InsanityInc
Automotive
- Aug 26, 2005
- 6
Well, I've been working with a Nissan KA24DE recently. 2.4L DOHC 4v/cyl 89x96 Inline 4, 9.5:1 compression ratio. Now, the undersquare aspect is a bit odd considering I'm trying to extract high-RPM power. The reason why I'm trying is that the engine redlines at 6900rpm stock, yet the stock power peak is at 5600rpm, and the engine goes dead after 6000rpm or so. The torque peak is waaay down at 4200rpm, and drops pretty fast afterwards. The other obstacle is the intake manifold. It had a set of secondary butterfly valves (now gone) to assist low end torque, and the runners are also very long (about 18").
Obviously, the first thought would be to change the cams. There are a few aftermarket makers of cams for the engine, but neither set of cams gives very good results at all. They gain what you'd expect from just increasing the lift (5-7 horsepower, no real change in the locations of the power/torque peaks).
Now, as I understand it, the purpose of the longer runners is to increase low end torque by creating a supercharging effect by getting the intake charge moving at a higher velocity, but the problem is they may restrict it at higher RPM because they don't build velocity fast enough to get a good cylinder fill. However, wouldn't it stand to reason that having a really late intake closing point would vastly improve high-end power with this setup, since the intake velocities are higher due to the long stroke and long runners? Some people have tried replacing the manifold with a plenum-less ITB setup, and that didn't have an affect on power by itself. So I figure something has to be going on with the cams, and I'm guessing that the aftermarket cam makers are probably used to making cams for more conventional high-performance motors, hence the poor results.
With all the hearsay and misinformation on cams that you can find everywhere, I'm looking for a more professional angle on this problem. Hopefully I'll find one here.
Obviously, the first thought would be to change the cams. There are a few aftermarket makers of cams for the engine, but neither set of cams gives very good results at all. They gain what you'd expect from just increasing the lift (5-7 horsepower, no real change in the locations of the power/torque peaks).
Now, as I understand it, the purpose of the longer runners is to increase low end torque by creating a supercharging effect by getting the intake charge moving at a higher velocity, but the problem is they may restrict it at higher RPM because they don't build velocity fast enough to get a good cylinder fill. However, wouldn't it stand to reason that having a really late intake closing point would vastly improve high-end power with this setup, since the intake velocities are higher due to the long stroke and long runners? Some people have tried replacing the manifold with a plenum-less ITB setup, and that didn't have an affect on power by itself. So I figure something has to be going on with the cams, and I'm guessing that the aftermarket cam makers are probably used to making cams for more conventional high-performance motors, hence the poor results.
With all the hearsay and misinformation on cams that you can find everywhere, I'm looking for a more professional angle on this problem. Hopefully I'll find one here.
