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Discussion Starter · #1 ·
im sure this has ran through the minds of a few people on here already if not then it might just be me thinking of a stupid idea, since the yfz450 and the yz450f share the same engine just the yfz engine is detuned a bit is it possible to swap the engines out with out a prob, thing is if im not mistaken they use a different ignition on the dirtbike and the dirtbike if 4speed, might it be possible to bolt up the yz450f engine to the yfz tranny and run it like that, reason for this is cause the dirtbike stock is putting out like 52hp when the quad needs some work to hit the 50's the work that is needed isnt much but when you do that same amount to the dirtbike engine it moves on up in the scale... any suggestions are welcomed and if it is a dumb idea that is fine, just havent seen anyone else ask and felt like asking
 

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Discussion Starter · #3 ·
thats why im wondering if the dirtbike motor will work with the gearing components of the atv
 

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It is possible to swap the guts ie: crank, rod, piston, into the YFZ engine but why... you are defeating the purpose of Yamaha spending hours and bucks to design an engine that would take the load the quad puts on it. So you risk breakage for 10cc's?

And as far as moding the YZ engine there is no cam mod it is already there, that is why we have to do it to our YFZ's, and the stock pipe flows VERY well on the YZ, aftermarket pipes don't make much of a difference.

So you really would not see much of a gain for the added expense and the risk of breakage to make the switch.

If it was worth it why would any of the pros run the YFZ motor and not just trash the new engine and replace it with the dirtbike motor?
 

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Discussion Starter · #6 ·
thats tru i guess that idea is out, o-well it was worth a try, like you said i will be better off moding the yfz engine
 

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What this person was saying is to switch to the YZ motor not necessarily because it has 10cc more displacement, but because it comes from the factory with 23hp more power. I would tend to think the 23hp extra you get from the YZ comes from more than just 10cc's of displacement. I don;t think anybody is getting 23hp out of a pipe and jet combination.

It might be that extra 1.2mm of stroke that critical to this engine making more horsepower. Maybe the YZ has a more agressive ignition map. Maybe the exhaust system is much improved. Maybe the hp comes from lighter engine components. I still would like to know why the YFZ has a lower redline than the YZ even though it has a shorter stroke. A shorter stroke means higher RPMs in just about every other 4-stroke engine.

From what I've gathered, the YFZ got the SLOW version of the YZ450F motor. The YFZ needs alot of work to reach the same performance level as the 52hp version of this motor.
 

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Originally posted by RPyfz450@Nov 6 2003, 10:12 AM
What this person was saying is to switch to the YZ motor not necessarily because it has 10cc more displacement, but because it comes from the factory with 23hp more power.  I would tend to think the 23hp extra you get from the YZ comes from more than just 10cc's of displacement.  I don;t think anybody is getting 23hp out of a pipe and jet combination.

It might be that extra 1.2mm of stroke that critical to this engine making more horsepower.  Maybe the YZ has a more agressive ignition map.  Maybe the exhaust system is much improved.  Maybe the hp comes from lighter engine components.  I still would like to know why the YFZ has a lower redline than the YZ even though it has a shorter stroke.  A shorter stroke means higher RPMs in just about every other 4-stroke engine. 

From what I've gathered, the YFZ got the SLOW version of the YZ450F motor.  The YFZ needs alot of work to reach the same performance level as the 52hp version of this motor.
well I guess you got a slow one :lol

there is no way my YFZ has 23 hp less than a yz450f.

uncork that SOB, ive dragged plenty of YZ250's and 450's and beat em through 4th gear at the track. there are also guys on here beating 426 motors in quad frames

besides the exhaust cam, 10ccs less and .5 compression and a little more rotating mass there is no difference in the motors. add up those things and they are minimal, maybe a few hp. and for the rev limiter ... i never hit it, if you are hitting it than you are loosing power. take a look at the power curve of a 4 stroke they dont make as much power at 11k rpm.

also my title says 39hp even all corked up. I find it hard to believe the YZ450 has 23 hp more than that ... or 62 :O
 

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trust me when I say this you would not want to switch out the engines. The preformance gain is minimal at best and it would be a big waste of time and money. first off the yz has 50+ hp because it is a bike with a red sticker. the yfz has less hp because it is a quad with a green sticker. The red sticker on the bike is because of the free flowing exhaust, carb properly jetted and the the cam timing. 10cc doesn't mean anything and niether does the stroke. the engine makes plenty of power when you make the proper mods and will last far longer than the yz engine in a quad. engine components are the same so there is no weight savings by switching engines. both have the same rev limit and the same valve and cam componentry. the real DIFFERENCE lies in the gearing. with a four speed the power may seem to be more plentiful yet it is really because the gearing is for short bursts of power and not much in the way of flat out speed and overall power. The gearing is also weaker on the bike because it is put under less load than the quad and you have to think about the weight difference the bike is only 222 dry and the quad is 350 big difference for power deliverly.
 

