Is their a big difference between the 686 and 720cc raptors? i just got a wiseco 11-1 102mm piston off of ebay brand new for $70. would you guys go with a hotrods stock stroke crank or a barker 4 mil that i can use this piston on? and my other plans are the stage 3 hot cams and springs. is there a better cam out there? i am sure megacycle are better but the hot cam is only $120 with no core. would i be happier with the 686 or 720 builld?

thanks
justin

 

I was in the same boat as you........686 with a stage two OR a stroker kit with a stage 3. I chose the 686 with the stage 2 because I have heard there are reliablilty issues with the stroker kit. I don't know how true that is but that's what I've been told. I'm not an expert but I would think even though the stroker kit gives you mores cc's and more drag power I would think that the engine would rev slower due to the longer stroke and extra weight of the longer rod.

Trust me, unless you are making a drag bike the 686, stage 2, throw in a port job and you will have all the power you could ever want from this bike. I did use the JE 12:1 comp piston however instead of the Wiseco 11:1. If all you want to do is drag Sand Mountain, then go with the stroker kit.

Just my 2 cents.

 

No significant reliability problems with the 720 that I know of.

Only reason to do a 686 instead of a 720 is if you can't afford it.

 

I'ver heard it's harder to keep the 720 cool. More cc's means more fuel burning with the same amount of cooling resources. More heat makes the motor wear faster, warp heads, valves wear faster, blown head gaskets, and the good stuff that comes with heat

Money wasn't the reason I decided against it anyway.

 

BTW maddog56 nice Raptor. Did CT build your bike? They advertise a kit that will make 60 HP plus at the rear wheels, although it doesn't look like you used their exhaust. Sweet looking ride. Did you put yfz450 shocks on that?

 

<div class="FTQUOTE"><begin quote>Originally posted by: Utah_Raptor

I'ver heard it's harder to keep the 720 cool. More cc's means more fuel burning with the same amount of cooling resources. More heat makes the motor wear faster, warp heads, valves wear faster, blown head gaskets, and the good stuff that comes with heat



Money wasn't the reason I decided against it anyway.</end quote></div>

The vast majority of 720 kits are running fine on stock radiators and I would imagine the same percentage of 686 riders are having cooling problems when compared to 720 riders. That is based upon the number of inquiries I see about them online, as these two are the most common builds for the 660R. Having a number of riding partners that have both builds I can contend that none have had cooling issues when using the stock cooling system, 50/50 coolant mix and in temperatures up to just over 100 degrees.

The cylinder wall thickness is identical, but the forces exerted by the stroker cranks is indeed greater than the stock crank. While I wouldn't disagree with someone who said it makes it run hotter because I've never held a thermometer in both I can say that from my experience the fan doesn't kick on noticeably more frequently with a 720 than it does on a similarly built 686.

I didn't mean to insinuate that money was your concern, I just meant that if I were trying to decide which to build myself I would not hesitate to build the 720 if I had the extra cash.

<div class="FTQUOTE"><begin quote>Originally posted by: Utah_Raptor

BTW maddog56 nice Raptor. Did CT build your bike? They advertise a kit that will make 60 HP plus at the rear wheels, although it doesn't look like you used their exhaust. Sweet looking ride. Did you put yfz450 shocks on that?</end quote></div>

Thank you. I had a CT exhaust for a long time but it wouldn't work with aftermarket carbs. Tim Barker did my headwork. I'm running yfz shocks on +2/+1 a-arms which works fine for my trail and dune riding.

 

id get ahold of craycraft racing.... bob craycraft builds some sick raptors !!! p.m. austin oneal on here.. he runs a craycraft 730 or 760 .

 

<div class="FTQUOTE"><begin quote>Originally posted by: maddog56


The vast majority of 720 kits are running fine on stock radiators and I would imagine the same percentage of 686 riders are having cooling problems when compared to 720 riders. That is based upon the number of inquiries I see about them online, as these two are the most common builds for the 660R. Having a number of riding partners that have both builds I can contend that none have had cooling issues when using the stock cooling system, 50/50 coolant mix and in temperatures up to just over 100 degrees.



