Obviously the most important factor is how much hp you plan to make before deciding injector size, but once you have an idea is there a rule of thumb on injector duty cycle?

I found this from another forum members post;

http://injector.com/injectorselection.php

According to this you do not want to go over 80% duty cycle, so for my set up I am looking to be around 725 flywheel hp which according to the formula suggest that I should use 72lb injectors? Is this too much injector for an eforce? Does it make more sense to just go with the bigger injector, is it safer, or can it cause other issues?

 

What do you have for fuel system currently?

 

It "can" cause issues if you go too big and don't know the injector's parameters and most injector manufacturers don't list the specs, at least not in gen 4 GM table format. Typically rough idle and off idle situations arise because the injector, or the injector parameters, will not be able to let a small enough amount of fuel in. I prefer enlarged GM injectors from the Fuel Injector Connection. Others will argue that its not "correct" but I run stock injector parameters except for the flow rate table because I am using stock LS2 injectors enlarged to 60#/Hr @ 3 bar of fuel pressure. Because the injector body and coil is the same I don't see why the other parameters would be different.

Another issue with going bigger is that the injector flow rate table caps at 63.5#/hr. So even with 60#'ers your fuel flow is off (60#'ers flow 69# @ 4 bar of fuel pressure) and thus your airflow numbers not accurate either but it's not far off. if you have 80#'ers your fuel flownumbers are further off and thus your airflow numbers. This gets to be more of an issue with automatics. If airflow is artificially low then calculated torque is also and shift pressure tables do not dictate the correct pressure. There are ways to tune around all of this if you know how.

With all that said I think 60#'ers will be enough for you. 725 flywheel is roughly 625 wheel and 60's will support that and stay under 80% IDC. I don't really buy into the 80% IDC rule. IMO as long as you're under 100% you're good in my book. Now having said that, it doesn't seem worth it to upgrade from the 52's? that come with the e-force to 60's. FIC has enlarged LSx injectors that would drop right in that flow, 60, 72, 80 and even 90#/hr.

I don't think I cleared anything up for you. Probably just muddied the water even more. Sorry.

 

That actually helps quite a bit, a little confusing but I get the point. I do know of guys running Andy's kit and they ran out of fuel pretty early with the 52lb inj. so I don't see using them, specially if I end up in the 650rwhp range. I did not know that the flow tables capped at 63.5, thats good to know.

I too know a lot of guys going over 80% with no problems, I figured 60's would be enough I just wanted to make sure. Do they make a 62lb? Thanks

 

Nothing yet but I plan to go with the HOB A1000 pump that they are working on.

 

I spoke with Seth at Hensen MSP today and I think I will go with the FAST 65#. They are designed for the LS3 and I definitely won't run out of fuel with these. He said there is no issue tuning these.

 

Double check because I want to say FAST rates their injectors at 4 bar. I recall something to that effect.

I'm tellin' ya.....FIC.

 

I checked FASTs site and their GM injectors are rated at 4 bar. So any other time you hear 60#'ers they mean 60#/hr at 3 bar but FAST does you a "favor" and rates them at 4 bar. I don't see 65#'ers in their GM section so maybe he's referring to the FAST 65# low impedance injectors. It doesn't say what pressure those are rated at so I'd be

 

Seth said they were rated at 58psi and they are not low impedance. I am not familar in 3 and 4 bar what exactly does that mean? And who is FIC?

Here is the link http://www.hinsonsupercars.com/p-646...ls7l92l76.aspx

 

I found FIC... great selection! Is there much if any difference between the Bosch, Siemens, and FAST? The injectors on FIC go from 60 to 72# and my thinking is the 65# would be the best because it will keep me at 90% duty cycle. Whats your thoughts?

http://www.hinsonsupercars.com/s-533...injectors.aspx

 

All injectors are rated at 3 bar (43.5 PSI) of fuel pressure. Except for FAST; they rate theirs at 4 bar (58 PSI) of fuel pressure.

So when I say I have 60# motrons or 60# siemens injectors they flow 60#/hour with 3 bar of fuel pressure. Our cars run at 4 bar of fuel pressure so those 60# injectors really flow 68#/hr. An injector which was rated at 65# @ 58 PSI os fuel pressure flows 56# at 43.5 PSI of fuel pressure. So you would be spending four bills on injectors that flow 4#/hr more than yours.

FIC is The Fuel Injector Connection, a forum vendor that sells aftermarket injectors as well as specializing in enlarging stock injectors.

 

Call Jon @ FIC and tell him what you are trying to do. He will set you up. I would go with at least 72#'ers (rated at 3 bar )

 

So if they are 72#ers at 3 bar they actually flow 81#s at 4 bar?

And are you suggesting the GM injectors or Siemens?

 

I am getting it now, I went to FIC's flow chart and injector sizing and at 740 bhp would put me at a rating of 69.375 at 43.5 psi, add that to the other chart showing the psi from 43.5 to 58 puts me right at 60lb injectors.

What do ya know I learned something today, thanks for all your help Bill!

 

If I were after your goal, I'd go with the Siemens 82's so many of us have run, lots of data on the injector... I run 200lb injectors in my current setup and Taylor has the car purring like a dream, I'm blown away at the new high Z injectors... of course it goes without saying they weren't cheap!!!
The 82's would be perfect for you and room to grow, the biggest advice I can offer is make sure the tuner you choose has experience with "bigger injectors"...

 

to add, I've run the 60's, 80's and now 200's...

 

200's!!!! How on earth do you tune an injector that BIG! I have seen the monsters they turn out and Taylor must be a great tuner. I plan to have Stephen (England Green) tune mine.

 

I'd run something bigger than the 60s. It'll give you some room to grow and will lower your duty cycle. You definitely need to stick with high imped. I run 82# and I'm in your neighborhood. I'm at 50% duty cycle.

 

I think I am going to go with the Bosch 72# from FIC. They are stock height so they will fit underneath the eforce and I don't plan to make more than 650rwhp with the eforce so these injectors should be plenty. Thanks for the input!

 

My pleasure BJ.

Here is a good spreadsheet for calculating injector flow rate changes in relation to fuel pressure:

http://www.hptuners.com/forum/showpo...64&postcount=5

Its used to build new injector flow rate tables but you only need to be concerned with the 0 kPa lb/hr column to determine flow changes.

Something else to condsider is that manifold pressure conteracts fuel pressure. 60#'ers rated at 43 PSI running at 58 PSI flow 68# at atmospheric pressure. If you have 10# of manifold pressure the injectors have to work against that pressure. Subtract 10# from the 58# of fuel pressure and run that through the spreadsheet and the injectors are now flowing 63# instead of 68#. The opposite is true also as can be seen in the spreadsheet. At idle, at say 20" Hg of manifold vacuum, the fuel is being sucked out of the injector and it flows more. Since there is a table in the tune to account for this it's all good but the table only goes up to atmospheric pressure, no boost.

Having said all that I think the FIC 72's are a good choice.