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testarossa wrote: Keen observation Mark. Joe at Pit Stop sells two versions of the 10.5 to 1 pistons. These are for longer duration/higher lift cams. He says not to use them with the stock cams as they will provide too much compression for a street bike. I told him that I wanted what ever set that would be best with those K410 cams, and this is what he said to use.
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Wow! Never heard that 1 before. i hope u dont get any ping.
You may want to reduce your squish area to help.

They are just standard 10.5:1 MTC pistons, so they will work great.

It should be a nice setup when it is done.

Pit Stop sells the same pistons with machined domes for stock cams.

Their sales pitch for them drives me crazy, although I understand what they are trying to achieve.

10.5:1 pistons are 10.5:1 pistons, regardless of the cams.

The 10.5:1 is the static compression ratio, which is can be derived using math. It is based on chamber volume and is not affected by the cams or cam timing.

I'm with tachrev, all of that doesn't make any sense to me. Compression ratio is compression ratio, cams have nothing to do with it. They might have deeper pockets to clear the valves due tot the greater lift/duration. In which case, if they're machined from normal MTC 10.5:1 pistons the static CR would be lower as you've removed material. I think Joe is either full of shit or you heard him wrong.

Sorry. i didnt mean to open a can of worm here. not to worry , it probably just that they look dif in the pic.

TDub. longer duration cams WILL bring down the compression ratio. thats why u need more compression to run bigger cams.

Compression Ratio: corrected vs. mechanical

www.bing.com/videos/search?q=Compression...D&first=0&FORM=LKVR2

Good Fortune!

Edit: Or should that be dynamic vs. static.

It'll bring down the dynamic CR sure. Also depends on how you have them adjusted, ie how much overlap you're running.

I always thought pistons were rated for static compression ratio, hence my statements above. If they are rated for dynamic CR then thats different.

No eBay APP ID and/or Cert ID defined in Kunena configurationHere's Pit Stop's ebay ad for these pistons:

If you click it and read his description, he expains his theory in the ad. I always thought like Tyler that "compression ratio" was determined as static. I also agree with Mark and Joe Hooper in that some "compression" is lost in the overlap phase, and so high lift/high duration cams will reduce "compression." Joe advised me that these pistons were designed to work with said cams to provide the type of "compression" that one would achieve with stock cams and 10.5:1 pistons. It's a little bit of a confusing way to advertise pistons, but Joe made sure that I got the right thing before he shipped the pistons. I give him all the credit in the world for clarifying this since I clicked the BIN on his Ebay auction. He could have easily just shipped them and left me to sort it out. I told him specifically what cams I was using and he advised me to use these pistons. I'll trust his advice since he's been in this business longer than I ever thought about it.

Craig asked earlier when I was planning on building this motor, and the answer is this winter. I won't miss the nice riding weather in fall, so I have to stick with the old stock motor until the days get short.

T_Dub wrote: It'll bring down the dynamic CR sure. Also depends on how you have them adjusted, ie how much overlap you're running.

I always thought pistons were rated for static compression ratio, hence my statements above. If they are rated for dynamic CR then thats different.

I agree...that's what throws me for a loop.

However, I think it is just a way for them to make it easier for potential customers to understand.

It's just something that drive me crazy in the eBay adds. Their prices seem fair enough.

Anyway...I think I've gotten us off topic. Sorry bout that.

i just thought your pistons look high and i hope it doesnt cause isues. some guys report pinging with 10.25:1 static compression pistons. here are some pics of mine. i use .425" lift cams.

1200cc J&E 2009


Wiesco 1135cc 1977



1327cc old


pit stop pistons

they remind me of an old style (long skirt) 13:1 piston that has been cut down ?
doent matter as long as they rip.

Mark, I think that your larger bore has an effect on the overall compression ratio as well. More cylinder volume compressed into the same size combustion chamber = higher CR right? That should be the reason for higher domes on the 1075 cc pistons. If I can't make it work with a combination of timing, and super unleaded, then I'll surely report back and make adjustments as necessary. I don't want to have to run this bike on race gas.

You're exactly right Josh about the dome height.

As for the CR crap, seems like Joe and them are doing the right thing, selling you pistons that'll work better with your combination. Manufacturers DO list pistons by static compression (ie, volume ratio), but dynamic compression is more important as it is the actual pressure ratio of TDC cylinder pressure to atmospheric. Dynamic compression is affected primarily by the combination of valve size, porting, and cam overlap. Basically, the higher your dynamic compression ratio, the higher your cylinder pressure at TDC, and the higher your power output.

