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8219
Joined
1/11/2016
Location
Tombstone, AZ, USA
Edited Date/Time
8/4/2021 6:29am
Bike has won 7 of 16 250SX titles (per matthes) and won 5 of 7 250 National titles since they turned the cylinder around in 2014. Not bad.
Pretty close to PC’s level of dominance from 2004-2012
Pretty close to PC’s level of dominance from 2004-2012
Outdoor: Jmart '14 & 15, Webb '16, Plessinger '18, Ferrandis '20
Indoor: Webb '15 & '16, Plessinger '18, Ferrandis '19 & '20, JCooper '21, Nichols '21
The Shop
Free shipping: VITALMX
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Luxon 4-Post Bar Mounts
$189.95 - $239.95
It came with a significant HP increase, and the bike is much more powerful in terms of numbers than the Yamaha. But, seat of the pants, everyone has always complained that the 2018+ CRF250 is weak on bottom, the opposite of the YZ250F engine characteristic.
So, as often has been the case in the little class, it's not about how much power, but the TYPE of power.
Of course I hear the bikes peak against the rev limiter, but I literally hear every sound from throttle-stop-to-stop. It is probably pretty challenging to come up with an engine package for those guys, and I would bet proportionately little time is spent chasing peak hp.
With so many choices in 4t engine design, 5 valves vs. 4, short vs. long stroke, SOHV vs. DOHC it's interesting to see where it ends up. It seems Yamaha made the decision to drop 5 valve and go for more bottom end and it has paid off. I can't believe no one has followed them yet.
Rumor is Beta is working on a 250f, and it will be interesting to see what direction they go. Their company's direction in engineering, from the Owner himself, is rideability. Beta engines are often overlooked because they feel slow, as is common in engines with smooth low end torque. They hook up though, and have deceptive speed, and the less you are dancing with the clutch and shifter the faster you can go by pulling taller gearing.
So strange and anyone complaining here can't ride SX at the top level to talk from a point of authority.
Moto GP 1000cc Yamaha 4's with finger followers and PVRS -ie no springs- but similar bore size and implied valve diameter are reputedly good for 260 to 280 HP so 65 to 70 peak HP at around 17500 rpm per 250 cc cylinder -ie but with less range.
Pit Row
As far as the Yamaha configuration, it certainly works great for 250s. I've had a couple now and they rev fast, produce great power and obviously the pro teams have been able to make monsters out of them. Any quirks that people have about the Yam chassis aren't that big of a deal on the smaller bike. The weight is lower as is the inertia. And the bike doesn't feel as big/wide as the 450 does. You can still toss the 250F around, which is a little tougher on the 450.
That is the entire point of the discussion: they have a good peak number and a lot under the curve
What’s more impressive is that they have developed a chassis, suspension, and mapping package that lets them put all that power to the ground in a way that still makes the bike very rideable for a variety of different riders. To me, this is way more impressive than peak HP/TQ numbers from the dyno.
Said to be developed in 2011, whereas the YZF450 came out in 2010, but you can be your arse that Honda had that reverse cylinder in 'development' well before 2011, with their machinations for 'all 4t stroke, all the time ' racing classes. Yams 250F Reverse cyl /head, came out in 2014, I think.
I'd say Honda were very pissed that Yamaha brought out their version before they themselves put it into use in a vastly larger sales market that the 250 and 450 Offroad and MX market is over the Moto3 side of things.
Honda would, I think, never want to be seen as following another manufacturers engine 'idea', especially Yamaha. I really do think it was a design they wanted to be 'theirs'. They got thoroughly gazzumped by Yamaha, who've adopted it as their USP on the YZFs and WRs .
Of course, there's been myriad reverse cylinder and head engines in bikes, both 2t and 4t for decades. TMs Moto3 engine (I think only used so far in Italian domestic Moto3?) is a reversed engine, but heck, I think most of their Kart Engines are 'reversos'. Well, many Kart engines from other manufacturers are 'reversos'.
What if:
1. another mfg decided to go this way?
2. Yamaha produced a 350 that would smoke KTM's version?
Post a reply to: Backwards Engine YZ250F Dominance