tecart

on the 1986 944 turbo, the stock injectors are 37 pound for sure but what OHM are they for sure?

Konstantin

4-5 Ohm

Konstantin

Danno

The injector flow-rates should have a fuel-pressure that goes along with it as well. Using the stock 2.5-bar fuel-pressure the injectors are 37lb/hr. But using the more standardized 3-bar of fuel-pressure, they are 43lb/hr for the same injector.

As for the impedance, I've heard 5.5ohms from a lot of people. I've also measured this exact impedance on a spare injector I have in my garage as well. However, the officlal Porsche DME/KLR manual says they should be 2-3 ohms. What's the story here?

<a href="http://boards.rennlist.com/upload/DMEManualCover.jpg" target="_blank">http://boards.rennlist.com/upload/DMEManualCover.jpg</a>



<a href="http://boards.rennlist.com/upload/BoschInjectorTestPg22.jpg" target="_blank">http://boards.rennlist.com/upload/BoschInjectorTestPg22.jpg</a>

IanM

I'm pretty sure the stock fuel injectors (Bosch 803's) flow 37 lb/hr at 3 bar, not 2.5 bar (and they're 4.8 ohm). Of course, I'm not 100% sure, but I did quite a bit of research when I was shopping around for my 52 lb/hr injectors, and this was confirmed to me by more than one expert. Download Motec's catalog from their website, and check out page 40.

txhedg

I just got my stock 951 injectors back from being cleaned and balanced by RC engineering. Their test results on mine (they have somewhere between 20k and 40k miles on them) came out to 42.9 lb/hr average at a 43psi (2.9 bar)after being cleaned.

IanM

I guess I stand corrected!

aka 951

Good info! Thats a lot of flow for a fatory injector. Maybe thats the reason why many tuners don't recommend upgrading until serious modifications!

aka 951

if you go to...

<a href="http://www.rceng.com/technical.htm" target="_blank">http://www.rceng.com/technical.htm</a>

you can calculate that with 300hp, the stock injectors at 42.9 lb/hr, and at 59 psi of pressure (3 bar regulator + 15 psi of boost), 85% duty cycle, the bsfc is about .57 (which is just about within turbo limits of .60). In other words, a chipped 88 S or 89 needs a 3.0 bar regulator to safely make 300 flywheel hp. A standard turbo will probably be ok with the 2.5 regulator at 15 psi.

tecart

Hold on guys the stock injectors with a 3.0 bar (944s2) fuel pressure regulator reads 38 psi of fuel pressure at idle with the vaccume line on and about 46 with the vacumme line off, at least this was my cars readings today, and with stock 37 pound injectors, now with 52 pound injectors at 3.0 fuel regulator what will my fuel pressure be with vac. hose on and with it off? also what are the OHM of the stock 944 turbo injectors 4.5 or 4-5 ohs? also are you all reporting your fuel pressure readings with the vaccume line on the regulator off? just making sure because your #'s seem too high so it must be with it off, right?

tecart

i'm also trying to figure out with new 52 pound injectors at 20 psi of boost with an adjustable regulator what will my fuel pressure be set at for reaching fuel requirements to get 20 psi boost? thanks

txhedg

tecart- I don't think you are talking about me when you refer to the 3bar reading, but FYI, on my car I have an adjustable FPR, and I set it to about 3 bar at idle with the vacumn line ON.

aka 951

A 3 bar regulator at idle is probably some where around 38psi as you mentioned. This is because of the vaccum in the intake manifold. With the line off, it goes to about 43-44. When the car boosts to 15 psi try 58-59 psi on the injectors.

Danno

[quote]if you go to...http://www.rceng.com/technical.htm

you can calculate that with 300hp, the stock injectors at 42.9 lb/hr, and at 59 psi of pressure (3 bar regulator + 15 psi of boost), 85% duty cycle, the bsfc is about .57 (which is just about within turbo limits of .60).<hr></blockquote>Erick's right on with his calculations here. That's why a lot of us run into that 280-300rwhp barrier with the stock injectors (shows up as high-RPM leanness). That's closer to 325-350 at the crank and we're pushing the injectors well over the advisable 85% duty-cycle. The unreliability of the injectors at high duty-cycles and/or high fuel-pressures makes tuning proper air-fuel ratios difficult at that power level. Getting higher-flow injectors at that point greatly simplifies the tuning and frustration.

BTW, that's 50% more power than stock; a serious increase for stock injectors.

[quote]i'm also trying to figure out with new 52 pound injectors at 20 psi of boost with an adjustable regulator what will my fuel pressure be set at for reaching fuel requirements to get 20 psi boost? thanks<hr></blockquote>I would start on the rich side to be safe. Set the FPR to 50psi @ idle (vacumn line off). This would yield 70psi at max-boost which is about the highest you can expect the injectors to operate reliably. Then do some dyno runs and see what your air-fuel ratio is. If it's rich across the board, turn down the fuel-pressure. If it gets lean up top, then you need to turn down the boost or get larger injectors.

Anyway, I still can't figure out why the DME/KLR manual states the stock injectors as being 2-3ohm when we all measure it around 5ohm?

Konstantin

the DME book has a mistake. The repair manual from 1991 on page 28-29 list 3,5 to 5,5 Ohm.

Konstantin

tecart

well guye huntley racing says that i need bigger injectors and i agree, he said the stock 944 injectors are 37 pound at 3 bar for a normal 944 and 44 pound at 3 bar for the 944 turbo also that the injectors are between 4 and 4.5 OHM further he recommended a 55 pound simens make injector for 600 bucks and they are rated for 10 OHM and run cooler then 2-3 OHM injectors, well i have to decide on $350 or $600 for my injectors also low OHM or high OHM, i dont want to melt the dme solder joints but i want a great idle too, decisions decisions?????