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machinest & A&P Mechanic
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Discussion Starter #1
hello guys, in reading the 6 inch rod thread i started to wonder about the combo i was about to but together... i got a 400 block from a friend, and a 327 crank, so i was thinking putting the two together and using the longest rod i could shove in their. now obviously this is not a normal "350", but i figured with a long rod the piston would dwell at TDC longer and thus better efficiency along with the less piston side loading (for reduced wear). however i never thought about piston rock with the "short" piston. in a big bore short stroke combo like this would it not be possible to put pistons in their with longer skirts? i have not bought pistons yet, so i do not have a good idea of the room i will have, so any help before i get the pistons is apreciated :)

-Leo-
 

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wind & fire = guides to power
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Short stroke and a long rod you should have very little piston rock, but if you are worried and plan on driving it many many miles by all means put longer pistons in it.
 

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I need someone to help me understand how a longer rod causes enough dwell at TDC to make a difference. Since the piston doesn't truly dwell, I'm assuming that the comment refers to the piston taking more crank rotation to travel a given distance near TDC. What is the piston travel near TDC that is considered dwell? I've run the numbers from .010" to .100" piston travel from TDC and get no more than 0.25 degrees crank travel difference between a 5.7" rod and a 6" rod. Does a 0.25 degree extra "dwell" at TDC (.100" travel) make a noticeable difference? I can't argue that it does "dwell" longer, but it's so small it seems improbable that you could tell the difference with a dyno or the seat of your pants.
 

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wind & fire = guides to power
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i've heard it's about timing myself but it seems more likely that extra power is gained from less friction between the piston and cylinder wall in addition to haveing a more direct route for the power to transfer from the cylinder to the crank(the angle is less and there fore better transfer of energy).

And it could just be a scam(I'm sure a little of the hype is just that...marketing hype).

There is power to be had but when you are talking 5-10...15 tops is the price really worth it in a street buildup?
 

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Beater Driver
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Leo,

Check out this link:

http://www.airflowresearch.com/

click on "articles", then on "412 hp 350 ci AFR 190 cc" article (second from the bottom).

They use the same idea you have to make a very slick, high revving engine.

Bear in mind that although what you're planning to do is very cool, you're going to be giving up 50 cubes and potentially some big power by not sticking a 3.75" crank back into your 400 block.

Matt
 

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Glad the Jeep is on the road
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NXS said:
i've heard it's about timing myself but it seems more likely that extra power is gained from less friction between the piston and cylinder wall in addition to haveing a more direct route for the power to transfer from the cylinder to the crank(the angle is less and there fore better transfer of energy).
That's the Smokey Yunick theory, and he built a lot of engines....
 

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machinest & A&P Mechanic
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Discussion Starter #7
TooSlow said:
Leo,

Check out this link:

http://www.airflowresearch.com/

click on "articles", then on "412 hp 350 ci AFR 190 cc" article (second from the bottom).

They use the same idea you have to make a very slick, high revving engine.

Bear in mind that although what you're planning to do is very cool, you're going to be giving up 50 cubes and potentially some big power by not sticking a 3.75" crank back into your 400 block.

Matt

yeah i dont mind loosing 50 cubes, this motor is all about efficiency, thanks for the link to, i just so happen to have that issue (thanks Ms. Karis). however, since this motor is about efficiency i was thinking of using cast iron heads, OOR i could maybe get alluminum and coat them, but i dont think i can afford that.... anyways, its a go, longer skirted pistons (than what they would normaly give yout) would fit???
 

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6.25 rod in 350

The biggest effect of running a long rod is that you have less rod angularity when the crank is at 90 degrees. According to Smokey, this has two good things happening. Less side thrust on the cylinder by the piston, and it also slows down piston speed. With the second one, you get into rod/ stroke ratios and all that physics stuff, which while I understand it, I could never explain it.
Dyno testing has shown that in MOST all cases, having longer rods has proved beneficial when it came to top end power. This will vary a lot depending on the engine, and just what going to a long stroke rod vs stock would imply. According to the powers that be, you should run a rod stroke ratio of at least 1.5:1, meaning that if you have a 3 inch stroke, the minimum rod you would want would be 4.5 inches long, and that the ideal rod/ stroke ratio is 2:1.

I do know that from the graphs Ive seen on this issue, that with a longer rod, your piston doesnt travel as fast during the first half of the down stroke, making for better combustion, and adding power to the stroke.
 

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Early this year I also read that article
on AFR's site. I'm alwaysinterested in
out of the ordinary combinations, so emailed AFR and asked them what heads
and cam they thought best for a similar
build.

They replied that they knew of several who had that tried that combo and were not happy with it, although they didn't say why.

I've also read a similar article on a long rod 351 Windsor, using a 6.58 400m rod, that seemed to deliver in a big way on torque and resist detonation well, but then read posts from people who tried it and weren't impressed.
 

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wind & fire = guides to power
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It's a simalr combo to the old 409s. The bore of a 454 and stroke of a 327. They rap out super quick but lack on the bottom end, kinda like a bike engine. Not for the street... but cc for cc the horsepower can't be beat.
 

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Might check with some piston manufacturers & see how the skirt length compares to a standard piston. An off-the-shelf piston for a 400 with 6" rods might be what you need. Hypereutectics use a tighter wall clearance, which would allow less rocking.
 

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The best thing about this short stroke long rod deal is if you run light rods and pistons you can take more off of the crank which is what I was after for the circle track. If I was running something on the street I would build a 6 inch rod 406. Torque and horsepower are king on the street.

JMO

Tom
 
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