Over the past 3 months I have been mostly driving the 125i, especially during when my own car was getting the M3 subframe and accoutrement installed.
Now before I go any further, lets agree.....it is a slug and will never be a very fast car, but it certainly is a great little car for daily driving. It has very little power but it doesnt really need it when all it has to do get up to speed limits and fit in parking spaces.
As I am taking a sojurn from any further modification to my 135i after a meth system is installed, (at least until the best turbo upgrade option is worked out) so I have been thinking about how to perk up the old N/A 3.0litre 6 for some fun (but also for cheap). Rather than just look at dyno results, what I want from my 125i is to run 13.X second ETs and retain its econo-box DD duties and comfort.
I am also in the process of relocating to Newcastle for 12 months (as work has sent me there) so to keep my sanity I have decided to put some money aside to have this as a pet project/hobby.
1st stage (and last stage)
Tune. This is the biggest bang for buck for these cars. I already have a tune on my 125i that makes about ~20rwkw more than other stock tuned 125s on Peter's Dyno Dynamics machine. This tune (Digi-tec) is still pretty conservative and I am sure there is more hp to be gained from tune only. Once the following mods are done, I will look into getting a customised tune using the Evolve-R system that has been recently released.
Removing the stock exhaust manifold and replacing it with modified LHD (to RHD) headers. From what I have read, the 125i uses ULEV 2 standard cats (US/California) whilst the 130i uses EURO 4 cats (according to RealOEM - look it up if you are dubious) within the exhaust stock manifolds; with the ULEV2 being the most restrictive. Then I would install some Euro 4 HJS 200 cell catalytic converters in the mid pipes. As my wife will be also driving this car, I dont want her to ever
get in shit from police, epa, neighbours etc. for emissions or noise. If we can extend the O2 sensors, and if the cats work as well as the ULEV2 versions, I could just leave the cats without an O2 sim. If they dont work as well, I can also just get them coded out with the flash tune.
3rd stage - Ditched
This could all be a pipe dream/thinking-out-loud exercise but I am a geek who likes a hobby so we shall see how we go. I think increasing the peak output by 15-20rwkw (~165rwkw) and making the car get to that peak quicker would make it a much more rewarding drive.
The best I have been able to get this car on the 400m was 14.4 @ 97mph. That shitty time was mostly due to bald(ish) rear tyres that had no grip what-so-ever, full tank of fuel and a 2.1/2.2 60'. I think with the above mods, better tyres (already have them) and better technique (getting better all the time) I could make 13.X ETs, which I think is pretty good for a N/A 6 3 litre.