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pros/cons of 680 vs hrc for XR650R

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ive done a lot of research trying to decide which way to build my uncorked 650R- im trying to decide whether to go w an hrc(or equivilent) or a 680cc kit, or maybe even both...it seems all are good options but im looking for more information from those that have experience riding both setups

this is for a dual sport bike that will see a wide variety of uses from 2 hr road trips to exploring single track...im looking for reliablity on pump gas but can still really rip when im in the mood for some grins..ive already decide to get a pumper carb and either a falicon or carillo rod..i want to build a rock solid stout 50-55rwhp engine that will last for many years

also im in north carolina- can anyone recommend a reputable engine builder that i can drive to and drop off the engine/bike?? i know you can spend as much as you have on this type of thing but im looking for a complete package without spending 5k+

thanks in advance for any help- i know the brp is yesterdays news but its been my dream to build a beast of a bike

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I've done both. Currently have a 11:1 piston 680, bored and plated cylinder by US Chrome, HRC valvetrain, FCR 41mm carb, mild porting, XRs Only Race series full meg exhaust. I did the 680 kit when I lost the big end bearing on my full HRC engine at around 100mph on a long gravel road in the middle of nowhere. Figured why not. This is what I learned...

As of now, I typically just use my pig as a dual sport (99% dirt) bike. Mongo Acerbis tank, Giant Loop Mojavi bags, rip off a couple hundred miles in a day kind of riding. Normally run 15/47 gearing while doing the d/s thing.

The 680 has a lot more bottom end than the HRC setup. I have the high comp piston, so CR ratios were the same as the HRC. It doesn't rev as well. It does vibrate more. The heavier piston just isn't as smooth. For what it is worth, the HRC piston is 10g lighter than the stock piston, the Wiseco 680 slug is about 15g heavier than the stocker if I remember correctly. I never run anything less than the best fuel I can get, and if I have it available I will run a splash of race fuel with it. But that isn't easy to do getting fuel in the middle of nowhere.

I have not changed out the rod yet (will do the Falicon). I know I have a ticking time bomb due to that. I have my old crank to rebuild, I just haven't gotten around to it.

Compared to the full HRC engine and a friend's HRC valvetrain with stock piston the 680 has more off the bottom. The full HRC has more through the mid. Stock piston with HRC valvetrain has more rev on top.

I don't trail ride or race my XR that much anymore as, frankly (and maybe this will sound blasphemous), it is just not smooth enough to be easy to play with in tighter terrain. With it geared up for d/s use, the 680 is great.

If I could do it all over again, honestly I would never have done the 680 and just kept the HRC full engine setup. For multi use, the straight HRC engine is by far the best setup IMO. Very smooth, easy to ride, abundant power. Was a lot more fun overall. The HRC setup seemed to rev a lot more freely to me than the 680 (which physics says it should) and that made it better overall.

But...

If I was to only d/s the XR? 680 with a standard compression piston and some custom work done to the slug to get the weight down to match the stocker for weight and balance. Easier fuel requirements with the std comp when out and about. I won't have an XR without the HRC cam. The 680 puts a stupid grin on my face when I roll the throttle on just from the torque. I've done some rides with 990s and I have never felt like I was lacking in power or speed compared to the bigger KTMs (up to 100mph!) and I still had a bike that was way easier to ride on tougher terrain.

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thanks so much eastreich- thats exactly the type of info/experience i was hoping to find..i appreciate the detailed reply- it really helps me to make some decisions

looks like im gonna take your advice and go with the hrc engine setup- just seems to work great for multi purpose bike...i do have a question regarding the hrc cam- can you still get one or would i need to go with an aftermarket equivilent? ive read some say its equivilent to a hotcam stage I, others say stage II - would a stage II make the bike harder to ride singletrack as well as lose the cool bottom end power? regarding a pumper carb- is the edelbrock quicksilver a good match or should i go with the more precise keilin or mikuni??

lastly what would you recommend as far as exhaust systems- do you think i should replace the header as well or keep it for the bottom end torque?? i want a SS system that isnt ear splitting loud..i been considering the fmf, staintune, akra, xrs only- do you have a favorite?

apologies for the load of questions- i just want to build and put everything together right the first time- thanks again!

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alright, after looking around a bit, it looks like the choices are fewer than i thought...akra, moriwaki and PC's 496 are no longer made..looks like my choices are narrowed down to staintune(which ive always liked), xrs only (dont know much about them) and fmf ((they are ok but not my 1st choice), PC i hear is very loud.., not interested in Big Gun... if i keep the stock header im sure there are more options...seems if i go stage II cam then i need to get a header to allow the pig to breathe..if i go stage I then will the stocker be adequate?? im leaning towards the staintune- maybe just the muffler w stage I and full system w stage II

on a side note- ive read people putting a muffler off a sportbike (gsxr1) on big thumpers- would that allow plenty of flow while keeping sound reasonable or will it just not be as good as a model specific setup??

sorry for all the rambling but i got the mod bug going! thanks for listening

Edited by Sumoman

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The advantage of the HRC cam over all the others is that it still has the auto decompressor that the stock cam has.  With the HotCam stage 1 (it mirrors the HRC cam in lift and duration) you get the same performance, but the starting may not be as easy.  Obviously you still have the use of the manual decompressor to get the engine nudged past TDC to help it light, but the lack of the auto system can be a deal breaker for some people.  No doubt about it the Stage 2 HC is a ripper and has more lift than the HRC cam, but for everyday use I just don't think it is as nice.

 

It is difficult to find the HRC cam anymore, and they are definitely not cheap when you do find one.  The biggest plus of the Stage 1 HotCam is that they were half the price of the HRC cam even when you could still get one, so I can only imagine the price difference now.  I haven't priced what a new (if you could find one) HRC cam is running (or what a used one would go for).

