[martinfan30]

Trying to decide which piston to buy... Need more power w/o pinging.

So, who runs a 11:1 and who runs 10.5:1?

Does the 11:1 require race fue3l to keep quiet, or is 91 OK?\




Hoping for that tax rebate!

Big tank, new meats, piston, chain/sprocketts! IF SHE lets me!!!

[stepho]

we run an 12 to 1 piston made by AAR with 91 shell from california. But I can tune that ping out with a tap of the finger. Depending on which cam timing we are using we keep it around 24 to 25 at WOT.

[martinfan30]

we run an 12 to 1 piston made by AAR with 91 shell from california. But I can tune that ping out with a tap of the finger. Depending on which cam timing we are using we keep it around 24 to 25 at WOT.

Is that a measurement of "PINGING"?

Is ceramic coating worth it?

[Norge]

I run 10.5:1 piston. No problems with pump gas (88 to 93 octane) and big power increase.

[martinfan30]

I run 10.5:1 piston. No problems with pump gas (88 to 93 octane) and big power increase.

Hey Norge, you run a hotcam also??

Which gained more power??

[dldavis_66]

I didn't think you could fit one of them in an L. Or can they be modified a little?? The 11:1(100 x 8.6) is made for the R, by Wiseco, and they say it will not fit in the L model...not the same stroke. Maybe its just a taller piston. If the dimension from the center of the pin to the very bottom of the skirt, then I guess you could put it in an L. I dunno....

Anybody care to add to this???

Wouldn't mind putting a 11:1 in my L's

[Norge]

Hey Norge, you run a hotcam also??

Which gained more power??

Yes, Hotcam stage 1 installed at the same time. I can't say what provided more gain, but together its much better than the mechanically de-tuned stock configuration.

[stepho]

the 24 or 25 is the timing btdc at wide open throttle where most of our pinging happens.

[dldavis_66]

Hey...I appreciate the info in the PM.

Geeze....I've heard about XRSOnly.com before...never though of giving them a peek.

Yeah...and about the 11:1 piston...wow. I thought JE stopped making pistons for the 650L...let alone a 11:1

Hey MartinFan, if you decide to go with the 11:1, keep us posted. I'd like to find out if your starter has any problems kickin that piston. But then again, it might not if you put in a HotCam ....

[cleonard]

I didn't think you could fit one of them in an L. Or can they be modified a little?? The 11:1(100 x 8.6) is made for the R, by Wiseco, and they say it will not fit in the L model...not the same stroke. Maybe its just a taller piston. If the dimension from the center of the pin to the very bottom of the skirt, then I guess you could put it in an L. I dunno....

Anybody care to add to this???

Wouldn't mind putting a 11:1 in my L's

I'm pretty sure that most if not all of the large RFVC motors from the original XR500, to the XL600, the XR600 and XR650L all are the same overall size. The piston height is kept the same by moving the location of the piston pin. That would make the piston pin location 1mm different between the XR600 and XR650L, with the 650L piston pin being 1mm closer to the top. If you tried a 600 piston in the 650 it would go 1mm too high. Would it hit the cylinder head or valves, I'm not sure. I do know it would screw up the squish. Same thing if you put a 650L piston in a 600. It would be 1mm too low, lowering the compression and screwing up the squish.

At least that is what I think. I've never held a 600 piston next to a 650L piston to see the difference.

[Captain Midnight]

I used a J.E. 10.25to1. Needed to mix in in a little race gas when lugging in the woods. Mostly OK on the street. Cut the piston down to 10to1. I like it a little better now.

[martinfan30]

I didn't think you could fit one of them in an L. Or can they be modified a little?? The 11:1(100 x 8.6) is made for the R, by Wiseco, and they say it will not fit in the L model...not the same stroke. Maybe its just a taller piston. If the dimension from the center of the pin to the very bottom of the skirt, then I guess you could put it in an L. I dunno....

Anybody care to add to this???

Wouldn't mind putting a 11:1 in my L's

Check this out... I called XR'S and they said you'd have to mix in race fuel...


http://www.xrsonly.com/content/index.php?page=shop.product_details&flypage=shop.flypage&product_id=495&category_id=145&manufacturer_id=0&option=com_virtuemart&Itemid=77

[martinfan30]

the 24 or 25 is the timing btdc at wide open throttle where most of our pinging happens.

I was thinking some sort of RPM count for measuring ping..

Maybe I shouldnt drink my breakfast!LOL!:bonk:

[martinfan30]

Any other thoughts on this piston? I am on the fence still...

