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#1
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Anyone used longer conrods in an engine and have noticed more torque and Hp!
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#2
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Sorry, I can't help on this one.
I think only a Dyno would notice the difference. I think the only common engine build up that you may see comparitive posts from is the 451 stroked 400 engine built with either the 383/400 rods or the 440 rods, but even that would be a hard comparison to make, because the engine with the 383 rods will probbly have a heavier (taller) piston. |
#3
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unless your reving the motor really high, the only thing that you will notice is that your pistons will be less likly to oval..after 200k miles..Keeping the rings from fluttering and keeping the piston from side loading the piston wall are what the longer rods will do for you. Maybe there is more..anyone else
Maxwedge |
#4
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Supposedly, longer rods hold the piston at top dead center for a longer time(1 or 2 milliseconds?). You can also get into the thing about head flow and higher piston speeds and how the longer rod will fill the cylinder better. Smoky Yunich once said that the longer rod will make more power, but dont go way out of your way to buy them, because money spent in other places will make way more power.
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#5
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There have been 2 articles in National Dragster in the last year written by Reher Morrison. Both articles they say that way to much emphasis is being placed on rod length. There was a graph that showed the piston through its travel in a big block chevy. They plotted the difference in piston height at the highest rod angularity during the stroke, with a .250 longer rod, it only made 1/10000" difference in piston hieght.
Basically, the article says if the rod connects the piston to the crank and the piston clears the counter weight, run it. Anyone seen the pro stock truck dodge engines? They have been decked so far that the water holes are no longer in the front of the block and my understanding is that they are using something like 5.2 or 5.3" rods. |
#6
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What that Reher didn't say is how much r&d and what length rod they picked for THEIR pro stock engines. You can bet they don't "just connect the piston to the rod" with any quality rod laying around like he would have us believe.
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#7
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I recently built a long rod Slant, (7.1" long rods) because it is the "In" thing to do. I sat down and had a serious discussion about it with J&M Engines and the consensus was that the major advantage with the long rod in a Slant is that you move the pin higher in the piston, making the piston more stable. (J&M runs the "Buzzin' Half Duzzin" '68 Valiant, 240" Slant, on gas and spray, 10:70@121mph)
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#8
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Exactly
It keeps the piston and the rings stable at higher RPMS..If your building a street motor that isnt going to see the other side of 5-8 grand often, then its not worth it. I bet you wouldnt gain more than 10-20hp..There are toher areas you might gain, but not that much HP with a street motor. IMHO Maxwedge |
#9
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DAVID REHER FAILED TO MENTION THE REAL REASON THAT THEY CAN'T FIND A PERFORMANCE GAIN WITH LONG RODS, THEY BUILD CHEVY'S. THE BASIC CHEV BLOCK HIGHT IS SO SHORT THAT THEY WOULD HAVE NO PISTON SKIRT LEFT TO STABALIZE THE PISTON. YOU CAN NOT MAKE A SILK PURSE OUT OF A SOW'S EAR!!!
DENNIS |
#10
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Actually also Wayne County had that principle with their Mopar engines; " The rod length is what ever it takes to get the piston and the crank together. They used 400 height blocks which are only 0.2" higher than a stock BB chevy 'low' block. Todays 500 cu in Mopar Pro Stock 'Hemis' have lower deck heights than small block Mopars, and significally lower that is. So I guess the rod lengths aren't that big either, unless they protrude through the heads. So, as far as the performance goes it may be important, but in an application where each gram is even more important, shorter rods reduced weights give more advantage than the rod length.
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#11
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Did a little research on this, and It seems that tendencies from rod length, are, pretty much out of our "packaging possibilities" The long rod tendencies start to be a tuning issue from about 1.9 and longer. Short rods show their attitudes, below 1.5. We all pretty much stay between those numbers, which explains why we don't see much either way. But David Reher's thing is full of holes, as his graphed example of a "long" rod was a 4" crank with a 6.435" rod. Wow! that's long, huh? I guess in bowtie world, it's trick.
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#12
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Even with a 'long' 6.435" rod a 454 has an inch less piston compression height than a Mopar 440 which means lighter moving parts. No wonder the 440 rods are so long since the blocks are so tall.
