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Discussion Starter · #1 ·
Well my stroker has been done for a while and is at Speed Inc. right now fixing a few things and finially tuning it. i just asked my engine builder about my rod size and piston size.

Now is there any advantage/disadvantage of 5.7" rods? i see alot of people running 6" rods, so i was just wondering information about the 5.7" rods compared to the 6" rods. also would the srp .030 pistons flat top pistons b good for my motor? he said it is making 10.1:1 compression and will see a 150 shot of spray.
 
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Discussion Starter · #2 ·
For years they have preached that it better to have long rods. But the Ferd 302 has only 5.135" rods and they do fine. Chevy with 5.7, and say a Pontiac 350 they have 6.625".

Unless it is an all out racing attempt, I don't know if there is much significant advantage.

The theory is that a longer rod will dwell longer at TDC boosting up cyl pressure some. Does it? Don't know for sure, it might be not enough to worry about.

Smokey Yunick did much of the theory on the long rod engines. He always recommend that a R/S ratio of 2:1 (301 Pontiac is factory 2:1, 3" stroke, 6.05" rod) is desired for circle track engines. Drag and street engines likely will vary. How much really matters? Good questions....
 
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Discussion Starter · #3 ·
Your 5.7" rod and piston combo will have a few advantages over a 6" rod/piston combo. One is that the piston can be designed to handle more nitrous and the other is the oil rings will not be in the pin boss area so that's good.

Karl

[ 11-20-2006, 03:16 AM: Message edited by: Karl Ellwein ]
 
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Discussion Starter · #6 ·
Or you could split the difference and use a 5.85 rod as Calloway and Lingenfelter did with their LT1 strokers. ERE-7 has the 5.85 rods
 
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Discussion Starter · #7 ·
Im running a 5.85 with my 396. Figured there would be enough piston for nitrous and enough rod to reduce side loading.

Not really sure about optimum rod to stroke ratio though.
 
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Discussion Starter · #8 ·
Originally posted by KW Baraka:
</font><blockquote>quote:</font><hr />Originally posted by AdioSS:
another thing is that the piston will be heavier
On what?

The 5.7" rod......or the 6" rod?

I'm thinking you mean the 5.7" rod???????

KW
</font>[/QUOTE]yes
 
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Discussion Starter · #9 ·
For a 383 a 6" rod allows a good balance of a light and stong piston. Remeber rods almost always fail under tension and piston weight plays a BIG role in how much stress is developed when the piston changes direction at TDC.

Why such low compression?
 
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Discussion Starter · #11 ·
I just started gathering my parts for a engine build. What rod length is good for the street and longevity for the engine?
 
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Discussion Starter · #12 ·
Originally posted by Da real Birdman:
I just started gathering my parts for a engine build. What rod length is good for the street and longevity for the engine?
[Slap Over The Head]---You have not been paying attention, Grasshoppa!!---[/SlapOver The Head]
Originally posted by 96capriceMGR:
For a 383 a 6" rod allows a good balance of a light and stong piston. Remeber rods almost always fail under tension and piston weight plays a BIG role in how much stress is developed when the piston changes direction at TDC.....
 
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Discussion Starter · #14 ·
There are more good 5.7" rods available for our motors and usually at lower prices than 6" rods. For a durable street motor with a shot of NO2, the money difference would be more wisely spent on better forged pistons and more top quality machining and balancing work.

Another thing is that there are just so many variables to chose from within a budget. For instance, what would you rather have? 5.7 rods, best forged pistons and a perfect deck or 6.0 rods, very good forged pistons and a "close" deck? These kinds of questions will eat on your brain and your wallet. That's why you must choose the best engine builder and machinest you can find and trust.

Good luck on your build!

Frank
 
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Discussion Starter · #15 ·
Originally posted by FrankLT1/9C1:
....Another thing is that there are just so many variables to chose from within a budget. For instance, what would you rather have? 5.7 rods, best forged pistons and a perfect deck or 6.0 rods, very good forged pistons and a "close" deck?....
Well.....if I'm going through the expense of a performance stroker......I would want best forged pistons and a perfect deck AND 6.0 rods
......

