Rod Length Discussion Video

Dibbons · Apr 18, 2022

I have a custom set of small block rods that have a 6.298" length (vs 6.123" stock connecting rod length). They are standing by inside my 305 Mopar de-stroked 340 long block to be finished some day soon (see photo).

QOTHL · Apr 18, 2022

When I saw the thread title I almost thought it should be in the Blue Forum...

dvw · Apr 19, 2022

I have those same rods in my 340 street engine. They are strong. But very heavy. The best advise I've seen? Find the stroke you want. Find a light piston that is as short as you feel comfortable with. Connect the two with what ever length rod fits. For a given stroke the biggest advantage of a long rod is a lighter piston.
Doug

biomedtechguy · Apr 19, 2022

Just curious. 7.1" rod on a 4.5 bore and stroke 572. (2.20 crank journal)
That is the rod length most are going with, yes?

Gunner1 · Apr 19, 2022

I’m building a 327 Chevy right now. It’s 4.030x3.25 with a set of Scat 6.125 lightweight rods. A DZ 302 Chevy has a rod stroke ratio of 1.9. Our long rod 327 has a 1.88. Nice lightweight pistons with a low skirt load at BDC. Rockover when the time comes for my 440 to be done I’ll long rod it too.

dvw · Apr 19, 2022

For sure use a long rod in a 440. A stock 440 compression distance is way to tall. Thus very heavy pistons. With a stock rod 6.768" and deck 10.725" it would take 2.082" comp height to get zero deck. With a 4.50" stroke with 7.100" rod allows a 1.375" nominal comp height (stock deck). Think about that. We add .750" of stroke and .332" of rod length yet still end up with a .707" shorter comp height. The 440s high deck is what makes it an excellent stroker candidate. Mine uses 1.35 comp height, 7.100" rod, 4.500" stroke. It has been decked a few times so right now my pistons are +.004". If people were really worried about rod ratio there wouldn't be any 430" SB Chevys or any 540" BB Chevys. And we all know they're dogs, right?
Doug

Budnicks · Apr 20, 2022

Engine Masters had a great show/episode on that very subject...

not really much difference in power
or "alleged" longevity either
many other factors are more valued as it comes to power

I've always had the longest rod I could get without really getting
to much into the oil rings, having to use buttons
makes for a light piston with a longer rod
short rod vs long rod
biggest difference is the time (dwell) it stays at
top &/or bottom of the stroke
& you need a camshaft that takes advantage of it too

I wouldn't really worry about it 'too much'
lots of short rod motors/engines make some serious power

Gunner1 · Apr 20, 2022

Budnicks said:
Engine Masters had a great show/episode on that very subject...

not really much difference in power
or "alleged" longevity either
many other factors are more valued as it comes to power

I've always had the longest rod I could get without really getting
to much into the oil rings, having to use buttons
makes for a light piston with a longer rod
short rod vs long rod
biggest difference is the time (dwell) it stays at
top &/or bottom of the stroke
& you need a camshaft that takes advantage of it too

I wouldn't really worry about it 'too much'
lots of short rod motors/engines make some serious power

You hit the nail on the head. LONG VS SHORT need different cam timing and profiles. The intake valve chases the piston on the intake stroke. And since piston acceleration is faster with a short rod it can stress the intake port differently. You can and need to open the intake valve more agressively with a short rod. i usually do longer rod motors with marginal heads.

RemCharger · Apr 20, 2022

I vote longer rods. All the same reasons.
As well as the stress of the wrist pin rotating faster. And dwell time vs rpm. A 383 is ripping the piston away from the expansion of the explosion at high rpms.
I'd like to build a 7.100 rod 400. With some real compression.

Geoff 2 · Apr 21, 2022

Read the Isky Cams Tech Tip about rod length.

RemCharger · Apr 21, 2022

Geoff 2 said:
Read the Isky Cams Tech Tip about rod length.

Good article for street enthusiasts.

moparedtn · Apr 21, 2022

Dibbons said:
I have a custom set of small block rods that have a 6.298" length (vs 6.123" stock connecting rod length). They are standing by inside my 305 Mopar de-stroked 340 long block to be finished some day soon (see photo).
View attachment 1272173

Sounds a bit like what they did with the factory Trans-Am engines in 1970, eh?

beanhead · Apr 21, 2022

Don't be fooled; no matter what they say they ALL prefer longer rods

66Satellite47 · Apr 27, 2022

My experience with my drag race 400/440 motors was that the low deck rod seemed faster at increasing RPM and better with the tunnel ram intake than the LY rod motor. Both had the same cam and heads. Seems that the gain from the intake effectiveness was import. No dyno, just track.

Rod Length Discussion Video

Dibbons

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QOTHL

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dvw

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biomedtechguy

Accelerati Rapidus Maximus

Gunner1

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dvw

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Budnicks

Jackstand racer #1 & proud of it, Sir Posts A Lot

Gunner1

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RemCharger

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Geoff 2

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RemCharger

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moparedtn

I got your Staff Member riiiight heeeere...

beanhead

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66Satellite47

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