at 80% duty cycle 140 flywheel hp is what 15lb injectors are able to provide and at 100% its 180 flywheel.
I have stock internals but the motor is rebuilt and has port work to the intake along with a dual throttle body upper and ported exhaust restrictions few other supporting hp mods nothing major. I plan on putting 1.6 rockers soon with stronger springs with the improved flow of my intake and then the rockers I am wondering if I should have went with the 17lb injectors.
The 15 lb. are fine for what you are doing. Only if you get into much more serious mods will you increase the fuel needs enough to dictate a switch in injectors.
If you gain 20 hp, to be on the safe side, using the stock Fiero fuel pressure of 43.5 psi and keeping your duty cycle at 80% so you don't start to lean out, it might be advisable to go to 17# injectors. It certainly would be best if you think you'll gain more than 20 hp.
I just went through this with my 85gt. 1.6 rockers, ported exhaust manifold but no duel intake.... I sent off my injectors to have them benchmarked and flowed to 16lbs. That way, I'm running perfect...and more importantly, NOT LEAN. Good luck
Edited to add that i second what Fierofool posted. Always better to be rich.
[This message has been edited by f85gtron (edited 06-16-2014).]
Well my intake on a rough running fiero from the manufacturer just replacing the upper intake , leaving the rest of the intake system stock and unported and without a tune produced a 15whp and 24 wheel torque gain with lean spikes.
I have a roller timing chain , ported exhaust manifolds , ported lower and middle intake , with the upper they used , and some other small stuff but with a tune I'm going to go ahead and guess i'll probable be 30whp minimum above stock. So sounds like i'll go with 17's eventually then just try to get some reimbursement for my accel 15's that have like 200-300 miles on them.
I have already noticed a power drop from changing out my old O2 and coolant temp sensor , which im assuming from aged readings made it run richer and it was a real noticeable power drop from replacing them , which I assumed was my stalling problem , hunting and host of other issues but turned out to be a lose coil connection but those sensor are long and gone. So I know it needs to run richer but so when having it tuned to run that way it sounds to me like doing it on 17's would be the way to go.
If I was to decide to drive it around for a while with 17's before my tune , of course it will be safer on the motor better being rich than lean , but how much would the computer have an issue with it?
If you install larger injectors you may need to retune. The stock injectors should be good to 190Hp but they will need to be at 100% duty cycle at WOT. Not the recommended way to run injectors but for the short duration that we use WOT it should be safe.
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I will definitely be replacing them, just hate I bought them at fierostore because of the price I paid. Now getting a set of 17's I'd like to sell my 15's to re-coupe , they have less than 300 miles on them.
If you swap injectors you MUST have the ECM programed for the larger injectors. At WOT the ECM will always go the richer of the two, the two being stock code or what it has learned. It will never lean it out at WOT. By programming I mean; to tell the ECM what size injectors you have.
So if you go bigger injectors and not reprogram, the ECM will lean it to make drivabilty work, but at WideOpenThrottle it will be dumping in gas.
Blowing a little black smoke on wot is better than none. The extra raw fuel pulls heat away from the heads when needed. 1: You could up the fuel pressure and keep the 15#, or 2: it may be cheaper to run the 17s....,you may even get away without having to retune anything. 3: Make an aldl cable so you can see what's going on through the sensors. Ron
If you swap injectors you MUST have the ECM programed for the larger injectors.
Of 3 upgrades to 3.4's and 17# injectors, I've never modified my ECM. The ECM doesn't care what size injectors you have since it doesn't get any information from them. The ECM adjusts the injectors based upon the information from other sensors on the engine, like the Oh-2 sensor. Now, if the ECM needs to adjust the fuel flow and maxes out within it's program range, then yes, a new reprogram might be in order.
Of 3 upgrades to 3.4's and 17# injectors, I've never modified my ECM. The ECM doesn't care what size injectors you have since it doesn't get any information from them. The ECM adjusts the injectors based upon the information from other sensors on the engine, like the Oh-2 sensor. Now, if the ECM needs to adjust the fuel flow and maxes out within it's program range, then yes, a new reprogram might be in order.
on a 3.4 yes, but there was no mention of it being a 3.4.
Correct. The size of the engine doesn't make any difference. The reason I used the 3.4 as an example is because I know what the stock HP is. It's 160 at the crankshaft. Engineers and manufacturers use that HP in their equation for determining injector flow because they don't always know what the hp loss will be through the drivetrain. We have two known values to compare. The 2.8 at 140 hp and the 3.4 at 160.
1. Using 80% duty cycle and 43.5 psi stock fuel pressure and a 6 cylinder engine on all the following: 2. The stock Fiero injectors flow 14.58 lb/hr with a 140 hp engine. 3. Modify the engine to produce 150 hp and the flow rate needed is 15.625 lb/hr 4. Bring it on up to 160 hp and the flow rate needed is 16.66 lb/hr
A stock 3.4 engine producing 160 hp at the crankshaft would require 16.66 lb/hr. With his mods, he may be approaching or surpassing the 160 hp mark. Assuming 160 hp, you could push your fuel pressure up to 55 psi, but you would still exceed the flow capacity of the stock injectors. As f85gtron posted on the Georgia Fiero forum, he was only getting 16.2 on a freshly rebuilt set of stock injectors.
[This message has been edited by fierofool (edited 06-17-2014).]
FWIW, I have run stock 15 lb injectors with a stock engine with a Miller Woods turbo installation. They didn't spec anything larger and it never leaned out at the 200-210 bhp limit, it ran within the capapbilities of the stock injectors, although probably near 100% duty cycle.