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#13
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I have built a lot of strokers,451,472,499, always use the longest rod you can, due to the side loading and also piston volocity, they make a better volumetric effi. ratio and fill the cylinder better.
Quote:
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#14
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Maybe I missed this somewhere in the postings but, did anyone mention the fact that a longer rod reduces rod angle hence relieving a lot of side stress on the crank...less side push=more tork to the crank and longer life....it's a good theory anyhow..
Don ------------------ Happiness is stomping a BBC with a 318 Mopar |
#15
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Long rod engines can be great but you can sure chase your tail until the correct combination is found. Several years ago, built a 3.31 stroke (oval track) engine with a 6.70" rod. We did it to minimize piston/pin and total bob weight. The long rod totally changed the shape of the torque curve, raised and flattened from 4200 to 6200. It made the car very difficult to hook off the turn. Several cam changes were in order before it became driveable. Went from a 255/259 @ .050 cam (106 C/L) to a 262/268 @ .050 cam (108 C/L) before we got it under control. The long rods love methanol and the taller cam means your engine loves RPM as well. If we got back into that type of limited engine again, I would use long rods if I could.
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#16
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Some additional opinions. I think long rods are a major benefit where cylinder head flow is limited. The application I described earlier used "stock" W2 heads. A professional 3 angle valve, 11/32 stems, etc, was all that was allowed, no port or polish. Flow was about 250-260 CFM @ 28". With our current cylinder heads (370 @ 28") I don't think the longer rod is very helpful.
Why is the benefit more for stock type heads? because in addition to less side stress, etc. I think the long rods help cylinder loading thus more benefit for poorer flowing heads. The modified heads don't need the help. |
#17
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Quote:
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#18
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Moforgo, Mine is, only I used 6.50" rods. Works great.
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#19
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one of the big advantages to the long rod
is that the piston spends more time at (TDC) this alows the cylinder to achieve a better burn all this makes a longer flatter power curve more hp and torque always run the longest rod in your budget if you whant short rods you need to get a chebby |
#20
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I read an article back in the 70s were Smokey Yunich said allways put the longest rods you can fit in any engine as long as you have the write cam to suit the rod lenght and good flowing cylinder heads.He told chev for years to raise the deck height its to short they just wouldnt listen guess what chev have now.
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#21
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Long rods have only one advantage,a less severe rod angle(which means less piston to wall side loading),so if you have a good rod angle(all V8 mopars do)then your ok,its like having a longer breaker bar,it turns with less required force.To add longer rods you will always need a custom piston with the pin located higher than stock and or an aftermarket crank with a different than stock stroke.Longer rods dont change the amount of time that the piston dwells at TDC,only a change in stroke will do that.Actually we destroked a 350 chevy to 342ci and picked uo .18 in et,why?because we made the rod angle more desirable(easier to turn the crank) and the power loss that we recovered outweighed the loss of power due to 8 cubic inches,so yes there is more hp and torq avail but not neccesarily if you have an existing Good rod angle...PRO...
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#22
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??????????? You tell that you destroked a 350 to 342 (~2%) to be able to use longer rods and picked .18? Are you really telling that the only change was the rod and the crank? Do you honestly think that a less than 2% change in connecting rod length is worth almost .2 seconds?
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#23
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I will have to find someone with a desktop dyno that you can enter different rod lenghts to see the change myself.
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#24
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These things you guys are covering are the same things that my mechanic friend is telling me about rod length. He said the 360 Mopar is better cause of the rod length. The SB Chevy everyne at the track he raced at had cheater rods cause they had to run stock length rods in the class but everyone inChevy had to to stay competitive! Hey, don't ask me he is a Chevy guy.
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#25
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Quote:
Every tech article I've read that discusses rod length changes emphasizes that a long(er) rod increases TDC dwell time vs. a short(er) rod that accelerates the piston faster from TDC. That's also why rod ratios & intake port volumes (flow vs. velocity) are believed to have a strong influence on optimizing camshaft lobe separation angles. |
#26
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#27
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