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4mm trail bike build


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So like its says, Im looking to build another motor, Im trying not to open up mine bc I actually love the way my bike runs right now, just looking for another project..

Jim @ passion built my current motor and I just sent him another set of cylinders to be ported for a 4mm, he wont have time to get around to them for awhile so i have some time to figure out othere things..

So what do you guys think about a 4mm for the trails?

what else would make this a great/strong/reliable trail motor?

carbs?

clutch?

Gearing?

I have T5's at the moment

Will stock carbs bored out do the trick?

I will be running 93 octane

compression will be around 155psi..

Im very rarely in 5-6th gear.I dont want to lose any bottom end with monster carbs..

thanks Joseph

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run one of jeff clutches and for the carbs i think stock ones bored will work fine for trail riding but keep in mind you can only safely get 27.5mm out of a set of stocker.i bored a set myself and i wouldn't feel safe going any farther.

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I would tame that compression just a hair....and have him cut you another set of cylinders.

If you rarely 5th or 6th and ride primarily trails, I think a 4 mil would be a waste, unless you plan on changing your locale.

 

If you never see 5th or 6th, that just tells me you don't have the room to let it rev...and strokers like to rev out.

 

Why don't you spend the money on suspension and stuff, if you haven't already!!

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I would tame that compression just a hair....and have him cut you another set of cylinders.

If you rarely 5th or 6th and ride primarily trails, I think a 4 mil would be a waste, unless you plan on changing your locale.

 

If you never see 5th or 6th, that just tells me you don't have the room to let it rev...and strokers like to rev out.

 

Why don't you spend the money on suspension and stuff, if you haven't already!!

my 4mil with mild porting and mid pipes had awsome bottom and mid. I didnt have to rev it out nearly as much as i thought i would.

 

if he gets a good woods/trail port and maybe some PT mids, bump the timing you should be good. just dont cut too much on the ports so your alredy lacking bottm end suffers even more

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Yea i just did my suspension..

I was told that 4mm give off alot of bottom end, so thats what i was looking to gain i guess..

The 4mill should give you more bottom end torque and top end also. If you are mainly looking for bottom to midrange power esp since you are not hitting 5th or 6th gear much, I would say a single carb would get you that extra power for that range. As its been discussed 1000 times, with a single carb you may loose a few ponies on the top-end, but you will have them instead on the bottom and mid, esp with the 4mill. :cool:

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  • 2 weeks later...

okay im still looking for a project motor but i have the jugs being ported..

I have heard about port matching the cases, what does that do/mean

what would be a good carb size, remember its going to be a recreational bike.

what is a good idea for the clutch, I dont want to worry about slipping

what kind of hp does a 4mm crank out?

also would cpi"s be a better pipe than my t5 for this motor?

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Not to burst you daydreams but I think that 4mil might be a waste fro the trails around here. If the passion port is running great then y fix something thats not broke. My bike has massive low end and mid range as well as a nice top. But im running the singl carb. I just think that you wont see the potential

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as long as the exhaust duration isnt over 192 degrees and transfer area stays conservative it should be real responsive with alot more lowend.. id throw some more igntion timing at it and bump up the compression to make the most out of it ,though of coarse youll need race gas then ,stock carbs or 28pwks would be your best bet for this to keep the signal and velocity strong for the tight stuff

Edited by flotek
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Not to burst you daydreams but I think that 4mil might be a waste fro the trails around here. If the passion port is running great then y fix something thats not broke. My bike has massive low end and mid range as well as a nice top. But im running the singl carb. I just think that you wont see the potential

 

I have read alot about the 4mm being a great setup for trails..

I love the setup that i have but im bored already...My bike runs fuckin awesome, speed freaks jetted it and holy shit..

Passion mx port and the other goodies is a blast to ride..Thats why imnot going to split the cases on this motor, its way to fresh, its only .20 over and everything has just been replaced/rebuilt..

I rather build another motor and then sell this one a whole..

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as long as the exhaust duration isnt over 192 degrees and transfer area stays conservative it should be real responsive with alot more lowend.. id throw some more igntion timing at it and bump up the compression to make the most out of it ,though of coarse youll need race gas then ,stock carbs or 28pwks would be your best bet for this to keep the signal and velocity strong for the tight stuff

 

 

That sounds good, I would def go with a coolhead, I rather not run race gas and stay at the 155 psi range, +4 timing..

thats what I have now, or do i need more compression and timing for the 4mm?

also whats up with port matching the cases, I may not be wording that properly..

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