How is it that possible , just looking for an explanation cause 15lb / hour is 180 flywheel hp at 100% duty cycle , assuming fuel pressure was increased?
[This message has been edited by Winfield1990 (edited 06-18-2014).]
Which 17lb injectors from what all vehicles will fit on the fiero so I can ebay them cheap and swap them out. I can get 19lb mustang injectors which I read will fit the fuel rail mount pressure keeps them in place and sealing.
19# injectors will probably be too much for anything under 180 hp. I've been there and experienced it. Use your injector calculator to determine your injector size. Email or talk to several injector manufacturers. Fuel Injector Connection will talk with you and guide you. Ask for John, one of the owners.
The injectors aren't kept in place by pressure. They are captured between the fuel rail at the top and the lower intake manifold at the bottom. Once the fuel rail is bolted down, the injectors aren't going anywhere, even without the retainer clips. I haven't used clips on mine and they've been in for over 3 years. New seals before installation is just common sense, but new or rebuilt injectors come with new ethanol resistant seals, anyway.
Check with your preferred rebuilder to be sure these will connect to your harness and are the same length. For another comparison, the Camaro/Firebird 3.4 Rochester 17# are the same size and have the same harness connection as the Fiero. I've lost the info on my BMW injectors, but I think these are the ones. FIC rebuilt for under $150 for 6.
Look at the number 0280150415 in my link to fcpeuro. Then look it up on this chart. It lists 16.76 lb/hr at 43.5 psi. This site has information on most all brands of injectors. http://www.justfuelinjector...flowchart/Page#BOSCH
Just note rockers, replacing 1.5 with 1.6 rockers, will add lots of wear to your cam. Most cam makers will void warranties if use go from the stock 1.5 to 1.6. IMO: You would be better off putting the money towards a set of headers and make better use of your improved intake flow. The stock headers, even ported just don't flow.
As for the injectors and a new chip: when you have it altogether -hopefully with headers- take it to a dyno -or someone with a wide-band- and get some data on your Air/fuel ration. BTW you can get useful data with just a wide-band, if you collect the data while driving under different load conditions and noting your MAP voltage. Changing injectors and/or chip profiles without the data will seldom get it anywhere near spot-on. Good luck.
Fierofool , I looked at your database thanks for the link. They list theres at that flowrate at 50.75 , and if I up the pressure of Accel 15's that I have to the same pressure I end up with a 16.21lb / hr flow vs 16.76 so they aren't much different.
So If I install them directly on my fiero with the same fuel pressure , they will perform pretty similarly and the fuel injector hp calculator puts it ~5 hp increase from going with these injectors at 100% duty cycle capability. I think I need to just put on an adjustable fuel pressure regulator and raise the pressure. It feels like more than 5hp that I've lost from changing out my old sensors for fresh ones.
[This message has been edited by Winfield1990 (edited 07-03-2014).]
Sorry I misread the chart , but I put a washer inside of my pressure regulator and got a nice power increase, still not sure how much more I have untapped. I guess I need to get some readings to know how far my air fuel ratios are off to know if I need to up the pressure some more to get it close before eventually getting a tune , or maybe one day I'll add another washer and see if I think I should keep it there.
[This message has been edited by Winfield1990 (edited 07-04-2014).]
Been there. Tshirt, etc.... This is endurance racing experience learned the really hard way and more than once....
IF you go with the 17# injectors you will need to get the adjustable fuel pressure regulator from Fiero Store. Easy replacement. Then find a Dyno guy to do a few pulls and get the FAR correct. I rebuilt (intake, manifold, 1.6 blah blah blah....) and stroked our 2.8l to a little over 180HP (crank). The first time we ran it, the 15lbs injectors had the manifolds glowing white and the detonation was constant. We killed it in a matter of hours.
With the 17# injectors I run about 28# pressure (FYI, my fuel pressure gauge never showed 43# - I wonder if that is the sender pressure? Stock for me was about 35# (old and new fuel pump both), so keep that in mind when looking at my numbers and doing the injector math). I know the math and the ECM is supposed to compensate, but the 17th are too big and the 15s too small for the 1980's ECM and the fixed fuel pressure. But, 17 and rich is way better than 15 and killing your engine.
BTW. Typically 6-9 Dyno pulls with fuel pressure adjustments etc is about 30 minutes and cost me about $200 - cheap for the performance gain (20hp over stock fuel pressure with 17# running rich), better millage (20%) and not spending $800+ for new crank, pistons, bearings, cam (yes, we even damaged the cam running too lean).
BTWW... Get a fuel pressure gauge and install it before you change the fuel pressure regulator, that way when you install the new one, you can adjust to the old pressure or at least 35# with the 17# injectors so that you don't blow the motor on the way to the Dyno guy.
[This message has been edited by plane (edited 07-04-2014).]
When I was buttoning up my motor I did a fuel pressure test and it was in spec If I remember correctly it was on the high side of fuel pressure range. I agree I do need to test pressures during my adjustments.
[This message has been edited by Winfield1990 (edited 07-05-2014).]
Sorry I misread the chart , but I put a washer inside of my pressure regulator and got a nice power increase, still not sure how much more I have untapped. I guess I need to get some readings to know how far my air fuel ratios are off to know if I need to up the pressure some more to get it close before eventually getting a tune , or maybe one day I'll add another washer and see if I think I should keep it there.
I had my stock fuel pressure regulator modified to make it adjustable. All that was required was to drill a hole in the top, and tack-weld a nut above the hole. Then you insert a bolt in the nut, and tighten it to increase the fuel pressure.
That said, it's important to have a fuel pressure gauge, especially if you have an adjustable pressure regulator. Because without a gauge, you're just taking shots in the dark.
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