I have a 200 honda 400 ex and im going to put in a wiseco 426 complete kit and probably stage 2 cams and I was wondering what anyone thinks is the better compression to go with 11:1 or 13:1. THANKS

 

if your gonna get a weisco, the 11;1 and the 13:1 are just about the same. if you get it dynoed you will soon find out. there just not "trued" like some piston makers.

cp pistons, or je will gaurentee<---sp, the compression is trued!! your going with a good set up, but kinda cheep. if you have money, i would take it to the 415 je high comp piston and a web cam rather than the 426, and a stage 2 hot cam!!

riders and a riders performace very, but you get what you pay 4! hope this helps.

 

if you are going 11:1 you can run pump gas, if you run 13-1 you will need race gas so it will be more expensive and harder to get gas.

 

im pushin a lil under 13.5:1. pump gas, 87 grade. its air cooled so it dont need to get so hot. 93 or higher gets HOT! Think about it. Your 4-stroke lawn mower runs no better with 93.

A lot of people think 93 is better in everything. WRONG!! Sum engines require 87 grade gas.

 

go-hard, you're bass akward on your thinking. An air cooled engine runs hotter than a liquid cooled one. Therefore, the need for higher octane when compression goes up is even MORE crucial.

Don't believe me?? The Suzuki Z400 has a 11.5:1 ratio STOCK & a person can get away with 87 octane. Another example.... my Yamaha 4-stroke snowmobile is 11.5:1 STOCK & also can be run on 87 octane. Both of these engines are liquid cooled.

A 400ex is 9.something:1 STOCK & can be run on 87 octane. The compression is low enough, this is why 87 can be used.

Next, higher octane gas burns cooler than lower octane, not hotter. That's one reason it's harder to ignite. I'm not a chemist. I know there are many reasons why, but this is an example.

3rd, the reason a lawn mower runs no better on 93 than 87 is because the CR on a nmower engine is MAYBE, MAYBE 8.5:1

 

this is a site to better help other people. if your "opinion", or "facts" are in fact true, dont waste his question space by correcting me. PLEASE write me. then give him your opinion[img]i/expressions/face-icon-small-smile.gif[/img] JUST AS I HAVE CONTRADICTED MYSELF. your right too. an air cooled engine does run hotter, never said it didnt.

also engine conponets have a big part in all of this. not just compression and gas. you could have the best gas and the highest compression, but if you dont have the valve springs to hold it by by engine. im no pro rider, or computer nerd, nor top mechanic...but i do feed my family and children with my "self-employed" mechanic buisness. i am also willing to learn more.

 

Back to original question. 11.1:1 is more than suffice for a trail quad. Another general rule of thumb for pump gas VS race gas is, 10:1 on an iron head engine & 11.5:1 on an aluminum head engine. The 400ex is an aluminum headed engine, so it fits the profile for a pump gas friendly CR of 11.5:1. 13.5:1 would need 100+ octane. The guy here saying he runs a 13.5:1 air cooled engine on 87 octane will have himself a bent or broken rod engine OR cracked piston at some point in time from all the detonating the poor thing is suffering from. But, that's his choice I guess.

Next, go-hard... I'm not going to argue over the 'net w/ someone, because arguing on the 'net & the Special Olympics have one great thing in common. Even if you are declared the winner, you're still a retard.

However, enlighten me how compression has ANYTING to do with valve springs or valve spring pressure. It doesn't. Cam lift & duration & valvetrain speed affect the valve springs. Compression may affect the head gaskets & test head bolt/stud strength, but not compression.

In your defense (and my error) I re-read you're post. I understand now that you meant not needing or wanting the air cooled engine to get hotter than it needs to. But, once again higher octane fuel burns slower & cooler than lower octane.

 

415 is nice, powroll has a site you can read about them.

 

valves or springs have nothing to do with compression? if there bent or damaged, you will have no compression. it has a lot to do with compression!!! do a compression check on your bike, then go bend a couple of intake valves. bet your compression will change. springs help with the closing of the valve. if you dont have the springs to support your engine, its gonna be a failure.

and "retard" is not the word to use, unless you are in fact one. "special people" would be the correct way to pronounce it!