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Originally posted by rtyfz450@Nov 6 2003, 07:35 PM
trust me when I say this you would not want to switch out the engines. The preformance gain is minimal at best and it would be a big waste of time and money. first off the yz has 50+ hp because it is a bike with a red sticker. the yfz has less hp because it is a quad with a green sticker. The red sticker on the bike is because of the free flowing exhaust, carb properly jetted and the the cam timing. 10cc doesn't mean anything and niether does the stroke. the engine makes plenty of power when you make the proper mods and will last far longer than the yz engine in a quad. engine components are the same so there is no weight savings by switching engines. both have the same rev limit and the same valve and cam componentry. the real DIFFERENCE lies in the gearing. with a four speed the power may seem to be more plentiful yet it is really because the gearing is for short bursts of power and not much in the way of flat out speed and overall power. The gearing is also weaker on the bike because it is put under less load than the quad and you have to think about the weight difference the bike is only 222 dry and the quad is 350 big difference for power deliverly.
Exactly what I said earlier...
 

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There's only about a 14hp difference between the motorcycle and the quad.
Quad = 36 hp
Motorcycle = 50hp

Just do the mods to the YFZ, it's way cheaper and less hassle in the long run.
 

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Discussion Starter · #12 ·
yeah im just gonna stick to moding the yfz engine, i prefer having a more reliable engine then an engine with a few more hp's
 

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take the yfz motor, put a good exhaust, jetting, remove the airbox lid and the cam mod. that will net you 47 hp to the rear wheels all day. and that will put you exactly at the same HP as the yz.
granted the yz will still make just a hair over 50 hp on the dyno. but remember that your losing those 5 hp to the extra wheel and huge axle that you have to turn.
then there is a little hp lose in the crank shaft assembly, as the yfz crank wieghs a mere 3.3 pounds more then the yfz, becuase of the extra flywheel weight with the oneway starter bearing and gear, then the crank halves themselves are heavier then the yz as well.
but your money is best spent just doing the above mods i mentioned and you will have an arm jerker that few machine scan keep up with.
 

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Originally posted by Brit Mansell@Nov 12 2003, 06:21 AM
Changing the engine to the YZF will make you illegal in most 2004 MX classes.


.brit
Whadda' you know about anything anyways FLIPPER? :blah :blah :blah What, are you mister Referee now? Just kiddin man. Hey, is that steering stem bent in that avatar pic :lol :lol :lol I heard Mary Lou Rettan was impressed with your dismount! Even gave you a 9.5! ;) ;)

Fred
 

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The quad is harder on a motor than a dirtbike, they made the dirtbike with a piston pin that was narrower and can't handle the torque and sudden accelerations the wide quad wheels give, it will break down on you I would guess, the gears are also not up to it and will wear away or break.

it would be worse than the stock 4550 on rebuild time.
as for power, 11 cc is nothing much, like one horsepower.
take off 15 pounds and your even again.

also if you port your 450 you will be over 55 hp, and that is about 300 bucks.
 

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Discussion Starter · #17 ·
Originally posted by Brit Mansell@Nov 12 2003, 06:21 AM
Changing the engine to the YZF will make you illegal in most 2004 MX classes.


.brit
well, not all of race mx and some of us don't plan on going mx anytime soon, daddogrider, do you recomend any specific for the porting job?
 

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Originally posted by Asher+Nov 13 2003, 07:35 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Asher @ Nov 13 2003, 07:35 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--Brit Mansell@Nov 12 2003, 06:21 AM
Changing the engine to the YZF will make you illegal in most 2004 MX classes.


.brit
well, not all of race mx and some of us don't plan on going mx anytime soon, daddogrider, do you recomend any specific for the porting job? [/b][/quote]
Asher,

Please don't take offense. I was simply stating a point.


.brit
 

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Originally posted by fsewelljr+Nov 13 2003, 05:37 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (fsewelljr @ Nov 13 2003, 05:37 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--Brit Mansell@Nov 12 2003, 06:21 AM
Changing the engine to the YZF will make you illegal in most 2004 MX classes.


.brit
Whadda' you know about anything anyways FLIPPER? :blah :blah :blah What, are you mister Referee now? Just kiddin man. Hey, is that steering stem bent in that avatar pic :lol :lol :lol I heard Mary Lou Rettan was impressed with your dismount! Even gave you a 9.5! ;) ;)

Fred [/b][/quote]
Avatar pic was pre-dismount. Actually, the only thing that bent was the cheap stock grab bar and the AC front bumper. The bumper just needs a little coersion and she'll be as good as new.


.brit
 

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Discussion Starter · #20 ·
Originally posted by Brit Mansell+Nov 13 2003, 07:54 PM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Brit Mansell @ Nov 13 2003, 07:54 PM)</td></tr><tr><td id='QUOTE'>
Originally posted by [email protected] 13 2003, 07:35 PM
<!--QuoteBegin--Brit Mansell
@Nov 12 2003, 06:21 AM
Changing the engine to the YZF will make you illegal in most 2004 MX classes.


.brit

well, not all of race mx and some of us don't plan on going mx anytime soon, daddogrider, do you recomend any specific for the porting job?
Asher,

Please don't take offense. I was simply stating a point.


.brit [/b][/quote]
none was ever taken, im sure what you stated some people where curious about
 
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