XR650L 11:1 piston

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.

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

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

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!!:cool:

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.

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?

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.

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

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

Ok, thanks to ALL my TT bros!

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

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.

first off,talking (super unleaded california gas) I was wondering if lets say someone figures out how to put an oil squirter on the bottom side of the piston, does the less temperature help prevent detonation. We have a FI bike and I just tune it out with the computer. With the 650l cdi you dont have that option. If you put a larger head gasket this makes the combustion chamber inefficent. So for my personal bike I would like to run at 11 to 1 or 11.5 to 1, has anybody tried it and found a serious detonation problems. This is a custom piston but we normally run the FI motor at 12 to 1.

Ok, thanks to ALL my TT bros!

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

My pig does not have the ceramic coatings, but after break-in I switched to synthetic oil. Congrats on becoming a Moderator! Was this a recent thing?

My pig does not have the ceramic coatings, but after break-in I switched to synthetic oil. Congrats on becoming a Moderator! Was this a recent thing?

Thanks! Just a few hours new! So far its been very interesting.

first off,talking (super unleaded california gas) I was wondering if lets say someone figures out how to put an oil squirter on the bottom side of the piston, does the less temperature help prevent detonation.

Yes it does help, but I do not know how much. The main reason I hear quoted for using squirters is to prevent piston overheating rather than ping reduction. I do know that the Honda VTEC engines come equipped with them and they have fairly high compression for a stock streetcar mill(10.5 to 11:1). Cylinder head temperature seems to be just as, if not more important.

I know you know this stepho, but for anyone else who doesn't, chamber shape, cylinder size, cam profile, volumetric efficiency, and powerband also affect ping resistance. Slow-revving, bigbore, open-chamber, aircooled XR600/650L engines are not not exactly ideal to begin with.

Has anyone tried lightening a piston? Would it be worth a try when I get one when wifey ok's it?

whew i think taking off material is prolly really tricky there, i dont think you would be able to get that much off safely too. I personally WONT let you try this on my bike but you can try it if you decide too. wonder if XRS has any info/input on that? you give them a shout?

Just get a 10.5 so i can ride your beast with the ghey luggage racks and decide what i wanna do with mine!!

whew i think taking off material is prolly really tricky there, i dont think you would be able to get that much off safely too. I personally WONT let you try this on my bike but you can try it if you decide too. wonder if XRS has any info/input on that? you give them a shout?

Just get a 10.5 so i can ride your beast with the ghey luggage racks and decide what i wanna do with mine!!

It'll be a while before I actuallly get the piston... Want to get some more miles out of this one before I have to get a new one. THEN its on! 103mm bore... 10.5 to1... 674 cc's if I remember right.

The cam works good enough for now, dummy.:thumbsup:

Here's pics of my 11:1, 98 mm Wiseco going into my 92 XR600:

208139315_4bPhF-M.jpg

208139429_Pbqjw-M.jpg

208139645_WrnSv-M.jpg

Has anyone tried lightening a piston? Would it be worth a try when I get one when wifey ok's it?

I have seen examples of lightweight forged pistons(like Cup Car type pistons) further lightened with a few select holes drilled, but I wouldn't even think about doing it to a stock cast or hypereutectic slug. The effort/risk:reward ratio is like 1000:1.

Of course, the effective compression ratio will also be affected by the type of cam used (eg If the intakes valves open early).

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