It's not meltdown hot but it is hotter. If your covering ground you should be getting enough air to keep you cool. If you are worried about heat Four Stroke Tech sell an extra oil cooler that he claims will keep the engine up to 50 degrees cooler. This will be my next upgrade on my 400. Just try the gas and see what you think. If you don't understand how to read the plug with no residue email me and I will give you more information.

 

Race fuel will help a motor stay cooler not hotter,,,,call sparks racing and ask him what's the best way to keep a 400ex cooler..

 

Pismoguy,
Premium pump gas (91 octane) is all you need in your 400. The ONLY outcome from using higher octane is a thinner wallet. It wont run hotter and it wont give you any noticable power gains unless your running a high compression piston. As rockey correctly stated, the higher the octane rating the more it resists detonation. This is where the fuel mixture ignites before the piston reaches TDC and can be fired by the plug, common with high compression engines. It simply resists pre-ignition, due to higher combustion chamber temp, so that it can be ignited only by the spark. Your 400, in stock form, doesn't generate enough combustion chamber temp to pre-ignite 92 octane pump gas so you don't have to worry about detonation or higher octane fuels.

 

In Calif premium pump gas is only 91 octane. Where are you getting 92 octane pump gas??? The owners manual recomends 92. I mix pump gas 1:5 with 108 octane race gas. This makes around 95 octane, and gets it over the 92 minimum.

 

Well here in Pennsylvania we buy 93 and 94 octane rated gas. Also I have heard about the even heat of high octane fuels, no "cold spots" and that they run cooler. This is not the case with the Cam2 in my 400. This is not the case with guys that run dirt track race cars that I have talked to that run the Cam2. And last the engine machinist that I bought the fuel from told me it burns hotter then regular gas. I am willing to bet that this man knows more about the fuel he sells than you people. Every fuel has different additives. Maybe this is why it burns hotter. Don't take anyone's word on this forum as gospel, think about what you know is true and go from there.

 

Well, Mitteer may be right about a few things, the higher octane "GAS" does burn hotter, but your ENGINE will stay cooler. I would use what honda recommends the 92 and go up to 94 without worrying about spark plug problems, but thats just my opinion.

 

The Premium gas around here is 92 i think. Is that ok if i go to a wiseco 11:1 piston?

 

i have a wisco piston and a cam in mine right now im running turbo blue racing gas but it is $3.75 a gallon i dont feel like payin that anymore so how high should i go with the octane like over 100. Someone told me it will hurt the valves if I just put regular gas in it. Thanks

 

then how come it says 98octane recommened fuel on the sticker thats on the frame?

 

I'm glad some people are shedding some light on the myths of high octane gas!

As mentioned,higher octane resists preignition and detonation better than lower octane.
That is because it takes MORE spark energy to ignite it!

The only time higher octane will yield more power is if the engine needs it due to timing advancement or elevated compression ratio or forced induction.

Many times on stock motors,you will lose hp from changing to a higher octane gas because the ignition system is working harder to ignite the mixture.
I've seen this time and time again while playing with Mustangs and other cars.

Higher octane gasoline does not instantly add power.
In order for that to happen you have to NEED the higher octane.

But also as stated,some motors have knock sensors and they will advance timing and fuel curves when higher octane is detected by lack of ping and knock and all those other wonderfully damaging sounds.

Ever hear a high strung motor ping with detonation?
I was told that the "marble in the coffee can" sound is the engine block ringing like a gong from the brutal forces within the motor as the air/fuel ignites while the piston is still traveling upwards.

But honestly,on a stockish 400EX,stick with 89-92 octane........