should i overbalence my rotating assy.

[DDSR240]

So I've heard that a slight over balance will cause some vibration in the low rpm but that slight overbalance is needed for the engine to survive in the higher rpm band. I just need to know for shure before my builder balances my whole assy. btw sr20det fully built gt35-r (so i need all the rpm I can get)

[renegade_ewok]

Would overbalancing cause more stress on the bottom end than normal? I don't know much about the theory behind this but you would think that a lot of the cranks mass would be to dampen out harmonic vibrations which could damage it. How much it actually does this, I don't know.

What are you revving the car to and what kind of bearings do you have? If your revving high it might just be worth it to get a better oiling system - i really haven't heard of any issues the SR cranks have with spinning to 8k. Just get a good oiling setup (dry sump?!) and I think it should take it.

[DDSR240]

prbly 9,000 and I'm using clevite bearings.

[drifts135]

I did some checking pooky, and YES overbalance the damn thing! DOOOO IITTTTTTTT.


"those guys" I know are overbalancing theirs.

You know the answer to this, now do it!! Oooooooohhhh, my motor vibes a lil at 3k.... Oh godddd My girlz boobies might jiggle.....ooooohhhhh.

Overbalance it pussy.


BTW, know who this is?

[DDSR240]

the only mother fucker in the world to 1jzvvti a perfectly good r32 ....and make me want to part my ballin sr out

[born2boost]

how can you over ballance somthing? My crank is vcut and the whole rotating assymbly is ballanced. Wouldnt that be ideal for super high rpm?

[drifts135]

I am not good with explanations, but Imma try. (will sound pretty bumb).

The way I understand this is... If you have something that is swinging the same distance out on both sides, then equal balance is fine at any rpm, but if one thing being swung around the center line is longer, the thing on the other side will need to be heavier by a tinnnnyyyyy bit at a low rpm, a tiny bit more as it speeds up, etc etc etc.

The weight of the piston/rod is being slung further out, it is also making an abrupt stop as the piston is moving straight up and straight back. It needs the extra weight on the counter balance to compensate for the different kind of motion(piston wants to keep going away from the center but gets snatched back) and for it being slung further away from the axis or whatever.


All of this mess is why arguements get made for the "longevity" (LOL) of a rotary in high rpm applications i suppose... cause a piston engine has some sucky flaws in that respect... (Does not mean Im goin rotary any time soon).

The trick with overbalance seems to be finding the right amount to overbalance for your rod lenght/weight, piston weight, blah blah blah, oh, and RPM you plan to turn.... Then deal with the tiny bit of vibration you get at some random lower number like oh say 3500rpms.... I would rather have a little non destructive vibration at 3500 than have my shit vibe till I spin a bearing or some shit at 10,000...



Sorta talking outta my ass cause I fail at words... but I promise I undersatnd the concept and hope yall do aswell now.

Wooo, I'm goin' to bed!

.

[born2boost]

ah ok, we balanced the entire rotating assembly to 10k, just never heard of it called overbalancing.