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SBC Connecting Rod Length

Posted: Tue May 19, 2009 7:59 pm
by GotSomeRust
I was told that I should use a 6 inches connecting rod in my Chevy 350 instead of the stock length of 5.7 inches. What are the advantages/disadvantages of using a 6 inch? Thanks in advance for the info...

Posted: Tue May 19, 2009 9:10 pm
by stealth
Oh No.... :shock:

Posted: Tue May 19, 2009 9:26 pm
by bigjoe1
The piston is very much lighter in weight-about 100 grams

JOE SHERM AN RACING

Posted: Tue May 19, 2009 10:14 pm
by GotSomeRust
bigjoe1 wrote:The piston is very much lighter in weight-about 100 grams

JOE SHERM AN RACING
Huh?

Posted: Tue May 19, 2009 10:36 pm
by bigjoe1
What I am saying is that the rod length is very UNIMPORTANT- but the piston for the 6 inch rod will be much lighter---GET IT ????

JOE SHERMAN RACING

Posted: Tue May 19, 2009 10:39 pm
by 1989TransAm
Right. Usally the longer the rod the lighter the piston and the rotating assembly.

Posted: Tue May 19, 2009 11:03 pm
by BGriff
Longer rod, longer dwell at TDC, better for high RPM HP.
Short rod, better for low end torque, more side loading at piston skirt.

Posted: Tue May 19, 2009 11:39 pm
by GotSomeRust
bigjoe1 wrote:What I am saying is that the rod length is very UNIMPORTANT- but the piston for the 6 inch rod will be much lighter---GET IT ????

JOE SHERMAN RACING
Yes, thank you.

rods

Posted: Wed May 20, 2009 7:37 am
by k-star
BGriff wrote:Longer rod, longer dwell at TDC, better for high RPM HP.
Short rod, better for low end torque, more side loading at piston skirt.
Can you share some of your testing data to prove this??

Like how much tq increase did you see in A-B-A testing with the shorter rod??

Please list all the info of each combo and the actual TQ increase numbers.


Keith

Posted: Wed May 20, 2009 7:52 am
by CNC BLOCKS
We see a big differance on the 2 bararrel circle track engines going from a 5.7 to 6.250 rods and from what I have seen they male peak power about the same RPM but the 6.250 rod will carry alot longer then the short rod engines.

The cam will be different for a longer rod engines as well.

Posted: Wed May 20, 2009 8:09 am
by 3V Performance
CNC BLOCKS wrote:We see a big differance on the 2 bararrel circle track engines going from a 5.7 to 6.250 rods and from what I have seen they male peak power about the same RPM but the 6.250 rod will carry alot longer then the short rod engines.

The cam will be different for a longer rod engines as well.

Seen the same here..

rods

Posted: Wed May 20, 2009 8:16 am
by k-star
Carl or 3V, can you give some actual numbers??? When you say carry it longer I assume you mean the peak HP father up the RPM range. How much farther???

Is this something that is only found with the 2bbl engines???

Keith

Posted: Wed May 20, 2009 9:33 am
by GotSomeRust
Sorry to be dumb, but (referring to CNC Blocks post) what needs to be different about the cam when using 6 inch connecting rods? That doesn't make sense to my little brain... Thanks

Posted: Wed May 20, 2009 10:24 am
by bigjoe1
What I have seen with the longer rod is that the engine does not nose over as bad above the HP peak-- say the peak is at 7000, with a longer rod , it can carry the better power way uo to 8000. On the other hand, with a shorter rod, even when the peak is at 7000, by 8000, the power will drop off 30 to 40 HP-- The differance might be 25 more HP with the loger rod at 8000


JOE SHERMAN RACING

Posted: Wed May 20, 2009 11:20 am
by williamsmotowerx
Friction kind of "squares" with RPM. Exactly what BigJoe said... doesn't nose over as hard.

I'd guess a faster ramp rate cam for longer rod, plus a tighter LCA