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Cams or big bore

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Been looking at big bore kits but have heard they can negatively effect reliability, would a set of performance cams be a better bet, probably wouldn't give the same power but would reliability be better?

Either option would be going hand in hand with a full exhaust system, 3x3 mod, K&N air filter and JD jetting kit.

Cheers.

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Big bore do not affect reliability. Given a choice between the two, I'd chose the Big bore, ignoring the difference in cost of parts and installation. Much more significant gains.

Big bore is a fair amount of work and takes a few hours. Cams are a less than one hour job and very simple to do.

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The issues with big bores are mostly mechanic/installer induced not from unreliable parts . Many don't verify ring endgaps or that the piston has the correct clearances , oil flow at startup not verified , reusing old gaskets , ect.. ect....

 

 

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Edited by jjktmrider
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Depends where you want the power. Cams will be felt more in the high rpm's , BB more in low to mid-range. 

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The biggest noticable difference from the anemic stock condition will come from the 3x3-rejet- full exhaust.

The stock intake cam is the biggest restriction of the 2. You can get overall gain just by replacing it.

On a related note, cams that are optimal for a 400 are small for a 434.

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6 hours ago, William1 said:

Big bore do not affect reliability. Given a choice between the two, I'd chose the Big bore, ignoring the difference in cost of parts and installation. Much more significant gains.

Big bore is a fair amount of work and takes a few hours. Cams are a less than one hour job and very simple to do.

I'm with William1 on this issue........nothing is quite like the extra cc's that a big bore provides.......and like ohio says above, the 3x3 and jetting along with a FULL exhaust give the engine some air/breathability.

Weigh your options both mechanically as well as financially and I'm sure you'll make a wise choice.

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I have a 434 with Hotcams. The big bore was a bigger performance boost. But, I installed the cams after the BBK. So I don't know the exact effect they have on stock bore.

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Here's my order of mods and results, butt dyno only.

 

Removal of spark arrestor- nothing

 

3x3, Dyno Jet kit, White Bros. slip on- Big difference! Bike able to lift front tire off the ground with low end response in 1st and 2nd.

 

Edelbrock carburator-. Noticably more responsive and snappier on the bottom. Faster free revving More top end power. Throttle response in between was strange to say the least.

 

Old stage 1 Hotcam intake(2047-1In). - Even more snap off the bottom, bike now can pull 3rd gear up off the very bottom. Let a dealer employee test ride and they said it's the most powerful SM they had ever ridden.

 

Old stage 2 exhaust(2048-1E)- lost a little bit of low end snap for a little more mid and a more freely revving motor.

 

Big Gun CDI- gained back the low end the exhaust cam took away but lost in the mid range. Also allowed bike to rev to 11k. I removed after few years later and felt it was an improvement without it.

 

Yoshimura RS3 full system.- small but noticable gain in mid-range and top.

 

YZ400F slant 39mm FCR with E airboot.-. More snap off the bottom and mid range power. Top end roughly the same. Overall throttle response greatly improved thru the range.

 

Trail Tech flywheel- much faster free revving , almost mx like. Noticable gain in low end hit and acceleration.

 

MRD SSW.- noticable loss of off idle power. Gained an almost mx bike like hit in the mid range and pulled longer on top. Bike felt more fun to ride.

 

434 Cylinder Works kit.- gained back the lost low end pull plus a little more. Power felt "play bike" like again, all low to mid, top end felt flat in comparison

 

TT 39mm FCR-MX kit.with S airboot-

Noticably better response across the range.

 

2003-1IN Hotcam intake and Web 540 exhaust-. Lighter exhaust cam immediately noticable when revving, bike sounds nothing like a stocker. Power pulls longer on top to almost the rev limiter without feeling flat. Feels more race bike than play bike. - downside, no decompression release. Need a strong battery to turn over the engine.

 

JDJetting FCR-MX jet kit-

Slightly crispier response than the commonly recommended needles.

 

 The bike dynoed 46 hp with all the above mods, putting it on par with the early 450 MX bikes. It's completely night and day.

 

 

 

 

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