Ron Earp
05-28-2008, 09:23 AM
Before this last weekend’s race at CMP I spent Friday morning on the dyno with the 260Z trying to get some more power out of it. As some of you know earlier this year (detailed in other threads) I suspected this Z might have an "A" cam installed by the builders of the car down in Atlanta and marked as a “C” cam, but can't be sure without having the cam profiled. Anyhow, to be sure I wanted to get that cam out of the car so it is 100% legal thus I got a legal “C” cam out of a junked 260Z that Rex D from Happy Jap’s turned me on too.
The C cam is a bit different from the A in that it has a bit more duration overall but slightly less lift on the intake valve. Still, both cams are very close.
The results are somewhat predictable. The car makes a tiny bit more top end horsepower and a bit less mid-range torque than before. I could maybe see why 240Z racers back in the day might choose to use this cam if they were limiting themselves to factory grinds. What we ended up with was 168 rear wheel hp at 6000 RPM and 160 ft-lbs of torque at 5000 RPM. It appears I did give up a tiny bit of mid range torque, about 4-6 ft-lbs, from 4200-5000 RPM, and gained about 8 horsepower on peak. Not too happy about the torque loss, but the cam is what is supposed to be in the 260Z and I know now for sure that the cam is 100% legal.
The peak hp comes in at 6000 RPM, which is a little bit surprising and leads me to believe that my actual cam timing is off. I’ve not properly degreed this setup, only set the cam up according to the marks I’ve made on the flywheel and therefore my next step is to really get this stuff dialed in correctly. I also know there are some mixture issues still going on that I must sort and I’m not sure I’m 100% happy with the ignition system, the power lines look a bit wavy. You can check out the plot below but bear in mind those two plots are both C cam plot at different timings, it is not a comparison of the old and "new" C cam.
How does the car feel on track? About the same as it did before, a tiny bit more seat of the pants top end but not a lot of difference. Any other 260Z racers or pilots please chime in if you’ve got some suggestions.
Ron
The C cam is a bit different from the A in that it has a bit more duration overall but slightly less lift on the intake valve. Still, both cams are very close.
The results are somewhat predictable. The car makes a tiny bit more top end horsepower and a bit less mid-range torque than before. I could maybe see why 240Z racers back in the day might choose to use this cam if they were limiting themselves to factory grinds. What we ended up with was 168 rear wheel hp at 6000 RPM and 160 ft-lbs of torque at 5000 RPM. It appears I did give up a tiny bit of mid range torque, about 4-6 ft-lbs, from 4200-5000 RPM, and gained about 8 horsepower on peak. Not too happy about the torque loss, but the cam is what is supposed to be in the 260Z and I know now for sure that the cam is 100% legal.
The peak hp comes in at 6000 RPM, which is a little bit surprising and leads me to believe that my actual cam timing is off. I’ve not properly degreed this setup, only set the cam up according to the marks I’ve made on the flywheel and therefore my next step is to really get this stuff dialed in correctly. I also know there are some mixture issues still going on that I must sort and I’m not sure I’m 100% happy with the ignition system, the power lines look a bit wavy. You can check out the plot below but bear in mind those two plots are both C cam plot at different timings, it is not a comparison of the old and "new" C cam.
How does the car feel on track? About the same as it did before, a tiny bit more seat of the pants top end but not a lot of difference. Any other 260Z racers or pilots please chime in if you’ve got some suggestions.
Ron