PassionRE

Stay away from the Vito's cranks...they are absolute junk. You need a H129 Wiseco crank, 795 series pistons. Also, I suspect you'll need to run standard base gaskets and stroker domes on that stage IV..otherwise your exhaust duration will be off the charts. Other porting changes need to be made going stroker route regardless(if you want REAL gains)...Jim

I was there Duece, but it wasnt exactly free love. I had to buy a chic a Milky Way once to get laid. .

Minimum squish clearance is simply the minimum mechanical limit a engine will not crash the piston into the head...literally , due to heat expansion and rod stretch in the harshest of circumstances. What is MUCH!!!!! more important is squish VELOCITY. It determines WHERE the power is going to be BEST, detonation control is also determined by SQUISH VELOCITY, and you can move it where you want depending if you want best power at peak rpm or best power prior to and up to peak torque curve. It must be calculated though using ex. port timing, bore, stroke, max rpm, squish band width, squish clearance, and compression ratio.... It is NOT a universal number just to be thrown around. especially if SAFE is your concern...Jim

Cherry pickin' on those Blasters I see...tsk tsk they are definately a few horses down...and to think I took it easy on those jugs...there is a TON of more performance left in them

Yes, its because a 70 horse Banshee will out-run it on a MX track..unless ofcourse you have 1/2 mile straights

Replace the o-rings with Viton O-rings(they WILL stretch over the webs). They shouldn't spin if your cases are in decent shape. If the Case journals are a little worn, plaed a few drops of red Loc-tite on both case halves(on bearing journals) before installing....Jim

The ring part # is the reccomended finish bore size. You should have 513MO6500's for 65mm bore...ring part #2559CD the 2559 stands for 2.559" finish bore size. If you want a ultra precision fit, measure the piston at the furthest down area of the piston skirt that can be measured and then add .003" to that number for reccomended finish bore spec. I personally set them up at .0035" clearance.. Also..... use a calibrated dial bore gauge to check this , telescoping gauges are a complete waste of time...Jim

Send me your specs on ex. port height from top of port to head surface and squish clearance (measured with solder inline with piston pin) and I will tell you exactly what to do to achieve a more livable squish velocity.....Jim

Broke, heres my latest RZ project 90+ horse 4 mill 12 port....Jim http://i57.photobucket.com/albums/g215/pas...land7-05068.jpg

YES broke, but your covered on your motor, and Dan took care of it on your other RZ motor too. Squish velocity's on those heads are very high to begin with, most likely an attempt to build decent bottom end on the original Yamaha design, although there were better ways to do this other than increasing squish velocity. Start milling the head, adding high volume expansion chambers, and running slightly leanish jetting and youve got a situation that is less than very reliable...JIm

How is your head/squish clearance set-up. RZ heads are border-line time bombs unless modified for off-road balls to the wall riding habits....Jim

Thats Brandon in NY's motor. Previously ported before the 12 port conversion and modified for a 4 mill. 80+hp on Shearers and 35's.....Jim

I dont know the complete story, but when Rockets were first introduced, I spent a good deal of time on the phone with Ron Borink and he told me they were originally developed around a 7mm stroker running 200 deg exhaust and 134 transfers. Granted, there is ALOT more to take into consideration on developing pipes but this was the actual format they were working around supposedly. I can tell you though, in at least theory, they are going to be a pretty decent Cub pipe mainly because of the transfer directional angles of that design ,although Shearers will most definately develop more peak HP....Jim

Wait to bore until after the porting...makes for a much better outcome.....Jim

Ducman, its not just your cc's and timing you have to worry about, the squish clearance and squish band width must be matched to your cylinders at rated peak HP rpm in order for your squish velocity to fall into the right range. Re-cut off the shelf domes wont cut it...especially on hi-output designs on pump gas...Jim

Yes, on that particular engine ,Shearers will just flat smoke CPI's, Rockets, etc. etc. on peak HP and Yes, Ive ridden that bike many times and it makes big power EVERYWHERE, regardless of the situation. The myth of not being able to have extremely hard hitting bottom end and radical top-end is just that, a myth. There is nothing that will keep up with that motor on big tracks. If you can handle it, you will totally dominate the big tracks on that ride. Better hit the bow-flex though, that bike will fatigue you beyond belief if your balls are big enough to stay on the gas .Are you in the Tulsa area?....Jim

Geesh Schizo....Man I feel your grief. Sorry to hear this news.

