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YZF267 v. YZF290
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Posted by: Indy92---------------------

I'm looking for input from YZF 250 owners that may have direct experience of the relative merits
of Eric Gorr's 267 overbore or the Thumper Racing 290 overbore.

I know this subject has been touched on before in the broader spectrum of overall performance
upgrades for the bike, but I'd like to hear more about these specific modifications. I'm looking for
an overall power gain, but with an emphasis on the low to mid-range.

Also, I've heard that Thumper uses a steel sleeve in their kit. Is this true and if so, is there really
as big a drawback to that as one would logically assume, or does it work OK?

Posted by: Indy92---------------------

C'mon, I know there are people on this board that can
give me educated answers to these questions.
Do I need to know a secret handshake or something?
Pretty please?
Hello? Bueller? Anyone?

Posted by: Rich Rohrich---------------------

Putting a steel sleeve in a YZF250 F is an IDIOTIC caveman approach and a generally foolish thing to do. Either go with a plated barrel 267 or wait till the proper plated aluminum sleeves are available to go to a bigger bore.

Feel better now?

Posted by: Indy92---------------------

No, do you? :silly:

Posted by: Rich Rohrich---------------------

So what is it you wanted?
Did you want someone to tell you it's OK to put a steel sleeve in a 250F?
It's NOT.

The rest of the info you seem to be looking for was covered pretty completely just a couple of weeks ago. The SEARCH function can provide the specific links.

Posted by: Indy92---------------------

Gee Rich, I really didn't come here to be scolded.
I merely thought I could pick the brains of some intelligent people.
Forgive me if I was wrong.
Sorry to have bothered you. Thanks for your help and have a nice day.
BTW, go easy on the caps lock. It's really not polite to shout.

Posted by: grunk250r---------------------

you'll have to fogive Rich for the scolding...he's still trying to figure out why
he doesn't have Ed Scheidler's job after "correcting" his "wrong" comment
on not running race fuel in a YZF....LOL!!!

Posted by: Rich Rohrich---------------------

You seem to be taking this personal and it's not. You asked a question and I gave you an accurate answer.
Your concerns about using a steel sleeve in a design like this are well founded. I get really annoyed when companies who are considered "qualified" do brain-damaged work and try to pass it off as a some great engineering feat. My disgust with what these companies are doing to these engines probably comes off as overly caustic towards YOU. That wasn't my intention at all, but experience has shown me that making a strong statement about these types of things is the only way to truly get the point across. Any other tactic and people will be e-mailing for months asking "should I put a steel sleeve in my 250F?".

As I've pointed out in previous threads IMHO these engines can benefit from a slight bore increase if your goal is to shift the the torque peak to a lower rpm range. I'm not convinced at this point that the increase to 290 (even with an Al sleeve) is a good idea unless you are willing to trade a lot of high rpm efficiency for a torquey woods bike type powerband. Changes to the cylinder head, cam timing and ignition curve would be required to retain the same rpm capability as the stocker with a bore increase of that magnitude. I haven't seen evidence at this point to make me believe the cylinder head will ever be up to the task.

Proper squish clearance, appropriate fuel, and good jetting is all that is really needed to realize this engines true potential. A 2mm overbore just makes the bike more friendly for those of us with less than stellar skill levels. My advice is to wait till you need to freshen up the top end unless you are a racer who truly needs every advantage.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by grunk250r
.he's still trying to figure out why
he doesn't have Ed Scheidler's job after "correcting" his "wrong" comment
on not running race fuel in a YZF....LOL!!!

Blind Faith in OEMs their reps or anyone else is naive.

Posted by: Indy92---------------------

Rich, that was EXACTLY (sorry for yelling) the info I was looking for.
Thank you (really).
Sorry we had to play Tom Sawyer and Huck Finn to get there. I apologize for being overly sensitive.
Another hot day with no A/C in my office

I'll be racing the 250F in the 30+ and 40+ Expert classes against 250/Open bikes, so I am looking for a "racer's edge" although I should probably just work on my reducing the size of my waistline before I worry about increasing the size of my piston:D
Aren't message boards great?

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by Indy92
I'll be racing the 250F in the 30+ and 40+ Expert classes against 250/Open bikes, so I am looking for a "racer's edge" although I should probably just work on my reducing the size of my waistline before I worry about increasing the size of my piston:D

On short tight SX type tracks it will likely be an advantage, on longer tracks you would probably be better served blueprinting the stock setup.

