TPI Batch Fire Question
Thread Starter
Drifting
Joined: Jan 2001
Posts: 1,408
Likes: 13
From: Dayton, Ohio
TPI Batch Fire Question
As most of us know, our beloved TPI systems are a "batch fire" system,
meaning that when the injectors are triggered, they do so in groups of
2-4-6-8 and 1-3-5-7. We also know that since the introduction of the LTx engines, FI systems have been using a sequential fire system. This fires off the injector in sync with the opening of the corresponding valve
and as such reduces fuel drop.
While I don't know of any way to convert our L98's to sequential, how about re-arranging things to work more closely with the mechanical timings of the engine components? IF I understand things, our injectors fire as I stated above, 1-3-5-7 and 2-4-6-8 while our firing order is
18436572. Ok, so would it work if the injectors were wired to fire 1-8-4-3 and 6-5-7-2?
I certainly recognise the fact that even at moderate engine speeds, things occur VERY quickly inside. But if it were of no value, why is the general still using sequential systems when they have the habit of using
last years idea whenever possible?
Constructive comments are very welcome...........
meaning that when the injectors are triggered, they do so in groups of
2-4-6-8 and 1-3-5-7. We also know that since the introduction of the LTx engines, FI systems have been using a sequential fire system. This fires off the injector in sync with the opening of the corresponding valve
and as such reduces fuel drop.
While I don't know of any way to convert our L98's to sequential, how about re-arranging things to work more closely with the mechanical timings of the engine components? IF I understand things, our injectors fire as I stated above, 1-3-5-7 and 2-4-6-8 while our firing order is
18436572. Ok, so would it work if the injectors were wired to fire 1-8-4-3 and 6-5-7-2?
I certainly recognise the fact that even at moderate engine speeds, things occur VERY quickly inside. But if it were of no value, why is the general still using sequential systems when they have the habit of using
last years idea whenever possible?
Constructive comments are very welcome...........
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
As most of us know, our beloved TPI systems are a "batch fire" system,
meaning that when the injectors are triggered, they do so in groups of
2-4-6-8 and 1-3-5-7. We also know that since the introduction of the LTx engines, FI systems have been using a sequential fire system. This fires off the injector in sync with the opening of the corresponding valve
and as such reduces fuel drop.
While I don't know of any way to convert our L98's to sequential, how about re-arranging things to work more closely with the mechanical timings of the engine components? IF I understand things, our injectors fire as I stated above, 1-3-5-7 and 2-4-6-8 while our firing order is
18436572. Ok, so would it work if the injectors were wired to fire 1-8-4-3 and 6-5-7-2?
I certainly recognise the fact that even at moderate engine speeds, things occur VERY quickly inside. But if it were of no value, why is the general still using sequential systems when they have the habit of using
last years idea whenever possible?
Constructive comments are very welcome...........
meaning that when the injectors are triggered, they do so in groups of
2-4-6-8 and 1-3-5-7. We also know that since the introduction of the LTx engines, FI systems have been using a sequential fire system. This fires off the injector in sync with the opening of the corresponding valve
and as such reduces fuel drop.
While I don't know of any way to convert our L98's to sequential, how about re-arranging things to work more closely with the mechanical timings of the engine components? IF I understand things, our injectors fire as I stated above, 1-3-5-7 and 2-4-6-8 while our firing order is
18436572. Ok, so would it work if the injectors were wired to fire 1-8-4-3 and 6-5-7-2?
I certainly recognise the fact that even at moderate engine speeds, things occur VERY quickly inside. But if it were of no value, why is the general still using sequential systems when they have the habit of using
last years idea whenever possible?
Constructive comments are very welcome...........
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".
Safety Car
Joined: Apr 2002
Posts: 3,531
Likes: 1
From: Conroe TEXAS!
Cruise-In X Veteran
interesting however, tpi's from gm fire all 8 at once contrary to popular belief. The 2 fuses are for the load but the grounds for all 8 are common. Here's an excerpt from gm performance. I was always under the same impression untill I put on two noid lights on the oppisite banks.
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".
So much for re-inventing the wheel.
Melting Slicks
Joined: Dec 2006
Posts: 3,374
Likes: 86
From: Corbin KY
What is really amazing is that the L98 gets the mileage that it does firing all 8 at once. I always wonder what % better it would get if it were sequential when I thought it was batch (bank) fire also, that % just went way up. Thanks to FIC for not only good products but good information.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Consider that even at 600rpm, assuming fireing once per rev, the injectors fire every .1sec; I don't think there will be much fuel loss up the intake runner in that time period, which is the only "escape path" for the fuel assuming the intake valve is closed.
