fuel pump

[qksubi]

I have been hearing that the stock cycle duty is too high on our fuel pumps and then I watched a show where they moded a Sti one mod was to change the fuel pump has anyone besides matt and I hear of this.
It is a cheap mod and is walburo pump plug and play!
I have read it changes the cycle duty from 105% to 90% so when you drive hard the #3 piston doesnt run too lean!
does anyone have any more info on this

[sperry]

I didn't think injector duty cycle on a stock STi was that high!

However, I'm not sure that having more pressure behind the injectors will change their duty cycle any. It would just add some reassurance that if an injector is maxing out there's at least no shortage of fuel.

In order to lower duty cycles, I think you have to simply get higher flowing injectors (and of course a pump that can supply them). Also, how do you get an injector to run at 105% duty? Doesn't 100% mean the injector is basically locked open?

Anyway, I believe the Walbro pump is a plug-n-play replacement for stock Subaru pumps, but the install still involves the gas tank, so you have to prep carefully. You don't want a fire!

[murphy]

by replacing the pump to a walburo 255 you will increas your amount of fuel and it will help a bit you will get more flow to your injectors but they will still only deliver so much fuel, you will get a little more per duty cycle % and it should drop in if anything you might need to do a trim on the ring the pump mounts on. but thats easy enough. I've done a few subie fuel pumps let me know if you need a hand

[qksubi]

I think thats what they are saying the #3 is stuck open under hard driving . So you think that higher cfm injector is the answer and the fuel pump?
this of course all after I can get the cobb accesport and high flow cat with down pipe what do think of this downpipe from helix?

[murphy]

using a higher CC injector will lower your duty cycle, but you need a way to control the fuel amount now since a cars stock ecu will not be able to compensat for the diffrent size. an Apex safc II will do the trick very well.
Question ..what is the stock cc rating for and sti 410? 510?

[MikeK]

I am not sure about the STi, but I was under the impression that for the WRX you only have to upgrade the pump if you upgrade the injectors.

[murphy]

you could try it..but stock ecu's can't compensate for higher flow injectors and you will run richer than you wish to. or you cold just try the pump and see how it goes. The pump will help a little. its also in what goals you have. you could also do the fuel delivery mod. that they use on the 2.5 rs when they go turbo so the #3 cyl. gets enough fuel.

[Nick Koan]

Originally Posted by MikeK

I am not sure about the STi, but I was under the impression that for the WRX you only have to upgrade the pump if you upgrade the injectors.

A lot of people do pump, injectors and reflash all at the same time.

[sperry]

Originally Posted by murphy

you could try it..but stock ecu's can't compensate for higher flow injectors and you will run richer than you wish to. or you cold just try the pump and see how it goes. The pump will help a little. its also in what goals you have. you could also do the fuel delivery mod. that they use on the 2.5 rs to the #3 cyl. gets enough fuel.

I thought the stock O2 sensor took care of that. Basically the larger injectors add more fule at a certain duty cycle, so the car runs rich, the O2 sensor sees this and tells the ECU to reduce fueling, so the duty cycle goes down.

Perhaps that's only something that's done with a remap of the ECU. All I know is, I wouldn't bother with a piggy-back AFC when you can reprogram the ECU to do it. The ECUs in Subarus are powerful computers! Use them to your advantage!

[Kevin M]

Originally Posted by sperry

I thought the stock O2 sensor took care of that. Basically the larger injectors add more fule at a certain duty cycle, so the car runs rich, the O2 sensor sees this and tells the ECU to reduce fueling, so the duty cycle goes down.

Perhaps that's only something that's done with a remap of the ECU. All I know is, I wouldn't bother with a piggy-back AFC when you can reprogram the ECU to do it. The ECUs in Subarus are powerful computers! Use them to your advantage!

