How difficult to tune for larger injector?
Thread Starter
Drifting
Joined: Aug 2009
Posts: 1,977
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How difficult to tune for larger injector?
I thought it would be as easy as updating the injector constant and then re-tuning VE. But, now I’m reading about injector offset tuning and I know nothing about that!
Why I’m considering a larger injector:
it’s a mostly “while I’m in there” and to have some buffer. It’s a 355 LT1 with LE ported heads and intake, larger valves, and mild cam. I plan on 6400 max but more likely 6200 rpm. I doubt I’m really maxing the 24s with this combo but I did see 90+% DC as I approached 6k rpm. The primary reason is I want to refresh the 30 year old injectors. I was initially going to just have my existing set refurbed by FIC, but then thought having some buffer and bringing down the DC in the high rpm would be nice and was considering the FIC injectors that they hog out to 30 lb.
am I nuts to consider 30# for this combo? Better served keeping 24# and refurbing my existing set? Just what is involved in adjusting the injector offset? My understanding is it is to keep it running smoothly in low rpm by ensuring the injector fires reliably at very small pulse width.
Why I’m considering a larger injector:
it’s a mostly “while I’m in there” and to have some buffer. It’s a 355 LT1 with LE ported heads and intake, larger valves, and mild cam. I plan on 6400 max but more likely 6200 rpm. I doubt I’m really maxing the 24s with this combo but I did see 90+% DC as I approached 6k rpm. The primary reason is I want to refresh the 30 year old injectors. I was initially going to just have my existing set refurbed by FIC, but then thought having some buffer and bringing down the DC in the high rpm would be nice and was considering the FIC injectors that they hog out to 30 lb.
am I nuts to consider 30# for this combo? Better served keeping 24# and refurbing my existing set? Just what is involved in adjusting the injector offset? My understanding is it is to keep it running smoothly in low rpm by ensuring the injector fires reliably at very small pulse width.
Melting Slicks
Joined: Jul 2005
Posts: 2,228
Likes: 302
Not hard at all, once you have the injector data.
If you're looking for 30 lb/hr, I'd get 0280-155-759... they have the exact datasheet so you know you have the correct voltage offsets. I've been running them for a few years now.
https://witchhunter.com/flowdatapix/b0280155759.jpg
They cross reference to Ford Motorsport m-9593-bb302
https://performanceparts.ford.com/pa...9593-bb302.pdf
The voltage offsets are there because injectors behave differently at different voltages. In order for the PCM to get the correct flow rate out of them at all times, it needs to be able to see the vehicle's system voltage and then an accurate voltage offset table so it can factor that into the pulse width calculation.
What you're thinking of is the low pulsewidth offset vs base pulsewidth table. On GM's earlier injectors, as I understand it, they weren't efficient at low pulsewidths, so they'd program in some additional pulsewidth in order to ensure the engine got the correct amount of fuel at low commanded pulsewidths.
What year is your car?
If you're looking for 30 lb/hr, I'd get 0280-155-759... they have the exact datasheet so you know you have the correct voltage offsets. I've been running them for a few years now.
https://witchhunter.com/flowdatapix/b0280155759.jpg
They cross reference to Ford Motorsport m-9593-bb302
https://performanceparts.ford.com/pa...9593-bb302.pdf
The voltage offsets are there because injectors behave differently at different voltages. In order for the PCM to get the correct flow rate out of them at all times, it needs to be able to see the vehicle's system voltage and then an accurate voltage offset table so it can factor that into the pulse width calculation.
What you're thinking of is the low pulsewidth offset vs base pulsewidth table. On GM's earlier injectors, as I understand it, they weren't efficient at low pulsewidths, so they'd program in some additional pulsewidth in order to ensure the engine got the correct amount of fuel at low commanded pulsewidths.
What year is your car?
Melting Slicks
Joined: Mar 2002
Posts: 2,882
Likes: 766
From: Sligo PA
I've tuned for different injectors a few times now. Like ULTM8Z said you just need the injector data. If you're using a GM factory injector instead of aftermarket you can look on other forums like HPTuners or even LS1Tech and find lots of injector data posted online.
