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Discussion Starter · #1 ·
Hey guys, i need to replace my cylinder and piston so im going to be getting a cylinder works big bore kit 727cc. I was wondering what compression ratio i can get away with without running into problems? Some people have told me 11.0 is the highest to go on pump fuel. However i've read in dirt wheela magazines that they've went up to 12.5.

Any feedback would be nice. I need some real answers here, not just speculation, im looking to buy in the next day or two..
 

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Three things you need to mention.
1. What is the highest octane (pump gas) you can get? (91 or 93)
2. What elevation are you riding at?
3. What piston? (some pistons are corrected or true, some are not)
 

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12.5 requires 110 octane u can run 11 with half 93 half 110 or just 93 just my .2cents and youll need to be tuned with a fuel controller on a dyno like i said just my 2 cents
 

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Discussion Starter · #4 ·
93 is the highest I can get. I am at about 1000 feet elevation. The piston is cylinder works I think it is called. I have a big gun fuel controller, but I'm no master tuner with it. By the sounds of it, I'm better off just going with 11 to 1.
 

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I would say 11:1 is about as high as you would want to go if you want to use pump fuel. One of my 700's has a 12.5:1 piston in it and I run 100 octane in it. CT Racing did my engine work and Allen over there said I could probably run pump even with the 12.5:1 piston, but he would be a little leary in high load situations, so I am just going to stay with 100.

As easystreet mentioned, elevation will also have an affect. Higher you are, the less octane you can use.

Doug
 

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93 octane at 1000ft. should be safe on a true 11.0:1
That would be about max though.
Not sure what brand piston Cylinder works uses. It may end up being less in reality.

Ask the retailer and/or builder the question. You want to know where you are for sure. It is a waste of money and counter intuitive to run much higher octane than required.
If you have a motor that will run on 93 octane with out detonation, but you choose to run a mix that puts you at 100 for instance, you are actually producing less horsepower than if you stayed at 93. The additive that raises octane level produces less power than the fuel itself. Therefore, your power level per volume is less.
 

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Cam selection will make a difference as well.
 

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Hey guys, i need to replace my cylinder and piston so im going to be getting a cylinder works big bore kit 727cc. I was wondering what compression ratio i can get away with without running into problems? Some people have told me 11.0 is the highest to go on pump fuel. However i've read in dirt wheela magazines that they've went up to 12.5.

Any feedback would be nice. I need some real answers here, not just speculation, im looking to buy in the next day or two..
i believe the cylinder works big bore kit has stock compression with an vertex piston
 

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Discussion Starter · #9 ·
Alright, thanks for the feedback guys. Sounds like I should just stay away from 12.5 if I want to play it safe. I was hoping to get an 11.0-1 piston but the closest I can find is a 10.5 one. I guess I'll have to go with that. BTW, I have a stage 2 hot cam as well.
 

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Alright, thanks for the feedback guys. Sounds like I should just stay away from 12.5 if I want to play it safe. I was hoping to get an 11.0-1 piston but the closest I can find is a 10.5 one. I guess I'll have to go with that. BTW, I have a stage 2 hot cam as well.
i think they also make a stock bore kit with the option to bump up to 11:1 compression with stk bore
 

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The power gain you'll experience between a 12.5:1 and 11:1 wouldn't be worth the hassle. There are a ton of variables in figuring exact compression and fuel requirements but with the general design of the XX (aluminum heads, water cooled & decent combustion chamber design) you'll be fine running 11:1 on 93 octane. I know some will say other wise so do some research and do what you feel is best.

I hadn't looked around lately but I thought there were a couple vendors who offered the 11:1 BB, Which have you looked into? Have you contacted any members who have ran the Cylinder Works kit to get some reviews. One member had a problem with there sleeve slipping and i won;t to say it was Cylinder Works, I'm not 100% sure though. Keep in mind Vertex pistons will be cast too and not forged units like most other kits. Not trying to discourage you from your choice but just want to make sure your informed on what your buying.
 

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I heard mixed reviews about cylinder works because I was looking to do the same thing. In the end I decided to go with the CP 11:1 +2 piston which should make it a 715cc if I'm correct.
 
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