90 lb Injectors
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90 lb Injectors
Simple question. I'm running 80 lb injectors on my 383 Vortec TBI setup. Would 90 lb injectors provide any improvement? I'm running GMPP Vortec Intake, Holley 670 TBI w/OEM pod, 255 l/hr fuel pump, & custom tuning. I understand that I would have to re-tune.
Last edited by fadetoblack; 05-14-2006 at 05:54 AM.
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If you cannot get enough fuel with your present injectors is when you want to increase the size.
Sorry but I am going to give you more questions than answers to begin with.
Are you running lean? Do you have any data logging capibility and or a Wide Band? What kind of "custom " tuning do you have? Are you doing it yourself? What cam are you running?
DM
Sorry but I am going to give you more questions than answers to begin with.
Are you running lean? Do you have any data logging capibility and or a Wide Band? What kind of "custom " tuning do you have? Are you doing it yourself? What cam are you running?
DM
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Originally Posted by fadetoblack
Simple question. I'm running 80 lb injectors on my 383 Vortec TBI setup. Would 90 lb injectors provide any improvement? I'm running GMPP Vortec Intake, Holley 670 TBI w/OEM pod, 255 l/hr fuel pump, & custom tuning. I understand that I would have to re-tune.
Ball parking the fuel flow requirement going by the 1HP/CI value. And a .45 BSFC value, both of which are reasonable by todays standards. We can calculate the fuel flow requirement:
383 HP @ .45 BSFC is: 383 * .45 = 172 #/hr of fuel
Staying within 85% duty cycle: 172 / .85 = 203 #/hr fuel flow
Then two injectors, so divide by 2: 203 / 2 = 101.5 #/hr per injector
To get that from 80 #/hr injectors need to raise the fuel pressure to: psi = 11.5 * sq(101.5 / 80) (11.5 being the fuel pressure for 80 #/hr)
19 psi = 11.5 * sq(101.5 / 80)
To ensure enough fuel to cover transients such as AE (pump shot) I'd just go with 21-22 psi. Stock GM TBI injectors and pod will operate in excess of 30 psi. So there is still room for growth.
This calculation ignores the RPM requirements. If staying below 6,000 RPM there won't be a problem.
RBob.
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#8
Re: 90 lb Injectors
As others have mentioned it depends upon the setup. Can patch the data stream and log the PW, along with WB data, this would tell you whether more fuel is required. Not knowing what cam/valve-train/exhaust the engine has, we can still run some numbers.
Ball parking the fuel flow requirement going by the 1HP/CI value. And a .45 BSFC value, both of which are reasonable by todays standards. We can calculate the fuel flow requirement:
383 HP @ .45 BSFC is: 383 * .45 = 172 #/hr of fuel
Staying within 85% duty cycle: 172 / .85 = 203 #/hr fuel flow
Then two injectors, so divide by 2: 203 / 2 = 101.5 #/hr per injector
To get that from 80 #/hr injectors need to raise the fuel pressure to: psi = 11.5 * sq(101.5 / 80) (11.5 being the fuel pressure for 80 #/hr)
19 psi = 11.5 * sq(101.5 / 80)
To ensure enough fuel to cover transients such as AE (pump shot) I'd just go with 21-22 psi. Stock GM TBI injectors and pod will operate in excess of 30 psi. So there is still room for growth.
This calculation ignores the RPM requirements. If staying below 6,000 RPM there won't be a problem.
RBob.
Ball parking the fuel flow requirement going by the 1HP/CI value. And a .45 BSFC value, both of which are reasonable by todays standards. We can calculate the fuel flow requirement:
383 HP @ .45 BSFC is: 383 * .45 = 172 #/hr of fuel
Staying within 85% duty cycle: 172 / .85 = 203 #/hr fuel flow
Then two injectors, so divide by 2: 203 / 2 = 101.5 #/hr per injector
To get that from 80 #/hr injectors need to raise the fuel pressure to: psi = 11.5 * sq(101.5 / 80) (11.5 being the fuel pressure for 80 #/hr)
19 psi = 11.5 * sq(101.5 / 80)
To ensure enough fuel to cover transients such as AE (pump shot) I'd just go with 21-22 psi. Stock GM TBI injectors and pod will operate in excess of 30 psi. So there is still room for growth.
This calculation ignores the RPM requirements. If staying below 6,000 RPM there won't be a problem.
RBob.
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Re: 90 lb Injectors
I would guess you are missing some step or have some operation out of order.
