Worth the upgrade?? I am maxed right now. And planning on getting to 380 rwhp.

 

I wouldn't think that you would get a gain from injectors unless your car is starving for fuel. The stock injectors are suppose to be good up to 450hp. Now with the N20 I would go with even larger injectors 36#-42#, because of the fact that I wouldn't want to risk running lean in the future.

 

I thought so too. But according to EFI, I am at 105% duty cycle @ 6000 rpms.

 

I'll give you 1000-1 odds that you're injectors are not maxed out. People who look at duty cycles think they're almost maxed out when the engines are bone stock. People who don't look at them get away with 475 RWHP on 26 lb injectors. I can't explain why the reported duty cycle is such a fib but it is.

If you were completely maxed out, you would notice a leaning of your S1 O2 readings.

 

If your showing over 100% your injectors are maxed out. In fact you should not run above 80% because you risk damaging the injector. You may not actually be running that lean just the computer thinks you are running lean. So you need to see what PE vs rpm is set from the factory and if you are getting COT (catalytic over temperature). Some cars from the factory are set pretty rich 12:1 or so and with COT you could be down in the 11:1 range. The SS and WS6 were set at 13:1 from the factory and thats about best afr for normally aspirated.

You can not go by the stock o2 sensors to tell if you are a little lean. You need to get the afr from a wideband sensor. Then you can tweak the PE etc. Either way the stock injectors (26.4 lb) are not going to support much.

Gary

 

The wideband A/F is around 12:1 to 11.8:1
And the PE is stock for now until I install the headers. And no COT.

I just don't know why it show my injectors are maxed but I am still rich. That was the reason for the larger injectors.

I am going to install a new fuel-filter and see if that helps.

 

"If your showing over 100% your injectors are maxed out."

One would think this but it just doesn't work out to be the truth in real life.

The stock 26.4 lb/hr injectors will support over 450 RWHP I don't care what the injector pulse widths say. Been there, done that.

Ed, you're rich because your injectors ARE NOT MAXED OUT at only 341 RWHP. Think about it. Simple logic says that if they were maxed out, your mixture would start to fall. You could run a 100 dry shot on top of that power without problem. People do it every single day.

As far as damaging the injectors by running them at over 80%, I believe that idea comes from other platforms that run higher fuel pressures in which case this is possible. However, I have NEVER heard of an LS1 injector locking up or being damaged from being maxed out. It just doesn't happen.

I wish Autotap would have never included monitoring of injector pulse widths. Something just doesn't add up with it. I've been watching this confuse people for years now and at the same time I've been watching these cars in every single case make power well beyond what the injector pulse widths would indicate is possible. I once believed in them too until I started running a 125 HP dry shot of nitrous with no problems. I ran 125 MPH with those injectors on nitrous. Later I pulled 480 RWHP with a 422ci engine and stock 26.4 lb/hr injectors.

 

"Either way the stock injectors (26.4 lb) are not going to support much."

I'm honestly not trying to butt heads with you but how much do you think the stock injectors will support? He's only trying to make 380 RWHP which is 100 RWHP short of what I've actually done with those same injectors.

 

It makes perfect sense that if I am still running rich, no way my injectors are maxed. But seeing over 100% duty cycle on EFILive worried me.

Could a clogged fuel-filter or low pressure cause a higher injector DC?

I just remembered twice at the track a month or so back, I heard the fuel-pump whining quite a bit after racing all night. Hasn't done it since. So maybe the pump can't supply as much fuel as before so the injectors are open longer?

But getting back on topic, is it worth getting the 29# injectors for $75?

 

A semi-clogged filter would result in a pressure loss at WOT but not during part throttle closed loop operation. Your mixture would be leaner than normal at WOT as a result. Since no fuel learning is taking place during open loop (which WOT is), the pressure drop at WOT would not effect the injector pulse widths. You would simply see a leaner mixture at WOT due to the lower PSI seen by the injectors at WOT.

You could install a fuel pressure gage mounted in an A-pillar pod. I found it very useful when battling a borderline fuel system.

 

Ok, I won't worry about the DC. Unless I start running lean. Thanks.

 

I guess I was not to clear. Since your computer is requesting 12:1 afr and you are maintaining 12:1 you are not lean but your injectors are maxed out at that afr. If you were to set your PE to 13:1 you would get lower injector duty cycles, yet make more horespower. No you cant look at just the duty cycle and ignore at what afr part of it. The duty cycle alone is not the whole picture.

You can get away with running lean or maxing out injector pulsewidths on a normally aspirated car for the short periods we are talking about (drag racing) for probably the life of the car. Just don't try to do any extended type high speed runs.

As an engineer I am ultra conservative. When I first setup up my twin turbo ls1 I had the stock 26.4 injectors, they worked great only had 86% injector duty cycle. But since they are undersized I got lots of tip in knock, rough running, etc because whenenver the throttle was mashed the car would go way lean for a second (in car wideband) before the injectors and the pcm could react. With the 50 lb injectors no tip in, no going lean on mashing the throttle.

The max horespower you can get out of the injectors depends on the numbers you throw into for bsfc (which is essentially the afr). Since the ls1 can get away with running leaner than some older setups you have to put in a smaller bsfc, probably down in the .35-.4 range instead of the usual .4-.45 for normally aspirated. You crank the bsfc up higher for turbo or supercharger cars because you want the afr a little richer.

I am not going to quote numbers for someone elses system.

The standard injector sizing equations work perfect as long as you know what bsfc you have to use.

Gary

 

Gotcha. My headers are going in this Sat. Once that is done, I will tune it and get the AFR up to around 12.8:1. Then see where my DC is. Thanks.

 

If you tuning on a dyno-jet its not full load so you need to be about .5 afr richer than you want. So you want an afr of say 13:0 on the street then you want 12.5 on the dynojet. If its a eddy-current dyno (mustang) then you can tune it the same as the street.

Gary

 

I had to change my 26# injectors up to 28# to keep my Ltrims at 0 under most loads. It was worth the $75 I spent doing it.

 

what is the stock fuel pressure setting for a stock 2003 ls1 motor?

 

Thanks guys.