[creeky]

My HRC628 had an 11:1 piston, it needed at least a mixture of 50/50 93 and race gas in hot weather conditions and/or riding in sand. Otherwise, it would get VERY hot and exhibit the death rattle.

[martinfan30]

Ok, maybe a 10.5:1 is what i need..

Thanks all.:thumbsup:

[husky123]

The 600 and 650 pistons are different diameters. Now the piston for the 628 kit and the 650l piston are the same bore with the 650L getting the additional cc's from a tad longer stroke. Don't know about the variances in the squish though between the two.


I'm pretty sure that most if not all of the large RFVC motors from the original XR500, to the XL600, the XR600 and XR650L all are the same overall size. The piston height is kept the same by moving the location of the piston pin. That would make the piston pin location 1mm different between the XR600 and XR650L, with the 650L piston pin being 1mm closer to the top. If you tried a 600 piston in the 650 it would go 1mm too high. Would it hit the cylinder head or valves, I'm not sure. I do know it would screw up the squish. Same thing if you put a 650L piston in a 600. It would be 1mm too low, lowering the compression and screwing up the squish.

At least that is what I think. I've never held a 600 piston next to a 650L piston to see the difference.

[martinfan30]

The 600 and 650 pistons are different diameters. Now the piston for the 628 kit and the 650l piston are the same bore with the 650L getting the additional cc's from a tad longer stroke. Don't know about the variances in the squish though between the two.

I wonder if the pin location in the piston may be a factor in his 600 over heating and pinging? The six hundreds piston sits up higher than the L, right? that could make a difference. The squish definately would, any one know?

[Denn10]

Check this out... I called XR'S and they said you'd have to mix in race fuel...


http://www.xrsonly.com/content/index.php?page=shop.product_details&flypage=shop.flypage&product_id=495&category_id=145&manufacturer_id=0&option=com_virtuemart&Itemid=77

If there selling it as 10.5-1 but saying its closer to 11-1 then you may wanna check specs vs some other pistons, see where you can see the difference or do all of em have the same just call it a 10.5-1 setup. Have you seen any specs anywhere for pistons? pin height, overall, anything? Either way im sure between the little comp ratio you wouldnt see that much difference to warrant it. if it were me id get the 10.5 setup, with your cam already and carb your gonna flip that damn thing or run from the cops again.

even if you have to mix 25% race fuel no big deal, just pay the $11 a gallon and buy a 5 gal jug LOL

[martinfan30]

if it were me id get the 10.5 setup, with your cam already and carb your gonna flip that damn thing or run from the cops again.

even if you have to mix 25% race fuel no big deal, just pay the $11 a gallon and buy a 5 gal jug LOL[/QUOTE]





Where can that fuel be bought? I'm also concerned about the heat. An oil cooler would probably be necessary with the 11:1.

RUN from the cops again!!!LOL!!:busted:

[Denn10]

you got any local shops that carry 5 gal jugs? i bought one once then just used it for storing since its alot better than plastic can as i mixed it. OR find a nice metal can but i think there pricey. You may not have to worry bout heat but summer time there like me too.

[tobinbakner]

Xr's only says that if you use a 10.5:1 XR600R piston in the XR650L you will get somewhere closer to 10:1. This would make me believe the distance between the pin and the top of the piston is shorter on the XR600R. What I think would make a cool experiment would be to run a big fin head and use thermal coatings on the piston, head, valves, intake port, exhaust port and headers and see how high you could push the compression. Unfortunately I don't have that kind of money. They even have a coating to coat the outside of the head to help it shed heat faster. It only comes in black though so you would either have to paint the bottom end or live with a 2 tone engine. Here is a link to a forum discussion on Thermal coatings. http://speedtalk.com/forum/viewtopic.php?t=1050 It gets interesting at the end of the first page when the president of tech line coatings starts to answer questions on their effectiveness. According to him if you coat everything you will reduce your chance of detonation. Unfortunately I haven't been able to find out any definitive numbers of how much it helps. I have no experience with coatings but they seem to be gaining popularity. Swain Tech seems to be a very popular company. They have prices on their website. The prices didn't seem too horrendous. If I go to higher compression piston I think I would try for between 9.5 and 10:1 hoping to have some wiggle room in case I got some bad gas. One other interesting thing to note about higher compression pistons is that from what I have read they benefit from advancing the timing. The higher compression ratio slows down the rate of burn. Supposedly the coatings cause the fuel to burn faster and more efficiently. Reducing the need to advance the timing.

