Why be afraid of big turbos?
94AWDcoupe, this is like ME101 here, but you are neglecting contact angle. Just because the lobes are different doesn't mean much.
Flat tappet cams actually have an issue with having too much jerk. The contact point is in the center of the bucket while the base circle is active. However, the contact point quickly goes to the edge of the bucket as the lobe comes active, the vast majority of that flat area on the ramp almost doesn't even touch the bucket and the nose of the cam becomes active very quickly.
Adding rollers actually reduces the contact angle movement and makes the cam less aggressive. This is why roller cams LOOK so much more aggressive. Unless you are looking at actual valve movement, and not just measured cam profile, you can't really compare cam lobes like you are trying to.
The limits of a flat tappet cam, like the 4B11 is the diameter of the tappet and then what kind of jerk and accelration rates the valvetrain can handle, along with side loads placed on the assembly due to the contact point being WAY off center at the highest acceleration point.
If somebody wants to take some measurements though, we could built up a quick model and I think you'd be pretty damn suprised how aggressive some of these cam over bucket setups really are.
Flat tappet cams actually have an issue with having too much jerk. The contact point is in the center of the bucket while the base circle is active. However, the contact point quickly goes to the edge of the bucket as the lobe comes active, the vast majority of that flat area on the ramp almost doesn't even touch the bucket and the nose of the cam becomes active very quickly.
Adding rollers actually reduces the contact angle movement and makes the cam less aggressive. This is why roller cams LOOK so much more aggressive. Unless you are looking at actual valve movement, and not just measured cam profile, you can't really compare cam lobes like you are trying to.
The limits of a flat tappet cam, like the 4B11 is the diameter of the tappet and then what kind of jerk and accelration rates the valvetrain can handle, along with side loads placed on the assembly due to the contact point being WAY off center at the highest acceleration point.
If somebody wants to take some measurements though, we could built up a quick model and I think you'd be pretty damn suprised how aggressive some of these cam over bucket setups really are.
Last edited by 03whitegsr; Sep 8, 2014 at 07:39 AM.
03white you added nothing to the conversation that shows 4g63 cams are not as aggressive as they look. they look aggressive because they are. you guys are making this waay more complicated than it is. cam profile is just that. cam profile. someone can post graphs of cams from same manufacture will only confirm everything I have said. untill then I have nothing to add.
EvoM Guru
iTrader: (50)
Joined: Mar 2006
Posts: 9,675
Likes: 132
From: Tri-Cities, WA // Portland, OR
Jerry, I think what 03white is saying is that because the way a flat tappet cam makes contact with the tappet/bucket, a wider valve opening duration will take place compared to if that same profile were used as a roller cam. No doubt though that the roller cam can acheive valve openings that are not possible with a flat tappet cam. I have no idea though whether the cams we use in our 4G63 Evos make use of that capability range.
94awdcoupe, just because you didn't grasp what I said doesn't mean I've added nothing.
Let me sum it up with a simple statement of what I said.
Unless you are charting actual valve motion, you are simply guessing which is actually more aggressive.
Let me sum it up with a simple statement of what I said.
Unless you are charting actual valve motion, you are simply guessing which is actually more aggressive.
