at what point are injectors too big?
Thread Starter
Teching In
Joined: Oct 2008
Posts: 47
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From: wyoming
at what point are injectors too big? Sorry for the newb question but i was told by a very reputable tuner in my area that i bought way too big of injectors for my setup.
My car is a 99 m6 camaro ms3, stage 2.5 prc 5.3 heads, ported fast 92 combo, 1-7/8 LT, true duals, k&n fipk, underdrive, walbro 255. I bought a set of lucas 42#flowmatched and he said i would be better off with the stock gm injectors? I am going to finish the install of the fast combo and injectors later this week and called him to talk about getting a tune, but now im confused. He said i should get some 30#. Does this sound right?
My car is a 99 m6 camaro ms3, stage 2.5 prc 5.3 heads, ported fast 92 combo, 1-7/8 LT, true duals, k&n fipk, underdrive, walbro 255. I bought a set of lucas 42#flowmatched and he said i would be better off with the stock gm injectors? I am going to finish the install of the fast combo and injectors later this week and called him to talk about getting a tune, but now im confused. He said i should get some 30#. Does this sound right? Uhm....no. 42's are good. With your heads and cam you would definitely max out the stockers or come close to it. I maxed my stockers out with just my cam. I have 42's and I'll have to probably upgrade to 60's.
The right sized injector for your application is a 36 lb/hr @ 3 bar (41 @ 4 bar). I agree with LS2nut, and always prefer to right size injector applications. 42 lb/hr @ 3 bar will support a bunch of naturally aspirated horsepower.
TECH Apprentice
Joined: Nov 2006
Posts: 369
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From: Copenhagen
it depends on the injector.. the minimum controlable injector pulse with time is the cut off.. in theory you could run 160 pound injectors if they would open and close fast and uniformly enough to give a good idle... but on the delphi ECU there really isnt any use for it since you cant phase the injection differently..
(on an aftermarket ECU like bosch motronic or autronic you can change phasing to coincide with valve opening.... ) listen to the pros.. go 42
(on an aftermarket ECU like bosch motronic or autronic you can change phasing to coincide with valve opening.... ) listen to the pros.. go 42
it depends on the injector.. the minimum controlable injector pulse with time is the cut off.. in theory you could run 160 pound injectors if they would open and close fast and uniformly enough to give a good idle... but on the delphi ECU there really isnt any use for it since you cant phase the injection differently..
(on an aftermarket ECU like bosch motronic or autronic you can change phasing to coincide with valve opening.... ) listen to the pros.. go 42
(on an aftermarket ECU like bosch motronic or autronic you can change phasing to coincide with valve opening.... ) listen to the pros.. go 42
The ratio of the highest achievable flow, within the 2% deviation, to the MLPT is the Dynamic Flow Range(DFR).
Neither of these data points are easy to find for any injector, which is why I prefer to right size the injector for the application. What you want to correctly size an injector is the shortest possible pulse width at full load while staying above the MLPT at low load.
TECH Regular
Joined: Nov 2002
Posts: 418
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From: Augusta Ks.
From what I've read and heard the idea is to keep the injector open percent between 20-85% this keeps wot from going lean and makes idle easier to tune.If you are planning on going with more stuff 42's will cover you but he is talking about the low end of the tune.I am at about 450 with bosh 30's and am close to the 85% at wot.
injectors can be too big when you cannot command a low enough pulsewidth along with a low enough pressure from your Fuel pressure regulator to get your idle at stoich.
From my understanding, obviously an injector has minimum and maximum operating pressures, so your fuel pressure is a variable.
the injectors pulse width is a variable.
when your idle is not at stoich (or what you set it at) and you lower your FPR (fuel pressure regulator) to below the injectors operating parameters and your pulsewidth cannot go any lower, then you got problems.
From my understanding, obviously an injector has minimum and maximum operating pressures, so your fuel pressure is a variable.
the injectors pulse width is a variable.
when your idle is not at stoich (or what you set it at) and you lower your FPR (fuel pressure regulator) to below the injectors operating parameters and your pulsewidth cannot go any lower, then you got problems.
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42's are 48 in your car that will support a lot more hp than you have. guys that put in too big say its runs great, but do they know if they had the right injector in how would it run then. You can only set the PW so far down. I am a firm believer that the engine should have what it needs, Over injecting leads to cyl wash, poor idle etc. IMO
He was suggested to go with stock and then suggested to go with 30's. Not a good suggestion IMO. If you want your injectors to go static, sure go for the 30's.
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Verdad Gallardo Sorry for the newb question but i was told by a very reputable tuner in my area that i bought way too big of injectors for my setup. My car is a 99 m6 camaro ms3, stage 2.5 prc 5.3 heads, ported fast 92 combo, 1-7/8 LT, true duals, k&n fipk, underdrive, walbro 255. I bought a set of lucas 42#flowmatched and he said i would be better off with the stock gm injectors? I am going to finish the install of the fast combo and injectors later this week and called him to talk about getting a tune, but now im confused. He said i should get some 30#. Does this sound right?
My car is a 99 m6 camaro ms3, stage 2.5 prc 5.3 heads, ported fast 92 combo, 1-7/8 LT, true duals, k&n fipk, underdrive, walbro 255. I bought a set of lucas 42#flowmatched and he said i would be better off with the stock gm injectors? I am going to finish the install of the fast combo and injectors later this week and called him to talk about getting a tune, but now im confused. He said i should get some 30#. Does this sound right?you will need 42# injectors, and those will do ya up to 500HP N/A.
if you want some injector advice and some sheets and such, PM me and we can talk further. What people are also saying up here is good, but your guy saying you would be better off with 30# is nuts.
rceng.com check it out, and check out their TECHNICAL SIZING PAGE.
if you need help with it call me (PM me to get my number)
Thread Starter
Teching In
Joined: Oct 2008
Posts: 47
Likes: 0
From: wyoming
well thanks for all the help and replies. I know that my stock ones will for sure be maxed out and i already bought the 42# lucas injectors so i guess i will take it to the tuner and see what he can do with it. Unfortunatley i dont know anything about injectors so all i have had to go on is info from reputable people on this site. Any further help would be great thanks
well thanks for all the help and replies. I know that my stock ones will for sure be maxed out and i already bought the 42# lucas injectors so i guess i will take it to the tuner and see what he can do with it. Unfortunatley i dont know anything about injectors so all i have had to go on is info from reputable people on this site. Any further help would be great thanks
