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Old 04-27-2012, 03:18 PM   #1
v84life
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Default Bigger injectors = more hp???

I just got a tune and the stock 28.xx injectors made 411whp/391tq he said he couldn't get anymore out of it safely. question is would I gain anything from going to some 30lbs injectors and going back for a retune will that allow for more power? the car is cammed,full bolt ons, ported fast 78 and on stock untouched 241 heads right now. I do have a walbro 255lph fuel pump.
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Old 04-27-2012, 03:35 PM   #2
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depends on the injector duty cycle. with the cam and intake with that much hp chances are you are over the duty cycle the stock injectors can support. if that is the reason why he cannot get more out of the tune then yes 30lb red tops would work. remembers the 30lb red tops are 30lb at the lower fuel psi of other cars. they are like 36lb at LS1 psi.
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Old 04-27-2012, 03:38 PM   #3
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The stock injectors are more than enough for your mods.

Russ Kemp
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Old 04-27-2012, 03:42 PM   #4
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Yes I have seen that a lot that the stock 28s are good over 450whp or so but Idk I dont know what the case was with the injectors didnt ask as long as the tune was safe Mike is the boss around here in upstate NY and he knows his stuff with the tuning I just built the car.
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Old 04-27-2012, 04:34 PM   #5
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Quote:
Originally Posted by v84life View Post
I just got a tune and the stock 28.xx injectors made 411whp/391tq he said he couldn't get anymore out of it safely. question is would I gain anything from going to some 30lbs injectors and going back for a retune will that allow for more power? the car is cammed,full bolt ons, ported fast 78 and on stock untouched 241 heads right now. I do have a walbro 255lph fuel pump.
Larger injectors will not give you more HP. Going to a larger fuel injector is needed if you greatly increase the amount of air your motor is pulling into it.

Ask your tuner what Duty cycle your injectors are running at Wide Open Throttle. Duty cycle is basically how hard your injectors are working.

Air/Fuel ratio is the name of the game. You need to determine the amount of air coming in, and match that with the amount of fuel you add. Typically for best fuel economy, most power, and still be safe to the engine you want to be around 12.6-12.9 Air/Fuel ratio. That's 12.6-12.9 parts air, to 1.0 part fuel. Air is a fixed value depending on the mods on your car. Fuel is the part you adjust with the computer tune.

In my case years ago I was running 448/428 to the wheels. My stock 28lb Z06 fuel injectors were running about +90% duty cycle at WOT. You just don't want to run anything that high. Your asking for early failure.

I went to the SVO Fuel injectors rated at 30lbs. Installed on our cars they actually flow 36lbs. My tuner made a computer change and said I should be in a good range now for duty cycle. I ran it like that for 5 years with no issues.

This January I installed a FAST 92 intake manifold/LS2 TB, and had it re dyno tuned. I got 471/441. I asked my tuner and he said I'm running just under 80% duty cycle at WOT (still have my SVO fuel injectors). I should be fine at that level, but I should have gone with 42lb injectors years ago.

If you have plans to be over 450rwhp then I suggest going to a 42lb fuel injector set. The SVO 30lb (36lb on our engines) injectors are good up to 450rwhp.

Just my experiences. Hope this helps.

Toque

Last edited by Toque; 04-27-2012 at 04:38 PM.
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Old 04-27-2012, 10:22 PM   #6
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Thanks a lot for the input I would assume the injectors looked ok at my power level or he would of told me I will get it back for a retune next month
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Old 04-28-2012, 11:58 AM   #7
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given the general consensus that 450 is the mark for 28#'ers and your at 411.. it might not be a bad idea.. BUT as stated I would look at the info first to make sure you actually need them. They are not that expensive but no sense in spending money if you dont need to
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Old 04-28-2012, 01:10 PM   #8
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Agree with above --NO extra Hp by ging to larger injectors if you don't need them!!
On my 400 RWHP car with stock 28's i am at the edge of my duty cycles at around 92% but thats only on the end of a drag pass-As long as you let the injectors cool off some in between runs -they are fine--
Another reason to NOT oversize them is that larger injectors can create idle and low rpm driveability issues (surging dyng huting etc) as the pulses can't get small enough to command such a small amount of fuel-
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Old 04-28-2012, 01:15 PM   #9
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Is there a chart or rule of thumb one should use that matches hp to recommended injector rates?
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Old 04-28-2012, 01:42 PM   #10
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NO---Best is to get or borrow any scanner that shows data in real time and check your duty cycles---Rule of thumb is to keep them under 80% before needing larger ones--but as i mentioned above depends on your cars use ---Mine goes up to 92% but i don't drive it like that all the time and it'sonly at 92 breifly at the end of a drag pass
28's like what you have would be good as a guess---up to 400 RWHP or aprx 480 crank HP
this would put the DC in the 90's--To keep them around 80% the max HP would be around 375 RWHP and 455 crank HP--
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Old 04-28-2012, 05:53 PM   #11
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Originally Posted by tblu92 View Post
NO---Best is to get or borrow any scanner that shows data in real time and check your duty cycles---Rule of thumb is to keep them under 80% before needing larger ones--but as i mentioned above depends on your cars use ---Mine goes up to 92% but i don't drive it like that all the time and it's only at 92 breifly at the end of a drag pass--
I have a LS3 418 stroker that I run in HPDE and on the street. It put down 522 rwhp when it was put in the car a few years back. It hasn't been on a dyno since. It's running 50# injectors and has some of the issues you described above; it surges and hunts at idle and low RPM, especially when cold. I'm thinking it needs a little bit of a retune, but now you've got me thinking it might have too much injector.
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Old 04-28-2012, 10:52 PM   #12
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I have a LS3 418 stroker that I run in HPDE and on the street. It put down 522 rwhp when it was put in the car a few years back. It hasn't been on a dyno since. It's running 50# injectors and has some of the issues you described above; it surges and hunts at idle and low RPM, especially when cold. I'm thinking it needs a little bit of a retune, but now you've got me thinking it might have too much injector.
You can find simple fuel injector sizing calculators using google etc. The main thing that you need to keep in mind....is most fuel injector sizes are rated @ 43 psi. The C5 fuel pressure runs @ 58 psi.

