THe Ka has low velocity at High RPMs, large ports?
THe Ka has low velocity at High RPMs, large ports?
I was reading mototuneusa.com they have a few articles about port velocity, I thought maybe this is the KA's problem at high RPMs, can someone check the choke point diameter and intake valve diameter. If its bigger than the valves or almost as big, then it can cause low velocity. a thats what mototune said, plus my car feels like it bogs up, even at low rpms and can't fill the cylinders. I think the engine might have a low volumetric effiency.
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Ubernoober
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No offense, but this is a semi-scientific motorcycle article as quoted by an automotive non-techhead. Results on one engine do not apply to all engines.Do some more research on the KA and engines in general. There is more to this engine and VE than port sizes.Also, I respect motoman and the vast experience he has, but good god, could he please use less crappy animated gifs and annoying page transitions? Jeez!
Re: THe Ka has low velocity at High RPMs, large ports? (dark-sky)
The problem with an N/A KA at high RPMS is that the intake runners are WAY to FREAKING LONG. Even with pretty agressive cams this causes the torque curve to drop like a rock right where you need it to peak. Get a short runner intake manifold and you will be able to move the torque curve over as far as you need to with agressive cams, and using adjustable cam gears to tweak the timing. You can easily produce 160 torque with I/H/E/Cams and good tuning. Get the torque curve to peak at 7000RPMs with this and you will have 213HP. Peak it at 7500RPMs and you get 228HP. Tuning is the key.
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Nismo_Freak
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- Car: 89 Nissan 240SX
Re: THe Ka has low velocity at High RPMs, large ports? (KADreams)
Torque will never peak in the KA at 7000 RPMsKADreams wrote:The problem with an N/A KA at high RPMS is that the intake runners are WAY to FREAKING LONG. Even with pretty agressive cams this causes the torque curve to drop like a rock right where you need it to peak. Get a short runner intake manifold and you will be able to move the torque curve over as far as you need to with agressive cams, and using adjustable cam gears to tweak the timing. You can easily produce 160 torque with I/H/E/Cams and good tuning. Get the torque curve to peak at 7000RPMs with this and you will have 213HP. Peak it at 7500RPMs and you get 228HP. Tuning is the key.
Work with the motor, not against it.
Mototune is a very good idea and theory that should be known and considered by people who do alot of porting to various types of heads from many makes and models.
but like ubernoober said, this does not apply to all engines.
Motorcycles in general have ports that are WAY too large. One example of how much port and air flow they have is the 98-99 GSXR750 came with 46mm throttle plates (necks down to 42mm at the port) It was a dog at lower rpms, and was a rocket up top. For the 00+ years the plates were reduced to 42mm (IIRC) and low rpm power was increased without decreasing top end.
The KAs problem, like KADreams said, is the fact that the intake manifold has very long runners, not to mention the fact that they're are curled, which in and of itself is a flow restriction. This was designed because what the typical American at the time wanted, and what the 240sx was marketed for, was a sporty car. One that can commute daily, but can run on the back roads. Thus torque was in the minds of the designers because you feel torque coming out of a corner.
THe KA is also cammed pretty mildly, but the biggest problem is the intake manifold, IMHO.
KADreams' suggestions are pretty spot on, but using the stock EFI system with the MAFS is going to be a problem and will cause you not to obtain the motors true potential.
but like ubernoober said, this does not apply to all engines.
Motorcycles in general have ports that are WAY too large. One example of how much port and air flow they have is the 98-99 GSXR750 came with 46mm throttle plates (necks down to 42mm at the port) It was a dog at lower rpms, and was a rocket up top. For the 00+ years the plates were reduced to 42mm (IIRC) and low rpm power was increased without decreasing top end.
The KAs problem, like KADreams said, is the fact that the intake manifold has very long runners, not to mention the fact that they're are curled, which in and of itself is a flow restriction. This was designed because what the typical American at the time wanted, and what the 240sx was marketed for, was a sporty car. One that can commute daily, but can run on the back roads. Thus torque was in the minds of the designers because you feel torque coming out of a corner.
THe KA is also cammed pretty mildly, but the biggest problem is the intake manifold, IMHO.
KADreams' suggestions are pretty spot on, but using the stock EFI system with the MAFS is going to be a problem and will cause you not to obtain the motors true potential.
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:: orion ::
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...and the stroke. Combined with a crank that's not fully balanced.
No matter how good you make the intake manifold, or what cam you put in it, you CANNOT rev to ~7500-8000rpm for an extended period. The piston speeds are too high and will break even aftermarket forged rods, eventually.
So while the intake mani may leave something to be desired (in theory, at least), there are other more prevalent problem to making the TQ/HP peaks higher in the KA.
- Brian
No matter how good you make the intake manifold, or what cam you put in it, you CANNOT rev to ~7500-8000rpm for an extended period. The piston speeds are too high and will break even aftermarket forged rods, eventually.
So while the intake mani may leave something to be desired (in theory, at least), there are other more prevalent problem to making the TQ/HP peaks higher in the KA.
- Brian
Re: THe Ka has low velocity at High RPMs, large ports? (dark-sky)
does anybody know the measurements of the manifold, and headers. I'd like to calculate their tuning frequency.