which compression ratio is best for me , using pump gas ?

[HOT-ROD]

i have stock valves and springs , stage one hotcam , 39fcr carb , dmc alien exaust ?

[jb400exxx]

get an 11.1:1 piston. it will run on premium pump gas. the Z-400 is 11.1:1. i'm gettin an 11.1:1 J.E. in march along with a hotcams stage II. i'm also wondering if the XR gasket would hold with the higher compression or would it blow. what are good gaskets to use if it won't?

[HOT-ROD]

Originally posted by jb400exxx
get an 11.1:1 piston. it will run on premium pump gas. the Z-400 is 11.1:1. i'm gettin an 11.1:1 J.E. in march along with a hotcams stage II. i'm also wondering if the XR gasket would hold with the higher compression or would it blow. what are good gaskets to use if it won't? i dont really know , how strong are the oem gaskets ?

[jb400exxx]

the reason i want the xr gasket is because it's thinner and makes a little higher compression but idk if it's strong enough to hold that high of compression or if i would need a different gasket. i want higher compression but i don't want to blow gaskets.

[frogburner]

I thought I read somewhere that a 11.1:1 compression required race fuel?? May I'm wrong but I thought someone told me to stay below 11.1:1 to keep running pump gas..

[jb400exxx]

anywhere above 11.1:1 needs race fuel. like i said the Z-400 is 11.1:1 and it runs on premium 93 or 94. i run octane booster in mine now (stock), and i will deffinetly just use it with the 11.1:1 piston just to help out a little bit. it's not an oxygenated octane booster so it won't make it run hotter or anything, it probly makes it run cooler if anything.

[QuadTrix6]

the reason the z can run that high of comp on non race gas is because its liquid cooled and wont detonate as easy. with an aircooled motor u need a higher octane. ther is a very good thread abt octanes in the FAQ if any1 is interested

[bmw500hp]

Originally posted by HOT-ROD
i have stock valves and springs , stage one hotcam , 39fcr carb , dmc alien exaust ?

your talkin about the same mods as me except I went for the 12.5:1 and plan on race gas.... look at my sig... will be interesting to find differnces... i am a little concerned with the compression and the gaskets....

[Dave400ex]

I would get a 10.8:1 to stay on the safe side. Even at that Rico runs half Pump and half Race Gas.

[frogburner]

:huh

[Dave400ex]

That is a good Compression. TC told me I should get that with his Motor kit when the time comes.

[KAWSAM62]

10.5 to 1 sounds good to me:devil

[OutlawEX]

11:1......You should make a poll to see more accurately

[frogburner]

I thought I was going to get a 10.5:1 but ended up getting a 11:1 Wiseco...

[Dave400ex]

Well let us know how it works out for you.....

[bmw500hp]

Warrior Man...

What options have you found with TC in regards to his piston compression and Cam suggestions... he has 2 cams primarily right...

[Dave400ex]

Yep he has 2 Cams that I know of. There is the XC Cam, which is mostly for bottom end power, and then the MX Cam, which I think is more of an all around Cam. He may have something for TT, but I have never asked about TT. You don't need Springs or Harden Rockers either. For Pistons, he says to go with 10.5:1 for the most part, but he may change if your conditions are different. If you race full MX then you would get a 12.5:1 I believe.

[Dune Surfer]

You would need to go 10.5:1 for pump gas. Mine ia a JE 10.8:1 with an XR gasket and I need to run 50/50 race gas. With that in mind just plan on going 12:1 and get much more bang for your buck.

[RideRed04]

Just as a side note: a JE 10.8:1 is a 10.5:1 with an ex head gasket.

[Dune Surfer]

RR04 I thinki you may be wrong about the JE. When I bought it is listed the compression as 10.8:1 not 10.5:1

[RideRed04]

exactly, the compression ratios are listed for the xr400, not the 400ex. They label it for the 400ex because it is the same exact part, it is just less compression because of the head gasket. If you use an xr gasket, then you will get the 10.8:1. If you can feel .2 in the compression ratio, you have a sensitive butt!

[Dave400ex]

Yeah you are not going to notice much difference between the 10.5:1 and the 10.8:1. Are you sure that when it says 10.8:1 it's only 10.5:1 with the EX gasket? If that's the case I think a lot of guys on here have 10.5:1 compression instead of 10.8:1.

[Tommy 17]

i have a 10.8:1 .040 (406) je piston with a tc mx grind cam... i'm runnin the xr head gasket... its been in for a lil over a year now with no troubles at all... i can't run anything below 94 octane... 94 octane i'm fine...

[RideRed04]

Originally posted by WarriorMan
Yeah you are not going to notice much difference between the 10.5:1 and the 10.8:1. Are you sure that when it says 10.8:1 it's only 10.5:1 with the EX gasket? If that's the case I think a lot of guys on here have 10.5:1 compression instead of 10.8:1.

I'm pretty sure. The piston is the same thing, but it wouldnt make sence for them to design a whole new piston just so you can get another .2 in the compression ratio. I wouldnt be supprised if it said that somewhere in the directions. The piston is 10.8:1, but that is in an xr. The ex has a thicker head gasket (think opposite of getting the head milled) so it has less compression. Just run an xr gasket if its an issue to you.

[eldoexrider01]

so if i were to run an 11:1 416 wiesco (sp) with an xr head gasket, then it should be 11:1 instead of lower????

[RideRed04]

Yup!