Injector sizing

[benz-tech]

I just used RC's calculator for fuel inj sizes and it would seem that if I want to make 180bhp then I would need to have 25-28 lb injectors. I'm still using the stock M44 ones and think they might be maxed out. I've read here that someone was told stock was good to 180 but I wonder if that was based on the (incorrect?) assumption that stock ones are 21 lb instead of 18 since my gut thinks Stan had a misprint. Either way I will check the duty cycle on Monday and decide from there. Anyone else run in to this?

[DesktopDave]

I'd like to see more info about this myself, but I have no experience in this area. I agree that there is some confusion about the proper flow rating on the M42 & M44 injectors. Bosch isn't very big on sharing, either. What's the stock pressure on the M44, 3 BAR (43.5PSI)?

[MLM]

Be aware there are differences between years. My 92 m42 had different injectors to my spare 96 engine. I did some research and found they were different sizes. I naively used the larger size. A flow pattern may have been a better assessment.

[Warsteiner]

I don't have exact measurements or documents but am telling you from experience.  When I just tuned my M42 stroker and its making over 210+HP I ran with 24 lb 250-260cc injectors and didn't have a problem at all. Another build I did on a S14 I ran 300-310cc injectors and it was ok for pump gas 93 octane making 320-330HP but when we tuned for race gas 104-110 octane (I don't remember exactly) and got into the 330-340+ range I range out of injector due to the weight of the fuel. The race fuel is much lighter. So the tuner compressed the stock FPR to get more pressure. (It was a weekend, in the middle of nowhere, with no BMW parts store carrying a 5 Bar FPR) Needless to say I needed to retune the 93 octane again on the higher pressure FPR now.

When I was sourcing injectors I spoke with guy who services mine and he said for the BMW's you can't go by the BSFC that is calculated because they run so much more efficiently....Ain't that the truth! LOL

So no definitive info here just my own experiences.

HTH
Cheers,
~Ralph

[benz-tech]

My stupid meter won't read the correct duty cycle.  I will try a scope later this week. Meanwhile, I'm looking for the part number of the stock M44 injector part number to see if I can figure out the actual flow rate. 

[benz-tech]

M44 fuel pressure on Stan's is 3.0bar, I haven't verified.  The stock m44 injector is also 18.3 lbs as well but with an air cup around the base for breather maybe? Dunno, I cut all that off to run in an e30 manifold. Today I just picked up 6 0280 155 832 22.5 lb injectors from a Volvo inline 6. I will set my SAFC to subtract subtract as needed, with a close eye on obd2 data fuel trim percentages. They're a bit larger than I wanted to try at first but for $50 I feel it was worth a shot. Length is perfect, high imp and 4-hole design. Will update as soon as they're in. Once I'm confident confident that I have some headroom,  I will get it off to the dyno for tune.
Oh, and  maybe install the 3.73LSD that I picked up. The stock 3.64 is just too much gear.