Tobin

[axarob44]

Martinfan30, Let me know if you might be interested in a 100mm 10.5:1 Cera coat piston kit from XR's Only. I was going to put it in my 07', but I'm selling it this spring. I also have a stage 1, which I know you already have, and an Edlebrock pumper, I know you have the FCR, but just putting it out there. Shoot me a pm if you want, or email. Andy

[cleonard]

if it were me id get the 10.5 setup, with your cam already and carb your gonna flip that damn thing or run from the cops again.

even if you have to mix 25% race fuel no big deal, just pay the $11 a gallon and buy a 5 gal jug LOL





Where can that fuel be bought? I'm also concerned about the heat. An oil cooler would probably be necessary with the 11:1.

RUN from the cops again!!!LOL!!:busted:

The way I understand it, if you use a XR600 piston the pin is 1mm higher from the 2mm longer stroke. That means the piston will be 1mm lower at TDC. What concerns me is the squish effect will be a lot less. Not sure how critical that is or if it is even critical at all in these engines.

I wish that I could find a 10:1 piston for my XR600.

I need an oil cooler with my 9:1 stock piston. I've been wondering if just adding some cooling fins to the frame oil tank might help. The usual setup is to us a XR250 (xr400 too?) oil cooler.

If you go with the lowest high comp piston that you can get you might not even really need high octane. Unless you are really flogging it, then more octane could be required. High altitude helps. Your riding starts at what 3500 feet? You might be OK with pump gas. If you took your bike to Glamis, which is near sea level, and it was hot, like 95F, it's a different story.

For extra octane there are a few options.

Some cities actually have 100 octane gas pumps. Doubt this is an option for you.
AV Gas. Cheap and usually easy to get. The issue is that it is leaded and it highly illegal to run on the road. No more putting gas from you tank in your car/truck when working on you engine. Lead is deadly to the cats on a car.
Race gas. Get it from a motorcycle shop. Expensive. Not really legal to use unless it's unleaded and road tax is paid. Several shops in my town carry it. Even the chain Cycle Gear has it.
Make your own. Get some toluene from Home Depot or where ever. Not much more expensive than race gas and 114 (117?) octane. Just average the octane numbers. For example 10% mix with 91 octane premium will give about 93.5 octane.

[Bibleman]

Forgive me if I'm hijacking, but I'm following this thread with great interest but can't figure out what "squish" is. Anyone have a nutshell version?

[cleonard]

The following is more based off of knowledge gathered from reading than actual application in the XR engine.

The squish band (aka quench) is the area usually are the edge of the piston. As the piston comes up to TDC there is a little space between the edge of the piston and the head. The narrow space causes the air fuel mixture to be squished out into the main part of the combustion chamber. The resulting turbulence can really help the combustion process. By using a 1mm lower XR600 piston in a 650L the squish distance is 1 mm larger. This will reduce the squish effect.

The question is will it cause a problem. My guess is that the lower compression will help resist detonation more than the lowered squish effect will enhance it.

[tobinbakner]

According to pictures I've seen in the cylmer manual the tops of the stock pistons are flat. What is the shape of the high compression pistons? If all they do to increase the compression on these engines is to increase the distance between the pin and the head leaving the top of the piston flat. Then the squish band will change the same no matter what piston you are using. If the piston is using a special shape to get the increase than the squish could make a difference. Does anyone have a picture of the high compression piston for the XR600R and the XR650l? I'm not sure if the pictures at xr'sonly are of the actual pistons. I kind of doubt it because it looks like they are using the same picture for every piston.

Tobin

[crmc33]

Its possible that the cylinder head dome is also smaller on the XR600 (97bore) motor and this will obviously affect the CR.
I use a 92mm bore head on my 102.4 bore to give me a 5mm squish band.
So the increased CR is slightly offset by the improved squish effect.
In theory anyway!
Never had a problem with pinging on my 675 but I run 97+ RON pump gas in the UK.
If I were you martinfan, Id just go with the 10.5:1 and use a bit of octane booster on the hottest days just in case. Id hate to say go for the 11:1 and then find you have terrible detonation or cant start the thing!

HTH

[martinfan30]

Ok, thanks to ALL my TT bros!

I still have the ? about ceramic coatings on the piston. Is it worth it?

[cleonard]

Never had a problem with pinging on my 675 but I run 97+ RON pump gas in the UK.
HTH

Over here across the pond the number on the pump is the average of research and motor octanes or (RON+MON)/2. The spread is usually 6 to 8 points so the 91 that we see in California and Nevada should be 94 or 95 RON. Not all that different than the 97 that you are able to get.

How hard do you run your XR? I'm guessing that you are mostly on the pavement in the UK and the temperatures are a lot less than we see in the desert southwest. Temps over 40C are not unusual. That makes pinging a lot more likely.