injector size

[bgoat]

What injector size would you guys recomend for a 700+ hp na ls motor?

[ameaglemike]

What size motor is it? What heads, what cam? It all matters. I would say that you need at least 50lb if not bigger. It also depends on your tuning.

[04GTOryder]

How do you plan on making 700hp na out of an ls engine? Are you talking flywheel or to the wheels?

[Pennybags]

Some good info...

Source (http://www.lonniesperformance.com/phpbb/viewtopic .php?t=44)

Here is some info for sizing your fuel system.

1. 60# injectors typically flow between 62-63# at 43psi. This equates to 72-73# at 58psi. This injector will reach 900rwhp, but will be maxed out.

2. A 72# injector at 43psi will do the same, but at lower required fuel pressure. A 72# at 58psi will be roughly an 83# injector.

3. An 83# injector should be good for approx 1045rwhp maxed out.

NOTE!!!!!!!!!!!!!!!!!!!!This is based on a car, using gasoline, with an approx 15% driveterain loss & a BSFC of .55. This is commonly done on manual trans cars & locked automatics. It is possible, but not recommended to drive the injector this hard. Keep in mind that dyno's vary greatly & these are based on Dynojet numbers.

If you have a 4L80E or a loose unlocked converter, you will see less rwhp for a given fuel consumption.

Also your air fuel ratio greatly effects these numbers. Example running 10:1 AF requires 10% more fuel than an 11:1 AF. This is a huge difference in flow.

Be aware you should not design your fuel system for a maxed injector at 100% duty cycle.

1. You should strive for 80% duty cycle as a general rule for continuous use, but can go slightly higher for short term drag racing etc. 85% should be OK. I would not design for 90% as at this point, you do not know your power output...... If you are off by 10%, you bought the wrong injector.

2. You should not design your system to run over 70psi or you will need an exceptionally large pump(s) to feed the elevated pressure requirements.

3. You do not design the fuel pump to feed the injector, you size it for the HP requirements at the correct fuel pressure.

Now with this out of the way............................................... .....

Start to size injectors with the following info:

Desired HP (Don't fantasize here, be realistic or you will have poor drivability & spend a lot of extra money)

Example:
I want 900rwhp.....
I lose approx 18% through my auto & 9" rear.
so... I need 1062 flywheel HP.
1062hp with a .55 BSFC (forced induction/nitrous) is 584#/hr
584#/hr divided by 8 injectors = 73#/hr each at 100% duty cycle.
The theoretical 72# injector is maxed at this power level.
Using the 80% DC theory, you should use a 91# injector.
Using a 85% DC, you come up with an 83# injector.

Next question.....
Can I use a 72# with higher pressure to get my 83# flow?

Take your highest boost pressure & subtract from 70psi.
Example 70-20psi boost = 50psi base pressure... not 58psi.
This would work for a car with 12# boost, but above this you are asking a lot of the fuel pump to run over 70# max pressure. If you notice, the cars running high pressure are the ones with lower power & small injectors. Probably FMU cars with series pumps & under 500rwhp.

Now size the pump.....
The problem here is that most pumps are rated at 43psi. Many do not publish flow curves.

Lets take the common 255 Walbro 340.
255liters is 67.36 gallons.
Gasoline weighs approx 6.2#/gal.
This means a 255 pump should flow 417.6#/hr.
Will it support the calculated 759 flywheel hp?
Maybe in a perfect world. There are flow losses for lines, filters etc.
A safe limit is 80% of this which is 607 flywheel or 515 rwhp.
I recommend 550rwhp as Ive seen this commonly accomplished.... 85% of capacity.

Again I would size the pump for 80% of required flow to be safe.

Unfortunately here is where you have to compromise....
otherwise you will have a huge race only pump in the car.

If you want to run streetable pumps, I would consider lower pressure if you are above 750-800rwhp. Start with a big injector.... like a 96, lower the base pressure to 35 or so. Now it acts like a 86# injector.

You boost reference 20-25psi to it & you still have only 55-60 total pressure. Now the pumps are happy & you get a lot more flow from the pumps. You will take a 10% penalty in pump flow between 60 & 70psi.

FYI.....
My pumps have already supported over 700RWHP on E85 & 980RWHP on gasoline. I still have not found the limits.


Last but not least......
E85 takes 25 to 30% additional fuel.

Take the above calcs & multiply the HP values by .7 to get the equivalents for E85. Ex. 900rwhp x .7 = 630rwhp

Multiply the injector calcualtions above by 1.3 to get the E5 equivalents.

A 60# injector needs to be a 78# on E85.

Hope this wong winded reply helps.

Remember your results may vary..... be safe & buy things once.

[bgoat]

Flywheel hp should be north of 700. It is a 448ci ls1, custom intake, and all the best components. I was thinking of 50lbs injectors would be plenty bc my LT1 made 600 f/w hp with only 38lbs injectors.

[04GTOryder]

80lbs or bust, you know your gonna end up throwin a 200 shot at it

[batboy]

(BHP x .5) ÷ 6.4 = Inj Size

(700 X .5) / 6.4 = 54.69

I say you need the Ford Racing 60# injectors (assuming a safe 80% duty cycle). The green top 42# injectors are not big enough and if you go bigger than the 60#, it'll be really hard to tune. Remember, the 60# rating is at 43.5 psi fuel pressure. The GTO 58 psi makes it closer to flowing 69-72 lbs.

EDIT: I see you said LT1, is the fuel pressure the same 58 psi as the LS1/LS2 engines?

[mistermike]

I did a good bit of research on injector and pump requirements a while back, and what I concluded, after talking to people who build fast EFI cars for a living, is that the fuel injector formulas seem to be using BSFC numbers that are more appropriate for an old school small block, rather than the much more efficient Gen III+ engines. You certainly won't go wrong using BSFC in the .55 range, but you may wind up with a certain amount of overkill. On the other hand, you should allow at least 10% over capacity on the pump, to allow for the fact that regulators don't work particularly well when they're being drained as fast as the fuel is coming in. IMHO, anything over about 900 at the flywheel should consider going up at least one size from 60 Lb Mototrons. In the past, this meant using a Versafueler or other injector amplifier with low impedance injectors, or going to an aftermarket ECM. The jury is still out on the new Hi-Z Siemens squirters, but they show some promise from the gossip I've heard.