What carb will be better than a 39FCR? You might be able to go up a couple mm's but for $500 to get just a little more top end?
You can't bore it so all you can really do it looks for compression, a pipe and wonder if there will be better cams coming out. From the sounds of the strong bottom and end screaming top end a cam change does not look all that necessary.

 

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Ummm...CAn some one tell me what was the deal in simpler forms????I read the car thing which i have no clue how that fits in in the whole quad thing.And .........I just dont get what he trying to say.

 

The Yamaha is like 2 grand more than the Z, dump 2 grand into the Z and you got one kick @ss quad, no matter if you go handling or motor mods.

Crackhead: If you read the Z vs EX vs Caniball issue of Dirt Wheels, you would have found that they rated the Z higher on handling due to its suspension. Just about every dimmension on the Z is 1/2 incdifferense at max when compared to the EX. Throw on some better shocks and it handles better, bar none.

 

I've already figured this trying to see if hopping the z up to stock yfz specs can be cheaper. So far the answer is no. The suspension upgrades are 2 grand and that puts you at $7600 then with a 440 kit (the 450 would be bigger than the yfz so I won't compare it) you would put at least another $1500 or more in it. That puts you at least $9300 in your quad and then all the yfz guys have to do (if they even have to do this) is remove the spark arrestor and airbox lid and rejet and it's still going to be way more powerful. I would say the mods I mentioned for the z above still might not put it even with the stock yfz. Plus there's the actual work you put into it if you do it yourself. I don't know I love my z but if I ever race pro production or anything, I'll be picking up a yfz and riding my z in the woods.

 

I wouldn't say better but there equal. The ex does have a tighter turn radius but it needs it without reverse. The z sits a little higher but it still doesn't feel any more tippy than an ex. I ride both quite a bit and I'd call it a tie for handling.

 

"Crackhead: If you read the Z vs EX vs Caniball issue of Dirt Wheels, you would have found that they rated the Z higher on handling due to its suspension. Just about every dimmension on the Z is 1/2 incdifferense at max when compared to the EX. Throw on some better shocks and it handles better, bar none"

...Your forgetting though...dirtwheels is full of ****!

 

Even though the yfz is nikasil it can be bored out. You will see both wiseco and JE offer larger pistons. I will bet you can take it to 480-500cc on bore alone. I know they have a 480 kit for the yz450 and a 500 kit for the crf 450. To have it re nikasiled is like 220-250 dollars. I bet sparks gets more than 60hp out of this engine.

 

Yeah they'll have bigger bore kits for it and some duners and draggers might want that but I figure all the mx guys either pro production 450cc limit or pros 440cc limit will leave there engine alone. They can still get great power and acceleration by just getting a full exhaust or removing the baffles on the stock pipe and jetting. Some guys will probably max it out for all it's worth though. I'd say it will reach 60hp or close.

 

Check out this month's ATV Action. They did a article on K&Ks CRF and YZF based race quads. They clearly state "close to 50 hp". I take that to mean 48 or 49, not 60. And this is from a shop that sells REAL "race ready" quads.

The hotter they come from the factory, the less you can uncork them. Yami freely admits pipe, jetting and intake mods will add 15% hp. I accept that as well. But 36 to 60, even 40 to 60 is much more than 15%. Every quad isn't as easily uncorked as a rappy or Z.