What's really frustrating is this this is one of those changes that has an effect disproportionate to its mathematical valve.
The difference in piston position, acceleration, etc. doesn't anywhere near support the changes in "personality" (for want of a better term) that occur when the ratio is altered substantially (10-15%). Short rod engines are much more tolerant of late intake closing, for example.

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Hey Jeffrey! Thanks for a better explanation of the rod angles and piston movement I observed as a young engineer. Nothing beats large piston steam engines for drama......and "personality"

Good science!

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Yeah....Im the one who destroyed this rare, vintage automobile.....

7.3" lenght 2" crank journal size, 1" floating pin. Those where fitted on "torinos", some argentinian version of amc's rambler american or something. Those came in 4 dr sedans and 2 dr hardtop versions. The choice of engines were 3 litres or 3.8 litres, up untill 1977 them blocks ("tornado", a derivative of the us "continental") had 4 mains, then they got a new block casting (I don't know if that was an argentinian redesigning rave such as the holley 1922 or happened the same in the states) (just like phord did with their inline 6 221 by the same time) with 7 mains. The thing is that those engines had a variety of shapes of conneting rods, so, but so very wide, that's hard to get a complete set this days. They had 10 diffrent shapes and weights and sizes (mains, wrist pins, some of them where "bent" not straight) for a production run of 10 years but very little numbers of engines made.

using renault 18 pistons with those rods (stock or custom made forged pistons) you have 20mm for fittng the oil ring and the comp rings. Pretty close but with thinner rings ("new" tech) can be done. Also you have a very tempting 32.5 mm distance from piston head to wrist pin center...

Renault did purchased AMC operation down here in '68 and gently slowed down (aka they frenchly crapped on local AMC branch called IKA - industrias kaiser argentina or argentinian kaiser industries) all AMC operations till 1970, when they introduced the infamous R12. they did used those "tornado" engines to produce the "torino" up to 1980. That's why most renault and AMC derivatives (at least from down here) do interchange or mix up with minimum fabrication or even none at all.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

that'd explain why my small 4 banger renault friend tells me (and we keep fighting about it) that he picked up "something" by using shorter rods on his radically cammed mill. I just wouldn't accept it... didn't know that shorter rods are more tolerant to late intake closing.

So, basically you're saying that there's no other advantage in using 198 or longer rods other than moving the wrist pin higher? I mean, moving the wrist pin higher does means less friction and side stress on the cyl walls, ain't that true? Moving the rings higher and using thinner "modern" compression rings sounds like a good thing to me... so does floating pins, ... can I get my asking turn and ask you the reason why shorter rods means more tolerance to late intake closing?
I missed that... who's jeffrey and where's his explanation? I'm getting really dumb or is the floo wearing my brains down?

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Panic = Jeffrey

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Well, a longer rod does reduce friction and internal noise, and may help breathing with bad ports and the stock 225 ratio is a bit low IMHO. I mean the change isn't enough to warrant the work in and of itself. Unfortunately, a really long rod makes for a very tight ring package because of deck height limits.

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"7.3" lenght 2" crank journal size"

Nope, still can't find anything on it. The pre-1965 Rambler 6 cylinder, which was 4 bearing and longer stroke (195.6" is 3.125 X 4.25") has shorter rods with 2.09" journals.

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The crank rotates in a circle, but the rest of what you said is not true.

With a hypothetical infinitely-long connecting rod, the piston moves in a perfect sine wave and the time spent at the bottom is identical to the time spent near the top.

As you start to shorten the connecting rod so that the rod length is less than twice the stroke length, the piston starts spending more time at the bottom of the cylinder and less at the top. The piston gets "snapped" up to the top and back down faster.

The ultimate extreme case would be a connecting rod 1/2 the length of the stroke (can't be done in the real world because the piston would smack the crank). But if you visualize it starting at TDC, as the crank rotates the piston will be at BDC after only 90 degrees of crank rotation, and the hypothetical wrist pin will be aligned with the centerline of the crank. On top of that, the piston will sit *still* at the bottom of the cylinder for a complete half turn of the crank (remember we're imagining that the rod is 1/2 the length of the stroke, or exactly the same length as the crank throw), then at 90 degrees BTC the piston would go flying up the cylinder again.

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OK, that's because pre-65 rambler engine was the model they took for doing the mods. First they used longer rods, then eventually reduced the journals (altought either me or the writer of an AMC book I consulted might have typo the journal... 2.09" is close enough to 2.00" to make me wonder if that guy just rounded off that way ) the funny thing is that they produced more con rods than engines! 10 diffrent shapes and not kiddin! some of them was like those special wrenches for hard to reach places (I mean, the journal and the wrist weren't connected on a straight line with that particular shape) and eventually they produced the longest 6 cyl rod (at least down here) using 7.3"

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

There are Nash engines related to the 195.6 but smaller, but also larger Packard etc. engines listed as Rambler since they traded parts.

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I'll see if I can get a pic of it and post it here.
they where OHC 230, 233 and 241 engines. some 233 where 7 mains, the others where 4 mains.

this seems either as a 230 or 233


this is the OHC 241 that went to Nurburgring in germany.


this is the 7 mains 233


this is the car (you have to bare with me here and try to remove the modifications in trim and etc they "criminally performed" on the original rambler car)

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.