advantage to using newer GM Injectors?

[Rhedalert]

Theoretically speaking,

I'm running '98 3400 Injectors on my Olds. These are the older style Multec's running around 40psi. The engine I'm using is from an '01 Impala, so I have in storage the injectors, which are the newer Rochester style, the FPR which runs 50ish PSI and I think I have the harness. With the higher pressure and different design, are they any better at atomizing fuel? Can I expect an increase in efficiency from switching to them? I can tune for the injectors at any time, so that really isn't an issue. Just curious if it's worth the swap. Thanks for any help!!

[IsaacHayes]

If you can tune for them I would run them. They probably run at a lower duty cycle with the higher pressure. Have you tuned for the 3400 injectors you are running now? What lb/hr are they?

Since you already have the 3400 injectors in there and if it's tuned for them I don't see much point in swapping to the new style other than they might be in better shape and might have a better spray pattern. I'd have to search again I can't remember what changed on the multec2's

[johnnymossville]

According to the 60*v6 site these are the current injector flow rares.

Engine Years Description RPO Type Flow PSI
2.8 MPFI 85-86 Iron Head VIN W LB8 Multec 1 15# 43.5 PSI
2.8 MPFI 85-88 Iron Head Fiero L44 Multec 1 ??# 43.5 PSI
2.8 MPFI 85-90 ?? LB6 Multec 1 ??# 43.5 PSI
3.4 MPFI 93.95 Iron Head L32 Multec 1 17# 43.5 PSI
3.1 TBI 87-96 Iron Head LG6 TBI ??# ?? PSI
3.1 MPFI 90-94 Aluminum Head, VIN T LH0 Multec 1 16.6# 43.5 PSI
3.1 MPFI Turbo 90-91 Aluminum Head, VIN V LG5 Multec 1 22# 43.5 PSI
3.4 DOHC MPFI 91-93 Aluminum Head, VIN X LQ1 Multec 1 21# 43.5 PSI
3.4 DOHC SFI 94-95 Aluminum Head, VIN X LQ1 Multec 1 21# 43.5 PSI
3.4 DOHC SFI 96-97 Aluminum Head, VIN X LQ1 Multec 1 21# 43.5 PSI
3100 SFI 94-99 Aluminum Head VIN ? L82 Multec 1 19# 43.5 PSI
3100 SFI 00-05 Aluminum Head VIN ? LG8 Multec 2 22.5# 55 PSI
3400 SFI 96-99 Aluminum Head VIN ? LA1 Multec 1 19# 43.5 PSI
3400 SFI 00-05 Aluminum Head VIN ? LA1 Multec 2 22.5# 55 PSI
3500 SFI 05-07 Aluminum Head VIN 8 LX9 Multec 2 24# 55 PSI

As you see the early 3400 inj. are Multec 1s and are 19 lbs. at 43.5 psi and the 2000 plus inj. are Multec 2s and are rated at 22.5 lbs. at 55 psi using the "00+ FPR. I imagine that you would have to do a little more tuning but it could be worth it.

[IsaacHayes]

Ah so the early 3400's ECM's must work them injectors harder then.

I guess the real question is how is your ECM tuned as of now?

[Rhedalert]

ECM is in good shape since I tuned with with the DHP powertuner. I had my current injectors serviced by witchhunter:




I haven't calculated the duty cycle on them yet. I have the fuel trims tuned to within -4 to 0. The newer injectors I never had serviced, but they're low mileage, around 40k, seem to be in good shape.

[Rhedalert]

Another thought... could I run the older 43 psi injectors with a 55 psi fuel delivery? I can tune the PCM so it won't run rich. Just thoughts going thru my head regarding increasing efficiency.

[johnnymossville]

According to the flow rate calculator on Witch hunter's site if you run the 19 lb. Multech 1s at 55 psi they will then be equal to 21.36 lb injectors, so you might have to tune it again. I believe that they would be more efficient because they wouldn't have to work as hard to produce the same amount of fuel. What is your duty cycle now at WOT near max RPM? If you are not near 80% then every thing is OK as you are running it now.

[Rhedalert]

I actually haven't calculated the duty cycle. I need to look up the method of doing that, unless someone here knows how to.

[Superdave]

I actually haven't calculated the duty cycle. I need to look up the method of doing that, unless someone here knows how to.

PULSEWIDTH / ((60 /RPM ) * 1000) * 100

[Rhedalert]

I scanned this morning, and under WOT it touched just over 19 ms at around 5500 rpm, so:

19/((60/5500)*1000)*100) = 0.01743 nothing that makes sense. Maybe order of operations is incorrect?

I found this site http://www.stealth316.com/2-calc-idc.htm

5500 rpm, 19 ms pulsewidth gives me 87% duty cycle. I guess it's high enough to suggest running a higher pressure?

[3400-95-Modified]

Either a higher pressure or a larger injector.

IIRC you have a walbro pump but if you dont I wouldn't suggest the high pressure, the pump may not be able to handle it.

[IsaacHayes]

Even swapping to the newer ones, they run at a higher pressure, so don't both injectors work out to be about the same when both ran at same pressure?

FWIW my FPR is 38psi at idle and 46psi with the vacuum tube off.

[3400-95-Modified]

Not sure, when I sent out my injectors I had them bench them at 55PSI since that was what they are supposed to be set at, and I got pretty darn close to 28# hr for flow numbers. But yes I assume if you were to drop the pressure the lb/hr rating would also go down resulting in close to the same injector.

He might want to just go to a M1 version of a high flow injector and scratch the high pressure pencil style ones.

[IsaacHayes]

Yeah that's what I was thinking, just go to a larger injector and forget with tweaking the ones he has. I guess the cam and exhaust is enough to bring the duty cycle up really high. That or they already were very high on the old 3400 setups from the factory. Personally I would just run what you have since you know they've been flown and checked out. If they crap out then upgrade.

I'm still running my 200,000 mile injectors and coil packs. Every port and spark plug shows it's running great.

[Superdave]

i was at about 92% duty cycle with my 32#'s at 43 PSI.. bumped it up to 55 PSI and sitting around 75% or so @ 36lb/hr.

It helps...