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Discussion Starter #1 (Edited)
I went for a ride yesterday on my TW with its new Wiseco piston. I swear I can feel an improvement, or an increase in power / performance. Nothing earth shaking but for sure better. Last night I began to wonder "how much better?"

I used as a base line 15 horsepower and the stock 67mm bore and the stock 9.5 compression ratio. Stroke is 55.7mm.
My upgrade was the Wiseco piston with a 68mm bore and a 10.25 compression ratio. The question is how much horsepower is being produced?

67mm = 196 cc.
68mm = 202 cc

15hp/196cc x 202cc = 15.46 hp @ 9.5 compression.

A little Google search (horsepower vs compression) and I found: Wallace Racing - Calculate New HP From Change In Compression Ratios Calculator Plug in the numbers and out comes the answer. Long story short: 15.78 horsepower for 202cc @ 10.25 compression.

A little disappointing -- I was hoping the increase in compression ratio would make a bigger difference but it is what it is and as I said earlier I can feel an increase in performance and to me the bike is more fun.

As an aside, I have a 70mm piston in a thin walled cylinder, the one Fred almost got.

70mm = 214 cc.

15hp/196 x 214 = 16.38 hp

Plug 16.38 into the compression formula = 16.72hp !

If I can feel going from 15 to 15.78, then going from 15 to 16.72 ought to feel like I am on a rocket ship!

Now I am starting to wonder what TWBrian's bike has. IIRC he has a 71mm bore with a 58mm stroke and an increase in compression........................and he did say it was a lot faster! Hmmmm..........
 

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Now I am starting to wonder what TWBrian's bike has. IIRC he has a 71mm bore with a 58mm stroke and an increase in compression........................and he did say it was a lot faster! Hmmmm..........
Tony,

I believe that I am at 70.5 x 58 which equals 226cc, and the higher 10.25:1 compression Wiseco piston. And I think that I said that the improvement was definitely noticeable and that the bike has more zip to it.

Are you planning on taking it for a test ride at the Wrench & Ride next weekend - Oct. 3rd?

Brian
 

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As an aside, I have a 70mm piston in a thin walled cylinder, the one Fred almost got.

70mm = 214 cc.

Hi elime, is this a stock TW cylinder bored out for the 70mm wiseco piston? So just how thin is the cylinder wall? I've got to fix my base gasket this winter and I could just put it back together (if it looks great), bore to 68mm w/wiseco or go 70mm w/wiseco.
I just don't want to lose any reliability, but would love to be able to pull a tooth or two less on the rear sprocket for the open road.
Any input will be appreciated:).

Thanks,
MAC


P.S. elime, I guess you already gave me specs on that thin wall cylinder (.060"). Sorry, I was confused at the time about which cylinder you were showing.
macbig, if you say it's OK I'm going to assume it will be reliable for an otherwise stock motor.
thanks again, mac
 

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Yes, you can use a 70.0 mm piston on the 200 cylinder. But this will be the last oversize for this sleeve.
In the future, if you need the next oversize you have to replace the sleeve to a new 200 cc or the bigger 225 cc (cylinder needs to be rebored).
 

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My questions for you higher compression guys:

My Tw seems a little soft right off idle, Does the higher C/R make a noticeable difference right off the bottom?

Any pinging when they get hot?

Do you need to run race gas to prevent pinging?

Thanks!
 

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I have elime's original 68mm "Big Bore" with almost 1,000 trouble free miles on it. I try to run E10 91 octane pump gas. Once in smallish Santa Margarita I could only find 87 octane and the bike did not seem to knock or suffer running one tankful of regular. This was the Russell Second Memorial Ride over the coastal range and onto the beach. I would say the hi octane recommendation is of concern but not an absolute requirement. This apparent flexibility is a relief as 91 octane is not always available on the dark side of the moon.
Subjectively I sense an subtle improvement in performance. I was not really expecting gobs of wheelie inducing torque nor screaming acceleration from punching that baby out to a mighty 202cc Big Bore but it did seem to out-race a friend's stock TW a few month's ago. A good deal of satisfaction comes from noting the seemingly superior quality of the Wiseco piston with it's multitude of oil ports for the rings and slickly milled surface. Darn purdy,looking thing, I did admire it before sealing it away hopefully forever.
 

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My questions for you higher compression guys:

My Tw seems a little soft right off idle, Does the higher C/R make a noticeable difference right off the bottom?

Any pinging when they get hot?

Do you need to run race gas to prevent pinging?

