12:1 std bore piston

[Snipe]

I have found a 12:1 std bore piston, I am wondering is this true I have yet to see any other company's make this piston and im wondering is there any advantage of having a bored out piston like a 86 to 89mm bore or do you get the same results with keeping a std 85mm bore.

Also will you run cooler running a std bore vs a bored over bore? preventing having to run such high octane levels

[IcutMetl]

I can imagine heat level may be a little bit less, as the sleeve walls will have more mass, but you'll still need the octane with a 12:1 piston; it's all about the compression.

When I had my 400ex, it was the fastest of the 3 guys I rode with, all who had 400ex's with the most basic mods of pipe & filter. I had a Yoshimura slip on, k&n filter, jetted with lid on, and a Sparks degree key. The other guys were about the same, except for the degree key. All stock gearing. One of my bud's was hooked on using 18" tires, which slowed him down in the open fields, as he was banging off the rev limiter quite often if I remember correctly. He took apart his top end to freshen it up, honed the bore, kept the stock cam, and replaced the piston with an 11:1 Wiseco, and installed a Sparks degree key after liking the way mine ran with it. After that, I couldn't touch him. He wouldn't leave me in the dust, but it was a DEFINITE difference. His revved so much faster than ours, and pulled great. Like they say; no replacement for displacement...but it was cheap, easy and ran awesome.

Depending on your bore condition, I bet you could run a good hone thru it, get a light, high compression forged piston, XR400 cam, and the Sparks key and it'll wake it up like no tomorrow. Those motors are bulletproof...I wish I still had mine!

[Snipe]

Its a 08 my bore better me squeeky clean or honda and I will fight lol.

I think the 11:1 is what I will do the 12:1 will cause me to run into higher octane and I dont know if I wanna do that.

Does anyone know how the XR cams compare to the Hotcam's Cam? I mean is it like a stage 1 or more like the stage 2 cam? I know there better than the stocker 400's cam but I can get a stage 2 cam brand new for $89 so if its more like a stage 2 then ill just get one of them instead if I can find a decent one lol.

[honda400ex2003]

12:1 is def big and would be a good idea to run hd studs too. i would stick to 11 if it was me. then you can run the pump gas and get it easy. i would get a stage 2 if you plan to run the 11. i think you will be happy with that unless you are looking for a ton of low end then get the stage 1 with the 11. it would be nuts in my opinion. good luck, steve

[honda400-4-ever]

dont u have to run race gas if u put in the 11:1 piston and sparks key together??

[honda400ex2003]

I think it is recommended. http://www.exriders.com/vbb/showthread.php?s=&threadid=237131

heres the link for the cams. the xr is a bit more of a mild cam compared to both the stage 1 and 2. it is between the stage 1 and stock cam actually. steve

[Snipe]

You gotta remember these are questions on using a standard 85mm bore. I am wanting to get some extra bang but keep the reliabilty of the bore.

When doing so im gonna also do a drop in cam and a XR400 head gasket.

If I went 11:1 would I have to run race gas if I kept it STD bore size?

[IcutMetl]

Big bore or small bore; compression ratio is the main determining factor in having to use race gas or not. At 11:1, you're probably right at the upper level, but the person I was telling you about ran that 11:1 piston and that advance key for years without problem on good premium pump fuel. At the very most, I would think a 25-50% mix of race fuel would be the most. It would certainly run slightly cooler with the race fuel added and provide some extra insurance. From what I understood, the XR cam is more aggressive than stock, but not too much- the XR motor was in a higher state of tune. Keep in mind that that 11:1 ratio is probably calculated using a standard 400ex head gasket, and an XR gasket may slightly raise it, as I'm sure it's a bit thinner. Running a thinner head gasket in my 250r raised my compression enough to be in the 50/50 race/pump mix range, but that's an entirely different animal.

[lilyamaharacer4]

Been running 93 pump gas all year on 12:1. No hd studs either. Even with running race gas i cant really tell any difference in performance.

[Snipe]

Well for cooling I have a Spal fan and air scoops as it runs now my motor never gets hot enough to tick after running very hard with the fan on. I might just have to do this I just dont know if I like the 12:1 std bore or not. I think 11:1 is the best bet in my case.

[killer400ex]

idk if it is a great idea using the sparks key after raising compression and putting in a cam, they say not to and it probly wont make that much of a difference so that you will notice it atleast. i would put either a stage 1 or a stage 2 in, when i first bought my quad it came with a 406 cc bore and it was a 11:1 piston with a stage 1 cam and a full hmf exhaust, it pulled and ran like crazy, i would deff suggest it, and i wasnt running a advance key either, you will be just as happy without it, let me put it this way, i had guys coming up to me who rode raptor 700s that were impressed at how well it hill climbed and how snappy it was and i was running regular 87 pump gas at the time, you will be happy with it, but i would think about raising it up to maybe a 406 because even thogh it is a slight difference you will notice it big time and it is still close enough to std bore that you dont have to worrie about the cooling issue, i rode it for 3 years like that with stock studs and never ever had a problem, and that was racing it 3 times a week and riding everyday in between, it would hit the rev limiter real quick and still had enough power to wheelie in 4th gear

[Wheelie]

I'm running my own advance key with 11.3:1 compression, granted I run 100+ octane fuel to keep it from detonating.

The 400ex responds VERY well to added timing, especially in modded form. Sparks recommends not using their key with an internally modded motor due to heat, in which they are correct from my experience.

6 degrees is too much on a modded engine. Adding 3 or 4 degress on an 11:1 engine works well as long as a minimum of 100 octane fuel is used, and/or additional cooling.