It probably has too small pilots. Jack always liked crisp hit on the bottom regardless of idle quality. You will probably need 65-68's on the pilots and a good sync on the carbs....Plus, you can pick up about 8 horses on that engine if you ditch the CPI's and install some Shearer inframes...Jim

He's in Hesperia CA

If you really dont care about bottom end power...go with the Cubs for sure. If you want a really well rounded motor with excellent bottom end grunt that will still haul the mail up top, a RZ conversion is alot cheaper than the Cheetah set-up if your willing to stay under 400cc. PM BROKE about his RZ conversion 12 port Jim

Mind boggling isn't it? Heres what's really happening. First of all, stroking a engine is simply increasing it's ability to draw in more fuel air mixture by increasing its displacement. A engine is really just a pump in its simplest form. Increased stroke just allows it to draw more in, like a syringe that's just a little longer than normal. As you pull the syringe, if it has more travel than normal, its going to pull in a little more fluid. Thus ,more fuel air mixture that's been drawn in, compressed at a given rate(compression ratio), will produce a more powerful explosion which is transmitted to the crank, trans., and ultimately, the rear wheels. In the case of a 4 mil vs. Stock stroke Banshee, this rate of increase is minimal in reference to the displacement increase itself. . The real power is increased in what it does to the port timings. Take a stock Banshee, throw in a 4 mil. crank and alter the transfers and exhausts just to compensate for how much further down the piston travels in the cylinder(2mm). Im not talking a full tilt port job, just enough to allow for full port opening at BDC. Your exhaust duration has now gone from 181.04 deg. To 182.35 deg., not much their going on is there. But now the transfers have gone from 119.69 deg. duration to 126.18 deg. Whoa...there's a difference. Its pretty apparent that stroking the motor has a lot more effect near BDC than it does near TDC. With this big increase in transfer duration we have increased the efficiency range of our transfer ports. They will now cause the engine to not only hit harder down low, they will be more efficient at higher RPM as well. This is just a port timing match up situation, not a port job, modify the ports even more, especially the exhausts, and we have the recipe for real HP. As for long rod vs. Standard rod, the long rods simply reduce the rod angle during operation which will reduce wear on our piston and bore surfaces. A 4 mil increase in stroke on a Banshee isn't really enough to justify this, but hey , reliability is a good thing, we'll take it with a smile. The long rod does have a slight effect on port timings too, and it does also cause the piston to stay at TDC while waiting for the crank to start moving the piston back downwards to the tune of an additional .64 degrees. It also decreases the transfer duration at the same rate at BDC. So, in essence the longer rod removes .64 degrees over-lap at BDC and adds it toTDC.......Jim

If you want the best drag pipe for YOUR bike, just call Matt Shearer and have him custom build for YOUR motors specs. It works best that way and you'll save yourself a ton of guess work and opinions will be worthless....Jim

Cub is hands down a better kit for all out HP. Older PV set-ups are a well rounded porting set-up and more versatile for some people that are not wanting a full tilt drag motor....Jim

250RHater, thats not you pipes killing them in the tights, its your porting, same on the straights Any MX port that is worth a crap will run fine on Rockets...problem is the physical size of the pipes themselves that creates the problem. As for gearing vs. pipes etc. etc. The best MX combo in most cases is a port job that will make excellent torque OFF the pipe and come on like a drag motor ON the pipe. This allows broad tractable power in the tights with enough acceleration to clear traffic for the next set-up for the turn. It also allow you to run taller gearing so your not shifting your ass off and not always looking for the right gear for the circumstance, not to mention with such broad power, youve reached enough wheel speed so when that drag motor acceleration kicks in your not going sideways down the track. Some drag pipes work good for this set-up as long as your porting isn't gutless down low like alot of what Ive seen.....Jim

Hey Dan, yeah, those east coast boys send me tons of work....5 cub builds just this week!...look forward to doing yours as well. Brads as good as gold...really nice guy...look forward to having him on the team next year...Jim