I have a hard time believing that Subaru allowed duty cycles to creep over 90% on a stock turbo, but I'll concede that for the monent. If it is the case, then adding a stronger fuel pump will cause all the injectors to flow more at any given Gamma time. Injector flow is always based on the fuel pressure at WOT/full boost since turbo cars almost always have rising rate regulators. Hence, raising the fuel pressure essentially increases the size of your injectors. Also, if you were to only add slightly larger injectors, say 650s to replace the stocks, the stock ECU can correct for them. Very large injectors of course require reprogramming. And I would never make a mod of any kind to fueling with reflashing the ECU. Piggybacks like EBCs and SAFCS are no longer the best solution for working with modded engines. There's absolutely nothing you can do with any combination of piggybacks that you can't do with a reflash, and there's a hell of a lot you can't do with piggybacks that you can with a reflash. We're past the days of rejetting carberateurs here- these are highly sophisticated machines, and shortcut methods are not the best approach.

[murphy]

yes the ecu in the subies are very good but I've never seen any cars ecu that will compensate for highr flow injectors because higher flow injectors will supply more fuel at every rpm range your cars stock ecu is programed to run a certain size injector. The SAFC 2 will control the fuel amount easly with no problems with running rich. remember scott all stand alone ecus require you to tell it what size injectors you will be using so it knows what the flow will be and calculate for it once you have you base map done same with a stock ecu at the factory. here is a link for where I read about the fuel delivery mod for turbo rs cars. http://www.ravensblade-impreza.com/

[sperry]

Originally Posted by murphy

yes the ecu in the subies are very good but I've never seen any cars ecu that will compensate for highr flow injectors because higher flow injectors will supply more fuel at every rpm range your cars stock ecu is programed to run a certain size injector. The SAFC 2 will control the fuel amount easly with no problems with running rich. remember scott all stand alone ecus require you to tell it what size injectors you will be using so it knows what the flow will be and calculate for it once you have you base map done same with a stock ecu at the factory. here is a link for where I read about the fuel delivery mod for turbo rs cars. http://www.ravensblade-impreza.com/

Yeah, I know Brian's site. But I'll bet that article was from before the Suby ECU was cracked and EcuTek came state-side. Like Kevin said, why use a piggy-back when you can have the stock ECU do it, as well as so much more! That's the reason why I ditched my UniChip for a reflash.

[Kevin M]

Originally Posted by murphy

yes the ecu in the subies are very good but I've never seen any cars ecu that will compensate for highr flow injectors because higher flow injectors will supply more fuel at every rpm range your cars stock ecu is programed to run a certain size injector. The SAFC 2 will control the fuel amount easly with no problems with running rich. remember scott all stand alone ecus require you to tell it what size injectors you will be using so it knows what the flow will be and calculate for it once you have you base map done same with a stock ecu at the factory. here is a link for where I read about the fuel delivery mod for turbo rs cars. http://www.ravensblade-impreza.com/

What you call the "fuel delivery mod" is normally called the "parallel fuel rail" mod. It's intended to ensure equal fuel pressure to all 4 injectors, and is usually helpful. Some cars are worse than others about leaning out #3. And like Scott and I said, the ECU will read the O2 sensor and trim fuel as needed to compensate for larger/smaller injectors, within reason. 10-15% bigger is within reason. And SAFCs are still not viable alternatives to a reflash, because the ECU is going to remap fuel around the SAFC, just like it has since the 2000 MAP engines came out. There really is no substitute for reflashing. There is not a single better alternative.

[Kevin M]

Originally Posted by sperry

Yeah, I know Brian's site. But I'll bet that article was from before the Suby ECU was cracked and EcuTek came state-side. Like Kevin said, why use a piggy-back when you can have the stock ECU do it, as well as so much more! That's the reason why I ditched my UniChip for a reflash.

No, the parallel fuel rail mod is a really good idea when you approach max duty cycle. Aftermarket fuel rails already incorporate it, but if you decide to skip fuel rails, I would definitely consider doing this. All UTEC users should do it too.