Posted by: vetwfo'er---------------------

Indy,

Keep us posted. I have a friend that traded his 426 for it's baby brother and races the Vet B class. He rails and if he could get a little better start, he'd be winning the four lap "sprint" motos.

vetwfo'er

Posted by: Indy92---------------------

vetwfo'er , I will let you know how I make out with the lil' thumper.
I currently run in the top 3-5 in my class, but hanging on for a whole moto is my biggest problem.
I ride and train when I can, but (as with most guys my age) working for a living keeps me from making
the real strides in the fitness area that I'd like.
I've ridden the 250F and find it much less tiring to ride than my CR250 and that's my primary reason
for making the switch. Not to mention that it sounds way cool.

And Rich, if you're still out there, I just dug out a copy of Dirt Bike with a test of the Thumper Racing 290F.
Don't you find it particularly contemptible that they would "forget" to mention the fact that Thumper uses a
steel sleeve? When discussing the sleeve in the article, they never mention what the sleeve is made from.
I can't believe that they didn't know. I think that stinks.

Posted by: TwinSpar---------------------

Indy,
You come from a background similar to mine (bike, age(don't know that one for sure), fitness level, etc)... You will love the BabyF. I didn't believe the whole "no arm-pump" theory until I got on the bike. It is a joy. When I first got on the bike and rode I thought "It's slow". Little did I realize that the slow feeling was not having to fight to hang on. It's competitive with the group of big bore bikes that I ride with.

I will be looking at the EG work when I have the $'s.

Posted by: DualSportr---------------------

Quote:

Don't you find it particularly contemptible that they would "forget" to mention the fact that Thumper uses a steel sleeve?

They wouldn't know what a steel sleeve was unless it came up and bit them in the backside.

They only regurgitate what information the engine builder feeds to them. Like mamma birds (i guess that leaves us, the reader, as the baby birds eating that crap!).

Sorry, was I sarcastic? Excuse me, I've been writing product releases all day - I'm grumpy.

Posted by: yz250-effer---------------------

Personally, I am not a big bore fanatic for the 250F, I want to compete with the 125's too. ( and the 426's, 250's). Without the extra juice of a 426 coming out of a corner, I find myself turning faster to keep up with them, and that is good.

I rode a 250F with a carbon airbox and a yosh exhaust last weekend and was not overly impressed with the difference for the money. I could go just as fast on mine - the other just had a little more bottom and a little more on top. It definitely had a little more oomph, but not 1100 dollars worth.

Sorry, I just don't think you can turn a 250F into a 426F, and even if you can get halfway there it is not worth the money when you could have purchased a 426 off the showroom floor. Heck, for that money, why not buy a 426 and spend a grand making it lighter?

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by yz250-effer
Sorry, I just don't think you can turn a 250F into a 426F

Clearly you can't but I don't think that's the intention. The idea is to tailor the power to the needs of a specific group of riders. Increasing the bore and setting the squish clearance is the logical path to that end and by far the most cost effective at under $400 dollars.

Posted by: bashn---------------------

I have the 267cc overbore kit in my YZ250F and I think it's a nice improvement. Is it like a YZ426? Heck no! It's 24 lbs lighter! The Yoshimura pipe added about 2-3 HP and a lot of throttle response. The 267cc kit added about another 2 HP. Compared to stock, these mods add noticably more low-end and mid range grunt. Corner exits and starts are faster. Unfortunately, when traction is abundant and and the track straightens out, you will still loose ground to 2-stroke 250's and the big-bores. You better learn to go faster wherever the track turns technical, and practice starts. These mods will make your bike faster and easier to ride on the track. I will say that I'm seriously considering adding a new YZ250 2-stroke to my stable. I'm not interested in going back to a YZ426 because of the heaviness and starting issues.

Mark
'01 YZ267F

Posted by: Indy92---------------------

Thanks for the input guys, especially from TwinSpar and bashn.

That really reaffirms my decision to switch to baby blue and helps
me choose the mods I'll need to fit my wants and needs.
I knew I could count on the DRN faithful

Posted by: theMotoMan---------------------

Quote:

Originally posted by bashn
Unfortunately, when traction is abundant and and the track straightens out, you will still loose ground to 2-stroke 250's and the big-bores. You better learn to go faster wherever the track turns technical, and practice starts. These mods will make your bike faster and easier to ride on the track. I will say that I'm seriously considering adding a new YZ250 2-stroke to my stable. I'm not interested in going back to a YZ426 because of the heaviness and starting issues.

