Destroked vs Long geared Stroker LS builds
06-05-2022, 05:20 AM
#21
I am not trying to be contrary but Smokey was incorrect. Unless your rod/stroke ratio is awful, like under 1.5/1, and your wristpin is still safely up inside of your cylinder bore and holding your piston straight, your cylinder pressure and torque are not affected.
As an example, the LS7 had a rod ratio that was just barely over 1.5:1, and its factory rev limiter was set to 7100rpm. It was the highest revving engine sold by GM up to that time, as far as I know.
The rod ratio does have some potential to give a different signal in terms of cylinder filling to the cam, but it is minimal. In the real world just connect your pistons to your crank with the best rod you have and don't worry about it.
As an example, the LS7 had a rod ratio that was just barely over 1.5:1, and its factory rev limiter was set to 7100rpm. It was the highest revving engine sold by GM up to that time, as far as I know.
The rod ratio does have some potential to give a different signal in terms of cylinder filling to the cam, but it is minimal. In the real world just connect your pistons to your crank with the best rod you have and don't worry about it.
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G Atsma (06-05-2022)
06-07-2022, 06:33 PM
#22
Smokey did cheat but he's better known as a great interpreter of rule books, It wasn't so much what the rules said he could or couldn't do, it was what they failed to define that he took advantage of. Why risk cheating on the size of the fuel tank when the rules didn't specify a minimum fuel line length or size so he made it big and long so it would hold more fuel. Nascar had to make many amendments because of his way of thinking.
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G Atsma (06-08-2022)
06-09-2022, 03:51 PM
#23
In testing a longer rod made a tiny bit more torque not because of cylinder pressure but because it makes the cam perform like it is a bit smaller duration due to holding the piston higher in the bore for a bit longer. The difference is on the order of 2%. Then the short rod (AKA the rod people say "oh that will kill your RPM") made a tiny bit more power at the very top of the RPM range.
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G Atsma (06-09-2022)
06-09-2022, 04:26 PM
#24
TECH Senior Member
I am arguing against a guy because today we have as strict as possible A-B dyno testing comparing shorter and longer rods and their performance under as controlled of a circumstance as we can get. The difference is nothing. Smokey was a smart man but on this subject the man was wrong.
In testing a longer rod made a tiny bit more torque not because of cylinder pressure but because it makes the cam perform like it is a bit smaller duration due to holding the piston higher in the bore for a bit longer. The difference is on the order of 2%. Then the short rod (AKA the rod people say "oh that will kill your RPM") made a tiny bit more power at the very top of the RPM range.
In testing a longer rod made a tiny bit more torque not because of cylinder pressure but because it makes the cam perform like it is a bit smaller duration due to holding the piston higher in the bore for a bit longer. The difference is on the order of 2%. Then the short rod (AKA the rod people say "oh that will kill your RPM") made a tiny bit more power at the very top of the RPM range.
06-09-2022, 05:02 PM
#25
When David Reher of Reher-Morrison racing engines says he did testing with NASCAR engines of different rod/stroke combinations and different cams and the difference is nothing, the difference is nothing.
06-09-2022, 05:27 PM
#26
TECH Senior Member
OK, you didn't say where the 2% was gained.
Smokey was experimenting with everything, and was working with whatever there was then.
There are so much better instrumented testing tools nowadays.
Smokey was experimenting with everything, and was working with whatever there was then.
There are so much better instrumented testing tools nowadays.