Melting Slicks
Joined: Mar 2002
Posts: 2,882
Likes: 766
From: Sligo PA
am I nuts to consider 30# for this combo? Better served keeping 24# and refurbing my existing set? Just what is involved in adjusting the injector offset? My understanding is it is to keep it running smoothly in low rpm by ensuring the injector fires reliably at very small pulse width.
To me if I was going through the trouble of tuning injector data I would go big enough that I knew it would be able to flow enough fuel for mods down the road. You can get GM 42 pounders that run very well. You would need injector hats and wiring adapters but there only around $100 a set.
Thread Starter
Drifting
Joined: Aug 2009
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Likes: 244
Melting Slicks
Joined: Jul 2005
Posts: 2,228
Likes: 302
Yeah, I posted the witch hunter link to show which injectors I was talking about.
As far as buying them, I actually bought a set from these guys last year on ebay and they continue to work flawlelssly.
https://www.ebay.com/itm/32297589449...UAAOSwZd1VbglZ
Southbay Fuel Injectors is another good source if you're not inclined to go with Ebay.
BTW, I have four of the 30 lb injectors left over from this effort...
https://www.corvetteforum.com/forums...l-s-1-4-a.html
PM me if interested. I think your 1994 is sequential EFI, so what I did may not be applicable since you have individual fuel trim capability (mine is batch fire).
But I can probably give you a deal on these four, then you can simply buy four more from Southbay.
As far as buying them, I actually bought a set from these guys last year on ebay and they continue to work flawlelssly.
https://www.ebay.com/itm/32297589449...UAAOSwZd1VbglZ
Southbay Fuel Injectors is another good source if you're not inclined to go with Ebay.
BTW, I have four of the 30 lb injectors left over from this effort...
https://www.corvetteforum.com/forums...l-s-1-4-a.html
PM me if interested. I think your 1994 is sequential EFI, so what I did may not be applicable since you have individual fuel trim capability (mine is batch fire).
But I can probably give you a deal on these four, then you can simply buy four more from Southbay.
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Melting Slicks
Joined: Aug 2003
Posts: 3,407
Likes: 400
From: Lakeville MI
The issue with large injectors is that they will run rich when operating at or below the minimum pulse width even with proper tuning.
The integrator will be reset to 128 and the calculated pulse width will be replaced by the default minimum pulse width. In this situation, the ecm cannot pull fuel. High rpm and light load is worse than idle. Double fire is worse than single fire.
The minimum pulse width and default pulse width settings must also be tuned properly for a given injector in order to minimize this issue.
Here is a log to illustrate the behavior after tuning (350 with (8) 60 lb/hr injectors in double fire mode running on E10 fuel):
https://datazap.me/u/tequilaboy/warm...1996-1587-4147
For most of the log, the integrator is frozen and the car runs rich but is tolerable. Note how the periods with elevated idle speed (2500 rpm) are even worse than the normal 700 rpm idle speed. Keeping the idle rpm as low as possible and retarding spark advance are some methods to cope with richness due to injector and ecm limitations with large injectors.
The integrator will be reset to 128 and the calculated pulse width will be replaced by the default minimum pulse width. In this situation, the ecm cannot pull fuel. High rpm and light load is worse than idle. Double fire is worse than single fire.
The minimum pulse width and default pulse width settings must also be tuned properly for a given injector in order to minimize this issue.
Here is a log to illustrate the behavior after tuning (350 with (8) 60 lb/hr injectors in double fire mode running on E10 fuel):
https://datazap.me/u/tequilaboy/warm...1996-1587-4147
For most of the log, the integrator is frozen and the car runs rich but is tolerable. Note how the periods with elevated idle speed (2500 rpm) are even worse than the normal 700 rpm idle speed. Keeping the idle rpm as low as possible and retarding spark advance are some methods to cope with richness due to injector and ecm limitations with large injectors.
Last edited by tequilaboy; Jan 16, 2024 at 03:01 AM.
Melting Slicks
Joined: Mar 2002
Posts: 2,882
Likes: 766
From: Sligo PA
Thread Starter
Drifting
Joined: Aug 2009
Posts: 1,977
Likes: 244
Melting Slicks
Joined: Jul 2005
Posts: 2,228
Likes: 302