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Whats the advantages and disavantages in runnin a 6 inch rod vs a 5.7 rod? I found some pretty bad scares on my old piston(sabatage when out of the motor) so i was just gonna buy new rods and pistons while i rebuild my 406. It will b mostly a street duty motor and sprayed at the track. I have no idea what would be better off for my motor.
Also im looking at some forged rods. Scat has some i beam rods that are rated 750hp and eagle has some h beam rods that are rated 750hp. Im unsure really which to go with. I will be spraying this motor at the track prolly close to 400hp and will see alot of street time. What do you guys think? Need some opinions.
Also im looking at some forged rods. Scat has some i beam rods that are rated 750hp and eagle has some h beam rods that are rated 750hp. Im unsure really which to go with. I will be spraying this motor at the track prolly close to 400hp and will see alot of street time. What do you guys think? Need some opinions.
The Scat I beam rod is a great bang for the price. I personally would never run another 3/8" rod bolt rod when you can get these with the 7/16" ARP rod bolts. $300 bucks is a great price, I have them in my 383 although I have the 5.7".
I did run the 6" Eagle H-beam rod in my last 406. Probably should have gone with a 6" rod in this 383, but it's done already and I run the crap out of it. It should easily go north of 500 hp.
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72 Nova -383, AFR 195s, Lunati #60113, 11.70s, next pass will be an 11.50
Last edited by sbc1320; 5th-January-2013 at 05:11 PM.
Lots of theories about long rods but for street use none relate to reality. It's still debated on engine builder sites all over the internet. If it was that clear there would be no debate. Lighter piston with longer (heavier) rod? Side loads? Ever see a chart showing rod angles vs. length? Miniscule differences. A 454 Chevy has a worse rod/stroke ratio than a 350. (1.53 vs. 1.64 ) Are 454s known for massive bore wear and lack of horsepower? (A 400 with 5.7 rod is 1.52) If the price is the same and no balancing issues arise and you're buying new parts anyway then go ahead and use the long rod combination. Just understand there's almost no power or longer life there.
From the article "Expert Engine-Building Tips & Advanced Theories Straight From Darin Morgan of Reher-Morrison"
"Most people tend to overgeneralize this issue. It would be more accurate to compare different rod-to-stroke ratios, and from a mathematical stand-point, a couple thousandths of an inch of rod length doesn't really change things a lot in an engine. We've conducted tests for GM on NASCAR engines where we varied rod ratio from 1.48- to 1.85:1. In the test, mean piston speeds were in the 4,500-4,800 feet-per-second range, and we took painstaking measures to minimize variables. The result was zero difference in average power and a zero difference in the shape of the horse-power curves. However, I'm not going to say there's absolutely nothing to rod ratio, and there are some pitfalls of going above and below a certain point. At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. What-ever connects the two is your rod length."
All pistons with a low compression height will have the oil ring support.
So what negative about it?
Al
Not sure if it is really a negative or not. Some people say it is and some say it isn't. I have ran two sets myself with an SRP piston and I have a set here for a Ford with SRP pistons. For my street car I prefer to stay out of the oil ring land.
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72 Nova -383, AFR 195s, Lunati #60113, 11.70s, next pass will be an 11.50
Last edited by sbc1320; 6th-January-2013 at 12:08 PM.
From the article "Expert Engine-Building Tips & Advanced Theories Straight From Darin Morgan of Reher-Morrison"
"Most people tend to overgeneralize this issue. It would be more accurate to compare different rod-to-stroke ratios, and from a mathematical stand-point, a couple thousandths of an inch of rod length doesn't really change things a lot in an engine. We've conducted tests for GM on NASCAR engines where we varied rod ratio from 1.48- to 1.85:1. In the test, mean piston speeds were in the 4,500-4,800 feet-per-second range, and we took painstaking measures to minimize variables. The result was zero difference in average power and a zero difference in the shape of the horse-power curves. However, I'm not going to say there's absolutely nothing to rod ratio, and there are some pitfalls of going above and below a certain point. At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. What-ever connects the two is your rod length."
================================================== == At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. What-ever connects the two is your rod length."
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