To Lighten or Not to Lighten

[Steam Driver]

That is the question. I'm starting to get into the machine shop phase of my rebuild here and was wondering if there are any benefits to lightening the connecting rods for a street engine? Opinions?

[neilca]

Nope

[JJ 911SC]

How much weight loss are we talking about?

[Walt Fricke]

Not even worth thinking about. There is little enough you can have ground off just to balance rods as it is.

If you want lighter rods, buy them.

In fact, for a street motor, lightening is just money down the drain (racing is all money down the drain anyway, which is why we feel we can spend money on lighter parts.)

[Steam Driver]

Pretty much what I thought. Thanks for reinforcing that opinion!

[HawgRyder]

My $.02
If you spend thousands of dollars to "lighten" the reciprocating mass of the engine....and that allows you to rev to ...say...10,000RPM....if it's a street machine you have to ask yourself..."how often am I going to drive around town at 10K in first gear?"
Race engines have a purpose....and with it...the need to refresh at very short intervals.
I love high winding engines...the sound of "ripping exhaust" at 10K or higher gives me "wood" so to speak...LOL
But...I also like the sound of 600 or 700 cubic inches of bellowing torque at probably less than 6K.
The big low turning engine will last for years...the small high winding one...maybe only an hour so so.
Your choice.
Bob

[JJ 911SC]

Originally Posted by HawgRyder

...the sound of "ripping exhaust" at 10K or higher gives me "wood" so to speak...

Love it too but this fall under the "too much information" category

[neilca]

[QUOTE=Walt Fricke;8156663]Not even worth thinking about. There is little enough you can have ground off just to balance rods as it is.

If you want lighter rods, buy them.

In fact, for a street motor, lightening is just money down the drain (racing is all money down the drain anyway, which is why we feel we can spend money on lighter parts.)[/QUOTE]

Truer words have yet to be spoken

[proffighter]

I made different expierence: If you lighten rotating or/and oscillating mass, there are not only benefits at 10`000rpms. throttle response may increase in every rev area. Similar effect if you fit a lighter clutch.

Downside: More instable idle (talkin about the clutch) and a bit different at the red light.

Back to the rods: I made a lot of motorcycle engine tuning years ago. Lighter rods and pistons were popular options. Response and dymanics of the engine was way better, engine break increased as well (downside or not is question of taste)

I would prefer replacing by lighter ones over lightening, too much damage if they fail...

if you wanne feel how big the difference can be, ride a 2-stroke motorcycle and then just replace the piston by a lighter one. You won't believe the difference

[Flieger]

Originally Posted by proffighter

I made different expierence: If you lighten rotating or/and oscillating mass, there are not only benefits at 10`000rpms. throttle response may increase in every rev area. Similar effect if you fit a lighter clutch.

Downside: More instable idle (talkin about the clutch) and a bit different at the red light.

Back to the rods: I made a lot of motorcycle engine tuning years ago. Lighter rods and pistons were popular options. Response and dymanics of the engine was way better, engine break increased as well (downside or not is question of taste)

I would prefer replacing by lighter ones over lightening, too much damage if they fail...

if you wanne feel how big the difference can be, ride a 2-stroke motorcycle and then just replace the piston by a lighter one. You won't believe the difference

I agree- buy lighter ones, don't try to lighten beyond balancing on your own. These parts are highly stressed.