Thanks!
I can't really say much for sure as I have only put about 50 miles on mine so far. I haven't noticed any softness, if anything it seems to pull stronger when starting off. Haven't noticed any pinging. I am currently on a first tank made up of about 1/3 of old stale regular gas and about 2/3 of fresh premium gas - clearly not race gas!

I was afraid that mine might be running too lean because it smelled like it was hot. But I pulled the plug and it has a nice tan color. I think that I am just baking on/burning off all the rattle can spray paint that I sprayed the engine with.
 

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I'm thinking the best way to go for me is to buy a cylinder off eBay and save mine for a backup.
Do you guys know if all years of TW cylinders are the same?:unsure:
IIRC there were differences with the chain tensioner.

thanks for the help, MAC
 

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I've never noticed a pinging on any condition/heat.
But here in Germany (an for sure in the rest of Europe) is no fuel under 95 octane (ROZ) available.
-->> I've checked on Wikipedia, 95 octane (ROZ) = 85 octane (MOZ)

You US guys have the MOZ octane fuel, right?

The most of our hobby motocross riders are using 95 octane (ROZ) [85 octane (MOZ)] fuel.
Just some riders using the next better 98 octane (ROZ) [88 octane (MOZ)] fuel.
Only a hand full riders buy real racing fuel (ex. VP Racing).
The stock compression of (nearly all) motocross bikes is 12.5:1 and I've never noticed, that a rides had a problem with pinging.

By this facts, a TW engine with 10.25:1 compression will not have this problem.


If I am wrong, please tell me that.


EDIT:
I've seen, AON (Average Octane Number) is correct for the US, right?
95 octane (ROZ) = 85 octane (MOZ) = 90 octane (AON)
98 octane (ROZ) = 88 octane (MOZ) = 93 octane (AON)
Not easy to compare fuel.
 

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Discussion Starter #12
I'm thinking the best way to go for me is to buy a cylinder off eBay and save mine for a backup.
Do you guys know if all years of TW cylinders are the same?:unsure:
IIRC there were differences with the chain tensioner.

thanks for the help, MAC
Look at Mac's EXCELLENT thread on parts interchangeability to increase displacement. YFM200, YTM200, BW200, TW200, etc. parts will work. This is what got me started.

http://tw200forum.com/forum/performance-customization/13306-list-parts-you-will-need-upgrade-your-tw-214-225-up-250-cc.html
 

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Sabastian's a great help around here!! :icon_thumright:
 

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Thanks Sebastian for the clarification. Good to know that american regular grade gasohol (10% ethanol, 85 octane) should not cause detonation issues with a 10.25 compression ration Wiseco piston installed.
 

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Discussion Starter #15
I have elime's original 68mm "Big Bore" with almost 1,000 trouble free miles on it. I try to run E10 91 octane pump gas.
Subjectively I sense an subtle improvement in performance. I was not really expecting gobs of wheelie inducing torque nor screaming acceleration from punching that baby out to a mighty 202cc Big Bore but it did seem to out-race a friend's stock TW a few month's ago.
A thousand miles? Your warranty is up. Its over. Its done. Seriously, if anything was going to go wrong it would have happened by now. I think you are home free -- knock on wood! I have 200 miles on the piston I installed last week and so far it seems fine. Knock on wood again. Big D and I traded TW's and he said he felt more torque in mine. The comparison isn't as perfect as it could be because I also have a 55t sprocket and he has a 50t. Still, his bike to me felt more less powerful than could be accounted for by the sprocket alone -- if that makes sense. Anyway, keep in mind we are picking up maybe 3/4 of a horsepower. Some will say it is not worth it. I say if you can feel it then it is worth it. It is a very easy and trouble free upgrade and I believe well worth doing.

As for gas, I always run premium. At most it is 50 cents more to fill the tank. Big deal! That is not even a Snickers candy bar.
 

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Mac big can I get your thoughts on milling the head to increase compression ? Wiseco piston 10.25 and milled head = 11.00 to 12.00 compression?

Ronnydog
 

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Discussion Starter #17 (Edited)

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Good observation Ronny. Those valve sized detents machined in the Wiseco piston top are not there for decoration.
 

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Discussion Starter #20
Wiseco is a truly high performance piston designed to accommodate high lift camshafts. I would be very surprised if shaving .025" interfered with anything valve wise. However, those plastic cam chain sliders and the cam chain adjustment bolt may present problems. The one slider gets pinched between the head and the block and is there enough adjustment in the cam chain adjustment bolt to take up the extra slack? Just wondering........we need someone to try it and report back.

The piston with the deep valve pockets is the Wiseco.

P3200023.JPG
 
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