[BBRMotosports]

I was curious if wiseco was making a high compression piston before I went to town on shaving my head. I emailed them and the reply was we are not making a piston for this bike. I asked if they were planning on it and they said possibly in the next few months. Now do I wait for a high coomp piston, or shave my head? Decisions decisions

 

[somebody5788]

I'm worried about the weight difference. The balance shaft in the engine was weighted to smooth the engine out against the factory piston not an aftermarket one. You may have to eliminate the shaft to do an aftermarket piston.

 

[BBRMotosports]

I don't see that being an issue, I run wiseco pistons in my MX bikes and my crf is basically the same engine design with balance shaft and I don't have any issues.

 

[Kurlon]

Wiseco will do a batch of 4 pistons to your specs if you want to go that route. Keep one, post dynos, sell the rest.

Or, if the myth is true that it's based on a CBR1000RR piston, Wiseco sells a 76mm 13.5:1 slug...
http://www.wiseco.com/ProductDetail.aspx?ItemID=40034M07600&ModelID=485&ModelYear=2008&AppID=42806

 

[DRC]

or you can get a stocker off of ebay...used. 12.7:1

 

[BBRMotosports]

I'm i'm gunna go pull the top end off my bike i'm not going to put a used piston in it.

 

[Kurlon]

I'm i'm gunna go pull the top end off my bike i'm not going to put a used piston in it.

Most of the people pulling top ends apart on liter bikes are doing it to new machines for racing, stuffing in higher comp units. That 'used' piston may have only seen one quick trip to redline on the factory dyno before it was shoved in a crate to be shipped to a dealer.

Or it may be a ragged out smoker, but it should be obvious from the pics which life it's led.

 

[BBRMotosports]

For the price of what 2-$250.00 for a slug plus gaskets isnt bad. I would rather just throw a brand spankin new one in and be done. Either way it's gettin head work or a higher compression piston. Or even a piston and some porting. No matter what I do I will run it on the rollers and post results. It wont happen until snow flys here though.

 

[BBRMotosports]

Does anyone by chance know the size of the wrist pin on the 250?

 

[cyanide]

As per this post
http://www.cbr250.net/forum/16396-post67.html

they have the same diameters, which should be 17mm.

If Wiseco are making pistons for these bikes, I want to see their skirt length, ring thicknesses and valve clearances before I'd put my money down for one. The CBR100RR might share a few things with the 250R, but with that tight of a clearance, I don't want to take chances with the valve relief angle or the weight.

From my experience, the stock 1000RR piston should be good to go. We've run it on a car engine which has perhaps a little better harmonics than a single cylinder bike engine (still an inline 4 though). As long as you have a good tune, the manufacturing quality of a OE Honda piston should be able to take the power. It is usually the connecting rod which either bends or breaks due to detonation. If someone can share a pic or two, along with various diameters and widths, I can build it in my simulator and do a FEA analysis on it to determine how strong it is. I have specifications of various forged and cast connecting rods in my database, so a comparison should be possible.

 

[cyanide]

Then again, I'm a proponent of a smaller combustion chamber rather than a domed piston for a compression increase. A flatter piston will give you an ideal shape for flame travel, along with a higher downward thrust which will result in better torque characteristics. Combine that with the quench pads that the 250R head has, and a tight squish, and you are looking at a very healthy combustion chamber that can resist detonation unless the tuning is done by someone incompetent.

 

[somebody5788]

Just throwing in a 1000rr piston might not raise the compression at all. The head on the 250 and the 1000rr might have different cc's making the compression come out different depending on what they are. What I mean by this is the cavity that the valves and spark plug sit in is also part of the displacement measurement and if the 250's is larger then the 1000rr then the piston may not change the compression ratio at all.

 

[BBRMotosports]

All this talk about taking the 1000 piston and putting it in the 250. I'm not going to do it. I'm either A: gunna wait til someone makes a high comp piston or B: Shave the head. I do own my own shop and have all the equipment needed to shave the head and possibly re chamber it if need be. I'll let someone else be the ginnuea pig on slapping in a 1000R piston.

 

[Redline]

So when are you going to shave the head?

No time like the present.

 

[BBRMotosports]

Once I cant ride anymore, probably in the next month.

 

[Amontgomery]

It stands to reason that if the stocker CBR1000rr piston fits (probably, as someone mentioned, having too much clearance due to the head design) then the high-compression Wiseco 1000rr piston should fit as well. The wrist pins are the same, as is the diameter. The only things that are unknown are the valve position and clearance, skirt shape/size, and balance issues associated with the stock 250r balancer.

The biggest thing I can think of, both in a positive and negative light, is the possible difference in head surface/valve clearance and how it relates to compression ratio. I'm ready for someone, anyone, to give it a try.

I plan on doing it as soon as I relegate my 250r to a track/fun bike rather than a daily-commuter/fun bike, likely after I get a larger sport or supersport in a few years. In that time I hope significant advancement has been made with the motor, as I feel it has great potential, if based on nothing but geometry alone.

 

[BBRMotosports]

I emailed both Je piston and CP piston and they said said they would make high comp pistons for the bike but they need a cyl and head to make them. Anyone wanna be the ginnuea pig? My bike is going to a company for R&D and it's getting the head shaved anyways so it someone elses turn.

 

[tygausa.com]

You guys keep tempting me to rip her apart and lockdown the head in this for a bit...

Maybe this winter

WW

 

[250 Tom]

Dont think to many buy a 250 to go fast, wouldnt it be easier to just move up to a 600 if your not happy with the power of the little CBR?. But then again you might be someone who just likes to work on motors. Good luck with your prodject. How much hp do you think could be gained by this modifacation

 

[tygausa.com]

Dont think to many buy a 250 to go fast, wouldnt it be easier to just move up to a 600 if your not happy with the power of the little CBR?. But then again you might be someone who just likes to work on motors. Good luck with your prodject. How much hp do you think could be gained by this modifacation

Agreed, Tom. For me, 4,500 base elevation, she needs a touch more. Moving to a 600 is easy (been there). Tweaking what you have for a bit more is a lot more fun and rewarding.

WW