Everything that I have been reading says that the 6.125 length rod is better for longevity due to the piston physically moving a shorter distance, and for compression due to the piston remaining at TDC for a longer period of time (I can't quite get my head around that one). Granted we are talking about microseconds and micrometers, but is this accurate? Are there any other pros and cons to a 6.125 rod vs 6.098?

 

How far the piston moves is strictly a function of the crank stroke. Rod length only locates the piston in the cylinder.

 

That is what I thought. So, the rod length means ****, as long as the piston height is appropriately changed?

 

What about the piston being pushed into the cylinder wall?

 

Longer rod has better rod/stroke ratio, with longer rod side forces exerted by pistons on cylinder walls are reduced to diminish wear on piston skirts and cylinder walls.
However, the difference in length between these 2 rods is not substantial.

 

I went with a longer rod. I prefer it when possible. Supposedly there’s lots of pluses to it. Maybe that’s why Chevy went to a 6.098 rod in the ls engines compared to the sbc 5.7 rod.

 

Anytime you can reduce rod angularity is a plus. It helps the torque curve too.

 

Fwiw - It's my understanding that another bonus of longer rods is it gives the piston a slight advantage of increased dwell at the top which will helps improve resistance to detonation. It's probably a small increase more more resistant to detonation seems good.

Maybe one of the gurus will give more details.

 

The only noticeable advantage of a 6.125” rod over a 6.098” is parts selection and availability. It’s more popular, so there are more rods and pistons to choose from for a 6.125” rod length.

 

The 6.125 rod is something left over from early LS engine builders using a SBC 6.125 rod because there weren't good choices back then that didn't cost a bundle. The problem with this is the rods had a beam offset and sideloaded the piston. Then because all the piston manufacturer's shelf stocking pistons were all designed for 6.125, all the rods because set up that way. It's not a bad thing because we get plenty of ring land thickness with a common 4" stroker even with the longer rod. As others have pointed out .027" doesn't really amount to anything with piston profiles or this thing called rod ratio, but it is interesting. The Summit Pro LS piston line is the first to cover all the Gen. 3 rods (.9449 pins), Gen. 4 rods (.9433 pins), and 6.125 aftermarket rods. No other piston manufacturers has all that do to their legacy parts and lack of reinvestment.

Another thing that a lot of Smokey Yunick old timers don't realize is the extra dwell does help on the power stroke, but actually hurts on the intake stroke. A shorter rod coming off tdc energizes the air charge earlier and has better net cylinder filling. So longer isn't always better and many of the best engines are in the 1.65 range vs. the old 1.8 and more range. Packaging is another big deal that really dictates what the measurements turn out to be.

 

I know that this is an old thread. But there is one important difference to consider when making this choice. And that is your piston choice. Forged pistons are available for either rod. But hypereutectics are only available for 6.098/.943 rods. If you plan to run hypereutectics (and possibly plan to go forged in the future) OR wish to go back to hypereutectics at some time, 6.098/.943 rods may be a better choice.

On the other hand, 6.125/.927 rods have longer been used in performance applications. For this reason, you may find a larger selection of high performance pistons for the longer rods. 6.125/.927 rods may be a better choice if you NEVER plan to use hypereutectic pistons. Also, 6.125/.927 rods are obviously your only choice if the pistons you want to use are not available for 6.098/.943 rods.

 

• I read through some of the comments and read your comment and was impressed with the professionalism and great information you provided that many people don’t even try to think about, the events that are actually taking place within an engine. Converting an uncontrolled chemical reaction (explosion of air and fuel) into mechanical energy! Most people don’t stop to really appreciate what we are expecting an engine to do. You cannot really think about a running engine as a collection of single events because of the speed at which they are happening, RPM, or RPS, but instead as frequency and wavelengths. An engine will never win a race, but it will lose them! Just ask the driver or crew chief !

 

Summit is LOST In SMOKE.
A higher R/L engine will BREATH better at high RPM, lower port air speed, than a Short Rod engine.
Summit FORGOT to ADD Piston Cooling Jets onto the rod crank side journals.
INDY TECH

 

Thanks, but no thanks! I don’t need for you to attempt to tell me about crankshaft stroke, rod ratios and engine breathing. I only spent 15 years in NASCAR building some of the best race engines that won major events like the Daytona 500 along with winning multiple series championships, hours and hours on engine dynamometers and SpinTron machines for valve train development! Quit being a keyboard warrior and “assuming” or “thinking you know” something! We don’t need any more people in this world to drag people down, we need people who lift people up. Have a good day/evening!

 

Do you know who you are talking too? Lance has some impressive credentials. You kind of sound like a bot.

 

100%.

 

Obviously your buddy Lance didn’t know who he was talking to! I always find it amazing how many people “think” they are so smart and everyone else is so stupid! I understand it to a point, because there are a lot of stupid people, but you can’t just assume everyone is!

I just have a very low tolerance level for STUPID BULLSHIT and DISRESPECT ! That's all !

You teach people how to treat you by what you allow, what you stop, and what you reinforce!

Nowadays, people don't defend what is right, they defend who they like and benefit from.

 

Dude, get over yourself. Post your real name and quit acting like an asshat.

 

I doubt it's an act....

 

Interesting. I was involved in Cup engines and major nascar R&D development myself. I have many friends still in the sport, and the nascar engine industry today. Who were you with? We might know each other. Lance here holds hundreds of engine patents, along with his father, grandfather, etc. He’s likely the smartest guy you’ll ever meet. His comment on long rods is spot on.