Rb30 Crank Durability And Harmonic Balancer

[Chids34]

Hey, recently purchased a 25/30 motor for my r34, runs r34 neo head. Been doing some research on the rb30 crank compared to the 25 crank and apparently the 30 crank due the it's design has bad harmonics that cause it to have revving issues. I found some info stating that rb30's have a tendency to break oil pumps over 7500rpm. Now I don't intend to spend buckets of money on my car, so I would prefer to avoid buying a good aftermarket counter weighted crank, however I was wondering if anyone has used the fluid style damper and if it helps eliminate some of the 30 cranks harmonic issues. Thanks

[KiwiRS4T]

I haven't heard about any RB30 crank problems but if you want to rev an RB30 way beyond its designed speed its long stroke starts to make itself felt. You need to make sure the whole thing is well balanced from clutch to damper. What revs do you plan to use anyway? If you are going way over 7,500 most people would get a suitable ATI damper or suchlike. Most cheap builds just don't rev the hell out of them and still make good power.

[Chids34]

I'd like to go to 8k if people reckon a ati balancer should see me there ill look at getting one

[GTRPSI]

I haven't heard about any RB30 crank problems but if you want to rev an RB30 way beyond its designed speed its long stroke starts to make itself felt. You need to make sure the whole thing is well balanced from clutch to damper. What revs do you plan to use anyway? If you are going way over 7,500 most people would get a suitable ATI damper or suchlike. Most cheap builds just don't rev the hell out of them and still make good power.

Its there, its real on RB30's its been seen and documented for a long time.

However its at certain RPM's in varying degrees, for example you may have one at 7640, a smaller one at 7980 and maybe a huge one at 8140 etc.

The point being is your not sitting at that exact RPM, you rev through it, doing so its just a slight harmless bleep while transitioning through.

Hold it at exactly the right harmonic point for long enough and expect the engine to be tearing itself to sherds....your just passing through it which does not leave enough time for anything to happen.

I have discussed this between quite a few big HP RB30 drag engine builders (1000Hp+) and none have had issues with it however all have agreed if you sit there long enough at that sweet spot it wouldn't be a good thing.

Who holds a engine at exactly 1 high RPM? (and it happens to be that right harmonic spot)

While on the subject, many different engines have a inherent harmonic issues due to design, i remember Cosworth having one with their Turbo F1 design and simply giving up on the engine and taking it back to the drawing board.

[GTRPSI]

Just thought id throw this in, below is the video of the Cosworth engine harmonics failure, dis-assembly and prognosis that i mentioned.

The 15 min mark is when they held it at the harmonic sweet spot on the dyno, 16min mark it failed, from there they tore it down and at the 25 min mark they say "incurable vibration at the crankshaft"

No amount of balancing will help it once the engine design has a inherit harmonics issue......