Should I be running out of injector?
Thread Starter
Joined: Dec 2004
Posts: 1,294
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From: Dallas (Richardson), TX, USA
Should I be running out of injector? Hey all,
I have a 346ci LS1, forged, stock heads, 230/236 cam, Procharged @ 14psi, and it's putting down about 635RWHP running up to 7k RPM. The fuel system is dual in-tank Walbros with an -8AN line to aftermarket rails with Siemens 60# injectors. I have a boost-referenced regulator that's taking it up to about 62psi, and the pressure isn't falling off.
The tuner said that the car was safe, but just barely... he said the injector duty cycle is at about 102-104% at the end of a pull. Does that sound right? I thought the 60#s would go a fair amount further.
Thanks in advance.
I have a 346ci LS1, forged, stock heads, 230/236 cam, Procharged @ 14psi, and it's putting down about 635RWHP running up to 7k RPM. The fuel system is dual in-tank Walbros with an -8AN line to aftermarket rails with Siemens 60# injectors. I have a boost-referenced regulator that's taking it up to about 62psi, and the pressure isn't falling off.
The tuner said that the car was safe, but just barely... he said the injector duty cycle is at about 102-104% at the end of a pull. Does that sound right? I thought the 60#s would go a fair amount further.
Thanks in advance.
A couple comments.. What do you have the IFR set at? [From the info you give, it looks like your base fp is 48psi. 62-boost of 14.]
If that's the case, then the math shows that:
Inj rated at 43.5 and run at 48 is actually a 63# inj.
@ 63#, and a "swag" for FWHP @ 730Hp, duty cycle at 85%, BSFC @ .6, the inj requirement is a 64# inj.
If you would run the inj at 58psi, then you would have a 69# inj.. A bit more cushion....
Bottom line>>>>>>>The tuner hit it dead-on.....
If that's the case, then the math shows that:
Inj rated at 43.5 and run at 48 is actually a 63# inj.
@ 63#, and a "swag" for FWHP @ 730Hp, duty cycle at 85%, BSFC @ .6, the inj requirement is a 64# inj.
If you would run the inj at 58psi, then you would have a 69# inj.. A bit more cushion....
Bottom line>>>>>>>The tuner hit it dead-on.....
Actually the 60's flow approx 63 at 43.5psi.
Approx 72# at 58psi base.
At .55bsfc you are at 131hp/cyl *8 = 1048 flywheel or about 875rwhp.
with a 58# base pressure, I have seen the 60's reach near 900rwhp to validate this.
Your numbers do not sound correct unless you are running a very low base pressure.
Approx 72# at 58psi base.
At .55bsfc you are at 131hp/cyl *8 = 1048 flywheel or about 875rwhp.
with a 58# base pressure, I have seen the 60's reach near 900rwhp to validate this.
Your numbers do not sound correct unless you are running a very low base pressure.
What do you have the IFR set at? [From the info you give, it looks like your base fp is 48psi. 62-boost of 14.]
If that's the case, then the math shows that:
Inj rated at 43.5 and run at 48 is actually a 63# inj.
@ 63#, and a "swag" for FWHP @ 730Hp, duty cycle at 85%, BSFC @ .6, the inj requirement is a 64# inj.
If you would run the inj at 58psi, then you would have a 69# inj.. A bit more cushion....
Bottom line>>>>>>>The tuner hit it dead-on.....
If that's the case, then the math shows that:
Inj rated at 43.5 and run at 48 is actually a 63# inj.
@ 63#, and a "swag" for FWHP @ 730Hp, duty cycle at 85%, BSFC @ .6, the inj requirement is a 64# inj.
If you would run the inj at 58psi, then you would have a 69# inj.. A bit more cushion....
Bottom line>>>>>>>The tuner hit it dead-on.....
Thread Starter
Joined: Dec 2004
Posts: 1,294
Likes: 0
From: Dallas (Richardson), TX, USA
The fuel pressure is hard to explain. It's a 1:1 boost reference, but the result isn't exactly what you'd expect. It may be pushing 61psi of fuel pressure at 14psi of boost, but at 12psi of vacuum, it's not showing the expected 61 - 14 -12 = 35psi. At 12psi of vacuum, it shows more like 44psi of pressure. It's not that the fuel pumps are keeping up, it's the opposite... it's that the FPR literally can't bleed it fast enough to bring it down to where it's supposed to be. For example, if I pull the vacuum hose from the FPR, it may show 51psi, but when I put the hose on at 12psi of vacuum, it'll show 46psi.
So, anyway, I know I'm not running out of pump because the pressure will go as high as I want it to if I adjust the regulator accordingly. However, the tuner is saying the injectors are done.... I just can't believe that. I know that Prochargers tend to require more injector (because while the RWHP might be 650, the engine is producing more like 750RWHP but is losing the difference to the drain from the blower), but I can't believe it's that drastic.
So, anyway, I know I'm not running out of pump because the pressure will go as high as I want it to if I adjust the regulator accordingly. However, the tuner is saying the injectors are done.... I just can't believe that. I know that Prochargers tend to require more injector (because while the RWHP might be 650, the engine is producing more like 750RWHP but is losing the difference to the drain from the blower), but I can't believe it's that drastic.
You need to pull the vac line off with the car running & set the pressure to 58. Reattach the line & it will drop.... this is OK.
It should then increase with boost from 58 up to appprox 72 at 14psi boost.
Also vacuum is in inches not psi.... it is not 1:1, but approx half. Meaning 15" vac will drop pressure about 7.5psi.
You should have enough injector then.... obviously retuning will be required.
It should then increase with boost from 58 up to appprox 72 at 14psi boost.
Also vacuum is in inches not psi.... it is not 1:1, but approx half. Meaning 15" vac will drop pressure about 7.5psi.
You should have enough injector then.... obviously retuning will be required.
Thread Starter
Joined: Dec 2004
Posts: 1,294
Likes: 0
From: Dallas (Richardson), TX, USA
I purchased HP Tuners and started doing some logging, and I've found that at about 5900RPM pushing somewhere on the order of 11psi of boost, the car is at 88% duty cycle. Since it makes about 61psi of fuel pressure at 14psi, I'd say it's at about 58psi of fuel pressure at that RPM. I can't say for sure because I don't have the ability to log the fuel pressure yet.
I realize that I need to bring up the fuel pressure to 58psi at atmospheric pressure, but will doing so make that big of a difference in injector duty cycle?
I realize that I need to bring up the fuel pressure to 58psi at atmospheric pressure, but will doing so make that big of a difference in injector duty cycle?
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You need to pull the vac line off with the car running & set the pressure to 58. Reattach the line & it will drop.... this is OK.
It should then increase with boost from 58 up to appprox 72 at 14psi boost.
Also vacuum is in inches not psi.... it is not 1:1, but approx half. Meaning 15" vac will drop pressure about 7.5psi.
You should have enough injector then.... obviously retuning will be required.
It should then increase with boost from 58 up to appprox 72 at 14psi boost.
Also vacuum is in inches not psi.... it is not 1:1, but approx half. Meaning 15" vac will drop pressure about 7.5psi.
You should have enough injector then.... obviously retuning will be required.
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