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4Takt

I want to put some hit in my XRR's power band

17 posts in this topic

Please forgive me for saying this, but I'm a two stroke kinda guy and always have been. Open class two strokes float my boat.

That said, I like my XR650R, but I can't help but wanting to make it feel a bit different. Like it should, it's got a nice bottom end hit, but from there it just revs out linearly like an electric motor. I mean, nothing happens.

What I want is a nice hit in the middle of the powerband. You know how a 500cc two stroke has almost the same bottom end, but then as it builds it screams and explodes when it suddenly jumps 18hp within 1500rpm like the old CR500 did?

That feeling of being kicked in the ass?

That "Holy Shit" adrenaline rush?

What will give me that? Higher compression piston, different cam, what exhaust?

Right now the bike is stock, uncorked, with a drilled out stock exhaust. Tabula rasa.

I have an Edelbrock carb, but it's sitting on the shelf since I couldn't get it dialed in for some reason.

4Takt

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Find an experienced engine builder who understands the 650r engine and knows what parts combos will produce the results you're looking for with the reliability you have in mind and have them do the work. You're paying for their knowledge and experience which won't come cheap, but unless you understand and can calculate the air flow to produce known and predicable results for specific port velocities to match a specific specific cam duration / timing, valve specifications, etc, while also taking into account the specifics of your carb and exhaust , then you're guessing at the outcome.

Some things to consider are:

- 680 kit with 11:1 piston

- send in your cylinder for machine work & nikasil plating with the piston & rings and have them set the clearances

- HotCams stage II or a custom grind

- head porting to match specific requirements

- ss valves with 'matching' springs

- rev box

- larger diamater header with new a cannister

- carrillo or falicon rod to beef up the big end

- have the crank machine balanced

- have the carb bored to match your airflow needs

- proper break in

Or...you can sell the 650r and get a CR500AF from Service Honda if you miss the big bore 2 stroke, which I can appreciate.

http://www.servicehonda.com/cr500af05.html

http://www.servicehonda.com/specs/05cr500af.html

http://www.servicehonda.com/afhist.html

http://www.servicehonda.com/cr500af05action.htm

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Aside from a complete engine bore and stroke to the MAX:

Slide the XR out from underneath you and slide an older CR500 back in. Only way. You're comparing apples to oranges.

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The header on the stock bike has a step down in it and that is what gives that incredable low end hit. it is also what kills the mid to top hit. With a header and more air flow (Uni air filter, holes in the side cover) you can get a much more responsive mid~top end but, the bottom will be a little lazy. That is where the pumper carburetor comes in. You will never get the two smoke instant power on but, you can have the top end pull that will keep the front end alive through the whoops at over 70 mph. I have setup a lot of BRP 's and for a stock engine I like the XR's Only or White Brothers Header with the White Brothers R4 Muffler the best. The Moriwaki full exhaust is even better on the top but, with a stock engine you have to run the spark arrester to make it work. It is more of a balls to the wall setup.

http://xr650r.borynack.com/

http://www.borynack.com/Bruce/XR650R/HorsePowerMods.htm

http://www.borynack.com/Bruce/XR650R/dynocharts.htm

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I rode a cr500 in the Glen Helen 24 hr this weekend. I'll I could think was this thing is a pos. I would've given anything for my 650 at 3 am. One good thing was when I got to a big hill . I had enough power to climb a wall. The more it hits the more it wears you out. I agree one bike won't do everything . If you want the hit by a 500 they're cheap. Buy the time you build the xr you could by a used 500. Keep the xr stock and it will run foreever. Cambell was on a 450x for the 24. The 450 hits better ,maybe thats a option.

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I already have a big two stroke, and I know the XR won't ever be like that. I'm also aware of the fact that the smooth power of the XR makes it less fatigueing. All I want is a little bit of that mid rpm peak, just because I happen to love that feeling.

I think I'll go with BWB63's advice to try a "peakier" exhaust first and in conjunction with that give the Edelbrock another try.

Thanks for everybody's input.

4Takt

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I'm looking for the same kinda thing you are. I haven't done it yet, but I plan on installing a Hotcams Stage I cam. From what I've read, it will give you a better hit in the midrange without sacrificing too much bottem end. Maybe someone will chime in who has had one of these cams installed and verify my claims.