42lb fuel injectors are actually 48lb injectors in a C5. Your #50's are probably actually 60lb'ers if they were rated for 43 psi.

Not sure on the specifics of your build, but sometimes half assed tuners and mechanics will drill a hole in your fly-by-wire TB...and that alone will totally screw up your idle. That ended up being my case.
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Old 04-29-2012, 11:12 AM   #13
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given the general consensus that 450 is the mark for 28#'ers and your at 411.. it might not be a bad idea.. BUT as stated I would look at the info first to make sure you actually need them. They are not that expensive but no sense in spending money if you dont need to
at 414RWEHP I was pushing my stock injectors (27#?) to 90%, went with Ford 30's and i top out about 70% now.
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Old 04-29-2012, 11:28 AM   #14
v84life
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what year is your's I know the 97-00 have 26s and the 01-04 have 28s
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Old 04-29-2012, 08:24 PM   #15
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what year is your's I know the 97-00 have 26s and the 01-04 have 28s

The 97-98 models also had 28lb injectors. There was only a couple of years that had 26's.
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Old 04-30-2012, 01:26 PM   #16
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Originally Posted by jcsperson View Post
I have a LS3 418 stroker that I run in HPDE and on the street. It put down 522 rwhp when it was put in the car a few years back. It hasn't been on a dyno since. It's running 50# injectors and has some of the issues you described above; it surges and hunts at idle and low RPM, especially when cold. I'm thinking it needs a little bit of a retune, but now you've got me thinking it might have too much injector.
Before panicing a common table left unchanged when going to bigger injectors is the "Minimum injector pulse width"--If this entry is left too high at lower RPM's no matter what else you change this will always be the min pulse allowed--Try LOWERING this table at idle/low RPM's I would start with -10% up to around 2000 RPM's EFILIVE table B4003
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Old 04-30-2012, 01:50 PM   #17
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Originally Posted by v84life View Post
I just got a tune and the stock 28.xx injectors made 411whp/391tq he said he couldn't get anymore out of it safely. question is would I gain anything from going to some 30lbs injectors and going back for a retune will that allow for more power? the car is cammed,full bolt ons, ported fast 78 and on stock untouched 241 heads right now. I do have a walbro 255lph fuel pump.
You probably misunderstood what he meant by safely. In general, safely means that he could probably get more power out of the car by leaning things out but you risk detonation and damaging your engine. It is not that the injectors can't pump more fuel.
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Old 04-30-2012, 02:10 PM   #18
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Yea I assume the injectors are keeping up just fine. So the consensus is that going bigger wont make more power where I am at now just going to have to wait and once I get heads on it then I will need bigger ones anyways.
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Old 04-30-2012, 05:12 PM   #19
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Yea I assume the injectors are keeping up just fine. So the consensus is that going bigger wont make more power where I am at now just going to have to wait and once I get heads on it then I will need bigger ones anyways.
Exactly. If you installled SVO 30's now, your tune would then be wrong, and you would actually lose horsepower due to running too rich, with a tune configured for 28lbs. Best to save your money for future upgrades and then have the 30's for the next tune.

So in hindsight, you could have squeezed a couple extra ponies out of the last tune by going with the 30's because your tuner wouldnt have held back.
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Old 04-30-2012, 06:25 PM   #20
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Yea thats what I was thinking if I get some 30s and get a retune he could probably push it harder without going lean and net a few more hp correct?
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Old 04-30-2012, 06:25 PM
 
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