This thread got deleted accidentally last night.... I'm going to try and reconstruct it. Be patient.

The name of the originator of each post is in bold.... Do not blame me for any of the content ..... did wonders for my post count thuogh.

Initial post:

Fbody1
Registered User


Join Date: Feb 2000
Location: fl,jax
Posts: 245 3.48 stroke +6.0 rod = ?

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was wondering if I used a 6.0 rod w/ 3.48 stroke , how many ci would it be, and any benifits( more torque or hp) over using a 5.7 rod ?
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Camaro97USAF
Registered User


Join Date: Sep 2003
Posts: 158
Re: 3.48 stroke +6.0 rod = ?

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rod length doesn't change Ci...
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danhr
Registered User

Join Date: Nov 2004
Posts: 27 Re: 3.48 stroke +6.0 rod = ?
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3.48 stroke + 4.000 bored = 350 ci
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GreenDemon
Registered User

Join Date: Nov 2003
Location: Chicago
Posts: 1,428
Re: 3.48 stroke +6.0 rod = ?
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A longer rod will give you less rod angle, which will give you more peak hp at the cost of low-end torque. Pistons with a lower compression height will be required, of course. If you're looking to go faster changing the rod length won't help by itself. You need a stroker crank if you want more cubic inches that you'll actually notice.
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MachinistOne
Registered User

Join Date: May 2004
Posts: 406 Re: 3.48 stroke +6.0 rod = ?
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We use long rod 355's in our road race cars, it is a proven way to broaden the torque band.

 

atljar
Registered User
Supporting Member

Join Date: Feb 2001
Location: Cincinnati, Ohio
Posts: 3,603
Re: 3.48 stroke +6.0 rod = ?
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A really basic explaination is that the rod becomes longer yet the piston shortens. Cubes are just the area above the piston top for its sweep, or stroke.

 

91Z-28
Registered User

Join Date: Oct 2005
Location: Chester, NY (Orange County/Hudson Valley)
Posts: 27
Re: 3.48 stroke +6.0 rod = ?
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I'm watching this thread closely. When I get my head/cam/valvetrain etc stuff I wanted to use the lightweight 6" forged rods as well to help with the 6k+ RPMs. I'm interested to see the other benefits.

 

rskrause
Drivetrain Tech Moderator

Join Date: Dec 1969
Location: Buffalo, New York
Posts: 7,135
Re: 3.48 stroke +6.0 rod = ?
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This has been discussed extensively on this site before. I suggest use of the search function. Many people are tired of posting the same opinions over and over again.

My opinion: Any effects of rod length are going to be neglible and insignficant except on a max effort motor where everything else is also optimized. For a blower motor though, the shorter rod is preferred because it allows an adequate compression height for a deep piston dish, thick rings lands, etc. Otherwise, it matters very little (between a 5.7 and 6.0" rod on a 35)0.

 

marshall93z
Registered User

Join Date: Mar 2003
Location: Mooresville, NC
Posts: 1,073 Re: 3.48 stroke +6.0 rod = ?
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Exactly!

 

RedThunder1994
Registered User
Supporting Member

Join Date: Nov 2003
Location: Indiana, Kokomo
Posts: 324 Re: 3.48 stroke +6.0 rod = ?
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well think of it this way guys, in tractor motors and such, they have enormous amount of tq from a motor thats relatively small, the way this is achieved is the use of longer rods, heres another way to think about it, if u have a rusty stuborn bolt that wont come out and your useing a 7inch 3/8 drive ratchet, what do most of you do, you either get a breaker bar to get some more length which in turn is easier for you to turn because you have more torq, by doing so or you get a bigger drive ratcher like 1/2 which usually is longer which also provides more tq, now ive been around many old school drag guys and they all tell me longer rod more tq, and this is proven by many years of racers trying new stuff to find secrets to more power, just a thought for you all to think on, some of you might not think this is true or agree fully but thats just my input on this post,

I want to sell you a bunch of stuff but I am not a paying advertiser.
Thread edited by tnthub

 

Mindgame
LS1 Tech Moderator

Join Date: Nov 2001
Posts: 3,140 Re: 3.48 stroke +6.0 rod = ?
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Yeah, since a "road race" engine is built for endurance I'd imagine that the lighter piston helps in reducing g's too. Well, actually I know it does.

As a matter of fact, I'd be willing to bet that in such a case that's where the REAL advantage is to running your longer rods.

Any change from say 5.7 to 6.0" isn't even going to be measurable in a 6500-7000 rpm street engine.

For a race only endurance racer, maybe a shorter stroke and longer rod is what you need. Comes down to the cycle time the parts will see and the maximum piston speeds.

For a drag car, I've seen just as many short rod winners as I have the other way. Which one works better is all just a matter of the combination. But then again... isn't it always.

 

SStrokerAce
Registered User

Join Date: Oct 2002
Location: Camshaft Heaven!
Posts: 3,746
Re: 3.48 stroke +6.0 rod = ?
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That's what I was going to say.... the lighter piston isin't offset by the slightly heavier rod, therefore you have less mass and with slightly less piston speed and g's you have a longer durability life of the parts....

As everone else has said. DO A SEARCH!

 

jerminator96
Registered User

Join Date: Nov 2004
Location: Wilmington, NC
Posts: 207 Re: 3.48 stroke +6.0 rod = ?
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So if I was going to turn an engine higher than 6500rpm or so, I would benefit from a longer rod? But otherwise there is no real gain right?

 

marshall93z
Registered User

Join Date: Mar 2003
Location: Mooresville, NC
Posts: 1,073 Re: 3.48 stroke +6.0 rod = ?
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SStrokerAce
Registered User

Join Date: Oct 2002
Location: Camshaft Heaven!
Posts: 3,746
Re: 3.48 stroke +6.0 rod = ?
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The difference in the rods and how they effect whats going on in the motor is been a long standing area of interest..... there are differences in what is going on there, but they are very small.

For example:

A 355 @ 6500rpm

5.7 vs. 6.125" rod

The difference in these two rods at 6500rpm going from TDC down the bore to about 90° ATDC is about 1.6% at it's maximum, with .7-.8% difference around peak piston velocities (75°ATDC) So not a whole hell of a lot. What this does is increase the pull on the intake port, which with the lag created by the inertia of the air creates higher velocities in the port during the area of max lift. This is good if you have a port that can handle high velocities, bad if you can't..... hence the reason I've said that a longer rod motor is better for a smaller or weaker velocity profile port and a shorter rod motor is better for a larger or better velocity profile port. Or the same reasons that 30-40 years ago Smokey liked the long rods in his race motors and 10-15 years ago when Vizzard found his gains on the dyno. Give these guys the knowledge of what a velocity probe gives you and the time to find out what works best, and hell the new cylinder heads of today and you would have gotten some different thoughts about it.

Now if you want to throw in the effects of dwell time and what motors are running now in comparison, you gotta look at the burn time as well. Back when 39-42° total timing was needed because of the piston, chamber and port designs, longer dwell helped the motors, but now with 24-28° a shorter dwell time doesn't hurt and matches the combustion time as well.....

There is no be all end all that everyone wants to find in rod length, there are very few differences if any and on top of that lots has changed over the last 40 years to effect the outcome of dyno and track tests where rod length plays into everything.

Bret
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