BlackDuk98

iTrader: (34)

Thank you for any help.

I have been going back and forth on feeling ok with my current injector size or needing to upgrade and feel like asking everyone here what they have seen and think is ok.

In regards to FAST 36lb injectors, tested at 42.5 or 43 psi, so at my psi, about 41.5lbs. I am consistantly reading 59-60 psi at the fuel rail even at WOT. Also running the Racetronix upgraded 255lph kit.

I am in the process of building a NA 408 stroker. CNC LS6 heads, Fast 92/92, GM 85mm maf, 98mm lid, 248/254 .615"/.622" cam.

Estimates for my engine are 600-625 at the crank, and with my power robbing th400 and 9", 450-475 rwhp. I have read of someone using GM 36 lbs doing 522rwhp w/ a 71% duty cycle (a little of 400rwhp NA), been told by one that the 36lb ones I have will do about 650 to the crank. Others have said I need at least 42lb ones. One Fuel injector calculator said I needed 42lb ones, and another said I would be able to do 36lb injector @60psi at 90% duty cycle. Then others say I can do over 550rwhp on them if I am NA, while many others say 42+lbs are needed.

Nobody seems to agree, so that has me worried. The 36's are already programmed in on my heads / cam LS1 w/ stock fuel rails and I would like to carry them over to this new motor. I have even read of people getting 500rwhp on stock 28lb injectors. I don't know what to think anymore, and I basically know nothing when it comes to tuning except enough to ask questions. If I absolutely have to upgrade, I need to figure out some that will work with my stock ls1 fuel rails since I already am over budget on this build.

what are the opinions of the tuning gods?

thanks

-mark jr.

Ed Wright

iTrader: (1)

The FAST 36lb at your fuel pressure will be fine. That's what I'm using at that power level. They are fine. Good choice.

ZL1Killa

iTrader: (17)

what is your duty cycle?
I have a feeling you are on the top end of those injectors.

BlackDuk98,
The answer is in what you have already posted. From your post, if you look at it this way what you found is:
- 36# injectors are at their higher duty cycles or on the top end of their use
- 42# injectors will work, and leave some breathing room for future upgrades, as 42# @43.5psi rating, used at 58psi are 48.5# injectors.

good research.

Ed Wright

iTrader: (1)

I'm running them at 60 psi, like he is going to. That makes them 42 lb. mid- high 80%. Haven't seen 90% yet. Many real world racers run over 90% duty cycles.

On what are you basing this? Why in the world would you think an engine at that power level needs 58lb injectors? You actually build and race a lot of engines at this level? You do know NA engines use smaller injectors at the same power level, right? They run leaner.

BlackDuk98

iTrader: (34)

I was just going to ask what duty cycle you were at with thr 36# ones and what exactly is you power level at? I read everywhere that once you hit 80%, thats when it's time to upgrade. I have read of some tuners saying that you are completely safe even at 90%. I know that these injectors are definately at their higher end of their duty cycle.

So lets say that they are at 90%, and possibly go to 95% when it's cold. I am not living at WOT all the time, and not for long bursts.

If I don't add any more power, except natural temperature change, am I ok? I cannot afford to add anymore power for a few years, but I would like to be safe for that time until I add more power and upgrade injectors. I don't want to lean out when it's on the dyno. I am not disagreeing because I want my injectors tobe ok, I just want to know if I still have a slight buffer even at the projected power level, or if I am just there at that limit where I just have to suck it up and purchase bigger ones.

Ed Wright

iTrader: (1)

When cold? You run yours WOT cold??
Actual competitive racers, but probably not many keyboard racers, do run them over 90%. Mine had not yet quite shown 90% on a data log. I never spin mine over 8500 like it is. You likely won't either.

"Injector calculators", as has been mentioned many times, are put up by people trying to sell injectors. Injector duty cycles aren't as stable at very narrow pulse widths, so bigger than needed injectors (just in case) are not a great idea.

BlackDuk98

iTrader: (34)

I worded that wrong. I meant when the temp drops outside like in fall. Due to a cooler iat reading during cold climate times, isn't there still a small increase in fuel consumption over let's say a hot summer day? Car is always fully warmed up before any WOT runs are done. I will probably run it to 7k I would think.

