KA revability

[InsanityInc]

We all know the KA has a long stroke, which diminishes it's ability to rev high. However, just how high is too high? Since it has a DOHC setup, lets assume that we have a crazy drivetrain with titanium double springs, uber valves, etc. So, how high can it rev before the bottom end blows up? I'm looking for concrete numbers, backed up by actual tests, because I've heard far too much hearsay about this.

[SMoKeM240]

well on my old KA24E, i could rev that thing up to 7gs no prob and still felt like it was pulling and wanted to go more. i think they could go to 75 or 8 if its tuned right

[Nismo_Freak]

well on my old KA24E, i could rev that thing up to 7gs no prob and still felt like it was pulling and wanted to go more. i think they could go to 75 or 8 if its tuned right

8 grand? ... right.

At around 7500 rpm the KA is asking for a failure. It's piston speeds are very high (above the limit most builders say is acceptable) and is asking way too much of the stock internals.

Not saying it won't rev that high but I am saying it will begin to fatigue at that high of RPM.

The KA's piston is fairly heavy, so are it's rods.

[InsanityInc]

so then how high would it rev with different pistons? Also, the stock rods are forged, so they can't be all THAT heavy.

[NateDogg]

All I can say about rpm is that it :

RuinsPeople'sMotors

There's probably a reason why JWT raises the RPM limit to 7200rpm and not 8000.

[InsanityInc]

considering that NISMO's KA powered truck peaks at 8200 rpms, I can't imagine that 7200 is the limit for a KA. Unfortunately, obtaining detailed information about that engine is rather difficult.

[deviousKA]

Regardless of components, due to the nature of the ka 2.4l rotating assembly you will see a very damaging harmonic from 8-9?krpm. In the common divisions where the ka is raced and allowed to be built competetive you will see a lot of what they have done. As for bottom end the crankshafts are 100% custom units retaining the oem dimensions, usually 4340 steel billet std race material. They will lengthen the rod 5-7mm and use a high quality forged unit. This gives the KA just a tad more headroom for operation at higher rpm due to its effect on piston acceleration. At operating ranges of over 7500 when stress is at its highest, the drivers side engine mount is a common place of failure (block crack). Most race vehicles run solid engine mounts, so the common A/C location on the block is what a lot use and i think is best as well (instead of std engine mount location). Block failure in other places is common at this barrier as well, large stress cracking due to harmonic.

The ka24de nismo/artschmidtt race trucks have basically identical modifications done to the bottom end. Nismo carrillo connection rods designed for nasport, and a race steel crankshaft. The cylinder head uses unknown valves and springs, but retains the stock cam base circle. Because of this and the fact that such large lift and duration cams are necessary (they are direct, biggest you can get as far as lobes) the buckets and shims have been enlarged. This is necessary so that the camshaft lobe does not fall off the side of the shim.

You can go ask any famous old ka builder, if you dont take my word, they will tell you the same. Try contacting Don Nimi up at pdm-racing.com . Most of the other guys have died or moved on, some still working for nissan.

[InsanityInc]

so for a non race engine, you'd say about 7500 at best?

[deviousKA]

Balance the crankshaft, allen plug it. Get some strong tight tolerance pistons and balance them with your rod set. You could also get some small knife edge work done but i wouldnt recommend anything extreme. That bottom end would have no problem spinning to 7500. As for the valvetrain you going to have to do upgrade the valve springs, and get a cam to suit.

People build similar described engines and bring them up and over 8k rpm in drag datsuns. 200whp and more. Needless to say short lifetime.

[InsanityInc]

now I just gotta wait for the guy that's supposed to be selling me the damn extra engine. blah.

Oh, also, are the OEM valves sufficient for decently high compression (about 10.6:1) and 7500 rpms, or do I need some kind of crazy sodium filled ones?

[deviousKA]

If all 4 cylinders are tuned properly you shouldnt have a problem with stock valves at this rpm. Though, 1mm oversize valves are to consider, these are available in stainless steel. Be sure to do complete port work including shaping the short side radius and enlarging the diameter behind the seat. You can also upgrade to full bronze guides for added life at sustained higher rpms.

I would go much higher compression, 11.1:1+. You will want you piston to come in very close proximity to your quench area (no more than .040"). True flat top is also the best option. This with an unwelded combustion chamber will put you in the 11-12's depending on all the exact specs. Higher compression ratio, you would be surprised actually how detonation resistant it can become when taking advantage of quench and the ka24de chamber design. Welding and cloverleafing is another option, to go huge compression, or to bring up compression on a destroked setup.

Implement a water/alcohol or similar injection system into your manifold, you can run pump gas and 12.5:1.

[InsanityInc]

the only problem with 11.1+ (well, anything higher than 10.6:1) is that I can't seem to find any non-custom forged pistons with that compression. Highest I can find is 10.6:1 (and that's with a .5mm overbore).

Oh, and I'm also in california, so 91 is all the octane I get.