Can't give you any real advice here, but Barrie (Midnight Tuning) and Mark D'Sylva (EAT Ultrachips) both make excellent chips for our M42s. I noted that Mark just started offering some really fun E30 bits:
- Now available but not yet on the list below: chip to remove EWS if using a grey label 0 261 200 413 DME in a motor transplant such as into an E30. This performance chip is $239 USD.
- Available: a chip developed for the 2.7 stroker with 10.2:1 CR and 19# injectors. This performance chip is $259 USD.
I
can give you first-hand advice on some of the little things. Updating the injectors, P/S delete, TB hose delete, diluting the coolant to 66% water and running 0w20 synthetic will really perk the car up. I also look for the highest quality synthetic lubes (Mobil1, Valvoline and Redline have all worked well). Fuel is another easy mod. One Marathon by my house has a really good 93 octane mix - according to my logs they're easily 2mpg better than Sheetz, GetGo or other bulk stations. I've heard good things about Shell too, but I'm not sure if that's the same everywhere else.
I also swapped the stock 4.10 for a medium case 3.73 diff. All those changes really helped my fuel mileage - improved by 10% (29 to 33)! Other cheap performance upgrades could include a fresh AGM battery, lower-amp alternator, deleting the engine-driven fan, single-mass clutch, lightweight 14" rims, undertray and lip spoiler, etc.