PC "Skinny" Sprint upgrade and overclocking of PCjr

Wanted to share one of my latest projects and talk about this one if people aren't familiar with it. Need to give credit to one of my favorite retro youtubers "Epictronics" - https://www.youtube.com/@Epictronics1 https://www.youtube.com/watch?v=sXqYadm3b40 - This video he talks about the skinny sprint project. For those unfamiliar, the PC Sprint was a board designed back in the 80s in order to overclock the original IBM PC/XT originally with an 8088 at 4.77mhz. If one just tried to drop a faster crystal in the machine to overclock, the computer won't function - to my understanding the ISA bus, floppy controllers etc just can't handle the higher clock speeds. The PC Sprint board goes in place of the 8284a clock generator chip - what it does is replaces the 8284a with two 8284a chips, along with an extra crystal. This PCB allows for the processor itself to run at a higher clock speed while maintaining the standard crystal/clock speed for the remainder of the hardware. You also need a processor that can run at the faster clock speed - the NEC V20 is a drop in replacement which has some of its own speed advantages, but can run at faster speeds. Can be done to any PC/XT clone/variant that runs the same way, so your 5150, 5155, 5160, PCjr can be upgraded. The difference between the classic PC Sprint design and the newly redesigned one by epictronics just had to deal with the size/shape/footprint. The standard sprint won't fit in all computers. The PCJr for example - the standard board would interfere with the floppy drive assembly. This redesign rearranges things and includes more SMD components for a more compact size. It isn't that difficult of a project to put together. The PCB also includes pin headers to have a reset button functionality, as well as an "on/off" for the overclocking that functions like a classic turbo button. Apparently the floppy drive can sometimes have issues writing at the higher speed, or if you have software that runs too quickly at the higher clock speeds. My first PC to have this mod was my PCjr. I have a soft spot for this machine as it was the first computer I ever used when I was very young. So far to it I have done: Tandymod from texelec to allow for Tandy software compatibility V20 upgrade JR-IDE also from texelec to max out to 736k ram and add IDE functionality (so I have a CF hard drive). And now can add the PC Sprint. The PCJr always felt particularly slow even by 8088 standards. The V20 helped a little bit but still pretty bad for certain applications. The screenshots show the difference between the 4.77mhz and the 8mhz I have it running at (I don't have crystals faster than 24mhz, but seems from epictronics experience the computer gets more unstable at higher speeds). Massive speed difference that is noticable not just on benchmarks but in actual programs. You can actually switch back and forth between turbo and regular speed on the fly, so you can watch your game speed up/slow down in real time. My personal benchmarks end up being the Sierra adventure games. The AGP games (KQ1, 2, 3, SQ 1, 2 etc) were playable at 4.77mhz but a little slow. The SCI games (KQ4, SQ3 and on) were unplayably slow on this machine. They are actually useable now with running at 8mhz and look great in the PCjr graphics modes. Games like monkey island and Loom still too slow but definitely improved performance (sometimes I just load them up to listen to the music from the PCjr sound). Ive also timed the initial ram check - 26 seconds at standard speed, 16s at 8mhz. Overall a super cool project. I like that this was a period-correct way of overclocking these machines whose design still holds true today, they just moved around components. I have a 5150 to restore that I probably will do this mod to (or at least socket the 8284a when I work on the motherboard so I can easily add it in later). My 5155 PC Portable could very much use it too - I added an adlib card but the combination of games+adlib music makes virtually all adlib compatible games unplayable, even with a V20 in there too. Also highly recommend checking out Epictronics youtube channel - tons of vintage apple and IBM projects.