I'm not sure why they switched........I do know the 5 valve head has worked very well for Yamaha in the YZ450F, YZ250F, and the 4 stroke sleds (I think)

 

Personaly, I'm beginning to think they put too much effort in making the 700 more fuel efficiant. It doesn't seem to want to burn fuel as well as the 660 did. My 660 loved fat jets for the top end (with the same mods and even pipe for that matter) but the 700 don't seem to respond as well to being rich. Just a waste of fuel. I find myself cutting back on the recommended settings from different sources..............WTF?

 

Ozark,

Respectfully, you may have missed the point. On any motor that is changed, how you extract performance has to change. I wouldn't get hung up on running an overabundance of fuel for top end power. If the 700R makes more top end while using less fuel........ Isn't that a good thing? Just do what the new bike responds to regardless of what you used to do with the old bike. BTW, even with EFI, the right mixture has to be maintained for proper combustion. If you really want to run more fuel through her, all you have to do is figure out how to move more air through. That is the million dollar solution. It might even cost you that much. LOL

My 700R feels twice as strong as my '03 660 did. It seems to go through about 15% less fuel stock to stock. [img]i/expressions/face-icon-small-wink.gif[/img]

Ron

 

Unless you guys have some flow measurements of the different head designs - which I'm quite sure you don't - then you can't make a statement like "the 5 valve head flows more air". Until we get somebody on this forum that owns a flowbench and has done some testing, we can't make any assumptions of which head is better for power. Just because it has three SMALLER valves on the intake, you can't say it flows more air. The 5 valve design isn't inherently better than a 4 valve design for all purposes. There's too many variables in valve shape, port design, as well as the rpm range for which the motor was intended to run to form a valid opinion.

Also, although dyno numbers are nice to compare total output, they don't tell the whole story. Acceleration is dependent on many other factors which a dyno cannot measure - including final gearing, flywheel mass, etc.

Given more development time, I would expect the 700 based motors to eventually make more power simply because of the precision of the EFI. It's just going to take some time for people to tune the systems. That's also one issue I personally have with the EFI. Unless there is significant work put into the tweaking of the data tables in the EFI maps, people might end up getting poor performance simply because the programmer isn't doing things as well as it should. Bad tuning will cost hp.

Carbs a a bit easier for the average guy to tweak and get very close to perfect jetting. EFI's are really easy for a backyard programmer to hose up and make the motor run poorly...

 

And the info your adding to this thread is?

 

Well yeah, it would be but the problem is it don't. It don't have near the top end the 660 does. Just by modding both of these bikes very simular I came to my own conclusion that the new head don't have the flow characteristics of the old. Now I could be totally wrong. It could be held back by the camshaft or electronics even. Who really knows for sure at this point. The motor has wicked power but the powerband signs off too early therefore you have to short shift in a drag race and to me thats harder to do as oppose to letting her rap up tight then banging the next gear. Thats just me and my opinion though.

 

It's due to the rev limiter.

It does not allow 5th gear to rev out to the same RPM's as the other gears.

I believe it stops at 7,000 RPMS in 5th gear while the other gears are 9,000 RPM's.

 

I don't think so Blazin. I've hit rev limiters before on other bikes and its not the same thing. The motor doesn't reach a certain RPM then shut down (cough, spit, sputter) like hitting a rev limiter it doesn't do that at all. Its more like it pulls like hell so far and then it just stops pulling and thats in all gears, its just more noticable in the higher gears cause they're more stretched out. Like its running lean on the top and needs more fuel to get more Rs but when I try to give it more fuel it doesn't respond with more Rs it just runs rich and uses more fuel.

 

I haven't read this whole thread so maybe this question has been answered. Did you pipe and intake your 700R without a new Power Commander? My 700R is neck and neck with my buddy's piped 450 and my '03 660 wasen't even close. You are the first person I have talked to that thinks the 660 is quicker than the 700. I know the 700's run like crap if you don't install a power commander with your pipe and intake. Stock EFI has the ability to adjust for air density but they cannot adjust for a dramatic increase in air volume.

Ron

 

Ron, no I have the Dobeck TFI and it works good. Its doing whats its suppose to. I know it sounds like I'm talking up my 660 but I've seen fast ones and slow ones and most of the time jetting made the difference. Don't get me wrong, the 700 is a bad **** but my 660 was a little faster. I never realized that these two were that different but they clearly are.