OK, Modifying the HP or any other SFF is difficult, but here's a good start:
I had a similar project this month with the same machine, (HP dc7700 SFF) I needed to upgrade the onboard graphics to something a little better, not top end but better than the onboard system. I spent many hours considering a variety of possible options, only to feel that any GPU upgrade would increase case heat, which in turn may put the PSU & possibly HDD's under pressure, (had never modded one of these before so had to experiment) yes the HP SFF would drive some graphics cards, but common sense and caution indicated some additional cooling would be preferred. However I can confirm that in standard form the HP SFF ran the 4350 without issues, but see following.
So, I had available leftovers from previous projects in the form of the XFX Radeon HD 4350 & the Saphire HD 5450, (both non Fan & 1GB) and purely because of the low current consumption, 19 to 22w max approx', I knew from experience that either would run on the 240w PSU, however I don't like stressing a PSU longer term because it may eventually fail under prolonged pressure and replacements are expensive, and anyway, PSU's deliver less current the hotter they get which is not ideal. I also had 2 x 92mm fans which were good quality units, so no cost for the project if I could utilise these effectively!
With the cards to hand being passive, the issue is the additional heat they may create and the additional PSU heat generated inside the case due to the additional load, though current draw I felt would not be a problem in itself for everyday use with either of the cards above. However I felt gaming and other advanced uses could be better accommodated if the PSU temp could be significantly lowered in line with other components. As I'm a pedant who likes a challenge I decided to try and improve this particular SFF across the board, mainly because many who considered themselves experts said it was a worthless proposition.
My solution after many dozens of hours consideration was as follows, bearing in mind available space was very very little, and low budget was a prime concern also! (I should add I tried several methods before achieving this result which was best by far)
First I established what noise level I was happy with by repeatedly raising and lowering the standard fan speeds in the BIOS (thermal section) using the original system components, for me level 2 was perfect, not too much audible noise as it's on my desktop! Had that not been a requirement I could have increased fan speeds to maximum and job done, only the Mrs to deal with then! However at that level cooling was not I felt as good as it could be, most components were running high middle temps, and under load quickly went to 75%, though even with the 4350 in place they never went above that, manageable but could do to be better.
That established I then looked for a replacement front case fan which could produce more airflow at preferably lower or maximum same noise levels as the standard Delta front case fan, as that was the easiest route to cool, I settled on the Arctic Cooling F9 PWM unit, which comes kitted to retain all features for automatic or manual speed control. That increased the airflow by some 35% for the same noise level, a nice bonus from stage 1 of 2! That mod in itself also reduced the GPU temp not just the CPU & MB temps by a couple of degrees C.
With the cards to hand being passive, the issue is the additional heat they may create and the additional PSU heat generated inside the case due to the additional load, though current draw I felt would not be a problem in itself for everyday use with either of the cards above. However I felt gaming and other advanced uses could be better accommodated if the PSU temp could be significantly lowered in line with other components. As I'm a pedant who likes a challenge I decided to continue and try to improve this particular SFF across the board, mainly because many who considered themselves experts said it was a worthless proposition.
Having considered and discounted after trial & error several additional cooling options, I finally realised that adding anything inside the case was futile as it simply destroyed airflow patterns internally.
That acknowledged I had to look beyond the inside, I soon spotted the perfect answer..I removed the grill over the PSU rear fan exit, then with a few minutes work on the holes in a Xilence 92mm ixtreme Pro Quiet fan, plus removing a little plastic on the fan frame to accommodate one interfering screwhead, I screwed that up to the rear of the case over the PSU fan exit using one of the original screws plus a self tapper into one of the case holes conveniently sitting in exactly the right spot! (only the top two fan fixing holes were used) I had to first use two of the original fanguard screws to hold the original PSU internal fan in place using the bottom two holes. Because the PSU internal case is well vented into the main case on at least 2 sides and is at the top of the case, the additional external fan pulls air right through the case, the resultant modified airflow is very effective.
That completed my "mods", collectively they dropped the internal temps at least several degrees in all departments, and added nothing to the noise levels. The Arctic fan has a little more oomph than the xilence so was used to replace the front case fan on that basis as it's blowing straight into the CPU cooler so needs a little more flow, but that's as required IMHO, as I did not wish to suck the brains out of the internal PSU fan, and the xilence ixtreme Pro really is quiet and perfect for that job, whereas the Arctic fan at the rear may have created more noise blowing straight into the wall 10cms away than it does drawing air into the case.
These simple mods totally changed the cooling dynamics of the dc7700, not only did they significantly improve general case and component temps, they also dragged down the PSU temps which is a huge bonus for running add on GPU's. I think with these two cheap & simple "upgrades" you could fit any number of cards in there and improve gaming performance considerably. This "upgrade" improves cooling throughout, and I believe PSU stability also, it works and is economic too..and of course you could always just stick with the original front case fan for the rear add on fan over the psu exit to reduce costs further!
NOTE: I spliced a standard adaptor multi plug lead into the original floppy drive supply plug to power the additional rear fan, also used this supply to power a USB 3.0 Pci card which feeds a Lindy docking & clone station, the new front PWM fan only needed the 2 lugs shaving off to fit the original MB socket. Finally now I 'm confident of the supply and cooling side I plan to swap out the 4350 for the 5450.
Long winded I know but I hope this helps others "upgrade" a somewhat difficult system case when it comes to performance modding, and without making it noisy.