Ross Pistons made some .001" oversize pistons for the std bore. They were made for Alan at CT. Good luck trying to get one --- he is a jerk about selling pistons without doing the work.

The 660 really wants the 102 piston. It gives you the power you want and allows the porting person to properly size and shape the chamber. With the 100mm stock piston, you cannot properly set up the chamber.

On the valve springs -- stock is 35lbs. seat pressure -- that is way too little. RD springs are 60-68lbs installed height seat pressure (no matter what they say). I actually buy two different sets of springs to use some intake and some exhaust springs (different heights) with some shims to achieve 50lbs seat pressure. My set up also provides the proper lift spring pressures for the cam I run.

 

hey raptor 720. I am gonna be out at sand mountain near reno this next weekend. You should try and come out. I have a raptor with full fmf exhaust and running a prodesign with the airbox lid off when running in sand. I have only been beat by a raptor with a cam and piston and of course knutz and jeff's ds 760's. It would be cool if you could make it cuz i would really like to see the difference. I can pull third up sand mountain. About how much does it cost for the 686 or 720 kit installed, i suck at motor stuff so i would have to have someone do it. Would love to meet u raptor 720. Sean

 

This weekend I would be at Lake Nacimiento getting in some end of season boating. That drive to Sand Mountain is all day for me. I only plan on it each Memorial Day weekend. If you were there last Memorial Day, you would recall me as the one on the Raptor with a black backpack. I raced about 100x each day and night -- unless I was doing the 500cc hill bike. Glamis and Dumont are my local stomping grounds.

By the way, what gearing and tires are you using to hit 3rd to the top of the mountain?? I can pull 4th easily with a 686 running a 13-42 combo on comp groove mini desert tracks. I doubt that you are pulling 3rd all the way with power unless you are starting way back on the hill and running at night.

I am also curious if Knutz (I must check the spelling of his name -- he got mad when I posted "Kuntz" no pun intended it is how my friend spells his name) can beat a 720 Raptor. I have a couple of models to try. First the 686 (102mm piston and stock stroke), then a 727 (105mm with stock stroke) then the 105 with a +4 stroke. Who knows, our hp ratings appear to be very close 75hp although Dirt Wheels said his 760 only hit 60hp. If he has 60, the 686 easily hits 63-65hp with a mild cam.

I suppose I could bring a toy along and hit Pismo on Sunday. Who knows.

 

Raptor 720,

I have been reading all you have had to say about Raptors and what you have done and I was wondering if I could ask you a few questions about your port and flow work. You made the statement that the exhaust already flows too much compared to the intake and I was curious what you think the exhaust should flow percentage-wise compared to the intake. Do you modify the cross over between the intakes and at what vacuum are you measuring at? What lift and what kind of numbers are you getting (both intake and exhaust)? Also, when you modified your stock head pipe, I take it you ground out the weld which makes it flow better but what about the anti-reversion effect the weld has on reverse flow? If the exhaust is flowing too much already wouldn't you want to take advantage of the anti-reversion as much as possible? Last, but not least, are you running into the rev limiter with the cams you run?

 

hey raptor720. My gearing is 12 tooth front and stock rear, not sure what that is. But ya, i can pull third no prob any time of the day, when we were out there at labor day it was 90+ degrees out so it was not cold dense air. Bye the top of the hill, knutz would be 100ft ahead of me and jeff(he has the other 760) is 150+ feet ahead. They sure haul ***, and now that jeff has NOS, he would be 200+ ft bye the top i am sure now. We will be at glamis from december 30-january 5th, we will have to meet, i wanna see those big bore raptors run. so u have a 686 and a 727 or just one? Sean

 

Well going to go with the Trinity 680cc kit what do you guys think!!I am going to start saving!!You think i will feel a big gain? Thankyou Skydog[img]i/expressions/face-icon-small-happy.gif[/img]

 

Ah Mickey, I can tell you are one of the few who has actually done some work in a performance shop.

All flow work was done on a Superflow 600 with all testing at 28" of water on the third scale (299). Lift was measured in .050" settings to .350" lift. Tests were performed with head only, head with carbs, head with full intake system (both stock and with various mods), and with a few different head pipes. Tests were also performed with various clay intake shapes and designs as was the exhaust. Tests were also performed with various size intake valves and various shape seating surfaces. Chamber design was also tested in various configurations, including weld filled chambers. CC's in the chamber and port areas were also noted. In all cases, the mount on the flowbench was a 102mm id aluminum cylinder with index pins for the head.

