low fps

Hello,
I have 40 fps running cocos2dx_box2d template demo on iPhone 3G in Release mode. The demo is very simple, cocos2d template has 60 fps. I’d prefer to use cocos2dx instead cocos2d. So how can I increase fps using cocos2dx? Is there some predefine limitation, that I should disable?

Sorry I can not find such an early type of iphone for test. But can you tell me your iOS version?

iOS version is 4.2.1.

This morning, I failed on convincing a friend to update his iphone3g from 3.x to 4.2 ios version.
He tell me that he downgraded from 4.x to 3.x several months ago, since his wifi module is broken, 4.x will cause many unstable problems.
So sorry I can do nothing on your problem now.