11.5:1
12.5:1
13.5:1

Which one do you pick (for stock bore)? Need pros and cons of each from those that have them - how high is too high. Keep in mind I'm not strickly a dune rider, spend plenty of time on woods trails too - much of which is very technical. I don't care about pump gas or octane boost - I just want the performance and I'll pre-mix to get it.

 

Compression is free horsepower since a 10.5:1 piston costs the same as a 13.5:1. This of course is ignoring the increased fuel cost, which can be substantial.

91-octane pump gas $1.45
101-octane avgas $2.40
108-octane race gas $4.50

Plug that 13.5:1 piston in there and each 2-hour ride will cost you $10 is fuel, ouch.

Heat is another byproduct of compression. your motor will run hotter.

You will also be stressing your top-end components. The head-gasket is probably the biggest problem. They tend to blow easier.

If you want performance compression is the way to go, it helps low-end grunt and top-end speed. But in the end it really isn't free.

 

i have the 11.5 and it works well and the gas is fine on pump it is a nice improvement over stock

 

had a stage III with the 11.5 piston ran 93 octane on the trails and racing. went to the 12.1 pami now must run 110 octane all the time ( octane boosters don't work that good up to 110) big jump in power, but when you start changing compression you have to think about the head flow,exhaust,instake,carb ect. there is a limit to how much hp with piston alone. the 11.5 with a good cam goes along way!!!

 

All good stuff guys, exactly what I was looking for - thanks alot, you all share my thoughts and helped to make up my mind!

 

You can run the 12:5:1 piston on the 100 or 101 octane gas from 76 or Trick! I can ride a full day and a half on one 5 gallon can. And thsat comment you made about the compression getting the engine to hot?! You are way off!! Yeah if you run a 11:5:1 piston 0n 91 fuel it will run a little hotter But if you run 100 or 101 in either the 11:1 or 12:1 it will run just the same as it would with the stock piston on 91. The higher octane fuels burns slower which translates into cooler combustion temperatures. That is also why you can run a step leaner in your jetting if you like also. It makes more power that way.

 

How about plug heat range? What do you run Angry - the stock 8, or did you go to a DR9 for faster dissipation of plug heat?

 

I run the stock plug. A number 9 plug is cooler than an 8, Your fuel burns better if you run a hotter plug but I would just stay with an 8.