Conecting Rod 6.535 to 6.700 Any Power Here

[41apache]

Is it worth any power to change from 6.535 to 6.700 rod? Its a 10.2 BBC with big chief heads about 1050+HP Top RPM 6800 4.5" stroke. Thanks for input

[bigjoe1]

LIGHTER pistons


JOE SHERMAN RACING

[Walter R. Malik]

Is it worth any power to change from 6.535 to 6.700 rod? Its a 10.2 BBC with big chief heads about 1050+HP Top RPM 6800 4.5" stroke. Thanks for input

Why, I don't know but, from personal experience the maximum horsepower will remain about the same ... the torque peak and horsepower peak will get closer together in the RPM range and torque BELOW peak torque RPM will usually get less.
SOooo, it all depends upon what you are trying to achieve.

[Alan Roehrich]

I would think that the increased time the piston spends at TDC and BDC, as well as the increased acceleration and speed, would require a cam change, and that assumes the cylinder head has enough flow to support it. If you're looking to optimize the engine with the rod length change.

[Walter R. Malik]

I would think that the increased time the piston spends at TDC and BDC, as well as the increased acceleration and speed, would require a cam change, and that assumes the cylinder head has enough flow to support it. If you're looking to optimize the engine with the rod length change.

With a longer rod, the piston will spend slightly LESS time around Bottom Dead Center.

[Strange Magic]

To answer your question: Yes.

Worth discussing? No, it's that slight.

Mechanical reliability: Yes, an increase.

Dynamic pumping losses? Reduced.

A better built mouse trap: Yes, most definitely.

[kirkwoodken]

I would think that the increased time the piston spends at TDC and BDC, as well as the increased acceleration and speed, would require a cam change, and that assumes the cylinder head has enough flow to support it. If you're looking to optimize the engine with the rod length change.

With a longer rod, the piston will spend slightly LESS time around Bottom Dead Center.

I know the sole purpose of the connecting rod is to connect the piston to the crank. But, this slowing down piston speed at the bottom of the stroke seems to be the only thing that could approach an increase in power. At the bottom of the stroke, the intake air column has its most inertia, I would think. With the piston moving slower, RELATIVE TO CAM ROTATION SPEED, it could allow for slightly more cylinder filling at BDC. Obviously, this argument must be a sophistry, since no one has been able to show it actually works that way..

[blackford]

From a purely quantitative perspective, that longer rod will net you a .010 difference in piston motion max at 90 degrees ATDC and less everywhere else. Your rod angle is still high at 19.6 degrees vs 20.1 degrees. I have a program that I can quickly plug the numbers into. Making a small change to rod length is generally not going to affect things appreciably.

[lorax]

I would think that the increased time the piston spends at TDC and BDC, as well as the increased acceleration and speed, would require a cam change, and that assumes the cylinder head has enough flow to support it. If you're looking to optimize the engine with the rod length change.

With a longer rod, the piston will spend slightly LESS time around Bottom Dead Center.

I know the sole purpose of the connecting rod is to connect the piston to the crank. But, this slowing down piston speed at the bottom of the stroke seems to be the only thing that could approach an increase in power. At the bottom of the stroke, the intake air column has its most inertia, I would think. With the piston moving slower, RELATIVE TO CAM ROTATION SPEED, it could allow for slightly more cylinder filling at BDC. Obviously, this argument must be a sophistry, since no one has been able to show it actually works that way..

What is the difficulty in understanding the piston moves thru BDC faster

[lada ok]

Man, this subject has been thrashed to death,
The only real advantage seems to be a mechanical one, where a rod / stroke ratio in excess of 2.0 seems to be the hot number

[wyrmrider]

by bigjoe1 » Sun Sep 28, 2014 5:28 pm
LIGHTER pistons


JOE SHERMAN RACING

slightly less side thrust/ cylinder wall loading/ friction
and if you ask me (or camking) the cam does need to be tweeked

Lighter is better

reread Walter Malik's answer