sure you could. but you would have to send it with your crank so it could be balanced to it and it would also increase your compression.

 

Can you elaborate on the means of increasing compression? Here is a link for Falicon...Pick Here. Falicon is a premiere crank company.

 

Carefull,if you do not know what your doing here,you could be in DEEP S### !!!!! I tried three piston designs before got it right!!!

 

Well this is why it increases compression.. when you put a stroker crank in you have to shorten the con rod.. this makes the piston go down further and up further.. what you doing is squeezing a larger volume in the a smaller space. so its like 13 parts into 1 space when stock is 11 parts into 1 space thats where you get 12to1 or 11.5to1..

 

You do not necessarily have too go with a shorter rod when increasing stroke. CHeck out Falicons web site, many times they use a longer rod. Makes no sense adding potential performance in one area and taking it and reliability away in another. Falicon must have had a very good reason too go with a shorter rod on the ds....I would inquire about this situation.

 

>>A shorter rod hurts bore/stroke ratio.

I suspect you mean that a shorter stroke hurts the bore/stroke ratio. The rod length has nothing to do with the bore/stroke ratio. But a shorter rod does transfer more load to the cylinder walls.

In the 'good old days', you had 'square' engines (bore and stroke were the same dimension), 'undersquare' (more stroke than bore) and 'oversquare' (larger bore than stroke). Generally, the undersquare engines produced great torque, but didn't rev as quick. Oversquare engines rev quicker, but had a loss of torque. Suzuki's RM250B had an undersquare engine, felt show but went very fast and was easy to ride. My old CAN-AM had a oversquare engine that made lots of power, and felt fast, but was hard to control and produced poor lap times.

But in the early 90's, it all changed. Formula 1 engine designers developed new combustion chamber designs and valve angles that allow extreme oversquare engine designs that didn't work in the old days. A 'square' engine has a bore/stroke ratio of 1:1. Today's Honda CRF 450R is close to 1.5:1. F1 engines are close to 2:1.

But what we are finding is they may have moved too far. When we put a larger bore on the Yamaha or Honda 450s, we see little power increase. When we stroke it, it comes alive. We have lots of pro riders that use our stroker cranks, not just for more power, but for more control of the power and traction.

About rod length: In _theory_ the longer the rod, the better (to a point). Some engines have a very poor rod/stroke ratio and work better with a longer rod. Others are toward the long size and work fine with a shorter rod. Let's say we stroke a crank 4mm. To do this, we move the crank pin 2mm futher out from the crank centerline. At top-dead-center (TDC), this will move the piston 2mm higher, and at bottom-dead-center (BDC), the piston will be 2mm lower - a 4mm longer stroke. If we use a 2mm shorter rod, the piston will be at the same position as stock at TDC, and 4mm lower at BDC. As long as the piston clears the crank, and the rod/stroke ratio is ok, then this is a good solution.

But if the piston hits the crank, or the rod/stroke ratio is poor, then we are forced to use a longer rod. That means you have to use a cylinder spacer, longer studs, and longer cam chain. Also, the top engine mounts may need to be changed, etc. So from an assembly stand point, the short rod stroker is easier, has fewer parts and looks stock. From a power prospective, the long rod stroker is better. For some engines, like the Honda CRF-450R, we offer both short-rod strokers and long-rod strokers.

Now, if you stroke it 4mm, by using a 2mm crank pin offset, and use a 1.5mm shorter rod, you piston will end up 0.5mm higher at TDC (2mm-1.5mm=0.5mm) and you'll have a higher compression. So the rod length can effect compression ratio, but not because of stroking the crank. If I put a +0.5mm longer rod on a stock crank, it will also raise the compression ratio, but the engine size remains the same.

There is a real art to getting the bore/stroke ratios and rod/stroke ratios right. Plus, theres also pin size issues, and compression height issues. Hope this helps.

 

Thanks for catching that. I meant Rod / Stroke ratio.

 

So bottom line the DS is getting a shorter rod for the sake of convenience.

 

>> So bottom line the DS is getting a shorter rod for the sake of convenience.

I guess you could look at it that way. But there's more to it than that. We've done both long and short rod strokers for the DS.

On the Honda, there is little difference on the dyno, but most (not all) riders prefer the long rod version. But many customers will not buy a stroker kit that uses a spacer plate because they want the engine to look stock. And frankly, it's easier and cheaper to sell a short-rod stroker. As long as you don't have any rod length/stroke ratio issues, in a minor point. In the case of the Yamaha YFZ-450, it was a real pain to get all the pieces together for a long rod stroker. We had to have custom bolts made, and lots of other issues. So long rod strokers can be a real pain to gather all the pieces. We have them all for the Honda and Yamaha. We don't for several other models. We usually work with engine builders who work out all the pieces and details, and offer it with our crank as a package. That's were we are with the DS-650.

You could send us a crank and we'd modify it to your specs, but then you've got a lot of work to do. Or you can send your engine to someone who has already worked out the details and you get a well designed, proven configuration.

In any event, if the design isn't good we won't build it. We don't want to be associated with bad design. We aren't perfect and the nature of racing engines mean some of our customers are really on the edge. But we try to be really careful and do good work. I believe any crank you get from us will be better than the OEM design, for the intended purpose.

 

Good explaination! and thanks for building my crank!!