Maybe a better way to word what I said is... Does your duty % change from a hot summer day when you make less power, to a colder day when you make more? Wondering if there is still a safe enough buffer to say that maybe 95% is the absolute extreme I would see from them with no more mods.

Just wondering, what is your hp/tq at the duty cycle level that you are at?

Maybe what I am wondering is how much rwhp gain is equal to 1% duty cycle increase?

ZL1Killa

iTrader: (17)

Firstly, no one said anything about 58# injectors. I mentioned 42# injectors at MOST, which at 58psi would be 48.5# injectors and I also stated you would have plenty of breathing room at that point for future upgrades. Which, again based on what BOTH of you are saying logically comes to the point of:
- 36# injectors at the top end of their output
- 42# injectors at medium output

I understand that, all I'm thinking about is durability and in the long haul.

I disagree about the injector calculator statement. An engine is an air pump and with x air you need x fuel to get x AFR at x RPM, etc, etc. Its all math, yes the "math" is just that and actual real world is and always will be different.

What I don't get is that we are both stating the same thing but yet we are going back and forth.

We both agree/stated that the 36# injectors will be at their peak. If the OP wants to ensure further breathing room for mods and have a lower than maximum duty cycle he should go with larger injectors.

ZL1Killa

iTrader: (17)

Are you certain on all of these injector calcs, that you used 58psi as the APPLICATION pressure and used 43.5psi as the RATED pressure? As at that point 85% duty cycle and 41.4# injectors... which means you will be at the high end of your 36# injectors. If you are certain that you did use the correct APPLICATION & RATED pressures, then those calculation websites are SCHEMING TO GET YOUR MONEY mwahahaha, because that calculation is wrong.

Ed Wright

iTrader: (1)

Yeah, I would go by some engineer's calculations instead of an engine builder's and racer/tuner's real world experience. If you have a blown or turbo engine they are close. A fast NA engine is a different deal.

He asked about my power. & torque: 600 fwhp, 528 ft lbs. Guys I race with LS engines making a little more use the same injector.

Some guys build, race and test. And some guys base everything on calculators. I love to race those guys. Good friend of mine is an engineer, he calculates everything, and assumes that is what he needs to do. Likes to tell me how I should be doing everything. He isn't just real fast. Listen to whoever you want to believe.

Btw, I mis-typed that 58lb.

I hope he makes his predicted hp. Not many do. I hope it exceeds that.

Slowhawk

iTrader: (12)

408/TH400/9" - I always run 60lb injectors. 36/42 would be too tight for power fuel consuming setup.

Ed Wright

iTrader: (1)

What is a "power fuel consuming setup"?

Russ K

iTrader: (1)

I also have the Bosch 36 lb/hr injectors. My set up is a 11.5 CR 418, TFS 215 heads, EPS 234/242 117+2 cam, Fast 90/90 intake, LG 1.75 headers, high flow cats, 3" cat back.

At 7000 rpm I hit 80% IDC with a 12.9 AFR. With the stock injectors on my old 346 engine, I would hit 98-100% IDC, Did that for years with out issue. I agree with Ed, that those injector size charts are done by the same people selling injectors.

Russ Kemp

murphinator

iTrader: (2)

arent the bosch "36's" really L67 injectors (supercharged 3800) ??? I have seen mention of them being the same in posts here and HP tuners... If yes I have also run them in the 90's IDC on my L67 car for a long time with no issues.

why not scan/log your new combo on its current injectors before assuming you need more injector ? you can always upgrade if needed.

ZL1Killa

iTrader: (17)

No an NA motor is not different. We are still saying the same **** repeatedly. Ed, you have said and the OP has said and all agreed that the 36# injectors would be at a high duty cycle >80%, all the calculations say the same thing. The issue for confusion may be that the particular calculator might have made assumptions or the user entered a value in wrong.
and I'm a tuner also with experience, not just an engineer fyi. I like to get out from the stupid asses that stick to the books all the time and actually do something.

