5.70 Inch rods in a Ls1
Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
5.70 Inch rods in a Ls1
Hi,
I just purchased a supercharger and came across a short block rebuild that has forged pistons and rods. Has arp bolts so I think its stout. I already have the blower cam and 243 cnc ported heads.
As I looked into the specifics of the shortblock I researched the pistons and found that the rods used for it are 5.70 inch, I know the stock ls1 is around 6.098. Builder says it was built for forced induction.
Why would these pistons and rods be chosen over the stock ls1 rods . I verified that the block is a ls1 with a 4.00 x 3.622 bore and stroke.
Would I be making a mistake with this set up? Are there advantages to 5.70 inch rod because I cant find anything online so far about it.
Thanks
I just purchased a supercharger and came across a short block rebuild that has forged pistons and rods. Has arp bolts so I think its stout. I already have the blower cam and 243 cnc ported heads.
As I looked into the specifics of the shortblock I researched the pistons and found that the rods used for it are 5.70 inch, I know the stock ls1 is around 6.098. Builder says it was built for forced induction.
Why would these pistons and rods be chosen over the stock ls1 rods . I verified that the block is a ls1 with a 4.00 x 3.622 bore and stroke.
Would I be making a mistake with this set up? Are there advantages to 5.70 inch rod because I cant find anything online so far about it.
Thanks
Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
Hi,
I just purchased a supercharger and came across a short block rebuild that has forged pistons and rods. Has arp bolts so I think its stout. I already have the blower cam and 243 cnc ported heads.
As I looked into the specifics of the shortblock I researched the pistons and found that the rods used for it are 5.70 inch, I know the stock ls1 is around 6.098. Builder says it was built for forced induction.
Why would these pistons and rods be chosen over the stock ls1 rods . I verified that the block is a ls1 with a 4.00 x 3.622 bore and stroke.
Would I be making a mistake with this set up? Are there advantages to 5.70 inch rod because I cant find anything online so far about it.
Thanks
I just purchased a supercharger and came across a short block rebuild that has forged pistons and rods. Has arp bolts so I think its stout. I already have the blower cam and 243 cnc ported heads.
As I looked into the specifics of the shortblock I researched the pistons and found that the rods used for it are 5.70 inch, I know the stock ls1 is around 6.098. Builder says it was built for forced induction.
Why would these pistons and rods be chosen over the stock ls1 rods . I verified that the block is a ls1 with a 4.00 x 3.622 bore and stroke.
Would I be making a mistake with this set up? Are there advantages to 5.70 inch rod because I cant find anything online so far about it.
Thanks
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
It's early on Sunday so give those who are in the know a chance to settle down after worship services and family time. Opinions are comings...
Unless the rod length help minimize side loading under the pressure of a supercharger I don't understand the reason for it.Is the crank still using the stock stroke?
Unless the rod length help minimize side loading under the pressure of a supercharger I don't understand the reason for it.Is the crank still using the stock stroke?
Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
It's early on Sunday so give those who are in the know a chance to settle down after worship services and family time. Opinions are comings...
Unless the rod length help minimize side loading under the pressure of a supercharger I don't understand the reason for it.Is the crank still using the stock stroke?
Unless the rod length help minimize side loading under the pressure of a supercharger I don't understand the reason for it.Is the crank still using the stock stroke?
Probe pistons 14cc dish
Scat I-beam Rods
ARP Rod bolts
Stock crank
Here are the exact pistons:I am going off the piston that was used in the rebuild. Summit PBP-12342-STD 4.00 bore 13.80 cc dish
Bore (in):4.000 in.
Bore (mm):101.600mm
Piston Style dish, with two valve reliefs
Piston Material:Forged aluminum
Compression Distance (in):1.560 in.
Piston Head Volume (cc):+13.80cc
Wrist Pin Style:Press-fit or floating
Pin Diameter (in):0.927 in.
Piston Ring Thickness:1/16 in. x 1/16 in. x 3/16 in.
Thanks for chiming in CaseyJones
Last edited by 4horseman; Nov 2, 2014 at 09:44 AM. Reason: add info
Instructor
Joined: Mar 2006
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From: ames ia
just a guess without putting any effort into looking... However, running a slightly shorter rod, will let them run a larger crown, lands, etc. Heavier piston, but heavier duty piston as well.
Pretty common failure on the stock ls pistons is that top crown/land area.
Pretty common failure on the stock ls pistons is that top crown/land area.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
A shorter rod means a taller and heavier piston. I'd agree that it might allow the rings to be further down the piston and spread further apart to make the piston stronger. The downside is the extra weight will stress the rods in the upper rpm range.
Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
You know the pistons say bore 4.0 but the ls1 should only be what...3.905 at most. If this is a ls1 it is bored to much and the walls are way too thin.Might be why its so inexpensive. Or maybe hes mistaken and its not a ls1.
Well thanks for your insight on the pistons. Not sure this is a good idea for a supercharged car reving past 6700 rpms.
Instructor
Joined: Mar 2010
Posts: 185
Likes: 3
One other, maybe old school theory, is that the shorter rod gets the piston away from TDC a little quicker than a longer rod (less dwell time at TDC). This would allow quicker cylinder filling on a turbo or blower setup. A piston will get from point A to point B in the same amount of time, given a certain rpm. But a longer rod gives a more consistent piston speed and smoother transition from stopped to moving, where a short rod kind of yanks it from its dwell at a quicker rate. I've always been told use the longest rod you could in NA setups cause it gives a lighter piston with the pin higher and a slight leverage advantage on the crank, but to use a shorter rod for FI due to its less dwell and getting away from the valve quicker for the boost to do its thing. Hope this helps
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Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
One other, maybe old school theory, is that the shorter rod gets the piston away from TDC a little quicker than a longer rod (less dwell time at TDC). This would allow quicker cylinder filling on a turbo or blower setup. A piston will get from point A to point B in the same amount of time, given a certain rpm. But a longer rod gives a more consistent piston speed and smoother transition from stopped to moving, where a short rod kind of yanks it from its dwell at a quicker rate. I've always been told use the longest rod you could in NA setups cause it gives a lighter piston with the pin higher and a slight leverage advantage on the crank, but to use a shorter rod for FI due to its less dwell and getting away from the valve quicker for the boost to do its thing. Hope this helps
Well anyways great info THANKS
Instructor
Joined: Mar 2010
Posts: 185
Likes: 3
Well, keep in mind that 5.7" rods have been used reliably in Gen 1 and Gen 2 SBC'S for years in high power, 7000+ rpm setups. Alot of circle track rule books won't allow a 6" rod. I'm not an expert, but I'd guess you wouldn't see much of a difference in power or reliability until youre getting near the mechanical limits of the components.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
I went through the calculations for a SBC. A curve of crank angle vs piston position for 6" vs 5.7" rods shows so little difference you can't tell there are 2 different lines. The largest difference in piston height is 0.267%. The biggest difference is the rod angle which is 5.46% more with the shorter rod.
Thread Starter
Instructor
Joined: Oct 2014
Posts: 236
Likes: 7
From: Abingdon Virginia
I went through the calculations for a SBC. A curve of crank angle vs piston position for 6" vs 5.7" rods shows so little difference you can't tell there are 2 different lines. The largest difference in piston height is 0.267%. The biggest difference is the rod angle which is 5.46% more with the shorter rod.