Rod/Stroke ratio and other questions
Originally Posted by TransAm
I bet you mph was also higher.thats what I would like to see as well. Still doing more dyno work. Only at the first stage of things. Fuel pump started getting funky last time, gota fix the line. Then back for more power. This is however a 98 f-body with our custom 2 bar map sensor in it now. No MAF here. I figured out how to make it work.
Rick
Registered User
Joined: Mar 2004
Posts: 199
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From: Austin, Texas
It really depends on the application, I built motors for the IRL back in the day Nissan was just starting to race IRL. We turned the motors 12500rpm and made good power. The problem was the motor made the same amount of torque and HP at the same rpm.
At Indy when a car comes down the straight to turn one they don't lift much. The car has about 5000lbs of down force holding it to the track, in the corners the motor would lose rpm due to down force and cornering. Once the car was going straight again it won't pull hard until the rpm come back up, this was do to the peak torque and peak HP being at the same rpm. So, we changed rod length, we went shorter. We made the same HP and the same torque but, we made peak torque about 1000rpm lower in the rpm band. This help the car pull out of the corners, pulling from peak torque to peak HP.
Just depends on what your building, but as a general rule I like rod ratio around 1.7. It's easier on parts and will make good power, if you have heads that flow 450cfm or more and your running 1320 feet then pulling the motor down. Rods just connect the pistons to the crank no doubt.
At Indy when a car comes down the straight to turn one they don't lift much. The car has about 5000lbs of down force holding it to the track, in the corners the motor would lose rpm due to down force and cornering. Once the car was going straight again it won't pull hard until the rpm come back up, this was do to the peak torque and peak HP being at the same rpm. So, we changed rod length, we went shorter. We made the same HP and the same torque but, we made peak torque about 1000rpm lower in the rpm band. This help the car pull out of the corners, pulling from peak torque to peak HP.
Just depends on what your building, but as a general rule I like rod ratio around 1.7. It's easier on parts and will make good power, if you have heads that flow 450cfm or more and your running 1320 feet then pulling the motor down. Rods just connect the pistons to the crank no doubt.
Rick, where do you find a 6.3 rod that will work in an LS1? I've been looking at the choices for rods for a while now and only seem to find 6.094 (stock), 6.100 and 6.125. I'm very interested in a 6.3 rod if it's made by a reputable company (and I won't have to turn the crank down for it).
This is good stuff guys. I have one question though, with the ever popular 4" stroke and 6.125" rod combination are all of these motors just ticking time bombs just wearing the rings and bearings at a very accelerated rate? Does anyone yet know the rod length of the ls7 motor? I'm having a 434 built and just a little concerned about everyone indicating accelerated where. Thanks.
Well, I just found the Eagle CRS6300B3D's...6.3 inches, h-beam, available with an ARP 2000 or L19 bolt...but I've never had good luck with Eagle stuff before. I'm going to keep looking now though, I'm sure I'll find something.
Originally Posted by Mike454SS
Well, I just found the Eagle CRS6300B3D's...6.3 inches, h-beam, available with an ARP 2000 or L19 bolt...but I've never had good luck with Eagle stuff before. I'm going to keep looking now though, I'm sure I'll find something.
When you guys start talking about using a 6.300" rod with a 4.00" stroke on a typical 9.2xx" deck, doesn't the piston pin height become a major concern? I though the 6.125" rods were pushing the pin up pretty high as it is.
I realize on a 9.8"+ deck this isn't a concern, but we don't have that, yet.
I realize on a 9.8"+ deck this isn't a concern, but we don't have that, yet.
Here is some info I found on the subject. Maybe it will help someone.
http://victorylibrary.com/mopar/rod-tech-c.htm
http://www.stahlheaders.com/Lit_Rod%20Length.htm
http://victorylibrary.com/mopar/rod-tech-c.htm
http://www.stahlheaders.com/Lit_Rod%20Length.htm
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Originally Posted by Wet 1
When you guys start talking about using a 6.300" rod with a 4.00" stroke on a typical 9.2xx" deck, doesn't the piston pin height become a major concern? I though the 6.125" rods were pushing the pin up pretty high as it is.
I realize on a 9.8"+ deck this isn't a concern, but we don't have that, yet.
I realize on a 9.8"+ deck this isn't a concern, but we don't have that, yet.
The trick is that I am using a 4" stroke piston with a stock crank.
Rick, would you mind if I PM'd you to ask you some more questions? I've been researching this a lot, but I'm having trouble finding a piston that'd work and net me the CR I want. It's not really on topic for this thread though.
Originally Posted by Mike454SS
Rick, would you mind if I PM'd you to ask you some more questions? I've been researching this a lot, but I'm having trouble finding a piston that'd work and net me the CR I want. It's not really on topic for this thread though.
Rick
Originally Posted by Mike454SS
Rick, I e-mailed you, but I'm not sure if it went through, don't know if I had my settings right in the user control panel. Let me know if you got it.
Thanks,
Mike
Thanks,
Mike
Rick
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Rod stroke ratio is just not that important. Ford, GM and Honda have all had some rod ratios traditionally considered "bad" and they go 200K miles all the time. Some of these are in the 1.4-1.5 rod stroke range right from the factory. Like Harold said I have friends from College in the engineering side of formula car engines at Cosworth and Ilmor and both have said in some engines they are stuck with rods that are "too long" because of packaging and it hurts the power they make. They simply can't push the deck down anymore to fix it because of other considerations.
Fritz Kayle's world dominating 24 hour endurance 7.0 liter stroker engines have "bad" rod ratios too but they probably go through more wear and tear in an entire 12, 24 or 48 enduro than most cars will in ten lifetimes. In these 24 hour Le Mans cars they can run smaller engines with much better rod ratios but they aren't as fast or as reliable. Using rpm to make up for cubic inches whether a "bad" rod ratio or not has never been known to help reliability or engine wear!
Fritz Kayle's world dominating 24 hour endurance 7.0 liter stroker engines have "bad" rod ratios too but they probably go through more wear and tear in an entire 12, 24 or 48 enduro than most cars will in ten lifetimes. In these 24 hour Le Mans cars they can run smaller engines with much better rod ratios but they aren't as fast or as reliable. Using rpm to make up for cubic inches whether a "bad" rod ratio or not has never been known to help reliability or engine wear!
