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Discussion Starter #1
So I just measured the stock pistons and they come in at 302 grams bare. Bare meaning no clips, rings, wrist pin. 405 grams fully dressed.

JE says their 10.5 compression (apples to apples) is 261 grams. Thats a pretty nice weight savings.

Anyone measure the CP's? I always prefere CP pistons but dont expect them to be any less weight than that JE.

Wrist pin wall thickness plays a big role in weight as well. Theres a fine balance between strength and weight there.....

I also notice CP makes a 2mm shorted rod. That gives us 4mm of extra stroke. Judging by the head shim I ran in the turbo, the cam chain, at least on my machine, is good for about 1.25mm of added deck height (base shim) before its out of slack entirely. Thats good for another 2.5mm of stroke. Thats 6.5mm of total stroke you could add without much trouble....except.....

How low can you go on the cylinder! These slipper pistons can only take so much rod angle as well, and we are now compounding the increased rod angle with a shorted rod AND a longer stroke. My magic number that I never wanted to go lower than was 1.6 rod ratio. Maybe 1.55 but thats cetainly my limit but would rather higher. Also depends on what your intention is on the engine.

So I need to either go measure the stock length rod or have someone who already knows the stock rod length tell me so I can come up with a ratio. CP does not say what the 2mm shorter rod length is so I need to do more homework.

Ive also used a "similar" piston with a smaller wrist pin and bushed the small rod end to gain a little more stoke in certain builds.

Of coarse you could have some custom stroker pistons made but that usually take 10+ pistons


Heres some #'s:

98mm bore with 6.5mm added stroke: 1070cc's

98mm bore with 4mm added stroke: 1032cc's

96mm bore with 6.5mm added stroke: 1026cc's

96mm bore with 4mm added stroke: 990cc's
 

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You can add the 6 mm stroke and be fine on the bottom side for clearance.You are going through all this work to stroke it,why give up the power on custom pistons.The shelf pistons are good but you can move the ring location and size,and all the other BS.
 

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Discussion Starter #4
You can add the 6 mm stroke and be fine on the bottom side for clearance.You are going through all this work to stroke it,why give up the power on custom pistons.The shelf pistons are good but you can move the ring location and size,and all the other BS.
Your so right, and I agree. Its just if someone hasn't produced any for sale yet, then in order to buy 1 from a piston manufacturer theres usually a 10 piston min to get what you want. Id spec my own valve pockets, pin/deck height and so on if Im going through that. I just need 9 other people to buy in!
 

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Discussion Starter #5
Also, stock exhaust valves weigh 40 grams and 32.24 mm in size.

Intakes are 44 grams and 37.73 mm in size.
 

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Almost as big as the new Ford coyote valves.Sad part is the XP head flows over 100 cfm less at .400 lift
 

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Discussion Starter #7
I believe it. I think its a real nice design though. Just needs to be opened up a bit and blended around the bowls and unshroud the valves a bit. Valves are big in this engine. I see no need to increase size to be honest.

the funny thing is, this pro star 900 engine almost mirrors a honda 450r engine. Its like having 2 450r cylinders connected together! Almost identicle bore and stroke (04/05) with a very simlar head setup.

I know if I spend enough time with this engine I could make some really good power with it.
 

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We will find out it looks like.You building over the winter?I think Nate from Alba might know the rod length off hand.
 

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He's been building it since he bought it! He's famous for this, I beleive he owned a honda 450r that never saw anything but the dyno! He can never have enough always in the pursuit of more power. This will be one nasty machine when its done. Remember thou buddy it needs to reliable so we can put some miles on it!
 

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We will find out it looks like.You building over the winter?I think Nate from Alba might know the rod length off hand.
Stock length is 5.059" from center to center.

Nate
 

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Discussion Starter #11 (Edited)
Thanks Nate!

So we are looking at an even 2.0 rod ratio. Wow thats a long rod in this setup!!

I would have no issues shortening that rod up...none at all.

In fact, id rather shorten the rod than modify the piston. You dont have that much room to lower the deck height/raise the wrist pin and fit rings between them.

Some will tell you that more rod angle creates more power due to the added leverage. Of coarse theres a point where it become too much. Reliabilty comes in to factor as you start side loading the piston. Thing is when the rod is at the most angle, cylinder pressure is quickly reducing, therefor gains are really not substantial.

Once you start going with a bigger stroke, piston speed increases as well. Another harmful reliabilty factor.

I just may have to stroke/bore/and boost this sucker :)

Nothing like dancing with the devil!! Good thing I only ride like twice a year...
 
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