Injector flow with pressure change is
(SqRT(NewPsi/Factory PSI)) × Flow Rate
So if you factor that GM flow rates TBI injectors at 11-12 psi (guessing why he used 11.5 since nobody can seem to actually agree). At 22 psi those 80 lb/hr injectors are about 108 lb/hr each.
Injector flow with pressure change is
(SqRT(NewPsi/Factory PSI)) × Flow Rate
So if you factor that GM flow rates TBI injectors at 11-12 psi (guessing why he used 11.5 since nobody can seem to actually agree). At 22 psi those 80 lb/hr injectors are about 108 lb/hr each.
#10
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Re: 90 lb Injectors
When I was setting up my new motor recently, I wanted to know exactly what PSI it took to flow my 90# injector at 90#. I took the injextors to a friend that does nothing but injectors and put them on the injector flow tester and they needed 14.8PSI to flow 90#, checked them several times to get an accurate reading. That is the number I used to calculate what to use to set my fuel pressure up for my engine. Based on that number (14.8), my 383 needed 24.5psi fuel pressure to support 438HP and flows 116#phr each and which is really close to the HP I got on the dyno. DC was hoovering around 85% - 88% which I'm OK with.
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Re: 90 lb Injectors
When I was setting up my new motor recently, I wanted to know exactly what PSI it took to flow my 90# injector at 90#. I took the injextors to a friend that does nothing but injectors and put them on the injector flow tester and they needed 14.8PSI to flow 90#, checked them several times to get an accurate reading. That is the number I used to calculate what to use to set my fuel pressure up for my engine. Based on that number (14.8), my 383 needed 24.5psi fuel pressure to support 438HP and flows 116#phr each and which is really close to the HP I got on the dyno. DC was hoovering around 85% - 88% which I'm OK with.
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Re: 90 lb Injectors
To get that from 80 #/hr injectors need to raise the fuel pressure to: psi = 11.5 * sq(101.5 / 80) (11.5 being the fuel pressure for 80 #/hr)
Divide 101.5 by 80 = 1.26875
Square it: 1.26875 * 1.26875 = 1.6097265625
And multiply by 11.5: 1.6097265625 * 11.5 = 18.5 psi
I used 11.5 psi as the fuel pressure as it is around the middle of the 9 - 13 psi GM based acceptable service pressure. Using 13 psi is likely a better choice.
RBob.
#13
Re: 90 lb Injectors
I would guess you are missing some step or have some operation out of order.
Injector flow with pressure change is
(SqRT(NewPsi/Factory PSI)) × Flow Rate
So if you factor that GM flow rates TBI injectors at 11-12 psi (guessing why he used 11.5 since nobody can seem to actually agree). At 22 psi those 80 lb/hr injectors are about 108 lb/hr each.
Injector flow with pressure change is
(SqRT(NewPsi/Factory PSI)) × Flow Rate
So if you factor that GM flow rates TBI injectors at 11-12 psi (guessing why he used 11.5 since nobody can seem to actually agree). At 22 psi those 80 lb/hr injectors are about 108 lb/hr each.
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Re: 90 lb Injectors
Here is a psi calculator , if your 80 #hr at 11.5 your 110#hr at 22psi.
http://www.megamanual.com/v22manual/minj.htm
http://www.megamanual.com/v22manual/minj.htm
#15
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Re: 90 lb Injectors
They are not 80# injectors. These are 90# from a 454 truck motor which if you look at those from injector dealers are rated at 15psi, not 9-13 like stock CF injectors. Mine flow 90# at 14.8, close enough and that's what I use.
#16
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Re: 90 lb Injectors
Here is a psi calculator , if your 80 #hr at 11.5 your 110#hr at 22psi.
http://www.megamanual.com/v22manual/minj.htm
http://www.megamanual.com/v22manual/minj.htm
That sounds just about right, since Jim at DCS runs his 383 with 80# injectors @22psi.
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Re: 90 lb Injectors
No such thing as true 90 lb/hr injectors from GM. What you have are 80#. Even the 454SS had 80# at stock fuel pressure. They do flow 90# at 15 psi, but that is not what the OEM regulator was set at. Highest factory pressure I have seen on the low pressure stuff was 14 psi on a 1992 G20 van 350. All the TBI engines had the same spec fuel pressure except the 30 psi regulated stuff.
#18
Re: 90 lb Injectors
I see what I did wrong now. I though "sq(101.5 / 80)" meant I had to take the square root of this number as there is no square root symbol on standard keyboard. I really appreciate the answers I got here. This has been a tremendous help. The mega manual is a really good source of information too. I thank everyone who responded.
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Re: 90 lb Injectors
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