David Salama

I am very confused as to which injectors to buy for my 1987 951. I have HR Stage 4 MAF, Stage II Turbo, Powerhaus head, WFHG, no cat, etc. Can everyone who has upgraded their injectors tell me how well they run, who makes them, what model #, and at what price and place that you bought them from. Thank you !!

86944turbo

Some time back, I was faced with a similar problem as you're having. I purchased a MAF form one supplier, turbo from another, cam from another, etc. I could not make it work long term. Sizing injectors while not as complicated as turbo sizing still borders on art form. I use very large Bosch injectors and run well over 5 bar of fuel pressure through them regularly. Some will tell you that 5 bar pressure is dangerous, and it may be unless everything else is correct. Bosch, in particular work very vell under higher pressures, and typically higher pressure results in better fuel atomization. At the end of the day, it is a safe Lambda number that needs to be acheived. That Lambda number will vary by temp, load, RPM, and most importantly boost. The advice I would pass along, is find someone familiar with sizing injectors and with modifications you're going to install & the H/P you expect. If they are experienced at this, they can recommend injectors (stick with Bosch Motorsports, they may cost more, but they perform) and have you're Lambda checked. It is best to do this under all types of conditions. Too rich is almost as bad as too lean. Wear out the rings/cyl. wall & bearings, or burn/drop a valve. What is nice about a good quality adj. fuel pressure regulator is that even if you miss the injector size by a little, the idle pressure can be adjusted, which (with a quality FPR) adjusts fuel pressure throughout the range. But, then you start from scratch again checking Lambda. Lambda should be checked often and analyzed closely.

rage2

Injector sizing / fuel tuning is only tough when you're using factory ECU with one set of chips (be it stock or aftermarket). Because the fuel maps don't change, you're forced to change injector size, fuel pressure, etc to compensate. Getting the proper fuel mixture across the rpm/boost range is next to impossible.

I spent a good year trying to tune my 951 to not run excessively rich at high boost/high rpm's (Autothority chips). The car runs way too lean if I get the high boost/rpm fuel tuned right, so the compromise was to have poor fuel economy when driving hard (at a slight loss of power too).

Finally, at the advice of my Mechanic, I tossed the stock ECU/Autothority chips and went with a standalone fuel management system. I now have MUCH better fuel economy for day to day driving (car runs closed loop at 1500rpm-3500rpm when off boost) and a proper fuel mixture curve throughout the entire rpm range and boost range. I haven't driven extremely hard yet (snow...) so I don't know if economy's been improved when driving hard. And it only took 1 week of fidding before getting it all right.

As for the original question, I'm about a week away from working with 72lb/hr injectors @ 3bar (not rising rate). I'll let you know how it goes once it's up and running.