So the injectors on a 2003 SRT-4 are 682cc/min at what psi? 43psi or 58psi? THe old standard is supposedly measured at 43 psi i believe, so these 682cc/min, if thats what they are rated at @58psi, might equivicate to something like 440cc/min at 43psi. So at 15psi of boost they will flow whatever they are good for at 43psi, seeing as 58-15=43. Is this how it really works on this car?
Also, why have i seen mentionings of the stock injectors only actually flowing somewhere in the neighborhood of 350-450cc/min? perhaps this is their supposed "true flow capabilities" at the standardized 43psi.
Jeff
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at idle the engine is somewhere near -10psi gauge pressure, or roughly 4.5psi absolute.....its a vacuum by gauges measurement, but in abosolute pressure its around 4psi.
So......
The vacuum causes the effective fuel pressure difference across the manifold to be around 58+10=68psi. This will cause the fuel injectors to flow even more fuel, seeing as the vacuum is essentially "sucking the fuel out of them". This makes the injectors seem bigger, and flow more fuel per duty cycle. This would make idling even more difficult to control, especially if you go and install even LARGER injectors.
In the wrx and many other vehicles that have a compensating fpr that keeps the pressure differential across the manifold/injecors the same, when you idle the fuel pressure in the line actually drops...so at idle my wrx fuel rail is at 33psi....and whne combined with the -10psi of vacuum the effective pressure becomes 43psi. This keeps idling easy, even with larger injectors, to a point.
Originally posted by Dietro You are exactly correct. That's why the injectors are rated at 682cc.
In most of what of what I snipped out, you also hit on the exact reason the injectors used on that engine are HUGE by comparison to "normal" systems.
That's how we got into this conversation afterall...
Time for a physics lesson. What fun!
Injectors live by the Bernoulli Principal.
Which basically says the flow rate change is the square root of the ratio of the pressure change. This pressure is the delta across the injector, so they do flow more at idle with a constant fuel rail pressure. Not using a manifold-referenced FPR kind of puts a cap on how big of an injector you can use and still flow little enough fuel to not cause your eyes to water at idle.
If the SRT injectors are rated at 682 cc/min @ 58 psi they would be (43/58)^0.5 * 682 = 587 cc/min @ 43 psi. Which is still HUGE.
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Last edited by 3barboost : 09-10-2003 at 09:04 PM.
According to This Link The stock injectors are nowhere near 682cc. They are more like 479cc/min at 58psi, or using the old standard of 43psi they are actually only around 350cc/min, for comparisons sake(relative to most other injector ratings seeing as most are flow tested and rated at 43psi). So they are actually very small injectors.
Originally posted by wrx-to-srt4 According to This Link The stock injectors are nowhere near 682cc. They are more like 479cc/min at 58psi, or using the old standard of 43psi they are actually only around 350cc/min, for comparisons sake(relative to most other injector ratings seeing as most are flow tested and rated at 43psi). So they are actually very small injectors.
Originally posted by wrx-to-srt4 Where on earth did this "682" number come from?
I was thinking that very thing this morning. I only quoted that figure because it was posted here. In the SRT-4 Tech article in SCC they say they are going to flow test the injectors at the 43psi standard shortly, so there should be a definitive and objective answer soon.
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Todd Dietrich
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'01 PT Cruiser
'91 Spirit ES Turbo intercooled
'89 Shelby Dakota #1062
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So the stage II injectors flow 682cc/min at 58psi. The stage one injectors flow something like 527cc/min@58psi, and the stockers flow 479cc/min.
All At 58psi
Stage 0 - 479cc/min
Stage 1 - 527cc/min
Stage 2 - 682cc/min
Converted to real-world measurements at 43psi for comparisons sake
Stage 0 - 412cc/min <<-cacluated by multiplying stg1 by (10/11)
Stage 1 - 453cc/min <<-because this is Stock * 1.1 (+10%)
Stage 2 - 587cc/min
I hope that all makes sense....I used your formula. The 527cc and the 682cc are known, the rest are calculated based on your formula, and based on teh fact that, "stage 1 injectors flow 110% of what the stock ones do" so divide the Stg 1 injectors by 11, then multiply by 10 to get the original "100%" which is what the stockers flow. That came out to be 479cc/min@58psi and 412cc/min@43psi.
If you agree with this please say so.
Im not trying to be right or wrong, I just want to contribute to the finding of the truth!
The wheel has been re-invented about 50 times in this thread. Every time a new turbocharged car comes out, everyone has to break every aspect of making power down to the basics. Us OldSkool Mopar guys have been dealing with these exact same issues since the mid-80s. There is NOTHING new here, other than a bunch of 17 year old kids whining about the cost of making more power.
You guys are spoiled.
You can make a ton of power with just about zero intelligence these days. There was about 2 vendors for the original FWD Mopar guys to deal with and the only information you got was over the phone and trial and error on your ride. You couldn't log on and print out a how-to. You actually had to see what worked on your ride and learn a whiole lot in the process.
These "I want it now and for cheap as hell" post make me sick.
GO make 300/300 on your own then, i challange you......
Originally posted by Bryan The wheel has been re-invented about 50 times in this thread. Every time a new turbocharged car comes out, everyone has to break every aspect of making power down to the basics. Us OldSkool Mopar guys have been dealing with these exact same issues since the mid-80s. There is NOTHING new here, other than a bunch of 17 year old kids whining about the cost of making more power.
You guys are spoiled.
You can make a ton of power with just about zero intelligence these days. There was about 2 vendors for the original FWD Mopar guys to deal with and the only information you got was over the phone and trial and error on your ride. You couldn't log on and print out a how-to. You actually had to see what worked on your ride and learn a whiole lot in the process.
These "I want it now and for cheap as hell" post make me sick.
GO make 300/300 on your own then, i challange you......
You must have been a customer of Forward Motion, Lambros, and Emrio then
I think it's the fault of MTV myself...
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