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Join Date: Mar 2002
Posts: 3,563
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Motronic: Injector Impedance?
Excuse the dumb question, but does the OEM '84-'89 Carrera EFI system run high impedance injectors?
What determines whether the injectors used are high or low impedance? Is it the internal injector driver circuitry in the Motronics ECU? I currently run 944turbo injectors in my blown Carrera motor and I want to upgrade to a set of Siemen 55# injectors. I just want to confirm that I need high impedance injectors before spending the $$$. Thanks in advance 
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition 
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01-16-2007, 03:24 PM
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Location: Terre Haute, IN
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Merv:
Porsche used low impedence peak and hold injectors. Yes, the injector driver is the "limiting" factor. In theory and extreme applications the peak and hold has the performance advantage. In all, but the extreme, this isn't an issue today but certainly was 10 years ago. Most the better priced injectors advertised in mag's are high impedance since they are more commonly used in OEM. Ford, GM, Holden, Honda etc. chose to go with the easy/cheaper to fire injectors. You can get conversion boxes to fire a different injector but this will eat the difference in $$ anyways. These were often used by say Mustang racers 10 years ago that went low impendance to find an injector big enough. You typically find very large expensive injectors in PH low impedance. Long story short: DON"T BUY those. keep your PH concept and just buy different aftermarket ones of equal size. Little more for the injector, but less hassle.
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Luke S. 72 RS spirit 2.7mfi, 73 3.2 Hotrod on steelies, 76 993 3.3efi TT, 86 trackrat, 91 C4s widebody,02 OLA winning 6GT2, 07 997TT, 72 914 v8,03 900 rwhp 996TT |
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01-16-2007, 04:59 PM
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Thanks Luke, but I'm confused now
 I was under the impression 944turbo injectors (which I currently use) were high impedance units?
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
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01-16-2007, 06:23 PM
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OK, I just GOOGLED for the 944 Turbo injectors and found they run at around 4.7ohm impedance, which IS low. Thanks, Luke
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
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01-16-2007, 08:23 PM
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Join Date: Dec 1999
Location: TX USA
Posts: 9,804
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Merv,
Bentley manual says 3.2 Carrera injector specs are 2 - 3 Ohms.
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Warren Hall, Jr. 1973 911S Targa ... 'Annie' 1968 340S Barracuda ... 'Rolling Thunder' |
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01-16-2007, 09:07 PM
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Thanks Warren. I actually run 944turbo injectors in my car, but am looking at running some 55# units, for better flow and safety magin
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Merv '89 911 Turbo Cab Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition
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01-16-2007, 10:29 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,126
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I have Siemens 3102's, 55lb injectors in my Carrera.
They are low impedance. I know this is an old thread, just posting for reference. |
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10-16-2011, 06:54 AM
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