[sperry]

Originally Posted by BAN SUVS

No, the parallel fuel rail mod is a really good idea when you approach max duty cycle. Aftermarket fuel rails already incorporate it, but if you decide to skip fuel rails, I would definitely consider doing this. All UTEC users should do it too.

I didn't read the article... I assumed it was about using SAFC for fueling on a home-brew RS-T. I agree that fuel rails are smart for any car that's nearing 100% duty on the injectors, just to make sure all 4 are actually putting out the same amount of fuel. No need to pop #3.

[Kevin M]

Originally Posted by sperry

I didn't read the article... I assumed it was about using SAFC for fueling on a home-brew RS-T. I agree that fuel rails are smart for any car that's nearing 100% duty on the injectors, just to make sure all 4 are actually putting out the same amount of fuel. No need to pop #3.

There's an unsettled debate about when you actually need new rails, but modifying the fuel route through the stock rails is definitely worth it.

[murphy]

thanks I couldn't remember its been a long time since I read it. I was going to do it but well no more turbo. well still if he just wants a little safty I'd suggest using that mod it should eliminate the #3 cyl running lean.
Man this thread became all about Scott, myself and BAN...I hope he got the answer he was looking for.

[qksubi]

The COBB acessport will do the the trick and does the helix down pipe with highflocat make a differnce from stock

[sperry]

Originally Posted by murphy

thanks I couldn't remember its been a long time since I read it. I was going to do it but well no more turbo. well still if he just wants a little safty I'd suggest using that mod it should eliminate the #3 cyl running lean.

Yeah, certainly the Walbro won't hurt anything, and it sounds like the extra pressure will result in lower injector duty cycles and an added margin of safety for #3. Plus you will be all ready to support larger injectors if you ever decide to do some power mods.

[Kevin M]

Originally Posted by qksubi

The COBB acessport will do the the trick and does the helix down pipe with highflocat make a differnce from stock

Actually, engine management won't solve the issues chris, Scott, and myself were discussing. When your injectors don't flow enough for your application, you gotta do something about it. More fuel pressure is the first fix.

Yes, you'll love the downpipe. The stock downpipe is the single worst part on the whole car, both WRX and STi. Go with the highflow cat, you won't really miss the slight gains from being catless, you'll stay in Street Touring/Street Mod autocross, and the cat will probably prevent boost creep up here.

[qksubi]

What size injectors are not over kill for what I want to do
New down pipe high flow cat and cobb acessport and feul pump
Perrin does do a core trade for a larger injector $219.0

[qksubi]

What type of engine managment is the answer

[sperry]

Originally Posted by qksubi

What size injectors are not over kill for what I want to do
New down pipe high flow cat and cobb acessport and feul pump
Perrin does do a core trade for a larger injector $219.0

I was under the impression that stock STi injectors and pump are adiquate for a TBE, intake, and reflash. Hell, your injectors are the ones that the WRX guys buy when they upgrade their stock turbos!

[Kevin M]

Originally Posted by qksubi

What size injectors are not over kill for what I want to do
New down pipe high flow cat and cobb acessport and feul pump
Perrin does do a core trade for a larger injector $219.0

the Perrin larger injectors are really big, and there's been a lot of talk that "modified" stock injectors work great at high flow rates, but don't idle well and mixtures are inconsistent at low loads. However, your stock injectors are big enough on the stock turbo. Add a fuel pump and/or do the parallel mod for peace of mind. Also, I'd recommend a reflash over the AP. Too many strange stories are coming from people who use the Cobb, while nobody has any complaints about EcuTek other than lack of real user tune, which Cobb's AP also lacks.

[Kevin M]

Originally Posted by sperry

I was under the impression that stock STi injectors and pump are adiquate for a TBE, intake, and reflash. Hell, your injectors are the ones that the WRX guys buy when they upgrade their stock turbos!

Close, WRX guys buy top feeds that happen to flow about the same as the STi side feeds.