Because of a stupid move on my part(dropping a screw into the intake)i am having my raptor motor torn down and i am switching from 11:1 to 12.5:1 while it is apart and i am wanting some input from those who have changed and what difference it made.I am hoping that the compression increase will help in the torque and low end area as opposed to the 11:1 but i am not sure how noticeable it will be.I am also wanting some input on what octane some of you with 12.5:1 are running because i plan on running straight 110 and although i could do a search i always like to hear the latest information available.

 

Since you are running 110, the results are all positive...everywhere. You was not planning on running the stock rod, were you?
Gary

 

garyc660r-I already have the carillo rod and just about everything else that i need to handle the added compression but with the probable damage i did after starting my motor with a screw in the intake i am having it tore down so that is why i am going to go ahead and have the compression bumped up. What i would really like to hear is some before and after stories of the added compression and its performance gains with all else being equal.I do appreciate the reminder about the rod because if i had not known about the need for a stronger rod with such a motor i would have to take that into consideration also.

 

I know a really great guy on here that goes by Yamaha660r...I believe he went from an 11 to 1 to a 14 to 1 and said the difference was very measurable...Did you not like the 11 to 1????...I am contemplating the Ross 10.75 to 1 because I wanna stay on pump gas so I can still trail with my kids on the weekends and still be able to kick a little butt at the hills

 

I bumped mine up and have had to go through a couple starters and starter clutches due to the increased strain. I recommend bumping the starter past compression stroke and then lay on, it'll start everytime with less strain. (In my experiences) You'll like the added pull down low.[img]i/expressions/face-icon-small-cool.gif[/img]

 

Your reliability will drop alot, it increases your chance for battery/ starter failure from the extra stress of turning over the extra compression. Also with that added compression the piston likes to go in the opposite direction when turning it off or starting it which can really kill your wrist pin and starter clutch. Since your running 110 yer fine there. I wouldnt do it unless you don't mind having engine work done often, or unless you can work on the bike yourself. Just my opinion from my experience with my Rappy.

 

Boosting compresion ratio gives you little net HP gain. But, it bumps your hp the same amount through out the entire RPM range. Therefore, your throttle response is boosted everywhere.

Personally, I think anything higher than 11:1 is not worth the pain of not being able to use pump fuel, hard starting...etc.

Check out this calculator:

Comp ratio change hp calculator

 

I run 14:1 compression in the raptor and have no problem, I came from an 11:1 to a 12:1 then to the 14:1 and i got faster every swap.[img]i/expressions/face-icon-small-happy.gif[/img]

 

ItalianStallion-I was happy with the 11:1 but i figure while the motor was apart why not gain a bit more power.To everyone else thanks for the input and i have already decided to go with the higher compression if for nothing else to gain torque.I dont mind spending the extra cash on fuel because when i add up what i spent to have the motor built the fuel seems like small change.I dont want to sound as if i have an endless supply of money because i do not but when it comes to things like starters and batteries i just figure that is part of what it takes to go fast.My plan is to have my motor or at least the top end torn down and inspected every season or at least every year and a half and replace what is needed.My opinion is that a lot of the reliability issues that people have with higher compression motors comes from doing too much of the work themselves and believing that just because they have put it together it is fine and in fact it is not that simple.I know where i stand with my motor at 11:1 against other machines so when i get it back at 12.5:1 i can report if any improvements were made but i still appreciate the input and opinions of others.I am having a lot of fun racing and beating a lot of quads that should according to the owner be faster than mine and it is even more fun with a big PRM front bumper and a PRM six pack rack holding my cooler on my not so tricked out (at least externally) raptor hauling my 230 lbs up the hill and the higher compression should only help.Yes i know i am not the fastest but i am also far from being the slowest.

 

MasterRaptor-Thanks for the compression ratio HP calculation site it is interesting .