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700cc Big Bore DR 650

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for now I'm looking for 10.5.

I'll see how that goes before I decide if I need/want to go higher.

I was under the impression the JE piston kit took it to this level?

So you're saying more work is required to achieve 10.5?

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I was under the impression the JE piston kit took it to this level?

So you're saying more work is required to achieve 10.5?

No, I'm increasing the compression without getting a new piston.

I like to learn what works & what doesn't for myself, thus my trying one thing at a time to see the results.

when I was learning on my R1 I tried a lot of things, JE high compression pistons being one of them.

long story short is that the JE's did not produce the compression that they were supposed to (13.5:1) & I heard of three others that used the same pistons & had the same problem.

along the way I've learned that you can often get the desired compression ratio by just using the parts that you already have so I'll be milling & using a thinner head gasket to see what I can get.

if after all that I decide I need more compression, I'll get a custom piston made that'll fit my bore.

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Thank you for the work, information, and help to the rest of us by posting as you've gone along with this project. Is the object of the end result to be operable on pump gas? i.e. maybe 91 octane perhaps? Thank-you.

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Thank you for the work, information, and help to the rest of us by posting as you've gone along with this project. Is the object of the end result to be operable on pump gas? i.e. maybe 91 octane perhaps? Thank-you.

I'm intending to stay with pump gas.

I ran my sportbikes with midgrade pump gas & they've had a lot higher compression.

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Nice head cleanup.

I did the same on my XR250 but there's a bit more room in the 650.

I'm tempted to do some MotoTune style velocity porting if I ever have the head apart.

There wasn't enough room on the 250's little intake ports for me to be comfortable doing it. Although I will give it a go next time it's apart in a few years.

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I'm intending to stay with pump gas.

I ran my sportbikes with midgrade pump gas & they've had a lot higher compression.

Any dyno numbers with the 700 kit before and after?

Also do you plan to dyno after head is complete?

Thanks,

Gary

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Any dyno numbers with the 700 kit before and after?

Also do you plan to dyno after head is complete?

Thanks,

Gary

I have not had the bike dynoed, I figure there's enough dyno runs on other 650's to assume that this one put out about 35 HP stock.

eventually I'll probably get it dynoed after I'm done but around here it's gonna cost me 75.00 & times are hard.

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I have not had the bike dynoed, I figure there's enough dyno runs on other 650's to assume that this one put out about 35 HP stock.

eventually I'll probably get it dynoed after I'm done but around here it's gonna cost me 75.00 & times are hard.

No prob, was just curious. I just called to schedule mine for a dyno run as I want a before and after for the JE High Comp piston and web cam.

Currently I have the MX_Rob flatslide, FMF Q2, header grind, airbox mod and twin air.

Since I've read some say the high comp piston doesn't do much, the dyno time will tell the tale.

Gary

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:worthy::eek:

Just getting the compression up seems like it should make the bike more intersting on the bottom end. I had a Jeep with the AMC four cylinder, before I did any work on it, it was a real dog. After I bored it .040", added a mild cam, a weber 38/38 and bumped the compression to just under 11.0 to 1 by decking the block and shaving the head the thing would out pull a 4.0 (doughnuts were really easy to do too!).

I'm going to be all ears on this thread. I bet this will be a really nice running DR!

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Gary, looks real nice! are you going to do the work yourself?

are you going to assemble wet or dry? have you seen this stuff?

BigBore008.jpg

BigBore012.jpg

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I'm having it done by a guy who builds motocross race engines.. have you used the ring sealer?

Gary

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yeah, the stuff seems to work good to me but who can really say for sure?

at least I felt better using it! LOL

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hey Gary,

how much does that piston weigh with the pin, rings & clips?

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hmm.. I'll have to find appropriate scales.. I have packed away my powder scales from my reloading days but I think I can weigh it all at work.

Will let you know.

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hey Gary,

how much does that piston weigh with the pin, rings & clips?

Just curious does anyone have the weights for stock piston, pin etc..?

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Just curious does anyone have the weights for stock piston, pin etc..?

I got 539.9 grams.

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I just weighed the JE standard bore high compression piston and pin - 490 grams

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