Well the real reason for a return system is you could use a 1to1 fuel pressure regulator, per every psi of boost you'll get a psi of fuel pressure.
example big turbo SRT4:
at lets say 21psi of boost no return system with big injectors and fuel pump.
all you are doing is adding an huge amount of fuel since a 750 cc injectors is normally rated at 43psi not 58psi. if the car doesnt have a piggy back it will be pig rich. with a piggy back you'll have to take alot of fuel out which it will add timing which it means you'll make more power but it will NOT last long.. Detonation.
with a return system you'll be able to better tune the car for driveability as well as WOT, and not worry about taking out so much fuel out, since it will be there only when u need it WOT under boost.
Great post
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Im leaving my sig like this because it looks stupid.
right my understanding is that 58psi of stock fuel pressure, along with 750s and say 20psi of boost, that is 78psi going through your fuel system, which is not good
Absolutely right, forgot about the rising-rate fpr with a boost reference. My previous post, however, is still valid. The question was, "Why do we NEED it."
Quite simply, we don't... it just makes things alot easier.
Last edited by gvilleSRT : 12-14-2005 at 09:56 AM.
right my understanding is that 58psi of stock fuel pressure, along with 750s and say 20psi of boost, that is 78psi going through your fuel system, which is not good
58 psi is what the stock injectors are rated at, not the stock fuel pressure. It is my understanding all returnless systems use variable fuel pressure to match the flow of fuel through the injectors = no need to return fuel since the fuel provided to the rail is only what is injected (per unit time).
right my understanding is that 58psi of stock fuel pressure, along with 750s and say 20psi of boost, that is 78psi going through your fuel system, which is not good
No not exactly, you have injectors that are rated at 43psi to be 750cc if you have the fuel pressure at 58psi they will be rated at 850cc or more (dont have the chart to give u the exact number)
You are at 20psi but the pressure does not rise with the boost, just remember that the 58psi of fuel pressure on the SRT is static and will lower once the motor is put under pressure.
Last edited by BlackSRT-4U : 12-14-2005 at 10:15 AM.
Absolutely right, forgot about the rising-rate fpr with a boost reference. My previous post, however, is still valid. The question was, "Why do we NEED it."
Quite simply, we don't... it just makes things alot easier.
Not just easier, but safer.. like i said before.. fuel will rise with boost.
On stock turbo it add's HP and on big turbo it makes it safer.
58 psi is what the stock injectors are rated at, not the stock fuel pressure. It is my understanding all returnless systems use variable fuel pressure to match the flow of fuel through the injectors = no need to return fuel since the fuel provided to the rail is only what is injected (per unit time).
BlackSRT-4U, are you saying the SRT-4 uses an in-tank pressure regulator to bleed off excess fuel, rather than pump voltage modulation? Just wondering since I haven't seen an SRT pump/regulator assembly yet. BTW, if it is static pressure, why does it drop off when the engine is under pressure? Do you mean under more boost than the stock level?
Last edited by gvilleSRT : 12-14-2005 at 10:39 AM.
Not just easier, but safer.. like i said before.. fuel will rise with boost.
On stock turbo it add's HP and on big turbo it makes it safer.
But you are still assuming a total dependency on the stock ecm. My point is that the SRT could be made to run fine, be safe, and have high horsepower without a return system. I didn't say it was practical (unless your Ethan) or easy at all.
The real reason you need it is becuase you could not control 750cc injectors with regular compuer , you will need safc or emange and still will not control injectors with stock pressure becuase it is just too much fuel.
Example when putting 750 on stock turbo and even with emanage taking away as much fuel as u can. 1 the car starts to detonate ebcuase too much time advanced since taking away so much fuel. 2 you are still running rich as hellll. That is why it is needed soooo much. All this is with 750cc, Now imagine those that are trying to run 700 whp with 1000cc injectors IE dougnutz. No way to control there with stock fuel pressure system and also car will not flow enough fuel through that FPR to make that amount of power ...
This is why i think its needed
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--------Dyno#s update 4/01/05--------
stock turbo spike 21 psi and drop to 15 to red line
307 whp/370 wtq
-----------Dont remerber the date --------------
last dyno i will spray on stock turbo
410 whp/435 wtq Now its running harder
---------------Bigger turbo in 24psi--------------
ran like a champ for 2 days then the motor messed up, now debating wa to get any suggestions
BlackSRT-4U, are you saying the SRT-4 uses an in-tank pressure regulator to bleed off excess fuel, rather than pump voltage modulation? Just wondering since I haven't seen an SRT pump/regulator assembly yet.
Yes the SRT's use an Intank fuel pressure regulator, which if i'm not mistaken it works with voltage too.. when u do the return system. you cap it off, so it will have nothing to do with the PCM.
But you are still assuming a total dependency on the stock ecm. My point is that the SRT could be made to run fine, be safe, and have high horsepower without a return system. I didn't say it was practical (unless your Ethan) or easy at all.
Well look at it this way, stage 3 for example, bigger injectors, new pcm.. why? to controll the big injectors duty cycle since it doesnt have added fuel pressure. How do you burn excess fuel? advancing timing, have you seen the timing on a stage 3?
I'm not saying it's not possible to make over 400whp with out a return system, i'm just saying it's not safe...
you asked why should u need it.. and i gave you the answers... if you want to try other wise, be my guest but just know timing will be very high. If you plan on not running a return system then get some 650cc instead of the 750's.
Yes the SRT's use an Intank fuel pressure regulator, which if i'm not mistaken it works with voltage too.. when u do the return system. you cap it off, so it will have nothing to do with the PCM.
I just did some looking around and this is correct, it is a combination of both the FPR and voltage monitoring/modulation.
Last edited by gvilleSRT : 12-14-2005 at 11:25 AM.
Well look at it this way, stage 3 for example, bigger injectors, new pcm.. why? to controll the big injectors duty cycle since it doesnt have added fuel pressure. How do you burn excess fuel? advancing timing, have you seen the timing on a stage 3?
I believe it does have more pressure, but referenced to manifold pressure not ambient pressure. The stg 3 comes with a bigger pump and a 4 bar fpr on the rail.
BlackSRT-4U, Thanks for all the info! Nice to hear from people that have some hands on experience and info that makes sense. When are you guys getting the web site up? When I'm out of school I'm heading back to S. Fla. again... I'll finally have money to do something wild with my SRT-4 and not have to drive it everyday.
Last edited by gvilleSRT : 12-14-2005 at 11:28 AM.
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