Paul

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4Takt,

I bought the bike used with exhaust system already installed. Curiously, the prevoius owner had never heard of uncorking the bike. He also said he was selling it because it had too much power! When I test rode it, it wouldn't get out of it's own way. Suffice to say, when it was properly uncorked it was awesome. I really like the FMF system though. Great power, quiet, and looks good too. Regarding the turbo, that's all I need in the tight woods of the Pacific Northwest! I'd need a cherry picker to extract myself from the tree tops!

Paul

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I'm looking for the same kinda thing you are. I haven't done it yet, but I plan on installing a Hotcams Stage I cam. From what I've read, it will give you a better hit in the midrange without sacrificing too much bottem end. Maybe someone will chime in who has had one of these cams installed and verify my claims.

Paul

The cam does increase the brute force power through out the bikes power band. With the stage one there is a sweet spot in every gear and once you find it and know when to shift it is a blast.

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The cam does increase the brute force power through out the bikes power band. With the stage one there is a sweet spot in every gear and once you find it and know when to shift it is a blast.

So, if I want to do some stuff myself short of having a complete engine rebuild, seems like this would be the way:

-11:1 piston

-hotter cam

-open exhaust

-Edelbrock

-open side panel

How much difference does that package make? Very noticeable?

Also, what's the deal with the different cams? I know Honda has a racing cam, then there's relatively cheap ones on ebay, etc.

Which one do I want? Are there quality/durability differences?

4Takt

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What you need is a good port job, a hotter Cam, a larger diameter header, a reverscone exhaust and an FCR thats properly tuned.

Here's the thing. When a 650cc thumper hits, its going to hit harder than a 500 two stroke, because it wont spin the tire the way a two stroke does. It'll hook up and throw your ass off the back. Thats the reason they build the big engine in the first place. So it'll be nice and mellow and still make all the power you need.

Think about it. The CRF450 makes roughly 50-52 hp. The 650's make an honest 48-50. But they do it over a 3500 rpm spread or more. Where the 450's make thier 50 for about 2000 rpm. If you tune the 650 up like the CRF it'll make 65-70 or more and wear your ass out.

I guess there's a middle ground to be had....

Call Thunder Alley for a pipe. That'll throw some hit at it. Bet your ass on that...

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So, if I want to do some stuff myself short of having a complete engine rebuild, seems like this would be the way:

-11:1 piston

-hotter cam

-open exhaust

-Edelbrock

-open side panel

How much difference does that package make? Very noticeable?

Also, what's the deal with the different cams? I know Honda has a racing cam, then there's relatively cheap ones on ebay, etc.

Which one do I want? Are there quality/durability differences?

4Takt

Hotcam's stage 1 and 2 are identical with Honda's performance cams with the exception of not having the auto decompression.

Personally all I did besides uncorking it was open the side panel a bit, stage 1 Hotcam, and the Edelbrock carb. I ride a KX500 also and they are two different bikes. No comparison to be made. The KX will go through the gears faster bit the XR650 is faster if you give it straight long distance but throw in turns and tighten things up a bit and the KX becomes the dominant beast.

With these mods the XR650 definately pulls harder in 3rd 4th and 5th than the stock configuration. It is still a 4 stroke and therefore smooth electric like power delivery. I wouldn't throw too much money at it beyond the mods I mentioned unless your really serious about winning Baja. The bike is plain fun in the desert and will get the job done in the woods. Just not in 2 stroke fashion and it never will.

Anyway that's how I see it.

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Everything I've read indicates the exhaust gives you the least amount of gain for the buck. Some test indicate that the stock exhaust uncorked is hard to beat when your just talking about horsepower.

The only significant gain with the after market exhaust is loudness and you shed a few pounds. Again this is what I have read online here at TT by those who should know. I prefer the quiet stock exhaust when uncorked.

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Opening the exhaust will give you only two maybe three peek horsepower gain is true but, that is not the whole story. At 6,200rpm you may go from 44hp to 46hp but, at 7,600rpm you will go from 39hp to 45hp! that is a big difference through the whoops in forth. More air in and out of the engine will help all the other modification that you do to add power. It is hard to leave the peek numbers aside but, they don't mean as much when you look at the whole picture. Where in the rpm range, how much power do you need doing what and when do you have to have it.....now. The pumper carburetor can help when you need it right now as you drop into and then back out of a wash, the header/muffler will give you that higher rpm power you need to straighten out the bike in the big whoop doing 60+mph. You don't live at 5,400rpm~6,200rpm very long or all the time.

http://xr650r.borynack.com/

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