What limits have you guys seen for 42lb injectors?

**Killercanary** · 03-14-2007, 10:52 AM

I have an opportunity to buy a set of 42's right now with a 80mm meter and I'm highly concidering it. I think they will be a bit much for my current dart combo (if it makes anything over 310rwhp I'll be surprised), and I'm not sure they will be enough when I put my PTK single setup on the car with a T64e turbo (rated at 700hp max) that I already have. If it'll "get me by" now and allow me to cut my teeth with the turbo before getting crazy with a new turbo head unit, I will probably pick them up. Please let me know your thoughts. If I don't get these I'm going to run my current fuel system until I put the turbo on. I currently have a 190lph pump, kirban regulator, 24lb injectors and a 75mm MAF. I do my own tuning via an eec tuner so I am able to tune pulse width and such no matter which way I go. I figure if I stay with the 24's for now I'll bump the pressure up and widen the pulse width, and I'll do just the opposite if I run the 42's. ANy input is appreciated as I'm torn on what to do.

**Viper_ed** · 03-14-2007, 11:08 AM

Paul, I have heard that they are done around 500 rwhp. This seems right cause I had to add a Boost-a-Pump in my Cobra at the 500RWHP mark cause the stock 39# injectors (Basically the same as a 42# injector) were at MAX Duty Cycle. In talking with John Urist about 60# injectors, he has said that the 60 lb high impedence injectors will support up to 700-750 turbocharged HP. Sounds to me that the 60#'s will be better suited for your combo.

I have seen sets selling as low as $300 on the Corral and TurboMustangs.

**yeahloh95** · 03-14-2007, 01:19 PM

i say get them ,that way you don't have to try and run your new motor on 24's you could probably make the 42's act smaller with your eec-tuner

**somethingclever** · 03-14-2007, 01:53 PM

42#'ers will be good to around 525-550rwhp in a v8.

**Stangman701** · 03-14-2007, 01:55 PM

I would think on a turbo car you could easily support 550-600 rwhp w/ 42's. The limit on 03-04 cobras with eaton's seems to be around 525 ish w/ the 39's and that's with the power robbing eaton. The limit should be a little higher with a turbo setup.

**Pure Stock** · 03-14-2007, 03:04 PM

Originally Posted by Killercanary

I have an opportunity to buy a set of 42's right now with a 80mm meter and I'm highly concidering it. I think they will be a bit much for my current dart combo (if it makes anything over 310rwhp I'll be surprised), and I'm not sure they will be enough when I put my PTK single setup on the car with a T64e turbo (rated at 700hp max) that I already have. If it'll "get me by" now and allow me to cut my teeth with the turbo before getting crazy with a new turbo head unit, I will probably pick them up. Please let me know your thoughts. If I don't get these I'm going to run my current fuel system until I put the turbo on. I currently have a 190lph pump, kirban regulator, 24lb injectors and a 75mm MAF. I do my own tuning via an eec tuner so I am able to tune pulse width and such no matter which way I go. I figure if I stay with the 24's for now I'll bump the pressure up and widen the pulse width, and I'll do just the opposite if I run the 42's. ANy input is appreciated as I'm torn on what to do.

A couple questions for you Paul. First, will this turbo application be a street and strip combo or exclusively track? From what I have gathered from reading pieces on injector duty cycle is for practical street useage injector duty cycle *should not exceed 80%.

What is your estimate of power production at the flywheel?

Fuel press. will be another variable to be considered when choosing proper injector size.

For truly accurate injector matching, many more variables must be taken into consideration, like displacement, air flow, RPM range, etc...

The 42's will be major overkill for the N/A version of your engine. I have seen the 42's handle 583@8300 / 410@6900 at the rear wheels in an N/A combo. IMHO, the 42's will fall short if you plan on making 700 FWHP with the hairdryer on it. I too would make the 60's the choice so you will be safe on the duty cycle.

**SonofaBish** · 03-14-2007, 03:15 PM

read this... i'm pretty sure its not LSx specific

http://www.ls1tech.com/forums/showpo...91&postcount=3
just fill in what u have into the equation, and solve backward

if you believe it, @ 100% duty cycle, they'll do 513 hp and @ 80% duty cycle, they'll do 413 hp (using .65 BSFC for turbo)

**mikeymustang** · 03-14-2007, 05:16 PM

Ditch the MAF...buy the AEM ...put in the map..then you can upgrade the injectors in seconds and the AEM will do the math when you upgrade so you won't have to retune

PS when you figure your fuel system out make sure you doing FLYWHEEL horse power not rear wheel...

just found this..killer deal even the "buy it now" and you can repin your harness to work
http://cgi.ebay.com/ebaymotors/AEM-E...96916296QQrdZ1

Mike

**mlowry1260** · 03-14-2007, 05:45 PM

Originally Posted by mikeymustang

Ditch the MAF...buy the AEM ...put in the map..then you can upgrade the injectors in seconds and the AEM will do the math when you upgrade so you won't have to retune

PS when you figure your fuel system out make sure you doing FLYWHEEL horse power not rear wheel...

just found this..killer deal even the "buy it now" and you can repin your harness to work
http://cgi.ebay.com/ebaymotors/AEM-E...96916296QQrdZ1

Mike

How about a megasquirt if cash is tight?

