[RemingtonSteel]

ok i looked. really i did. and couldnt find anything on this, im planning on doing a build in the spring if all goes well. i dont here much about anyone running a 12:1. whats the pros and cons compaird to the 11:1. im gonna be running a stage 3 hot cam and porting the head. most my buddies run 13.5:1 in their 450s and all their quads haul ass and are not tempormental at all.

 

[Red-N-BlackXX]

Mo powa!!! Somebody on here's got a 12:1 piston? Can't remember who though?

 

[RemingtonSteel]

yeah nothing wrong with that and you can still run 91. i remember hearing that a few of matlocks blew up runing 12:1 but i will never be running my quad that hard.

 

[jake99buell]

I think it comes down to what octane your willing to run. I think I read where someone claimed matlocks bike would grenade at 12:1 but not for sure. You aren't putting your bike through 500 miles of hell so I dunno.

 

[D Bergstrom]

yeah nothing wrong with that and you can still run 91.

I didn't think you could still run 91 with 12:1 on a 700XX, I thought the 11:1 was about the max compression you could run on 91 octane. Might want to double check on that with an engine builder.

I can't imagine that a 12:1 piston would be any less reliable then a 11:1 piston, as long as you use the correct octane fuel with it.

Doug

 

[VelociRaptor]

I wouldnt, to be totally safe on premium pump you need to go no higher than 11:1

 

[RemingtonSteel]

I wouldnt, to be totally safe on premium pump you need to go no higher than 11:1

it that just something for our type of engine? i guess im a little confused cause my buddy runs 91 in his canam 450 that has a 13.5:1 and it runs great and is fast as hell. and a lot of the 450 dirtbikes are 13:1 and run 91. thats why i figured it would be fine.

 

[jake99buell]

Yea is there an explanation as to why our bikes need higher octane with the same compression?

 

[VelociRaptor]

Ive explained this before here I believe Ill look and see if I can link it here.

 

[VelociRaptor]

I can elaborate even further if needed:

How did all of those '60s muclecars run around on the street from the factory on pump gas and 11:1 or more compression along with iron heads? The cam was bleeding off cylinder pressure and the use of leaded gas. How does all of these crotch rockets and450s run around doing the samething today? Camshaft profiling and technology in FI and combustion chamber shapes.

 

[HosRacn]

I didn't think you could still run 91 with 12:1 on a 700XX, I thought the 11:1 was about the max compression you could run on 91 octane. Might want to double check on that with an engine builder.

I can't imagine that a 12:1 piston would be any less reliable then a 11:1 piston, as long as you use the correct octane fuel with it.

Doug

Doug you are right!!! Scott from CP Piston told me you would have to run race fuel with 12:1 but, you could run prem 91 with their 11:1.


If somebody is running 13:1 on pump fuel he is robbing himself of alot of hp!!!!

 

[ceballos]

:stupid:

 

[RemingtonSteel]

ok so since our engines are better built nowdays they do not lose the compression like others therfore dont need as hi of compression to make the same power? ive been skimming other forums raptors and 450's and for the most part they are saying under 13:1 if fine. im not really trying to fight for the 12:1 over the 11:1 veloci makes since regarding the cars. but i still dont understand the big difference between these newer 450's and our 700. sorry i know im being a pain.lol

 

[boost addict]

I might try a 12:1 cp with my new build. Being the 700xx is water cooled with a fan it might be possible, if not a 50/50 mix of 93/100 octane Sunco is all you should need. Thumper Racing claims their big bore 727cc Cp 12:1 will run of 93 octane.

 

[D Bergstrom]

but i still dont understand the big difference between these newer 450's and our 700. sorry i know im being a pain.lol

There are a bunch of factors. The main ones are cam choice and ignition timing. More timing, the more octane you need. (This is set at the factory, so it is what it is.) Can choice comes into play as Velociraptor noted. The more "overlap" a cam has, the more it bleeds off compression, basically one of the valves is still open as the piston starts to come up on the compression stroke, compression does not start untill all the valves are closed. So if you install a 12:1 piston with a high overlap cam, your true compression may only be 11.5:1.

Another factor could be load on the engine. Higher the load, the more it will want to detonate. Lets say your quad is right at the edge for 91 when you are just riding the trails. Works just fine on the trails, but take it to the dunes, and the 91 octane will not be enough. Sand puts more of a load on the engine.

Can't speak on any 450 other then the TRX450R. Most people that run a 13:1 piston on pump fuel are using a high overlap cam. Again, load on the engine has alot to do with it. I bet with a 13:1 piston in a 450R with pump gas, it would detonate big time if you took it to the dunes on a hot day. I run 12.5:1 compression piston in my race 450R and I use a 50/50 mix of 91/100 octane in it whenever I race. I will sometimes run straight 91 if I go out play riding, but I feel it is right on the edge and I don't do it very often. I would never run 13:1 piston in my 450R with pump gas, not in the "high load" areas I ride in.

Not even close to a expert on this kind of stuff, this is just what I have learned over the years. Hope it helps. I am sure Velciraptor can expand more if needed.

Doug

 

[RemingtonSteel]

Another factor could be load on the engine. Higher the load, the more it will want to detonate. Lets say your quad is right at the edge for 91 when you are just riding the trails. Works just fine on the trails, but take it to the dunes, and the 91 octane will not be enough. Sand puts more of a load on the engine.

Doug

i would be perfectly happy if i could trail ride and mess around at home on 91 and run a 50/50 mix when i go to the dunes

 

[08700xx]

i would be perfectly happy if i could trail ride and mess around at home on 91 and run a 50/50 mix when i go to the dunes

I just picked my quad up from Alba Racing today and I went with the 12:1 piston. Alba says for trail riding as long as its not hot out side 91 is just fine but for the dunes or any riding during high temperatures to run a 50/50 mix.

 

[boost addict]

I just picked my quad up from Alba Racing today and I went with the 12:1 piston. Alba says for trail riding as long as its not hot out side 91 is just fine but for the dunes or any riding during high temperatures to run a 50/50 mix.

What did your new build end up making? Did you use the pcv?

 

[08700xx]

My PCV did not come in yet and I think im going to order a new exhaust because the HMF was holding me back some. It made 58/47 with at HMF optimizer and HMF exhaust, they are thinking with a new exhaust and my PCV it should be around 63/50

 

[boost addict]

Ditch the POS Dobeck and you should be good to go. I am going with the Sparks full X-6 Racing exhaust with my new build. I should have the dyno #s between the exhaust in the next week or two.