The cylinder wall thickness is identical, but the forces exerted by the stroker cranks is indeed greater than the stock crank. While I wouldn't disagree with someone who said it makes it run hotter because I've never held a thermometer in both I can say that from my experience the fan doesn't kick on noticeably more frequently with a 720 than it does on a similarly built 686.



I didn't mean to insinuate that money was your concern, I just meant that if I were trying to decide which to build myself I would not hesitate to build the 720 if I had the extra cash.

</end quote></div>


That's interesting...I'm wondering if riding conditions have something to do with it. I ride A LOT in sand dunes in the desert. In the summer you are looking at 100+ degrees most of the summer plus you get an extra 5 degrees or so with sand reflecting sunlight. Even running the 686 I have minor heating issues if I run my machine more than 30 minutes of hard riding. In the sand I am constantly running at wide open throttle up hills in thick sand. Even with the fan going there are times I boil out a little bit of water and I run Engine Ice which is supposed to keep it up to 20 degrees cooler. However if I ride in cooler temperatures or take it easy on the throttle in the higher temps then I have no issues. I am currently working with a mechanic to diagnose my minor heating issues.

I talked to a friend that rides at the same dunes and had done the 720 kit and had since sold the bike. He said that he had to resleeve twice because heat had put hair line cracks in the cylinder and water leaked into the cylinder. He said his bike was the fastest Raptor out of his circle of freinds but he got tired ot being towed back to camp. He said his friend that had the 686 never had a problem.

Even though I don't have major heating issues I was very hesitant to subject my motor to more heat in harsh conditions. I would guess in most conditions there is no material difference between the 686 and 720. But I wonder in the harsher conditions if there may be issues. Throw into the mix I ride nearly EVERY weekend so I put a lot of miles on my motor.

The guys I personally know DON'T have issues with the 720 kit but they built their bikes to be drag machines. They drag "Sand Mountain" a few times racing other ATV's then shut it down for a little while so the motor can cool. So they haven't gone on longer rides (several miles) over the dunes or drag a steep sand hill several times to be able to say what subjecting their motor to prolonged wide open throttle, in high temp weather, with the drag of the sand on your tires will do to them.

I haven't asked or heard anything but I think the other factor to consider would be the stage 3 cam you MUST use with the kit. Do valves, seals, springs wear out faster? Do you have to adjust them more? Is there machining involved? Even with a stage 2 cam 3 out of 5 mechanics I asked recommended that I have the vavle guides shaved by .040 thounsands on the intake side or the valve seals would be "smashed" over time and lose their integrity. The other 2 said there is no concern. It took me a month to convince my wife that a stroker kit was what I wanted and the money was ok to spend, after asking around and calling local mechanics I decided against it for reliability issues for the conditions I would be using it in and the purpose I would be using it for. It just stands to reason to me that more CC's means cooling becomes more and more of an issue.

Again i would think the motor would rev slower due to the longer stroke and extra rod weight so it wouldn't be as good in shorter runs, like motorcross or duning, but that's just a guess. Raptor's already have a disadvantage against today's fast revving 450's. Longer runs would give the stroker kit a decided advantage however in my mind.

We all know the cylinder wall is the same thickness but you are getting more fuel plus 4mm more movement from the piston within the cylinder. Perhaps making this decision is based on 1 - Your riding conditions and 2 - What you are going to use it for.

 

Update - With the stroker kit Hot Rods recommends using a piston with 10.5:1 compression piston with their kit. The lower compression, I am running a 12:1 comp piston in my 686, should help to keep the motor cooler. So I suppose compression ratio is the key to keeping it cool. i didn't think about this when I researched this before. They also recommend using a CDI where you can limit the RPM's to 8200 rather than the stock 9000.

Assuming you set up your jets right cooling should probably be no more of an issue with the 720 vs. the 686. The only concerns I still have is would it be a slower revving motor giving you a disadvantage on short runs, and the head work you would have to do if any.

I suppose my buddy who had problems with his 720 probably wasn't jetted right.

Again I suppose it would just amount to what you are using it for.