Power differences???


I have a XR650L that I just got bored out to 102mm to accomodate a new Wiseco piston. I'm told by the machine shop it is higher compression than stock at 10.25-1. My question for one of you knowledgable Honda people is this. What is my new displacement and what if any detremental effects will the higher compression have? I wasn't unhappy with the stock power output. I have an XR's only pipe, jet kit and all smog junk off so it moved pretty well. I rebuilt because of smoking and oil consumption. Can't wait to finish assembling it but the Knuckleheads at the Honda dealer ordered the wrong head bolts (two were stripped) so now I have to wait until after Christmas. I've heard an oil cooler wouldn't be a bad idea so I'm considering that. Any other suggestions or information????????

Well its bore*bore*pi*stroke/4. The stroke is 82mm. It comes out to 670 cc. That makes for a 3% increase. Not much. The higher compression and new rings that hopefully will seal better will make a lot more power difference. Higher compression will cause it to run a little hotter. An oil cooler will help get rid of the extra heat. It shouldn't be a problem unless you ride it in conditions that make it really hot.

The stock compression ratio is only 8.6 to one. With compression that low, the bike would run fine with octane of 85. The higher compression will require premium fuel. Even with premium, if it's too lean it may ping. Listen for it. A little pinging is no big deal, but if it starts doing it severely it can melt a hole in the piston in no time.

Great responses cleonard, also when riding the slow stuff, woods/technical, it will stall easier so you will have to be more attentive with the clutch lever. Congratulations I want to do the same with my L please update us on how it all works out for you. Jetted right you should be putting out around 42 hp (at least). Oh, welcome to TT, and merry christmas

We had a simular setup and we got 48.7hp on the dyno. That is a 10hp increase in power. It had a Mikuni carb., cam, S/S valves, XR's only header, with the older supper trap type muffler. Over 30% increase in power is amazing! The stock XL650L cam is real mild as is the compression. If you get the cam, higher compression, it will be a good idea to have a hot start button. This bike wasn't real hard to start hot but, it did have some hot start problems. Our 628cc XR600R had 12:1 compression and was a nightmare to start hot. We didn't have a hot start button and that would have fix it. If we took the spark plug out, put it back in, the bike would start first kick. We had no problem with the XR650L on 91 octane but, we did have pinging with the XR600R at times.

Thanks for the info. Before I started having the smoking problems this bike ripped, it would smoke a friends '93 XR650L with similar mods. (White Bros. pipe was the only difference.) I'm looking forward to having it strong again. I'll get it broke in and post up some results of performance testing. I put about 10K miles on it with the old engine so I kind of know what it felt like. I should be able to compare pretty well. Thanks for the info.

I have 10,500 miles on mine and it still runs good will easily run on the rear wheel all the way through 3rd gear, 14/48 gearing, has started using a little oil though.

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