Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB

- Scion FR-S / Toyota 86 GT86 General Forum (https://www.ft86club.com/forums/forumdisplay.php?f=2)

- - Rod length (https://www.ft86club.com/forums/showthread.php?t=25050)

Does rod length affect torque output of an engine?

It's not the size of the rod that matters, it's how you use it.

My rod length is of no concern to anyone but my wife...

That being stated, what matters is overall stroke for TQ output, which would be related to rod length. Longer stroke=more TQ, in theory.

The smaller your rod, the more torque you will require everyone to think you have.

Quote:

Originally Posted by GTB/ZR-1 (Post 628170)

My rod length is of no concern to anyone but my wife...

That being stated, what matters is overall stroke for TQ output, which would be related to rod length. Longer stroke=more TQ, in theory.

So would this imply that (all other engine attributes staying the same) a longer rod would give you a shorter stroke, and thus less TQ?
Edit: I'm using this diagram for my logic. A longer rod would then result in less room for the piston to travel and compress the gas? http://en.wikipedia.org/wiki/File:Ar...e_Zweitakt.gif

Are you trying to shrink or extend your rod?

Quote:

Originally Posted by lantsalot (Post 628194)

So would this imply that (all other engine attributes staying the same) a longer rod would give you a shorter stroke, and thus less TQ?

Mounting position of the rod inside the piston is also related. A longer rod which is closer to the surface of the piston can give the same stroke as a shorter rod mounted further from the piston surface with nothing else changed.

This is all talking Honda engines, but it's still relevant to your question:

Quote:

A longer rod makes more torque with the same piston force, and since it's less angular than a shorter rod, reduces sidewall loading and decreases friction. All of this adds up to more power.

Longer rods also give the pistons more "dwell," the brief periods of time the piston is at top dead center and bottom dead center. A longer dwell allows for better flow of intake and exhaust gases since the piston moves slower between up- and downstrokes.

Read more: http://www.hondatuningmagazine.com/t...d_stroke_ratio

Quote:

Originally Posted by lantsalot (Post 628194)

So would this imply that (all other engine attributes staying the same) a longer rod would give you a shorter stroke

Rod length doesn't have anything to do with the length of the stroke. Crankshaft throw is what determines the stroke.

Go look at an engine assembly; CHANGING ROD LENGTH WILL NOT CHANGE YOUR STROKE. You'll need a new crankshaft to change your stroke length and swept volume. I haven't looked at the dynamics in a long time but you may get a change in compression ratio and the details that Aetyrno went into seem to have some validity.

The only reason to upgrade/change your rods are if you have a new crank and need a new rod to make sure your piston is in the right place as well as stronger rods if your engine is putting out more torque due to other mawds.

Quote:

Originally Posted by Bill_Rockoff (Post 628326)

Rod length doesn't have anything to do with the length of the stroke. Crankshaft throw is what determines the stroke.

Depends which rod we're talking about... if your rod isn't long enough it would make for a short stroke.

Are we all talking about the same rod?

such a dirty thread. :p

Wtf lol best thread name ever