Oversized injectors OK?
08-20-2009, 02:57 PM
#3
Is there any reasons why I shouldn't go with too big of an injector. The only thing I can come up with that the injector is like a hose nozzle. When trying to get a mist, you need it to be @ a certain pressure, anything below turns it into a sprinkle/drip. Going with too big of an injector causes the injector to drip/sprinkle instead of mist?
Am I in the same ball field of fluid dynamics?
Am I in the same ball field of fluid dynamics?
08-21-2009, 06:56 AM
#5
Why do you need larger injectors? If it's a cam/head swap then the SVO30's will be perfect and will support 400+ RWHP. I have 30's on mine now and I am a little close to 80% at WOT so all good.
FYI - The SVOs actually flow a little higher then their rating on our cars as we are running higer PSI - 42.5 vs. the ford standard of 30'ish I believe.
FYI - The SVOs actually flow a little higher then their rating on our cars as we are running higer PSI - 42.5 vs. the ford standard of 30'ish I believe.
08-21-2009, 07:36 AM
#7
Correct, it's better to get injectors that match your application as if you go too big then you do not get a good spray/atomization from the injector. If you are going to spray alot or go FI then go with 42, but if you are NA then that is wayyyy to big for you. As before, I recc the SVO 30's if you are just doing a cam swap and/or head update. Let us know your goals/plans so we can better recc a good injector for you.
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08-21-2009, 08:03 AM
#10
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Rule of thumb to find an optimal injector size:
flywheel hp x 0.07= injector size
500hp X .07= 35#
From what I've read and have been told, injector calculators use an 80% duty to be on the safe side.
flywheel hp x 0.07= injector size
500hp X .07= 35#
From what I've read and have been told, injector calculators use an 80% duty to be on the safe side.
08-21-2009, 08:46 AM
#12
My point would be that you can get just about anything to run. Hot Rodders are always looking for something to enhance their cars. In this section they often seem to lean towards injectors, intakes, and throttle bodies. Three things that they rarely actually need.
08-21-2009, 08:54 AM
#13
Yea you are right, I don't know why people think that with larger injectors they will make more horsepower, of course if you are maxed out and "Need" larger ones to keep climbing the rpm band the I guess you could say with larger injectors I made more horsepower.
08-21-2009, 09:14 AM
#14
Bear in mind, the 80% duty cycle is considered the maximum. If you go over that, you need to increase the injector size.
You can safely go over to a certain extent, if you expect to do further mods down the road. The danger is (IIRC) the idling characteristics. If the injector is too large, it can't idle correctly b/c it wants to spray too much fuel.
You can safely go over to a certain extent, if you expect to do further mods down the road. The danger is (IIRC) the idling characteristics. If the injector is too large, it can't idle correctly b/c it wants to spray too much fuel.
08-21-2009, 11:58 AM
#17
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I run 42's as well. Overkill for my setup but I got them for $100 brand new through a friend. I'm going to be trading/selling them shortly to get smaller ones..
Car is tuned though and runs decent. I'm sure a smaller injector would be better
08-21-2009, 01:05 PM
#18
The trouble with too big an injector is idle quality and low speed are going to suffer. It takes a particular amount of time to open and close an injector. When you start to idle on very large injectors and you end up with injector timing below about 2ms you start to get into trouble. The stock pcm only has so much resolution for control over how long it holds injectors open. Anyways the point of this is you end up with a very coarse adjustment for idle and low speed fueling. The stock injectors will idle around 5ms and usually it adjusts in 0.1ms increments, now 0.1ms out of 5 is a lot less % diff than 0.1 out of 1.5ms. That is why injectors should be sized properly for the job if its a street car you plan on driving. This is also the reason why really high powered turbo cars will run 16 injectors, as they work in stages sort of like a nitrous window switch.
Now depending on what you're doing and the hardware involved, there may be other cases for race only pieces.
The advantage of slightly too big injectors for a street car is the ability to run e85 if you have a good way to regulate the fuel pressure up to get the extra room required. A good way to regulate fuel pressure does not mean a stock replacement type adjustable rail mounted regulator, it means welding an fittings on the rails and running a good race quality regulator.
Now depending on what you're doing and the hardware involved, there may be other cases for race only pieces.
The advantage of slightly too big injectors for a street car is the ability to run e85 if you have a good way to regulate the fuel pressure up to get the extra room required. A good way to regulate fuel pressure does not mean a stock replacement type adjustable rail mounted regulator, it means welding an fittings on the rails and running a good race quality regulator.
08-21-2009, 01:09 PM
#19
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What do you mean by poor idle? 0_o My car idles plenty fine and drives excellent. Granted, I'm sure with a more properly sized injector it would be even better, but I don't experience any noticeable abnormalities in idle quality (low rpm speeds are kind of mushy though)
08-21-2009, 01:12 PM
#20
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well my a/f is whatever i set it at. it made to most power on a mustang dyno running an 11.8. got a track rental coming up will see what it actually runs the quickest at. fuel pressure is at 44 at idle. never checked it at WOT since my gauge is under the hood. i can't recall my duty cycle id have check an old log. im thinking its in the 70s though.