whats my compression?

[buck440]

i feel stupid about asking this but what is the compression in my 400ex, its got a usual 426 wiseco piston in it and what is the best gas mixture for max performance without messing with the carb like mixing e85 with premium or regular with premium or premium......

[2muchquad]

What comp piston do you have in it?Use premium unless you have super high comp and your motor calls for race gas.You could have 10 to1,11to1 or 13 to1 in your motor,wiseco makes the 88mm piston in several comp ratios...

[buck440]

man i have no idea, when the dealership rebuilt it they said they didn't know :ermm:

[2muchquad]

they should have seen the box that the piston came in at least,if a dealer doesnt know what piston they put in,thats trouble.Thats why i havent had work done at the dealer in about 15yrs..

[dunatic]

do a compression test and let us know. that will help to guess what it is

[buck440]

i think i know someone who has one

[f4istunna]

:eek2: if your dealer/mechanic doesnt even know what piston they put in. Id definately consider going somewhere else next time or get yourself a manual and do the work yourself Alot cheaper and you get the satisfaction of knowing you can fix it yourself.

[buck440]

i don't if i should say this but when i called about the motor and asked them about the piston they said it was not a 406 not a 416 not a 426 but a 431 and im like:huh and said there is no such thing and he said he thinks there is so now there dead to me, the 20% discount just isn't worth it to me but at least the motor runs smoothly still :p

[GPracer2500]

There are 88.5mm pistons for the 400EX which would make it:

((44.25mm)^2) x (3.14) x (70mm) = 430.38cc

[buck440]

motor wise, there still dead to me:devil:

[AZ440ex]

I cut this out of an artical by "Mickey Dunlap"

As far as figuring out what your compression ratio is when your engine is completely together, you need to measure the cc's of fluid it takes to fill your combustion chamber up to the bottom of the spark plug hole, make sure your engine is at top dead center and you tip your motor back and forth to make sure there are no air bubbles in the combustion chamber. For example, if you have a 440 motor and it takes 50cc's of fluid to fill it up, you would take 440 + 50 divided by 50 to give you 9.8 to 1 compression. To get a true 11:1 440, you will have to have a 44cc combustion chamber volume. Most so-called 11:1 pistons will have closer to 50cc's. You can get a syringe that measures in cc's at your local pharmacy and you can use just regular motor oil to fill your combustion chamber.

You could try this way to check you Compression Ratio.

[buck440]

i just need to buy a guage plane and simple