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difference b/w 11:1 and stock piston?

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i have a ross 102mm (670) 11:1 piston. i was comparing it to my stock piston and the 11:1 doesnt seem to be any taller. how does it make the extra compression?

i lined the wrist pins up, and even stuck the wrist pin in each side of both pistons to ensure that the wrist pins were level, and the tops of both pistons were flush.

how much more is 11:1 than the stock 10:1, b/c i cant figure out how it makes the extra compression, the valve reliefs even appear to be cut deeper.

to the naked eye, should 11:1 and 10:1 be noticable when comparing pistons?

nothing is wrong here, im just curious and trying to understand

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My JE 11:1 had about a 3 to 5 mm dome on it. Does not take a whole lot of change to take up a lot of cc's on a piston that size.

Also the outer edges of the piston will be the same height as stock so they don't hit the head in the quench zones.

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That is a possibility. Check for a part # on it. The JE is laser etched on the inside. The Weisco is stamped right on the dome.

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Here's my wiseco 102.5 11:1 its' a flat top also i also checked the part number and it's correct006-2.jpg

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mine's flat on the top just like the wiesco. how many cc's of air difference compresison is there b/w a 11:1 and a 10:1?

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How sure are you that your is a 10 to 1.

Or could the bigger piston crown overall give it the comp?

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Here is the stock piston, ry%3D400

and a bad pic of the Wiseco 10:1 piston...ry%3D400

as you can tell both have a slight dish to them...I know other things can build compression, deck height, head gasket thickness, etc...but for all practical purposes both are stock compression without other context.

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damn what happened to the weisco in that pic?

on another note, does anyone know if 11:1 JE's, Ross's and weisco's all have the same amount of valve clearance?

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Broken valve would be my guess.

And yes I forgot the stock piston is slightly dished.

Your correct, valve broke at the stem...long story but it was a combination of mislabeled part and wrong clearances for said part. But I threw the pic in just to show what a couple of 10:1 pistons look like so Matt can compare to his 11:1

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Valve seize in the open position? Little tight on the stem to guide clearance?

Ok I'll get into it. there were a few different things found as a result and its not 100% sure which is the chicken or the egg.

I've given up on pointing fingers because its all hearsay and word of mouth.

results:

a) You can see below the exhaust valves are warped towards the center of the head

:lol: the broken intake valve stem was blue from heat at the point of the break. as well as hot spots on the intact intake valve.

c) I was specifically recommended Kibblewhite valves so I ordered over the phone the valves from XRs ONLY which I specifically asked and was verbally told were special order from Kibblewhite for XR's Only 3mm over intake and 1mm over exhaust. Because of the short lifespan (300 miles) and proper clearances Kibblewhite had me send them my head and parts so they could recreate it and measure everything only to find out that the valves were not even their valves (and they stated they don't make that size (3mm over), didn't see any performance gains with larger than 1mm over, and the stem was smaller diameter than theirs or even stock meaning that the blank was even to small to be theirs, but more importantly the retainer groove was not in the correct height?) When I asked XRs Only they denied that they ever claimed they were kibblewhite but say they are just as good and that its the only ones they use?

d) The bike had an edelbrock QS on it and it was a little lean as well as the check needle was found to be missing afterwards but I was told that it'd have to have been bad gas for it to run that hot, (which vapor never read over 250F at the time of the seize) and that the check needle in the carb only helped the accelerator pump and at wide open throttle like it was it was working under pure vacuum.

it ran for 90 miles that day without issues. then racing Wide open for only 1/2 mile it had the result you see.

ry%3D400

After opening the valve cover everything looked perfect on top of the head with proper oiling but once the head was removed you saw the damage.

It was rebuilt in the fall with confirmed Kibblewhite valves on a used head and the same clearances with all the same kibblewhite springs and hardware, and has been flogged for 3 K miles and runs like a dream.

so it could have been clearances, lean, faulty valve, or rider I don't care anymore...its done and fixed right now.

But My take-home point...measure everything and double check. and don't ask sales people making money off of you what parts you need.

Sorry Matt, Don't want to Hijack your thread so to make it relevant...clearances for stock compression pistons are still important.

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WOW!

Sorry to hear about that.

I will note that the KibbleWhite valves are laser engraved at the tip of the stem with KPMI. Wish I would have taken a picture of this. I installed their +1 mm valves just a few weeks back. Very glad I did not go with XR's for the +3 after seeing this mess.

I would have expected a hole in the piston from being lean, if it was, not melted valves.

The other funny thing about getting a motor really hot is that the valve seats usually fall out before the valves break.

After thinking about it I did buy "KibbleWhite" valves from XR's only and put them in my L about 6 months ago. I should go check those things before they do this!

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so did XR's send you black diamond valves instead? ....cuz i JUST recieved my black diamonds from XR's only... (they were stock size though, not oversized)

damnit... i hope mine dont fall apart

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so did XR's send you black diamond valves instead? ....cuz i JUST recieved my black diamonds from XR's only... (they were stock size though, not oversized)

damnit... i hope mine dont fall apart

I didn't want to start anything...because many have used their valves and are still using them with good results. Just double check all measurements and still clay test it even if you install it by the book.

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so did XR's send you black diamond valves instead? ....cuz i JUST recieved my black diamonds from XR's only... (they were stock size though, not oversized)

damnit... i hope mine dont fall apart

Are they laser engraved near the tip of the stem with "KPMI"?

The blackdiamond valves I just installed in my XRR were engraved and I got them from http://www.lukesracing.com not only did they ship the parts out way faster than XR's could even dream of, they also were cheaper.

Might be worth a call or email to the KPMI folks to find out if all of their valves receive the engraving and for how long they have been doing it.

EDIT: I have sent an email to KPMI and we shall hear back shortly.

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