Many Motor Questions!!!

[bleedhondared]

I have a trail ridden 2005 400EX. Its all stock cept for Pro Armor Skids. I'm thinking of doing some engine mods, mainly a stage one hotcam, higher compression piston and an exhaust, but I have a few questions. What is the stock compression? How high can you go on 93 octane pump gas before it causes problems? 10 to 1, 11 to 1? Is a full exhaust system worth the money? Does it give more power with my planned mods or is a slip on enough? Anything else i should be thinking about? Spill your guts boys, learn me up!! Thanks!

[jordan_m6]

A 11: 1 comp piston is the max before hd studs, and race gas. The stock head pipe is pretty descend for the woods and the set up you want. I can beat a 440 with stock internals with a slip on in a drag race (300ft).

This set up is a fast reving setup. i love it. may need to go with a cdi to add more R's, they really help. and depending on what you do (all trails or just about everything) you need to gear it to your likings. i want to try a 16 and put the 14 back on to see how i like it. i havent got to ride much but so far I like it,still need to do some tweeking.


9: 1 on stock comp.

[Chin_Chilla]

Originally posted by jordan_m6
I can beat a 440 with stock internals with a slip on in a drag race (300ft). :eek2:

A 440 Kit will make AT LEAST 30% more power than a stock 400EX. Even with just a slip on, you won't add near 5% power to the stock 400ex, so how do you think you can actually beat a 440 with just a slip on?:huh

[jordan_m6]

440 mods:
12.5: 1
Slip on and thats it


My mods:
in my sig
minus the carb.


sorry for the confusion. was trying to say the 440 only had a bigger piston.

[krt400ex]

the srtock comp is 9.5:1...i wouldn't go any higher than 10.5:1 before using a 50/50 of race and pump gas. soemppl run the 11:1 just fine others get detoing....i would rather be on the safe side.

a full exhaust is better than a slip on. when u put on an aftermarket pipe, it is not just for the extra airflow. many aftermarket companies re design the shape and lenth of a headpipe to add more top end or more low end. a longer headpipe will give u more off the bottom, and a shorter one will give u more top. i would get a full osh system, they will give u more off the bottom.

a stage one cam is ideal for ur application, and personally i wouldn't use a stage 2 or stage 3(stroker cam) on a stock bore motor. it seems to be just to much cam

[krt400ex]

EDIT: the stock comp is 9:1

[bleedhondared]

So a 10 to 1 piston, a stage 1 cam, a full exhaust system, jet kit, uni filter and a vented airbox lid would make for a nice boost?

[400eXr1d3rZ]

Originally posted by bleedhondared
So a 10 to 1 piston, a stage 1 cam, a full exhaust system, jet kit, uni filter and a vented airbox lid would make for a nice boost?

Great combination of mods, will give you a big noticeable boost in power.

I would go for a JE 416 87mm piston, Cometic Gaskets (thinner, increases compression), Sparks full exhaust/Duncan/HMF/Yoshimura, no need for a jetkit (check out www.jetsrus.com for all jets), UNI filter is good, no vented air box lid, just take it off and get a outwear for the uni filter.

[jordan_m6]

definetaly do the JE piston. heard they are a little more accurate on the compression ratio.

[bleedhondared]

if i buy a standard bore piston then I won't have to get any machine work done, right? Or will I still need it honed out?

[jordan_m6]

i didnt touch mine cause i could see all the factory hone marks and very faint up and down marks. runs just fine no smoke, but befor build it had maybe a total of 25 hours run time on it.

depending on how it looks you may need to re hone

[400eXr1d3rZ]

I would just get a bigger bored piston.

[bleedhondared]

Ballpark me a number on what it costs to overbore the cylinder. Thanks for all the info.

[krt400ex]

not that much. i have heard from anywere from $50- $150. it depends on who does it. just make sure that u send them the new piston with the cylinder, so they can match the bore with the piston perfectly

[400eXr1d3rZ]

Mine costed(is this a word?) me about 40 - 50.

[Ex'r Marlin]

Depending on how much riding is done on your '05 400EX... I think going with a standard bore JE piston is a great idea!

Having someone do a "quick" hone job to it should not cost much at all... Heck, you may even be able to do it yourself!:cool:

NOTE: Most likely the higher the bore, the hotter she will run.

If it means anything, I am not convinced that you need a "full system" exhaust... A slip-on should be just fine. (You will definitely want an aftermarket exhaust if you go with a higher compression engine).

Good luck, and Happy Trails!:macho