No eBay APP ID and/or Cert ID defined in Kunena configuration

testarossa wrote: Here's Pit Stop's ebay ad for these pistons:

If you click it and read his description, he expains his theory in the ad. I always thought like Tyler that "compression ratio" was determined as static. I also agree with Mark and Joe Hooper in that some "compression" is lost in the overlap phase, and so high lift/high duration cams will reduce "compression." Joe advised me that these pistons were designed to work with said cams to provide the type of "compression" that one would achieve with stock cams and 10.5:1 pistons. It's a little bit of a confusing way to advertise pistons, but Joe made sure that I got the right thing before he shipped the pistons. I give him all the credit in the world for clarifying this since I clicked the BIN on his Ebay auction. He could have easily just shipped them and left me to sort it out. I told him specifically what cams I was using and he advised me to use these pistons. I'll trust his advice since he's been in this business longer than I ever thought about it.

Craig asked earlier when I was planning on building this motor, and the answer is this winter. I won't miss the nice riding weather in fall, so I have to stick with the old stock motor until the days get short.

good good.....that is when i think i will pull the 900 out of the frame and take it all down too....

maybe have it together and painted by spring and the quail just to ride it to the sunday show and park in the cheap seats.....exciting.....build it tough as you want but by god see that it is ready to ride by spring aye....my worst fear always...MKII and its phase II maiden ride was the quail going 100 and hitting cattle gaurds...see if i can have my spring rides ready in spring from now on......cool pistons and ripper

the static compression ratio is simply the volume of the cyl as it relates to the volume of the chamber, as a ratio. if the cyl volume is 10 times that of the chamber it is 10:1.
if u put the piston at bdc.(grease the rings first) and measure the amount of water it takes to fill it. then put the gasket and head on and torque it . now put the piston at tdc and measure how much it takes to fill it. this is the 2 #'s needed to figure out the static compression.

But, the only thing that matters in the end is that u dont end up with too much cyl psi.
if u get over 200 psi u may need more octane, or more overlap in the cam.
with the cams i have ,i run at can 200psi, with premium gas.

What grind are you running Mark? Also, what octain rating is considered premium in Canada?

531blackbanshee wrote: nice pistons there sir !

that should be a very good running combo.

i cannot believe that craig slipped on getting the evidence on adam .riding in flip flops .

jee wheel lickers wally!!!!!


leon

Awwww crap! Craig's right, I was in flip flops. I hadn't planned on riding a bike that day, let alone stop by Craigs place. But he offered the ride on his beautiful blue MKII, and I couldn't turn it down. I needed an incentive to help me h=get back in the grove with my bike, can you blame me? Craig might be needling me for riding in flip flops (and shorts and a t-shirt as well), but he forgot to mention a few other incidentals about that little ride Thank you for your generous hospitality Craig. The girls needed some time to unwind out of the car, the baby ate her own weight in blackberries, Marina got a handful of awesome produce out of your garden, and I got a much needed shot in the arm on your MKII. Thanks for providing a great little detour and distraction for my family.

ok as long as we both are ok on it...jack thread...

i had a wires for a starter button and had been riding the bike to work...on the last ride,like it always is,friday riding home from work i fried a fuse...i fixed it with an extra but it was not the right one and in my haste an unexpected great visit i forgot to mention that the fuse box is under the seat and may pop ....in my defense it was on my notebook on the bench "fusses"...then with the kids running around and activity i figured you would cell phone if stranded...man i did not want to leave the house and ride looking for you ....next time i will trust my gut...i was 3 times almost on the 900....nice thing of that lady to give you a ride .....

adam and craig

josh,
if,
big ol if.
there is a bit high compression,what is wrong with installing a thicker base gasket to correct any problems?

i have some plans for a stock bore 1015 with mtc 10 whatever to ones (that i bought from a member) and just figured if i had any pinging i would just space up the cylinders and head to make everything happy.

elevation plays into that whole compression deal also.

leon

It sure does Leon. Moving the cylinder up by small amounts can drop compression significantly.

Good call Leon. Seems I remember some company that made base gaskets in different thicknesses. Save that, I can just stack in more layers of Frosted Flakes box DIY gaskets. They're GRREEAATTT!!!

On a serious note, I guess that raising the cylinders via thicker gaskets does also affect cam timing as well. I'm gonna have to degree the K410's in anyway, but just sayin'.