I was thinking about getting my 400ex ported and polished. But now i hear that i'll need to run race gas or pump gas with octane booster? Is this true? Or can I port and polish and just run straight pump gas?

 

The compression you decide to run will determine the kind of gas you will need.

 

Yep, porting and polishing will have no effect on whether you need to run race gas or not.

Actually polishing of the combustion chamber will make the bike less likely to experience detonation problems.

There are many factors going into whether you will need race gas or not, but you WILL NOT even need to consider it until you raise the compression.

Porting and polishing will probably have little effect on the engine until you put a larger carb and a free flowing exhaust on it (along with other supporting internal mods, higher compression, bigger bore, more agressive cam, etc). The 400's head flows fairly well from the factory.

 

My 453 EX has 11:1 Compression, it runs good on 94 but i was wondering if Cam2 112 octane would make it run better, cooler or hotter, and give it more power??

 

Thanks for the info. But tell me if you think this would maybe work out. Port and polish, high compression cam (high as i can get w/o running race fuel) and a cdi rev box. Think i'd notice some difference in my bike. Also how high can i go with my compression w/o running the race fuel? I would also like to get a xr400 cam but it could be a short while before doing so. But will the rev kit, higher compression piston, and port and polish give me some more power?

 

These are the mods I have done to my bike...

Went with an 87mm JE piston @ 10.8:1 (416cc)- you should be able to get by with premium - I use a 50/50 mix of race fuel and premium just to be on the safe side, but think I would be ok, otherwise.

XR400 Camshaft

Ported and polished head, with stock exhaust - ported headpipe (blended in the welds, basically)

XR250 CDI box.

Yes it will give you more power, all the way across the board (mainly midrange throttle response, but noticable gains elsewhere). I have just over $400 in my setup (including machine work & head porting). With a pipe you should notice even more difference. These mods alone will make substantially more power than bolting on an exhaust system, for the same money.

As far as FAST453EX's question - it probably won't run any better unless the engine is suffering from detonation (which can be inaudible). I would try a 50/50 mix to see what you think. They say getting within 3-5 points of your engine's actual octane requirement will make the best power.