Longer rods - Team Camaro Tech
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post #1 of 12 (permalink) Old May 6th, 15, 12:29 AM Thread Starter
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Ron
 
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Longer rods

How would 6" rods on a 3" stroke crank work? Would it be worth
paying the Xtra money for the floater pistons? I am about to build
a 302 and have a new set of Crower rods taking up space on the shelf.
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post #2 of 12 (permalink) Old May 6th, 15, 02:29 PM
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Sean
 
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Re: Longer rods

Quote:
Originally Posted by sam81663 View Post
How would 6" rods on a 3" stroke crank work? Would it be worth
paying the Xtra money for the floater pistons? I am about to build
a 302 and have a new set of Crower rods taking up space on the shelf.
6' Rods would be fine, just need the right pistons. And floating pin pistons probably won't cost much more, I would go that route just for purposes of rebuilding etc.

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #3 of 12 (permalink) Old May 6th, 15, 03:44 PM
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Don
 
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Re: Longer rods

Quote:
Originally Posted by sam81663 View Post
How would 6" rods on a 3" stroke crank work? Would it be worth
paying the Xtra money for the floater pistons? I am about to build
a 302 and have a new set of Crower rods taking up space on the shelf.
If you have access to a desktop dyno, you can plug in those longer rods and see just what they are worth in hp.
As for floating pins, I have always considered it a must for me , as it eases assembly when you tear down frequently. On one set up, I ran Teflon pin buttons, just to get away from the retainer rings. This was on a hemi, but when running long rods on a sbc, you will have the pin probably intersecting the lower oil ring rail, no biggie.
I have this on my 383 stroker with 6.0 rods, been running fine for last 30k miles.

In the performance header, Everett has posted a "calculators for anything" from Wallace Racing. There may be something in there to help you make the long rod decision if its critical.

Don
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Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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Last edited by zdld17; May 6th, 15 at 04:00 PM.
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post #4 of 12 (permalink) Old May 6th, 15, 09:12 PM
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Anne
 
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Re: Longer rods

The longer rods will do squat for HP and the pistons will probably cost a fortune unless you can find a deal on some used ones.

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post #5 of 12 (permalink) Old May 8th, 15, 07:02 AM
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Tom
 
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Re: Longer rods

Are you makimg a max effort class racing type engine? If not longer rods are of no real benefit per dollar.

71 Camaro 355 NA
11.1650 @ 119.30
1.5028 60'
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post #6 of 12 (permalink) Old May 8th, 15, 09:31 AM
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Dave
 
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Re: Longer rods

Quote:
Originally Posted by Lawrence454 View Post
The longer rods will do squat for HP and the pistons will probably cost a fortune unless you can find a deal on some used ones.
I disagree. Pistons are a consumable. I change them on every rebuild.

There are people that argue the relationship between long rods and those that say the rod that allows the piston to attach to the crank is the correct length. As an retired engine builder and some one with an engineering degree as well I can state that I have always used the longest rod that I can find if for no other reason than it results in a lighter piston. The advantages of piston dwell vs. piston rock can be argued and tested on a dyno till that hot place freezes over. The horsepower gain, if any, as measured on an engine dyno is small enough to be lost in the variance due to weather changes between tests on the exact same dyno. Consider it personal preference.

Personally I much prefer snap rings over the current dual spiral locks. I have never lost a motor (and I have built several hundred over the last half century) to a piston pin being pushed out. But then again I don't twist a motor to 11,400 RPM the way a PRO does that actually thinks the spiral locks are better than snap rings. Unfortunately amateurs wishing to emulate their racing heroes have caused the piston makers to only sell spiral locks as an off the shelf piston, regardless as to being effective or not.

If you are going to convert to full floating pins I strongly advise buying a tool designed just to install those &%$(! spiral locks. Here is a one that works well and can be used by anyone to get spiral locks installed without stretching them so far out of shape that bubble gum would work better at retaining the piston pin.

http://www.lockintool.com/

Big Dave
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post #7 of 12 (permalink) Old May 8th, 15, 03:58 PM
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Tim
 
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Re: Longer rods

Dave, I've been considering the longer rod scenario and an engine builder I trust and respect advised me to not go above 2:1 rod:stroke ratio. That would be the case with 6" rods on a 3" stroke 302 crank. Has this also been your experience?