If you gotta skimp on a stroker build-up, then maybe you should stick with a stock displacement motor
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KW
 
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Discussion Starter · #16 ·
I always understood the longer rod increases the time it has to dwell at top dead center. This has a couple of advantages:

1. With the longer dwell time it means that the pistons rate of change up top and down low will be less. Restating the previous line: The acceleration forces as the piston nears TDC/BDC and passes TDC/BDC are less. The acceleration forces on the piston are spread out over a longer period of time. Thus it is less of a strain on the piston and increasing reliability.

2. The relationship between piston travel and crankshaft angle changes with a longer rod. For example a short rod engine will rotate 30* and the piston will move 1". A longer rod engine will rotate the same 30* but the piston will only have moved .5". The numbers are exagerated, but illustrate the differance in crank rotation and piston travel between the short and long rod.

...and tying it all together.. because of this you can retard the ignition a few degrees and get increased mechanical advantage. In other words your timing should not truly follow crank position, but rather the pistons rate of departure and position relative to TDC. The mechanical advantage is important because the same cylinder pressure exerted on the piston at 5* ATDC will produce less torque than the same cylinder pressure when the crank is at 90* ATDC.

This is a good thing as retarding the timing allows for a slightly leaner mixture. If properly tuned the time the mixure is in a combustion state the overall chamber temps are going to be slightly lower.. thus you can lean it out....

I think smokey yunick quoted a 3% gain in torque as a result of a longer rod. However that book was written long long ago. I would believe that with good tuning that more of a benefit could be had, but I honestly don't know how much.

Well that's the physics behind it. We studied this in college in the automotive department for fuel economy projects. (like machines that get 3500 miles to the gallon type projects, yes close the worlds record). But aside from that I have not much experience with what gains could be expected with just a rod lenght change on an otherwise identical setup.
 
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Discussion Starter · #17 ·
I still think you folks are making WAY WAY TOO MUCH over dwell and crap. Piston weight or loss there of is the biggest advantage you will see on a street motor. Since the same crowd who gets a hardon for all this truely race tech gets ahardon for the LS1 and anything related look into LS1 pistons once, so small and light they look like a little hockey puck on top of the rod, defenetely a part of why they rev well.
 
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Discussion Starter · #18 ·
FWIW, One of the magazines (maybe Hot Rod?) did a test with a 454 and with the setup they tested they found no signifficant difference going to a longer rod from the stock 454 rod and stock rod-to-stroke ratio on a 454 is 6.135/4=1.534.
 
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Discussion Starter · #19 ·
Short rods, long rods... All power is made in the heads, everything else is there just to transmit power or help the heads do their thing. The combustion chamber shape matters somewhat but the ports are what really determine what your engine can do, with the intake port being more important than the exhaust port. And that is why those GM 330CFM LSx heads are dirt-cheap metal Viagra.
Tim
 
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Discussion Starter · #20 ·
both have avantages and disadvantages.

I have a 5.7 rod in my 383. When using a 6 inch rod the pistons pin interfears withe the lower oil control ring and requires the use of a special ring. Now over time this can cause problems on the street with the ring sticking and minor oil burn. I know people running 6.0 inch rods on the street and never had a problem with it granted, they really arent daily drivers stacking on 10K miles a year either. 5.7 rods are also usually cheaper to buy.

a 6.0 rod allows more piston dwell time and better piston to rod angularity. Whats this mean? not necessarily more power but a much better overall powerband and flatter torque curve. Using a 5.7 rod in a stoker application like the 383 because of the poorer rod agularity can cause increased cylinder wear.

so do you want oil burning from stuck oil control ring or from excessive cylinder wear? j/k i havent really seen a problem with either. Its really up to you to decide. Really id rather have a 6.0 inch rod in my 383 but i was talked out of it by my machine shop before i did research of my own.

I have SRP flat-top 11:1 pistons. If you looking to spray a 150 shot then they will take that all day long. They are a very good piston, much better than the speed-pros and such. A friend of mine was running a chevy 383 in his mustang, 6 inch rods, SRP pistons. Motor held together for 2 years and the track and street running between a 300 and 400 shot of spray and going 8.60's. fyi, he never hurt a piston, he broke the stock block and the pistons are still perfectly good
 
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