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bigpaulo

200 rods into 250?

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Ive read about people with v8s putting 302 rods into their 351, apparently it makes it rev more and increases compression?

So...what would happen if you put 200 rods into a 250? Would it work? Would it be an improvement?

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same thing mate and it works as well

lots of 6inch rod 250 combos around i mean im not am massave fan for my own stupid reasons but i have 2x 200 rod engines they work fine and are happer to rev then a 5.8 rod combo

 

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...happier to rev

Most of the time when im asking questions its because i dont understand... im just repeating words that ive read on the internet. doesnt mean i understand it. hence why i ask questions!  :)

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What exactly does it achieve over a standard engine? does it give you more horsepower or torque or something?

 

Short rods have the piston decelerating/accelerating at the top of the stroke much more abruptly than those on a long rod. This gives a rapid rate of compression and expansion accordingly. At lower rpm, this is supposed to help make more torque as the rod is acting at a more advantageous angle on the crank right at the peak of cylinder pressure occurring. At high rpm, this is a hindrance, as that rapid compression is very sensitive to ignition timing and the rapid acceleration of the piston after top dead starts to outrun the combustion, meaning power is lost. Imagine pedalling a BMX bike up to the speed where most of your energy is used pumping your legs rather than pushing on the pedals. There is a point where the pedals start to travel faster than what your legs can.

 

The piston also undergoes more stress as the acceleration happens more suddenly, also there is more side thrust on the piston and bore due to the increased sideways angle of the rod.

 

Imagine a ski boat being the crank pin, the rope is the conrod and the skier is the piston. The skier is being towed behind the boat and 20 metres offset to it. There is a certain amount of force trying to pull the skier sideways. Shorten the rope further and this angle increases, and force trying to pull the skier sideways becomes stronger. The force on the rope increases too because you are towing the same load but at an increased angle.

 

Longer rods work better at high rpm for a few reasons: more gentle acceleration of the piston, more "dwell" time at tdc (to allow more time for combustion to occur before acting on the piston), less side thrust on the piston and engine is less sensitive to ignition timing.

 

Gentler acceleration/deceleration of the pistons makes an engine smoother as there is less secondary vibration involved. I won't go into that as I have crapped on enough.

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^^^^^ there it is.

Long rod = less side wall frictional losses, also greater mid bore piston speed which draws harder on the cylinder head at that time (good thing) and all of the above. Bad thing is try getting a set of pistons to suit the 200rod 250crank combo.

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that is why I use the 200 rod and piston combo in speedway - less friction and better breathing - funny thing is that GT (my guru - sadly now departed from this earth) loved the short rod combo over the long rod. 

I've built Jason's new speedway motor as a tribute motor to GT. Exactly how he liked his x-flows so we will see how it compares to mine which is essentially the same but with 200 rods. 

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Basic knowledge that's been around for nearly half a century on these engines yet we all think we've just invented the wheel

No one acted like they invented anything, they merely explained the theory behind doing this conversion to someone who asked the question. If we all knew everything we wouldn't be on here would we? No need to be a condescending smart arse, we are all here because we like cars.

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It's all been said and done before but please stop making out its all your own idea, it happens way too much on this forum

No you are wrong, I invented it all. You're extremely lucky that I am generous enough to share it all with you... Such is my vast, immeasurable talent that I am sometimes, wait... always in awe of myself for coming up with such mind-blowing, god-like, pure and original ideas. I also have a gargantuan, tree trunk-like penis.

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LOL yeah still a knob who thinks he owns everything to do with a xflow...Shame the world lost soo much of the late Dave Adams knowledge due to him just trying to make money off Dave's ideas.

 

Nothing constructive to say ever unless he is making money off you...real nice bloke.

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