The only way "improvement" could come is if an intake valve were partially open when fuel is injected; then sequential injection just before valve opening would benefit in power/economy.
The only way "improvement" could come is if an intake valve were partially open when fuel is injected; then sequential injection just before valve opening would benefit in power/economy.
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Drifting
Joined: Dec 2005
Posts: 1,313
Likes: 2
From: High Ridge Missouri
No point to converting it.
Even the early LT1s (92-93) were batch fire.
Now knowing that what performance, emission, milage or even idle characteristic differences are there between a 93 batch fire LT1 and a 94 sequentally pulsed LT1 the answer is none. The main reason for going to sequential fire was for the future implementation of OBD2 diagnositics with missfire diagnostics, not for performance.
Even the early LT1s (92-93) were batch fire.
Now knowing that what performance, emission, milage or even idle characteristic differences are there between a 93 batch fire LT1 and a 94 sequentally pulsed LT1 the answer is none. The main reason for going to sequential fire was for the future implementation of OBD2 diagnositics with missfire diagnostics, not for performance.
Safety Car
Joined: May 2002
Posts: 4,010
Likes: 26
From: Somewhere nowhere
that;s interesting, even with noid lights, could the human eye detect even if the firing was a milli second off?
you would need an oscilloscope to see it I would think.
you would need an oscilloscope to see it I would think.
interesting however, tpi's from gm fire all 8 at once contrary to popular belief. The 2 fuses are for the load but the grounds for all 8 are common. Here's an excerpt from gm performance. I was always under the same impression untill I put on two noid lights on the oppisite banks.
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".
"Most early EFI systems were batch-fire systems where the ECM fired all eight injectors simultaneously. Usually batch-fire systems fire the injectors once per engine revolution. This way, the injectors could be sized small enough to be more easily controlled at idle. Later, sequential EFI systems were refined to fire an injector a few degrees before the intake valve opened. Generally, sequential injection offers more precise fuel control at the price of increased complexity. But on production engines, the benefits are more in the area of emissions and driveability than in performance".
Thread Starter
Drifting
Joined: Jan 2001
Posts: 1,408
Likes: 13
From: Dayton, Ohio
It looks as if I've once again learned something here on the forum.
As I said, the events that occur inside an engine happen at a high rate of speed, so it's no wonder that there's little to be gained by going sequential. Thanks for the help on this. This and ?'s like it are some of those things I end up wasting my daydreams on, when I could put them to use trying to increase performance on ..... something...
Thanks guys, I do appreciate the responses. Bob
As I said, the events that occur inside an engine happen at a high rate of speed, so it's no wonder that there's little to be gained by going sequential. Thanks for the help on this. This and ?'s like it are some of those things I end up wasting my daydreams on, when I could put them to use trying to increase performance on ..... something...
Thanks guys, I do appreciate the responses. Bob
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 14
From: backwoods upstate ny
"all-out" small and big-block racing engines have used "constant flow" injections from hilborn/kinsler/etc for decades, strictly "mechanical" with ZERO electronics..."idle" below 1k rpm is "iffy" due to radical cams + difficult triming of fuel flow, but top end power is very "satisfactory"
Last edited by redrose; Oct 24, 2008 at 10:32 AM.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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No point to converting it.
Even the early LT1s (92-93) were batch fire.
Now knowing that what performance, emission, milage or even idle characteristic differences are there between a 93 batch fire LT1 and a 94 sequentally pulsed LT1 the answer is none. The main reason for going to sequential fire was for the future implementation of OBD2 diagnositics with missfire diagnostics, not for performance.
Even the early LT1s (92-93) were batch fire.
Now knowing that what performance, emission, milage or even idle characteristic differences are there between a 93 batch fire LT1 and a 94 sequentally pulsed LT1 the answer is none. The main reason for going to sequential fire was for the future implementation of OBD2 diagnositics with missfire diagnostics, not for performance.
The later was explained to me a couple of years ago, but I had a hard time with it. And, I think there's still room for improvement, Bob. I think injectors that atomize the fuel best will provide much of the improvement you might have hoped to get thru a conversion to sequential firing.
Reports from owners who've converted to the BoschIII type injector (as documented by FIC) have shown that atomization is an issue where you might want to focus your attention. At least that seems more promising.