 

I am obviously using an FCR carb as stated before: OEM carb from a CRF450R, matching CRF throttle assembly, and fuel tank modified to work with that specific carb which means I moved the petcock to the opposite side of my IMS 3.2 gallon and stock tanks (the Acerbis 6+ gallon tank does not need this) and the tank heated and remolded to clear the throttle wheel on the carb.  Again, more modifications were required for the stock and IMS tanks with the big Acerbis needing little changes for the necessary clearance (compared to the other two).  I also had to make an adapter to get from the back of the bell on the FCR to the stock airboot.  It was work, but nothing that was a deal breaker for me.  YMMV.

 

I had the SUDCO FCR conversion carb for the 650R in the past, and it performed very well.  However, this carb is the first gen street bike type FCR and frankly, I just wore it out over time and was difficult to keep running consistently due to air leaks past the slide (even with replacing the slide wear plate and cushioning o-ring).  The FCR from SUDCO is nice in that it will clear everything: the throttle wheel, fuel inlet, and intake bell are setup so that it all works with the OEM XR setup.

 

I had a friend that had a Mikuni on his A-Loop XR440 years ago and it worked well.  It did not seem as easy to tune as the Keihin, but we both felt that had more to do with the fact that we were both just a lot more familiar with Keihins than Mikunis.

 

I have no personal knowledge of the Edelbrock, and am not sure you can still get one (it may be under a different brand name now?).  From what I have read there are lots of people that were very happy with them, and they are easier to initially tune than the other carbs.  I think for the general application of a pumper carb they are better than the Keihin or Mikuni, but if you know what you are doing you will be able to extract more performance out of the Japanese carbs.  This will always be an issue when you are converting over a bike such as a 650R since none of this stuff is stock, and baselines for jetting are hard to come by as everyone rides differently, has different modifications, etc...

 

As for exhaust, really the stock can isn't bad and can be made to flow better.  If you do a search on the forum I posted a thread a few years ago that shows how I modified a stock can to work VERY well.  I still use this one if I know I am going to need to be at least honest about noise (like if I am going to a race with a sound test) as it will consistently blow 96-97db on the 20in test.  The XRs Only systems are typically really loud (108+ db on a 20in without the S/A screen).  The bigger the megaphone, the louder they are.  I did try the quiet insert that XRs advertises for their pipes and it killed how the bike ran.  A total waste of money IMO.  My race system is noticeably louder than the "normal" XRs Only system on a friends 650R.  With any cam upgrade, it is better to go with a larger headpipe.  The FMF headpipe will work with any slip on muffler (or the stock one) and is probably the best all around option at this point.  Nothing wrong with the XRs Only headpipe either.  I am running the XRs headpipe on my 650R, but, that is because the race system I run uses a headpipe that is larger yet than the FMF or standard XRs setup.  I had to modify the slip joint on my modified stock silencer to work with the headpipe I am running.

 

Even with an HRC or Stage 1 HotCam, the stock silencer (if you use the HRC tip or modify it as shown in my old thread) is perfectly adequate.  You will lose power if you just thrown an open tip on the stock can, but as that will make it stupidly loud at the same time I am pretty sure you were not looking at that option anyways.  One very nice thing about sticking with the stock can (and it really is not that heavy in the grand scheme of things) is that it is all mechanical so you never have to worry about repacking it.  It just doesn't have the cool factor of an aftermarket silencer.

 

I am sure that if you want to put in the work a silencer off of a superbike would work great.  They have to flow a lot of gases, so theory says that it should work.  One thing to think of though is that the internal baffling of those is meant to work with multicylinder exhaust pulses so they will not be as efficient (at least in how they were tuned to sound stock) with a big single such as the XR.  But I am sure they would be quieter than almost any aftermarket setup designed for our bikes.  I have also thought about going that route, but I just have not felt like putting in the time or effort to do so (yet).

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thats a lot of great info and i really appreciate your time to write all that out- i have a pretty good idea of what direction i want to go..what im not sure about is whether to run a stage 1 or stage 2-...if i would run a stage 2, would that really hurt the bike in the slow going single track?? does it hurt the engines reliablity? im interested in the stage 2 because part of what i want to use the bike for is to run 17" wheels and really rip up some backroads but i may stick to a stage 1 if its gonna make the bike a handful on trails and wear the engine/piston prematurely...another consideration if if i run a stage 2 is that i'll need to run an 'open' system which might be too loud...any idea how loud the full staintune system is? maybe i'll just do what you did to the stock can if i go stage 1

thanks again for posting eastreich- its too bad a lot of XRR parts have been discontinued but it has been almost 10yrs since its demise

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In regards to the Stage 2 HotCam, I've never ridden with one or know anyone who personally has one. We all run the HRC cam. However...

One thing that is possible with the FCR carb is near limitless tuning options. You can tune the carb if necessary to take some "hit" out of the engine with a Stage 2 cam. For example, my KTM 505 is not exactly a kitten in the power department. Although the KTM is equipped with changeable ignition maps allowing you to have smoother power on one setting or a midrange hit and ridiculous too end pull with the other I do not use that feature. I have found that with the use of an externally adjustable leak jet you can make the power off the bottom on that bike do just about anything you want. Want a hit that makes you giggle? Close off the leak jet to let more fuel through the accelerator pump. Want to smooth things out in technical or muddy terrain? Open up the leak jet to bleed off fuel so the AP has less effect.

I have been using a Merge ALJ for years on my KTM this way. Current plan is to swap the ALJ over to my XR's FCR in a few weeks and I will put a R&D Power Bowl on the KTM. FWIW, I am running a Boyesen Quickshot 2 on the XR (when I did all this stuff, the Quickshot 3 w/ ALJ wasn't made yet).

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