On the flow data, I will pull the info from my files asap. I recall that the exhaust out ran the intake by 10-15% --- I want to see 8-10% intake over exhaust. This is how torque is built. CAVEAT: Don't rely on my numbers as my memory on this project is faded at best. I recall that with stock valves, chamber work and some port corrections, max flow on the intake was found at a low lift -- .300" with something like 279cfm. The flow did not increase with lift about @.300" Exhaust was something like 219cfm @.300 lift and 217 @.330". As for the stock CV carbs, I have a number of mods that are done to make these carbs work well. It simply does not pay to install $1000 worth of FCR's for the little to no gain. A single carb will net a large torque increase but you will have a substantial loss of over rev and top end hp. The stock CV's easily flow more air than the ports allow. The carbs are not the limiting factor. Once the stock air lid is modified and a White Bros foam filter installed, the air box is not an issue either. Want to mess up air flow?? Install the Pro Design air filter system. Not only will you need one for the foam filter and another for the K&N, the mount is a air flow mess.

As for the cross-over from the left single port to the dual intake port, it was enlarged a small percentage and the shapes were text book design for best flow characteristics -- fluid dynamics. Intake port floors were not altered except towards the pocket. Intake ports were widened and the pocket area received some welding. Exhaust ports got raised and reshaped. Both intake and exhaust guides were changed but not shortened. Caution: DON'T go too big on the cross-over. You will get a cracked head and coolant in the intake system.

Anti reversion cones from the old days. I thought about the application but a true cone has a sharpe exit angle and that is hard to achieve from the weld alone. What I found was that a quick radius on the weld accelerated the air and helped correct the intake/exhaust issue. ALSO, the large diameter exhaust used my many will in every case, slow air speed. This is the other problem with big exhaust systems.

Now you should have the basics that will help you build a good running 686. You should also understand why the chrome shops and their bigger is better exhaust systems are selling a bill of goods. I would love to see some of the popular atv shops provide dyno results on a 686 with proper jetting, stock blue printed head pipe and GYTR tip vs. their full exhaust. I bet (I know) you would see more torque from the GYTR and only a slight hp gain on the full exhaust at peak rpm (1-3hp). BUT if the chrome shops produces dyno sheets that told this picture, they would have a wall full of their exhausts. This isn't to say that a full exhaust will not help. There are some systems that I would and may have used with a modified engine. But a stock or near stock engine should not have the full exhaust.

One note, if we all keep using loud exhausts on the 4 strokes, that includes the GYTR tip, we will not have any places to ride. The new demand for 4 stroke power is great but it will be the end of more riding areas. I can't stand using ear plugs while riding the Raptor. --- Just a word to the wise and to the chrome shops.

Never had a rev limiter problem as the cams I use produce power in low to mid range rpm. I stay away from high rpm power as we are not talking 2 strokes here. My next hill to climb is the CDI. I have tested the 49 state vs. California. What I found is that I would use the 49 state box on all stock or near stock Raptors BUT I would use the CA box on all built and especially the stroked Raptors. The CA box has a better retard curve for the long piston dwell of a stroker or a built engine.

Now I have posted more info than any performance shop would ever dream of posting. Even with this info, you cannot just go out and build a good engine. Port and chamber design is an art. Each cut requires a trip back to the flow bench. Mickey, I suspect you build a fine product in your neck of the woods. Your questions tell me that you are one of the few that has actually done some testing and that you understand flow design. Perhaps you can also share some of your info in this thread.

On the remainder of the engine... The 686 will run fine on pump gas and the stock rod (depending on cam selection and the resulting cylinder pressures) and clutch springs. If you go 105mm install a Carillo rod and back cut the gears. Since the intro of the engine in 92, Yamaha has improved the original problems with weak counter balancer gears and a timing chain that would run dry and break. It is a great powerplant.

My thought on the 2002 with the lower 1,2,3 and reverse gears... Who cares. If you have a stock or near stock engine and ride in the tight woods, the lower gears may be nice. I suspect the gear parts will cost about $200 to change your 2001. For the built engines, I want the 2001 ratios. With all the power, I don't want to spend extra time shifting. If I can pull a hill in 3 gears, I will be faster than someone shifting 4-5 times. Airshifter you say?? It will not work in the sand. Override?? Only on a Banshee.

 

Skydog,

I know Trinity's work. On the Raptor, you will be pleased to say the least. I also understand that their new all stainless dual exhaust has a reflective silencer that is being offered. I will get one for my personal consumption. I must reduce the noise of the toyz.