Where did you get that 8.3 number? Is that from your experience with these motors? Not questioning your info... this is something I have been wondering about for a while now- just how high DCR to run for 93 octane in my Al headed stage 2 SE motor.
From the calculator on Pat Kelly's DCR page ,it has the downloadable calculator at the bottom of the page. Also some good discussion.
jimmy, Assuming 4 deg cam advance, your combo will give a DCR of about 9:1, too much for pump gas, I assume you're planning on race gas.
Ok... That's what I've been using too. I have some questions about the accuracy of it though. I wonder how accurate using the seat to seat numbers actually is, since I have been told that flow doesn't actually start until somewhere close to the .050" lift point, which is why it is typically used. What happens if you have a cam with a lot of seat to seat duration, but with conservative .050" lift numbers?
You're right about significant flow not starting until the .050" point. But that's not the issue here. It's "when do you start building compression?" You will build compresion with the valves closed. Obviously with the valve open by 0.006" (advertised) you won't build much compression. But, we have nothing else to go on so that number is used, you need to get as close as possible to the actual valve closing. The DCR numbers are all relative, so absolute ones aren't needed, the "accuracy" is sufficient for that. A cam with lots of seat-to-seat dur but low .050" numbers is probably an old one; easy on the valvetrain. You still used the advertised numbers (0.006", which is what most, but not all manufacturers use).
That's not necessarily true though. Take the KB107 cam: low lift, huge advertised duration, and a bigger split between advertised duration and .050" duration than all of the TA cams. It is still considered a fast ramp profile. What you said makes sense- it's about compression, not flow. Thanks.