I certainly don't miss f@#king with MAF sensors & tweecer. The data-logging on the AEM makes life sooo much easier tuning.

Mike & I could help if you go the AEM route.

**Viper_ed** · 03-14-2007, 05:53 PM

Originally Posted by mlowry1260

Mike & I could help if you go the AEM route.

I'll keep that in mind since I sold my PMS. Trying to decide between the AEM, DFI or FAST.

**mikeymustang** · 03-14-2007, 06:09 PM

Originally Posted by Viper_ed

I'll keep that in mind since I sold my PMS. Trying to decide between the AEM, DFI or FAST.

We said we would help HIM...not YOU

Just kidding...if your going to tune yourself AEM is the way to go...if your going to have someone else tune it...do what ever they are a custome to tuning...you don't want to have to pay them to learn your new software

Mike

**Rodeheaver's** · 03-14-2007, 06:29 PM

i don't know about that, i have talked with sean hyland about this and he seems to have very good luck with 42s on 6-700hp engines.. just my .02$

**mikeymustang** · 03-14-2007, 06:35 PM

Originally Posted by Rodeheaver's

i don't know about that, i have talked with sean hyland about this and he seems to have very good luck with 42s on 6-700hp engines.. just my .02$

42 lbs injectors are 42 @38 psi base pressure... bump up the base pressure to 48psi and the will "ACT" like a 52 lbs injectors but now you have to tune the lower end for the added pressure.

Mike

**gmkillr** · 03-14-2007, 10:10 PM

I believe the 42's will support 500-550 rwhp on a TURBO setup.
On a supercharged setup they are good to around 450-500rwhp.
Id also ditch the 190lph fuel pump & get a GSS 340 255lph pump.

**Pure Stock** · 03-15-2007, 09:59 PM

A 42 lb. injector will not support 700 FWHP in a turbo-charged application. Here is why:

Engines require a certain rate of fuel refered to as lb./hr. which is determined from their Brake Specific Fuel Consumption or (BSFC) BSFC can be defined as a representation how much fuel is required (in lb) per hour per each brake (or flywheel) horsepower the engine makes.

Duty Cycle of injectors:

The definition of injector duty cycle can be referred to how much time is available to supply fuel vs. how much time you actually need to use it. When you have used the entire alotted time window available, this is referred to as a 100% duty cycle. There also is a misconception that running an injector over 80% duty cycle is bad for the injector (overheating it) Actually it has a cooling effect. The constant fuel flowing through the injector cools the injector. You could potentially run an injector at 100% duty cycle with no adverse effects on the injector.

Most will want to run an injector at 80% duty cycle to have a *cushion* As the weather gets colder and/or the barometric pressure increases the air will become more denser (more oxygen) The engine then theoretically will make more power. This power increase will require more fuel. This is why the *cushion* (running the injector in the 80%-90% range is recommended) is employed in regard to injector duty cycle.

Taking an injector that is capable of flowing 42 lbs/hr. at 40 psi delta using a fuel with a specific gravity .72@65 degrees F and using the accompanying formula will reveal an approximate estimate of how much FWHP the 42lb. injector can support in a turbocharged application using a BSFC of .65 Extreme efficiency *can* lower the BSFC some. This is meant to be a guide so there is some *cushion* with the injector.

To determine proper injector size use the following formula

[(Injector size)x(#of injectors)x(Duty cycle)] / BSFC
42 x 8 x .90 /.65 = 465.23 FWHP

Taking the same formula and plugging in .5 BSFC (what most street N/A applications usually run) we arrive at 604.8 FWHP

The injector can be made to appear bigger, however the fuel pump will be affected from this pressure increase. As pressure increases the fuel pump flow decreases. For example a 255 LPH pump at 40 psi may only supply 200 liters @ 58 psi. Additionally fuel line sizing also plays a role. Using a fuel line that is not large enough can result in decreased fuel volume due to the pressure drop across the fuel feed line. 255 LPH at the pump may on result in 225 LPH at the fuel rail.