Mark
'01 YZ267F

bashn,

I'm right there with you man! I love my 250F, but I too am thinking about a 250 2-stroke for 2002. I can ride faster than most of the riders in my class, but if there is a long start, they toast me (vet class). I then have to play catch-up while the front runners are roosting away!

What we need is a 325 kit for our 250F's! Maybe Yamaha or someone like KTM will come out with something between the 250 and 400 that will fill a need in the vet classes. KTM makes a 300 2-stroke, so why not a 325 4-stroke that is still based on the lighter chassis?

Posted by: osheen---------------------

The stock bore and stroke of a YZ250F is 77 X 53.6 which is 249cc. If you add 2mm of bore the displacement changes to 262.7cc. Where did 267 come from? cc= Pi X R squared X stroke. Numbers are changed to cm. 7.9/2=3.95 radius)

3.95 X 3.95 X 3.1416 X 5.36 = 262.73012cc You try it...........

Posted by: XRpredator---------------------

Quote:

Originally posted by osheen
3.95 X 3.95 X 3.1416 X 5.36 = 262.73012cc You try it...........

YZ267F just sounds cooler than a YZ262.73012F, dudn't it?:confused:

Posted by: EricGorr---------------------

Regarding the discussion on the sleeve issue, some people use cast iron sleeves. Cast iron and nickel composite have their pros and cons. But in a high performance 4-stroke engine the cons of a sleeve are the reduction of heat transfer which results in a greater percentage of fuel used to cool the cylinder walls. Also the cast iron wears and contaminates the oil. The other obvious reason is that theres only one sized piston, so when the cast iron bore wears (faster than nickel composite because its softer) you'll have to replace the liner, which is expensive.

My feelings are that the YZF series cylinder are too weak to handle the stress of being heated to 450F then having a cold cast iron sleeve dropped into them and wedged in a 10 ton press until it cools. The pundits may argue that cast iron contains graffite and produces a lower coefficent of frictiion than nickel and is softer so the rings seal better, but the thermal and wear issues are paramount on a dirt bike.

I'm not going to blow smoke about this kit making another 5hp at any rpm over the stocker because I heard enough of that bovine fieces over in vendor's row at the recent Amateur Nationals, but the simple fact is the Wiseco 2mm oversize piston with a 13.2:1 compression ratio is a better bargain than any aftermarket exhaust system on the market.

Steve Simpson and Pete Payne ran over 140 dyno runs on Pete's Dynojet rig and they said that the fuel made the biggest difference over bolt-on products like exhausts and air boxes.

Pete if you're reading this please feel free to chime in, Eric

Posted by: Pete Payne---------------------

Yes , Steve and I did a lot of testing on the 250F. I feel that the MR2 fuel was the best improvement. It gave us an increase in performance no matter what combo of parts were on it. No need to worry about mismatched parts combinations or super loud exhaust systems ,the DSP full race exh gave a good increase, but is super loud, I think this is a bad trade off. If they phase out 2-strokes and the noise level of the 4-stroke stay up to keep the HP level up, a lot more practice tracks will be closed down due to neighbors complaining about the noise.

The carbon fiber air box also proved to be a bad choice. The stock air box out performed it on the Dyno. Willie at DSP took the air box back , but could not believe we did not get an increase. He wanted us to try it on the track, and assured us we would like it due to the assumed increase in throttle response, but at$500.00 Steve did not want to chance not being able to return it.

I to do believe that a 2mm overbore, NICASIL cylinder , will be a good choice as far as bang for your buck and a solid increase in performance.

Steve can comment more on track performance.He is an excellent test rider and notices very small changes.

Posted by: sm219---------------------

So with this mod, is the bike still legal for the 125cc class ?

Posted by: EricGorr---------------------

New AMA rules regarding the YZ250F
Starting in 2003 the maximum displacement of a 4-stroke racing in the 125 class 250cc. But for this year 2mm overbores are allowed for modified amateur classes.

For those of you thinking about racing 4-strokes in the open or 250 classes. In 2003 the maximum displacement of a 4-stroke in the 250cc class is 450cc. The minimum displacement for a 4-stroke in the open class is 475cc.
:scream:

Posted by: osheen---------------------

Then your screwed and can't race at all. They probably won't even let you trail ride. They might even confiscate such a cheater bike. :scream: I don't know why the geniuses at the AMA and FIM left a void of 25cc in there. Probably a throwback from the 70's and the 2mm overbore limit. C'mon AMA, wake up, we don't have boreable cylinders anymore! The whole thing is so messed up. Currently you can't ride a '78 YZ100 in the 250 class but you can ride a KTM520. What sense does that make? Any smaller displacement bike should be allowed in a higher class. If you can beat the other guys on a lesser bike, more power to you..........