1969 04A Van Nuys-built Z/28. Cortez Silver with dark blue interior and VE3. Sold Clippinger Chevrolet. Raced at Lions in LA.
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post #8 of 12 (permalink) Old May 8th, 15, 04:38 PM
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Re: Longer rods

Here's an article about the actual math of rod/stroke ratio:

At the other end of that spectrum, the connecting rod on a typical (circa 2007) 2.4-liter Formula-1 V8 engine is about 4.010" long, what your average race-engine mechanic would call a "very short rod". However, the stroke in the F1 engine is in the vicinity of 1.566", which produces a very large R / S ratio of 2.56.

http://www.epi-eng.com/piston_engine...ion_basics.htm

"For those that will fight for it...FREEDOM ...has a flavor the protected shall never know."
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post #9 of 12 (permalink) Old May 8th, 15, 06:01 PM
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Tim
 
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Re: Longer rods

Thanks, that is a fascinating article that I'm going to need time to read and understand all the math properly!

1969 04A Van Nuys-built Z/28. Cortez Silver with dark blue interior and VE3. Sold Clippinger Chevrolet. Raced at Lions in LA.
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post #10 of 12 (permalink) Old May 8th, 15, 07:09 PM
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Dave
 
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Re: Longer rods

The thermodynamic Otto cycle burning gasoline is a very abrupt way of converting chemical energy into mechanical power (not a very efficient way either, which is why Diesel was able to improve upon it). The gas burns very quickly. Which results in a very large pressure spike at the top of the stroke making for a light yet powerful power plant. Great for air planes made out of canvas and a prayer and for moving the old horse drawn wagon.

By keeping the piston at the top of the bore longer with a longer stroke you can exert more leverage on the crank shaft. So early engines that were made by hand in a work shop had a small bore and a long stroke to try and capture the energy before it leaked away. They were closer to an antique John Deere putt, putt two cylinder engine that reved to only 1,600 RPM, than a Formula One race car engine that spins to 17,000 RPM.

Today we hone the bore with a deck plate holding dimensions to the fourth decimal place, and have a choice of five different ring faces for piston rings that are ground so flat that there is no break in period.

What hasn't changed is the fuel we burn. We are back to burning the same swill that was available before WWII in octane quality, yet our engines are making more power thanks to improvements in design and manufacturing. Can we improve on the design by using a longer rod to hold the piston at TDC longer a micro second longer than a shorter rod would? To me for a new rod I was going to buy any way, buying a longer length is a no brainer as it can't hurt. I like the reduced piston weight for the reduction in rotating mass that allows a motor to rev higher and faster.

But that is me. I generally do not use any Chevy parts to build a Chevy motor. New JE pistons, or from Mahl or Diamond, rods and crank from Callies, and block from Dart heads from whoever has the best head when I screw it together (technology changes every six months now). Cam and solid roller lifters are no where near stock. Intake from Edelbrock or Dart or AFR, Carb from Quick Fuel, Distributor from MSD and the bolts to screw it all together from ARP. I use an SFI front damper (usually ATI) and the two piece cast timing cover behind that seals to an aftermarket oil pan and matching oil pump pick-up. I might use a reproduction Chevy displacement and rated horsepower decal for the air cleaner that is often the only Chevy part on the car.

Big Dave
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post #11 of 12 (permalink) Old May 8th, 15, 07:31 PM
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Re: Longer rods

The long rod debate will go on and on. Not sure on a 302 it would be worth it, but it might.

I know there are some difference with a 406 SBC (0.030 over 400) running 6 inch rods. But guys can get even the standard short rods to work well.

68 Camaro SS 396 - 468 BBC now, M21, 12 bolt 3.73 coded housing but w/ 3.31 gears.
Looking for 68 Camaro with body number NOR 181016
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post #12 of 12 (permalink) Old May 8th, 15, 11:56 PM Thread Starter
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Re: Longer rods

Dave thanks a bunch. talked me into it. a good friend worked for
Carl Wagner for many years. Wagner automotive. I have him do all
fun assembly stuff. And Tim, Good point. I had that in mind when
I rejected the thought of using the 6.2 set that stare at me from the
same shelf as the 6.0 rods. Now! Stock rockers and 142 springs,
OOOR 1.7 T&D shaft(that are also crying my name from the next
shelf down) & New Comp cams springs? Except for gasket matching
I would almost hate to go grinding the stud bosses down on a pair of
68 camel humps for the shafts. thanks for the advice.
And everyone don't forget Mother's Day!
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