Big Bore Question,Need Help!!

[trx400exrider14]

i am looking to buy a 440 wiseco big bore kit for my 400ex,it doesnt have any head work or anything like that either,it said its a 11:1 compression,what kind of gas is needed to ride that compression on a 400ex?

[Scro]

You will be fine with premium pump.

[trx400exrider14]

how much of a difference is it,and i heard they blow head gaskets bad,is this true?

[CJM]

Originally posted by trx400exrider14
how much of a difference is it,and i heard they blow head gaskets bad,is this true?

93 octane is fine.

If they didnt put heavy duty headstuds in it may be prone to blow.

I personally will not buy anyones project quad like that ever. You never know what they actually did and how the quad was worked on.

[duroc825]

You' better to go smaller if possible.
Copy from old post below:
More reading info....quoted from Mickey Dunlap's tech article...

I prefer to build a motor that pulls quick and hard through the RPM range and the piston with higher compression will build more cylinder pressure which develops torque and will rev quicker and run faster through the RPM range. On most after-market pistons, the pin to deck height is the same as stock. You should have a minimum of .040 clearance between the piston and head with everything torqued down. Right now the piston is about .043 too low and you are not getting a true compression ratio as advertised by most piston companies. For instance, a 440 11:1 flat top piston advertised is really only about 9.75:1 if you measured the volume correctly. In order to get the deck heights better, I use Honda HT silicone seal on the cylinder base and an XR400 gasket if you are running an 80 over piston or smaller. This will get you close to what your deck height should be. Keeping the squish clearance down to .040 gives a better quench area around the outside of the piston keeping it cool and less chance for detonation. You will be able to run an 11:1 motor on pump gas in most cases and have a more efficient flame travel and quicker burn rate across the top of the piston. I have read on the forums here how everyone thinks a 416 is faster and revs quicker than a 440 kit with the same compression. I think most people are not running as high a compression ratio with the 440 kits as they think they are and when you put a cam with it, you end up with lower cylinder pressure making the machine rev slower than the higher compression 416 motor. Just my thoughts anyway. Without talking to each individual, it's hard to figure out why people think the 416 is faster than the 440. Any time you put a longer duration cam in, you have less time to build cylinder pressure. This is why it's important to put a higher compression piston in when you install a longer duration cam. You can get more torque the higher you go on the compression ration and your cam will give you the mid-range to top-end without losing low-end.

[jzexrider]

I have that exact setup and Ive always used pump premium.

[duroc825]

Originally posted by trx400exrider14
how much of a difference is it,and i heard they blow head gaskets bad,is this true?

GT Thunder heavy duty head studs recomended

[426kidz]

X2^^^^

[jzexrider]

Mines gone over two years and still on the same gasket and OEM studs but Im sure they would be worth putting in.