Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) > Mac CPU Upgrades

How much is safe overclock a G3 ?

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Hi, I have a Beige G3 @ 266MHz. It's pretty fast with OS 9.2.2 but really slow when verify dmg images and unstuff things, so i'm thinking to upgrade it. Considering that in 2019 is pretty difficult to find an accelerated card (probably it will cost much too) i want to overclock the puppy.
According to various sites found via lowendmac there are various possibilities just moving some jumpers on the logic board and teorically there is the possibility to push all over 600Mhz but is a smart thing to do or i risk to kill something ?
The system bus can go up from 66MHz to 83MHz and the cpu has multipler up to 7 (actually it should be set around 3.5).
In old Pc's pushing on FSB make the system overall unstable (PCI side), here i don't know what can happen, how much are solid hardware and operating system. I want have a stable upgrade (thinking to install Tiger in next future ), not a test configuration.
Working cpu side instead how much can rise temperatures ? The default configuration mount a passive and short heatsink. Ideally i should replace it with something bigger (need to add another one on the asic chip ?) but in the outtrigger case there is very few space. The shorter ram modules know something: installing the standard sized ones, stop the system from booting probably because the top block of the case, when it's closing, moves the modules in the slots or, worst, short circuit their signal to mass.

What can i do in relatively tranquillity ? Thanks

Little update:

Tonight i kept on the system at standard speed for several hours, browsed web and played some games. At a certain point suddenly, all shut off. Restarted, a few minutes are passed, new shut off. The problem, i think, must be related to temperatures. Some months ago I changed heatsink paste with a new and better one but now probably it is not sufficient. Here,, i read something unclear but bad about temperature sensing (wrong reads even of 20C) even if the maximum temperature that the CPU can reach is 105 C
Yesterday i've tried two software hoping to read a reliable value: Jeremy's CSM didn't sense anything and Gauge Pro which pretended to read ever ~32C without any variation.
Had I the cpu much hotter and It went to thermal protection or what's happened ?

you could probably push it to 333 with the addition of a cooling fan, otherwise those really old early G3s were not good for overclocking. later generations of G3 were a different story.
G3 ZIF cpus aren't too expensive and pop up on ebay relatively often, you could probably find a 350 or 400mhz relatively easily and cheaply.
dont hold your breath on finding a G4 zif, but they do pop up from time to time.

It's been quite awhile, but I've  got a card I used in a Beige as a 500/83. That seemed to be where it was happiest. The board was originally a 333. It's either a Powerlogix or an Xlr8, either a G3 or G4 zif I bought from OWC. I've got maxed out ram for it and all the parts in a box minus case and PSU which went south.... I've  got a few other 400/450 cards for 8500/9500 boards. I have no use for these now.

Where can i mount a fan ? The heatsink almost touch the top block. On the left ram modules block the air. On the front there is the hard drive, toward the back there are ide cables and on the right, the only free area, there aren't holes.
Yesterday i noticed, if i remove the plastic case the system hardly shut off for temperatures (tried various round of macbench, unstuffed big archives, moved files through ethernet, runned quake 2 demo in software rendering, all ok).
Externally this system seems well designed but internally the cpu is caged and fresh air flow doesn't seem move much. This thing doesn't melt like chernobyl only because the G3 is much better designed compared to intel's of same era, it consumes very few watts and cool down rapidly but it's a risky game.
Apple believes it knows how to design but it is absolutely not new to certain messes.  :(

Anyhow the cpu version is 2.2: where can i find some usefull information for it ?

I run all my machines bare board.  Throw away the case. Just set a fan directly on the heatsink. Your cpu will run cold. It's a waste of time fussing with cases.


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