Posted by: DualSportr---------------------

Quote:

Willie at DSP took the air box back , but could not believe we did not get an increase.

We found the same thing when testing it on the 400, then the 426 a year later. Each time we received the same response as you, surprise from the mfr. at our test results.

Tried again (at a customers request) on the 250, and got basically the same results.

But they look so cool!!!

BTW, our results with the ti exhaust system were considerably different than yours - hp was good, but torque numbers really dropped off the scale with our hydro dyno.

Posted by: Pete Payne---------------------

Dualsporter,
Steve 125 and I had the same results with the carbon fiber air box on the 250F . And we got pretty much the same answer from DSP. They could not believe there was no better result anywhere across the RPM scale. We didnot put it on the track , as they claimed there was a much better response feeling on the track. But--- They do look cool. Oh well--Pete.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by osheen
Where did 267 come from

Probably the same place that 420 instead of 417 (2mm over YZ400F) came from. After it gets repeated enough times I think it just sort of sticks. I guess I'm as guilty (or lazy

) as the next guy in this case .

I stand corrected. Thanks osheen.

Posted by: jimt_yz400---------------------

Pete Payne,
Cnn you share with us what you jetting specs were with the MR2 fuel (as well as elevation).

If we can get a decent improvement with just changing fuel why bother with those expansice bolt-ons!!
Thx Pete!!

Posted by: Ando---------------------

There is one more important option that should be mentioned. Thumper racing also sells a 4mm overbore in a plated cylinder. It specs out to 276cc displacement, which of course Thumper refers to as a 280 kit. Currently this is only available through Thumper, as they have some sort of agreement with Wiseco to supply the piston only to them. We have one customer with this set up, and so far it has worked pretty well. The only real question with this kit is, will the cylinder wall support this much overbore without any problem? Our customer hasn't had any trouble... yet.

The results were very impressive compared to my all stock YZF.

Posted by: DualSportr---------------------

If you guys want to get grumpy at anyone for playing the 'displacement game', how about Honda.

The one that comes to mind the quickest is their TRX300EX (quad) - it's really 282cc's. Talk about fudging the numbers!

Posted by: utvols---------------------

Why doesn't anyone talk about the 280 kit from thumper. I have a 01 WR250/280 that has run flawless for the past three months. This is not a sleeved cylinder and has not exhibited any of the problems discusssed about the 290 kit. I can't find any negitive to the kit and this bike has been harescrambled every weekend since it was put together.

Just a Thought!!!

Posted by: Tex Labo---------------------

Now, I may be wrong here....but I believe Thumper Racing also makes a 280cc kit. This eliminates the sleeving, and puts the largest piston possible in the factory cylinder.

You may want to double check me on this, but it seems I read a post over on Thumpertalk that mentioned this.

Just trying to help...

Tex Labo
'01WR250F
'01DRZ400e (For Sale)

Posted by: Ando---------------------

Did anybody even read my last post? ^^^^

Posted by: DualSportr---------------------

Hey, Ando, did you hear that Thumper makes a 276cc kit? But they call it a 280. You should check it out!

Posted by: jimt_yz400---------------------

I wonder why more people haven't purchased the 280 kit? I'd think that this would be perfect for an off road (enduro/hare scramble) bike.
Ando, how much was the kit?

Posted by: Ando---------------------

My recollection is about $400 including plating, piston, rings, and gaskets. Thumper also has bored, plated cylinders in stock, so turnaround time is very quick. We would have gone with Eric, but he could not get the larger 4mm over piston, as I said above, that is only available from only from Thumper. I also tried to get it straight from Wiseco, but they said NO.

Posted by: Rich Rohrich---------------------

Quote:

Originally posted by Ando
We would have gone with Eric, but he could not get the larger 4mm over piston

He wouldn't have done it even if he could get the piston from wiseco (it's no problem getting them from JE in small batches). He and I have come to the conclusion that 4mm + plating clearance is too much to take out of that barrel and still maintain bore stability.

I wish you the best of luck with that customer.

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YZF267 v. YZF290

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