with high compression.. Stock is fine enough.. 12.1 cant get much higher than that.. 13.1 will not notice much difference... If you run pump gas do it at your own risk.. THAT my friend will be a big waste of money.... It's like buying a drag car with a 502 big block 13.1 and tryin pump gas... WASTE!!! I'm not mad just tellin how it is.. and from 30 years experience... Thats why you turn to the forums right cause YOU dont have the experience.

  • MountainMax

Posted January 15, 2007 - 01:30 PM

#15

as for the stock 95 octane rating, you need to read it again, there is another thread on this as it's the European rating, equivalent to 91 here in n/a

And i agree with using the lowest octane fuel you can, lower octane fuel can actually give you more power as it explodes with more force, however that force and too much compression (low squish band) can cause the piston to detonate and ping causing damage, but i guess this is just opinions, and everyone has one..... I too have been racing snowmobiles for years, i know it's a bit diff the bikes but the fuel issue has come up and I use race gas for my ultra high compression 440 racer and i mix it 50/50 with 87 octane for my other 800 racer, not as high compression, and i have no problems, just keep the detonation away.........

  • BIG HAL

Posted January 15, 2007 - 02:39 PM

#16

The lower octane burns faster thus gives more power!! If the bike is jetted right with race fuel it will produce even more power and without detonating!! I have no clue why ya'll worship pump fuel!!:lol: I for one could turn the fuel pressure down on my race car and run 2 tenths faster in the 1/4.. But would get a little risky.. Nitrous Oxide does'nt like lean conditions..

  • j753301

Posted January 15, 2007 - 03:56 PM

#17

what i was implying was that you should run the lowest octane you can get away with for each application WITHOUT DETONATING!!so running 112 vp would be cool in a 8.5 to 1 cruiser,i dont think so,it will accually run like crap.thats all

  • windaddiction

Posted January 15, 2007 - 04:18 PM

#18

cuase when i have a dual sported WR that i ride to work race fuel doesnt make much sense..... besides no detonation and no red hot header no overheating... it cant be that bad.... I'll let you know when it blows up though 48.9 HP on 91 pump gas is good IMHO

  • BIG HAL

Posted January 15, 2007 - 06:34 PM

#19

what i was implying was that you should run the lowest octane you can get away with for each application WITHOUT DETONATING!!so running 112 vp would be cool in a 8.5 to 1 cruiser,i dont think so,it will accually run like crap.thats all


Dude this thread was about!! HIGH COMPRESSION!!! Not a cruiser... 13.1 not 8.1 And as for the ride to work no you dont use race fuel... YOUR NOT RACIN!!! If your just playin dont pimp out the motor.. It's not cool to pimp yer motor just to drive to work or play once a month!!!

  • BIG HAL

Posted January 15, 2007 - 06:36 PM

#20

Besides.. Where in the world did you learn that lower octane is the best for HIGH compression anyway!!! Maybe you should go back to racin class 101...:lol:




 
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