Now we got 3 sets of information
- keep 36#
- upgrade to 42#
- upgrade to 60#

My opinion if it was my car is I would upgrade to 42# and sell the 36#; shouldn't be that much difference once you sell the 36#.

Ed Wright

iTrader: (1)

An NA engine is not different???

YOU don't put bigger injectors in a blown or turbo engine?? Really?
Maybe because of the different air/fuel ratio?

People are here saying "this what I have, and this is my duty cycle", and YOU know better? Really?

We wouldn't want you to learn anything, would we? :-)

MontecarloDrag

iTrader: (3)

For that engine I would go with 42# injectors if I had to buy them first time. If I already had the 36# I would just rise fuel pressure.
NA engines need less fuel per HP, unless you want to grow in the future, keep those injectors as long as the AFR stays good.
However, running small injectors with raised pressure will kill pumps faster, don't go too high
All engines are different, give yours what it wants. If the AFR stays good, no need to upgrade.

soundengineer

iTrader: (16)

Real world Experience......

ME:

I ran the FAST 36# injectors(also knows as the Injectors on the ASA Corvette) using an adjustable Fuel pressure regulator set to 58psi
11.2:1 compression Naturally Aspirated 408 ci LSx Iron block
Lonnies Performance Dual In Tank Fuel pump Setup
8an Feed, crossover between rails, and 6an return

made 525/508 to the Rear Wheels on a Chassis dyno that reads like a mustang dyno....thru a TCI 6x and a 9" with a Detroit Locker and 3.50 gear.
was around 85%~87% IDC
13.1:1 AFR

BlackDuk98

iTrader: (34)

Here is the only calculator that I found where you can pun in you hp in either crank or to the wheels, cylinders, Na or Forced, and duty cycle percent:

http://www.rpmoutlet.com/injector.htm

The lb rating really changes when you go from crank hp to rwhp. at a 90% duty cycle, it ranges from a 33-36lb injector.

I know it would be better to have a little more room with 42's, but if I don't do anything at all, I think I am at the absolute limit of safe, extreme borderline. I know last year that I tested my fuel pressure directly off the rail test port and cruising and WOT it was 59-60 every time. I am running the upgraded Racetronix 255 pump and hotwire kit that gets power off the alternator. I am no longer worried about the pump.

If I found some 42# ones, I would just have to install them and haul my car to get them tuned in. I can break the motor in on what I have and avoid any WOT, then haul my car down there aswell. Or break it in, dyno tune and see find out what my injectors are reading at. If they are upper 80's, Then I will leave them alone because there is some point that I have to stop spending for awhile. I have been trying to stop for 7 years now and it never happens, lol.

These hp ratings on my motor are just estimates. Unfortunately I have never met or went above any estimate ever, so I would be a little safer, and a little more dissapointed. The formulas say bigger, but the real world numbers say I may just squeek by. This was soposed to be a budget build. I was looking up 42# injectors last night and didn't see any that said that they would fit on stock LS1 fuel rails. Found some from Fast for $715 which is nuts. Still researching and thinking. still torn

If I get and adjustable fuel pressure regulator and set it to 59 psi, which the car is already at, I need to see where to hook it up, never even thought to research that one.

03EBZ06

CURR INJ SIZE * SQRT(60/43) =NEW INJECTOR FLOW.
~42lb/hr = 36lb/hr * 1.18, so you are there already.
Your fuel pump may or may not support this.

Try looking over the BFSC calcs. I'm using 0.5 BFSC as an example. This will help you make sense of fuel req in future.

FUEL REQ (LB/HR) = BFSC (LB/HP.HR) * HP

Say you are making 800hp, then
you need fuel flow around
400 = 0.5 * 800, for a given BFSC for N/A of 0.5
400/ 8 cyl = 50lb/hr injectors required.
Some will then add 20% for safety.

In any case, I have made 566rwhp w/my current setup on 42lb/hr with zero problems. The stock LS7 is about your power level on the same injector. Not the FAST inj, but similar size.

try reading up at:
http://www.rceng.com/technical.aspx