That sounds like a good idea! De-stroking it would decrease the engine size cc's, but would also make it rev allot quicker with a shorter stroke. Look at the Z400, it has a very short stroke, also this is what makes the 426 such a screamer! So you might loose some low-end torque, but it would rev faster and maybe accelerate harder. I think it would work best with a different cam, one that is designed for higher RPM and more top end power. If any of you guy's do this, let me know I am very interested. I can visualize a 686-Bore (I'm not for sure how many millimeters it is over stock) with a shorter stroke, 11:1 compression and a high performance cam with no rev limiter, or at least one suited for the new cam! But with out a new cam, I don't think you would see a real benefit, since the cam is designed to make max power between 6,500 and 7,000 rpm. Anyway, keep me in the loop I would love to see what this de-stroked engine could do, I be it could really be nasty!!!!

 

Yes, it will rev amazingly fast. As already stated, look at the other smaller cc quads out there. The C-dale and Z for example, both have strokes much shorter then the Rap or DS.

The cam, rev limiter and porting are all the things that "at this particular point" are not just available to anyone from any builder. The items to make this happen need to be custom made and are very specific. There are a GOOD handfull of other items that have to be considered as well when doing this.

I will say this though, it is just around the corner! [img]i/expressions/face-icon-small-wink.gif[/img]


And 14mins, are you overwhelming "Rapattack" with all the PM's yet?

 

No i have everything except the rev box figured out.

 

<< 2001 black and white,13.4-1 deburred lightened piston, stainless steel valves, trick springs, all rotating parts coated, custom Porting and polishing by CRAYCRAFT MOTOR WORKS. Stage 2 cam. By far the fastest raptor i have had. >>

It's got too be the deburring!

 

Think about this. If you pull 5mm off the stroke, you can add the 5mm to the rod length and still use a stock piston. The longer the rod, the longer the piston stays at TDC, so more combustion is allowed to happen. Plus, the angle the rod is shoving the piston sideways when at BDC is corrected and side load on the piston skirt is decreased. Shorting the stroke will make it rev quicker, but the increased rod length is what makes is rev higher since friction is reduced.

If you destroke and use a big bore, it should unshroud the valves some, and you still have the cc advantage. Since it will be a high reving engine, you will want a lot of duration on the cam.

If you look to the CBR bikes, and the F-1/2/3/4 compare the stroke on them. The best for torque is the F-2 and they just kept dropping the stroke for the F-3 and even more for the F-4. The F-4 is VERY fast reving and the quickest of any CBR600. It also makes the most stock horsepower.

 

14 mins- Be sure and have it balanced before you put it back together. Money well spent. [img]i/expressions/face-icon-small-smile.gif[/img]

 

Look at the Predator. It has basicly the same size bore (99.2mm) as the Raptor and DS650 (100mm). But has a much shorter stroke (64.6mm) then the two (83mm). It really loves to rev, and the top end power is explosive, but is a little shy on bottom. But is know to give the Raptor and the DS a run for there money.

 

Here is the answer to you prayers, 14mins. The Dyna FS ignition box! It has 4 different timing curves. The first one is same as stock, with a stock rev-limiter. The other 3 have various advanced timing curves and come with NO rev limiter. You can custom program the 3 different curves and I think you can assign a rev-limit to them, whatever suits your engine. PM AlkyBurninX about this. He has alot of experience with the DYNA system on his Banshees. Good Luck.

RR1

 

One more note. Just remember that the higher up the RPM scale you move the horsepower, the less torque you will have. 70hp @ 6500 rpm will have ALOT more torque than 80hp at 12000 rpm. Just think - an INDY car has 800-1000 hp and revs to ~15000 rpm. But you would never use this engine for drag racing. Have you ever seem an INDY style engine in a dragster. Probably not. What you do usually see, though, are huge displacement Torque Monsters. Just a thought. Good Luck!

RR1

 

Air- I am not going to do it. I am putting the 2001 back together with some killer headwork. I expect to have a 686 with at least 75HP on race gas. I am hoping for more but would be thrilled with that 75HP number