Thanks for the good advice. This is part of my goal. I have already found a shop nearby that has a dyno and fine tunes cars for racing. Hopefully they will not laugh at my project. But I definitely want to track the changes and am hoping they are noticeable!
A good friend of mine has a sorta hot-rodded (let's say OEM+) 280SL, not on this forum. It's been his wife's daily driver for like 35 years or so now. Some of the work he's done might interest you.
Ported/polished the head, hotter Euro cam (this was a US-spec car), somehow through head work or whatever he eked out about 2.96L or so displacement . . . a while ago, before I thought it wasn't much use for my 230SL considering its stock tubular headers, I'd contemplated custom headers through Renntech which is somewhat local to me or through Stahl. Both were very interested, Stahl more so, but they weren't local. I just cerakoted them instead. Getting this engine to
breathe will make a difference. Reducing unsprung weight will make a difference - consider the oft-discussed aluminum 'steelies' from the W123 cars (very VERY light) or Maxilite (or similar) bundt repros if that's your thing, though they're getting a bit overpriced. One of our members, Alfred, has some very well-priced aluminum hubcap wheels for sale right now. People have converted your engine to EFI, that's worth some research, if you care to go down that rabbit hole, but it's much more intensive than these other changes. An electronic distributor will make a small difference. There was a guy a while back I talked to who turbocharged your same engine for his unimog. I think it takes 4-5lbs of boost. Also much more intensive, and if it were my car, that would lead me to a cascade of other 'improvements' for longevity (forged pistons and that kind of thing).
I understand what you're wanting to do as I've been there myself on my own car. Mercedes really didn't leave much headroom in this era for modifying their engines. The M180/M130 block is a bit difficult too because of the cooling passage elimination between the cylinders to get that extra displacement, hence the added cooling by the radiator. I'd be concerned about that. To be clear, I am not a mechanic and in fact I don't know much of anything at all, just opining from the people I've spoken to who have poured money into trying to get a little bit more out of these engines.
Another one is you could change the rear end gearing, like putting a 4.08 limited-slip rear axle like I did in my car. I already had a 4.08 but in the small amount of driving I did after putting that in, I enjoyed the change in handling.
All of this
REALLY ADDS UP. W114 cars are not expensive. I'd still strongly encourage you to get an M110. People are more warm to nicely-modified W113s than they are W114s unless you went full-Mechatronik on it. I do not think you will recapture even 50% of the money spent, should you aim to sell it, unless you're replacing parts that are at the end of their service life anyway. It's easy to end up in a cascade of changes and if you really love the car, then great. Otherwise, holy smokes, it's way easier and probably more fun/rewarding modifying another car. I know you're not me and I also hate when people go 'well why don't you just get xyz' (I'm into vintage stereo junk and this happens constantly), but still, I'd rather a C107 or W123 coupe if I wanted to modify things and I wasn't a mechanic or I didn't have a Rudy Klein-sized junkyard to pull things from and experiment. Those cars have a bigger community and more legwork already done for you.
Anyway, bottom line. Get lighter wheels and more direct plug-and-play mods.
There was a discussion about your very car here (a '72 250C) 12-years-ago with some opinions shared by people whose mechanical knowledge I respect greatly, see:
https://www.sl113.org/forums/index.php?topic=17750.0
