Well, itsfinally time to go internal on the mods for my rap. Needs more umph. What compression piston do you guys suggest? 12:1 JE good enough for a good power gain and still keeping it reliable enough for hard MX racing? or could i even go higher? I have access to any gas i want... from 93 all the way up to 110 octane. Also, what cam combo would be best with this piston? Hotcam maybe? ive heard good things about them... help would be appreciated... thanks

 

I can highly recommend Craycraft's signature engine (14mins.com). It's a 12:1 JE with Hotcams Stage 2. Looks like you've already got the suspension to handle the extra power, smart way to do a build. I've heard of a new 13:1 686 piston out there in the Craycraft stable, you may want to talk to Bob about it when you call. Craycraft also has a stock carb mod package that will make your life much easier with race gas.

 

Ok, would a 686 with a 12-13:1 be reliable enough to race hardcore motocross? Would i lose any snap to my revs with a bigger bore? i had just planned on going with a stock bore high comp piston and a cam, but ive recently ran across some money, so i could go ahead with full engine work if i chose to. Also, when i get the work done, its either FCRs or Edelbrocks for my fuel ingesting needs... thanks UBET..

 

im definitely thinking of changing out me J+E piston in my 686..... ive heard too many horror stories about them cracking!

 

Once I got past the stock carbs, my Raptor became reliable as a stone. I had to run one grade colder plug than stock after a particularly hard day of MX showed some porcelain flecks but other than that, it's much more reliable than I hoped. Temp light never comes on and the fan only runs for 30 seconds or so after a moto. I upgraded the clutch and basket and suggest you beef up yours, my stocker wasn't going to last with this much power.

There is no comparison between a high compression 686 and the stock engine. Whatever "snap" you think you have now will be doubled with good mods. The Stage 2 cam and port work just keep pulling waaay past the factory top end. I run 12/40 with 18" rears and cannot believe how hard this thing launches out of a sliding turn in the middle of 2nd. Most of the MX tracks around here are short so I keep the gearing a little high so I can get into the middle of 3rd.

The FCRs are excellent but I am still learning how to jet them. I don't have access to a dyno with a gas analyzer so it's taking a little longer. The FCRs respond to jetting changes just like the stockers but the transitions between idle/needle/main are much more tunable. That little accelerator pump is awesome, the bottom end difference alone is worth the money.

 

Ok, so is the part about the JE pistons cracking true or not?? I thought they were some of the best out there... hmm... I think i might end up getting the craycraft 686 if it truely is reliable enough. UBET, where in VA are you from? Do you ever ride at Birch Creek? I ride there all the time... ive raced there twice, and i usually race in Reidsville, NC, near the VA border...

 

I'm in Stafford VA, about 30 miles south of DC. I've raced at Budds Creek MD, Tomahawk in WV, Mountaineer in WV, and VA Sports Park near Richmond. I've heard good things about Birch Creek, might have to make a trip down there. I haven't heard anything bad about JE pistons.

 

I'll second the bottom end with the FCRs. Mines STILL being jetted (supposed to be done tomorrow!!!) by a local shop. The difference was HUGE. I could jet my stockers for EITHER mid range or bottom end and never seemed to get both. With the FCRs I Instantly had both. I'm hoping for a nice improvement in the ONE area it stumbled, after the dyno jetting that I'm spending bazillions of dollars on.