SpeedTalk Store - Opinion Columns

SBC Connecting Rod Length

General engine tech -- Drag Racing to Circle Track

Moderator: Team

SBC Connecting Rod Length

Postby GotSomeRust » Tue May 19, 2009 6:59 pm

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...
83 Cutlass
GotSomeRust
Pro
Pro
 
Posts: 238
Joined: Mon Mar 17, 2008 7:37 pm
Location: South Dakota

Postby stealth » Tue May 19, 2009 8:10 pm

Oh No.... :shock:
stealth
Expert
Expert
 
Posts: 753
Joined: Fri Jun 30, 2006 8:37 am

Postby bigjoe1 » Tue May 19, 2009 8:26 pm

The piston is very much lighter in weight-about 100 grams

JOE SHERM AN RACING
bigjoe1
Show Guest
Show Guest
 
Posts: 5159
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Postby GotSomeRust » Tue May 19, 2009 9:14 pm

bigjoe1 wrote:The piston is very much lighter in weight-about 100 grams

JOE SHERM AN RACING


Huh?
83 Cutlass
GotSomeRust
Pro
Pro
 
Posts: 238
Joined: Mon Mar 17, 2008 7:37 pm
Location: South Dakota

Postby bigjoe1 » Tue May 19, 2009 9:36 pm

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
bigjoe1
Show Guest
Show Guest
 
Posts: 5159
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Postby 1989TransAm » Tue May 19, 2009 9:39 pm

Right. Usally the longer the rod the lighter the piston and the rotating assembly.
1989TransAm
Guru
Guru
 
Posts: 3272
Joined: Thu Feb 15, 2007 8:43 pm
Location: Cypress, California

Postby BGriff » Tue May 19, 2009 10:03 pm

Longer rod, longer dwell at TDC, better for high RPM HP.
Short rod, better for low end torque, more side loading at piston skirt.
Too many hobbies
BGriff
Member
Member
 
Posts: 119
Joined: Sun Dec 14, 2008 8:28 am
Location: NE Arkansas

Postby GotSomeRust » Tue May 19, 2009 10:39 pm

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.
83 Cutlass
GotSomeRust
Pro
Pro
 
Posts: 238
Joined: Mon Mar 17, 2008 7:37 pm
Location: South Dakota

rods

Postby k-star » Wed May 20, 2009 6:37 am

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
“If I hit you with this you’re going to be numb, that’s why they call them numb-chucks “Si Robertson
http://www.kstarautomotive.com
User avatar
k-star
Guru
Guru
 
Posts: 1798
Joined: Mon Oct 04, 2004 1:17 pm
Location: york pa

Postby CNC BLOCKS » Wed May 20, 2009 6:52 am

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.
CNC BLOCKS
Guru
Guru
 
Posts: 4405
Joined: Thu Jul 01, 2004 5:34 am
Location: NORTHEAST

Postby 3V Performance » Wed May 20, 2009 7:09 am

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..
3V Performance
" ENGINES WITH AN ATTITUDE "
3V Performance
Guru
Guru
 
Posts: 1086
Joined: Thu Dec 28, 2006 8:41 am
Location: Sherrills Ford, N.C.

rods

Postby k-star » Wed May 20, 2009 7:16 am

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
“If I hit you with this you’re going to be numb, that’s why they call them numb-chucks “Si Robertson
http://www.kstarautomotive.com
User avatar
k-star
Guru
Guru
 
Posts: 1798
Joined: Mon Oct 04, 2004 1:17 pm
Location: york pa

Postby GotSomeRust » Wed May 20, 2009 8:33 am

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
83 Cutlass
GotSomeRust
Pro
Pro
 
Posts: 238
Joined: Mon Mar 17, 2008 7:37 pm
Location: South Dakota

Postby bigjoe1 » Wed May 20, 2009 9:24 am

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
bigjoe1
Show Guest
Show Guest
 
Posts: 5159
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Postby williamsmotowerx » Wed May 20, 2009 10:20 am

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
williamsmotowerx
Expert
Expert
 
Posts: 649
Joined: Sat Feb 10, 2007 1:24 pm

Next

Return to Engine Tech

Who is online

Users browsing this forum: Bing [Bot], BrazilianZ28Camaro, engineman1642, goldmember63, jet, Meehan Race Engines, Pappy and 38 guests