6.125 rods
Thread Starter
Staging Lane
Joined: Jun 2006
Posts: 73
Likes: 0
6.125 rods I have come to the conclusion that my stock rods will be good enough for a h/c setup and a 125 shot, but I know the stock rods aren't a 6.125 I keep hearing that 6.125 is better is there a reason for that? Does it create a better balancing effect or something I dunno. I know aftermarket rods like Scats, Callies, etc. are better material than powedered metal, but why do they choose 6.125?
Stock rod length is 6.098 for stock pistons,aftermarket pistons use a 6.25 rod length because the pin hole is in a different location.They make rods for a stock piston in the 6.098 length.Both would be the same in strength.
TECH Regular
Joined: Jan 2008
Posts: 458
Likes: 0
From: Bellaire, TX
Short Rod is slower at BDC range and faster at TDC range.
Long Rod is faster at BDC range and slower at TDC range.
A. Intake Stroke -- will draw harder on cyl head from 90-o ATDC to BDC.
B. Compression Stroke -- Piston travels from BDC to 90-o BTDC faster than short rod. Goes slower from 90-o BTDC to TDC--may change ign timing requirement versus short rod as piston spends more time at top. However; if flame travel were too fast, detonation could occur. Is it possible the long rod could have more cyl pressure at ie. 30-o ATDC but less crankpin force at 70-o ATDC. Does a long rod produce more efficient combustion at high RPM.
C. Power Stroke -- Piston is further down in bore for any given rod/crank pin angle and thus, at any crank angle from 20 to 75 ATDC less force is exerted on the crank pin than a shorter rod. However, the piston will be higher in the bore for any given crank angle from 90-o BTDC to 90-o ATDC and thus cylinder pressure could be higher. Long rod will spend less time from 90-o ATDC to BDC--allows less time for exhaust to escape on power stroke and will force more exhaust out from BDC to 90-o BTDC. Could have more pumping loss! Could be if exhaust port is poor, a long rod will help peak power.
AKA- A better rod angle.
http://www.stahlheaders.com/Lit_Rod%20Length.htm
Long Rod is faster at BDC range and slower at TDC range.
A. Intake Stroke -- will draw harder on cyl head from 90-o ATDC to BDC.
B. Compression Stroke -- Piston travels from BDC to 90-o BTDC faster than short rod. Goes slower from 90-o BTDC to TDC--may change ign timing requirement versus short rod as piston spends more time at top. However; if flame travel were too fast, detonation could occur. Is it possible the long rod could have more cyl pressure at ie. 30-o ATDC but less crankpin force at 70-o ATDC. Does a long rod produce more efficient combustion at high RPM.
C. Power Stroke -- Piston is further down in bore for any given rod/crank pin angle and thus, at any crank angle from 20 to 75 ATDC less force is exerted on the crank pin than a shorter rod. However, the piston will be higher in the bore for any given crank angle from 90-o BTDC to 90-o ATDC and thus cylinder pressure could be higher. Long rod will spend less time from 90-o ATDC to BDC--allows less time for exhaust to escape on power stroke and will force more exhaust out from BDC to 90-o BTDC. Could have more pumping loss! Could be if exhaust port is poor, a long rod will help peak power.
AKA- A better rod angle.
http://www.stahlheaders.com/Lit_Rod%20Length.htm
Thread Starter
Staging Lane
Joined: Jun 2006
Posts: 73
Likes: 0
hmmmmmm.... I see but for my car just being a h/c car then buying aftermarket rods and forged pistons would just be waste huh? I am planning on building a 400+ci motor in about 3 years when I am outta college and actually can afford to get FI. So if I am just a H/C car then stock rods and hypereutectic pistons would be just fine with no issues right?
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
6.125 rod length was just what was already out there in SBC rods that also fit closely into an LS1 so the aftermarket pistons guys made and still make most piston for that rod length. Now the majority of all LS1 stuff is 6.125 on-center so it's way easier to get better pistons when you already have that rod as well.
Plus you need better rod bolts with the stockers and it you want full floating you need newer stock rods or add bushings to the older rods. Not worth it IMHO. You could get a cheap set of scat I beams which have a larger ARP rod bolt and bushed from the factory. I don't like the cap of the stock rods as it has no rib in it for strength.
