Have you talked to the machinist that would be doing the work? If its a machinist that specializes in engine components he or she would likely know how to figure it out.

Beyond that, I do not know anything about calculating compression and machining, so I'm not of much use.

 

Yea I asked everybody I've talked to but they all go on a rant about how many variables there are and conclude that there is a formula to figuer that out but they don't know it.

 

They used to shave the heads in the auto race engines to raise the compression. Maybe the machine shop can fabricate a thicker head gasket for you, which would increase the area of the combustion chamber and therefore lower the compression. This would eliminate the need to modify the engine or any internal components.

 

I suggested that to Rossier in Plover. He is supposed to be the best in the area. He told me that his concern with that is it might screw with the timing. I already have two sets of head gaskets and base gaskets. If somebody has more expertise on that please let me know. I will just glue two base gaskets together and go that route if possible. But then I have the same ? of how many mm would change to the compression I'm looking for.

 

My Outlaw is 12.5:1 and I run 93 octane with no problems what so ever.

 

How long have you been running it like that?

 

Been running it like that since it was new (after break in), it's an "08", Full FMF pipe, jet kit (160 main I think) K&N, modified airbox. Goin on 6 years old, and it will still rip your arms out of the sockets!

 

This is a joke...right?

 

Would you like to enlighten me there poleman? This is no joke, I don't want to have to run race gas and if you know of a simple, reliable way to avoid that please feel free to say something.

 

They could machine the piston top down a hair and drop the compression that way. Or enlarge the combustion chamber in the head.

 

If you are intent on lowering the compression, they make concave top pistons for exactly that purpose.

 

I've already purchased the JE 560 big bore kit because the jug was junk anyway. It was gonna cost me about the same to go with OE so why not. JE kit said it would require race gas. I just want to make sure it is reliable and runs on pump. The head and jug will be done at the shop this week so If I don't figuer out a cost effective way to bring it down a little bit I will just run it like that regretfully and very carefully.lol

Oh and remember I just want to know how much I would have to take off the piston or add to the base gasket to aquire my lower desired comp. ratio? I know all the options I have (I think) just need someone who know the mathmatical formula or the answer. Thanks to anyone with an idea.

 

Try here, these guys all have highly modded bikes----->Polaris Pro Riders

 

I just posted my ? on there so I will see if they got any info on the subject. Thanks for the lead. Doesn't mean I giving up on here though if anyone has any more ideas on this let me know. And if I get a solution I will post it.

 

You can also try here---->Engine Compression Ratio (CR) Calculator

 

So I got alot of the same opinion on the other forum. Almost all of them running 12.5:1 or more are running pump premuim gas 92 and up. No problems with theirs. So I'm gonna run mine on pump 92-93 and just make sure I keep it a little on the rich side.
Oh and thanks for that calculator. I have no idea of how to figuer the cc volume of the head without maybe filling it up with a liquid or playdough and dumping it out in a beaker or something.lol

 

I'm running a 12.5:1 on 93 octane no problem. Mine is a 400L (2stroke) but I don't think that makes that big of a difference.... I say go for it!

 

Just keep an eye on your plug for signs of a Lean condition. I don't think you'll have any problems, throw in a few ounces of Startron to keep fuel stable.

 

fast, I didn't mean to sound like a smarty. I just never heard of someone building a big bore high compression engine and then trying to LOWER the compression. It will run just fine on 93 octane with a little booster in it. If you wanted to run regular fuel why did you get a high compression kit?
If you want reliability, I wouldn't be adding any extra gaskets or anything. IMO you'd just be adding the potential for problems.

 

I like JE pistons and they were the most affordable bbk I could find. But they only made the kit with 12.5:1. I guess JE only list it as a race gas only kit to cover thier own a**. I usually don't go aftermaket on internal engine parts so not much expierience with high comp. pistons. I'm an OEM kind of guy for reliabuility purposes.

 

You can always buy race gas and mix a little each time with the 93 if you want to run it a little higher. Mix 3 gallons of 93 with 2 gallons of 100 and get 95.8 octane.

Ronnie

 

I got a tip on the best stuff to use. It's called Torco Accelorator. This is what their website sais.

Mix a 32 oz can of Torco Accelerator with 10 gallons of 91 Premium Unleaded to make an efficient 102 Octane race fuel. Mix a 32 oz can of Torco Accelerator with 5 gallons of Premium Unleaded to make a whopping 105 Octane!