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2grimjim

Anyone using the CP/Carrillo long-rod kit?

11 posts in this topic

Mine is getting put in shortly. I got the whole Project X kit from CP-Carillo. Crankshaft is getting new rod put in, machined and balanced. The CP piston has the wrist pin mounted higher into the piston to maintain head clearance issues. Supposedly, the longer rod gets a more complete burn during the cycle.

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Mine is getting put in shortly. I got the whole Project X kit from CP-Carillo. Crankshaft is getting new rod put in, machined and balanced. The CP piston has the wrist pin mounted higher into the piston to maintain head clearance issues. Supposedly, the longer rod gets a more complete burn during the cycle.

Oh, I fully understand the purpose of the long rod kit and the theoretical benefits. I was just curious to see what performance gains were noticed or if anyone had the forsight to do before-and-after dyno comparisons.

The other thing I was interested in is potential cam timing changes required when using this kit.

Are you using stock cams with this combo?

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Increasing the rod length reduces the rod to cylinder bore angularity. This in turn puts the connecting rod at a mechanically favorable angle to the crankshaft radius later in the engine's rotation, and for a longer period of time, both of which favor power production at very high engine speeds.

http://www.thumpertalk.com/forum/showthread.php?p=6844321#post6844321

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Increasing the rod length reduces the rod to cylinder bore angularity. This in turn puts the connecting rod at a mechanically favorable angle to the crankshaft radius later in the engine's rotation, and for a longer period of time, both of which favor power production at very high engine speeds.

http://www.thumpertalk.com/forum/showthread.php?p=6844321#post6844321

Another benefit is the increased dwell time at TDC and moving the point of peak piston velocity closer to 90 degrees ATDC/BTDC (as the rod ratio decreases, peak piston velocity falls closer toward TDC).

To take maximum advantage of improving the rod/stroke ratio, camshaft profiles or lobe centers should be altered accordingly.

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The longer rod would also put less stress on the pin area in the piston which would be a good thing. I have seen a few failures of aftermarket pistons with the pins pulled out of the pistons when used in high RPM applications ( supermoto ) A modern High rpm engine say an R6 yamaha will have a rod length/stroke ratio of over 2-1 the 03-09 450 is on the order of 1.65-1 to get into the modern high RPM arena the 450 rod would need to be something like 20mm longer. A few years ago Falicon made up a kit with a shorter stroke and bigger bore ( still 450cc) enabling a longer rod to fit in with out spacers. Not sure how that worked out but it would be the right direction if you want to really spin them up

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I am using the GYTR head with this combo so the cams are not stock. Head is out getting the valve seats recut and then new springs and valves. I should have it all back together by mid January.

Oh, I fully understand the purpose of the long rod kit and the theoretical benefits. I was just curious to see what performance gains were noticed or if anyone had the forsight to do before-and-after dyno comparisons.

The other thing I was interested in is potential cam timing changes required when using this kit.

Are you using stock cams with this combo?

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The YZ450 actually stands at 1.76:1, which is a little on the short side, but within a range considered ideal for engines producing most of their power between 5-8000. The YZ450, of course, peaks at 8500, and pulls to 9500 pretty freely. One of the engineering compromises that gets made is the use of a shorter rod to lower the overall height of the engine and lower the CG of the complete bike.

Rod length isn't the only way rod angularity can be changed, though (although it's much simpler than some other ways). Yamaha addressed this on the '10 by offsetting the bore axis forward of the crank radial center line, which has the effect of reducing the rod angle and relocating maximum mechanical thrust later in the stroke as a longer rod would, but only on the down stroke. It has the opposite effect on the upswing, which coincidentally reduces the engine braking some people complain about. Offsetting the wrist pin in the piston is another more common approach, but one needs to be careful not to develop an excessive rocking load on the piston by doing so.

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How would the longer rod effect the reliability of the crank? Or the whole engine?

From what I can tell, there is no negative impact by increasing the rod ratio on reliability.

The only real negative point (at least in the case of the YZ) is the non-standard piston and the cost difference when it's time to rebuild.

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Longer rods in and of themselves probably enhance longevity overall, since they reduce thrust on the piston skirt, reduce loading on the crank near TDC, and reduce ring inertia over TDC (more of a factor on engines revving beyond 16K than below that).

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