Indy92

Member
Mar 12, 2001
22
0
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?
 

Indy92

Member
Mar 12, 2001
22
0
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?
 

Rich Rohrich

Moderator / BioHazard
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Jul 27, 1999
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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? :)
 

Rich Rohrich

Moderator / BioHazard
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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.
 

Indy92

Member
Mar 12, 2001
22
0
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.;)
 

grunk250r

Member
Nov 16, 1999
144
0
oh well....

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!!!
 

Rich Rohrich

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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.
 

Rich Rohrich

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Re: oh well....

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.
 

Indy92

Member
Mar 12, 2001
22
0
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:p
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? :cool:
 

Rich Rohrich

Moderator / BioHazard
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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.
 

vetwfo'er

Member
Dec 18, 2000
124
0
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
 

Indy92

Member
Mar 12, 2001
22
0
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.
 

TwinSpar

AssClown WannaBe
N. Texas SP
Aug 18, 1999
6,880
109
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.
 

DualSportr

Member
Aug 22, 2000
527
0
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.
 

yz250-effer

Member
Nov 4, 2000
305
0
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?
 
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Rich Rohrich

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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.
 

bashn

Member
Dec 6, 2000
65
0
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
 

Indy92

Member
Mar 12, 2001
22
0
Thanks for the input guys, especially from TwinSpar and bashn.:cool:
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:)
 

theMotoMan

Member
Jan 12, 2001
60
0
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?
 

osheen

Member
Feb 27, 2000
202
0
Do the math, where did 267 come from?

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...........
 
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XRpredator

AssClown SuperPowers
Damn Yankees
Aug 2, 2000
13,510
19
Re: Do the math, where did 267 come from?

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:
 

EricGorr

Super Power AssClown
Aug 24, 2000
708
1
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
 

Pete Payne

MX-Tech Suspension Agent
Nov 3, 2000
932
38
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.
 

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