fuel pump
 

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 :?:

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!

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

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?

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?

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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.

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.

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

What type of engine managment is the answer :?:

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! :lol:

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.

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

On a mildly related note, I remember reading recently about UR600 (?) injectors where each injector in the set had a slightly different flow rate to compensate for the fact that some cylinders run richer or leaner than others in our engines. So if you end up going with bigger injecters you have to install them the right way. Or something.

I have read the cycle duty is too high so you guys think this is not needed for down pipe and high cat all I want is a little more power for track days and autox without blowing up my motor :?:

That's an interesting solution to the problem! But still, if the fuel pressure drops, #3 will be the 1st to starve... but the matched injectors might provide a slightly more balanced fuel delivery, but I'm not sure that it would make much of a difference in performance.

That's doing it the hard way. :lol: I'd rather convert my STi to top feed rails and have a plethora (I said plethora in a sentence!) of injector choices.

I've seen STis put 280 to the wheels with stock fueling. You should always run out of stock turbo before you run out if stock injector.

Not quite, the STi pinks are JDM STi injectors which are top feed and have a higher flow than the USDM STi injectors. (Assuming I have a clue what I am talking about I mean).

And Eric, if you change your injectors you WILL need a custom ecu map, which means the accessport will be useless unless you drive out to cobb for a custom tune ... or they pull their finger out and finish their tuning software so that you can get maps made locally, but that doesn't look like happening until well into next year.

I think it wasn't for performance so much as for the fact that the cylinder that goes lean first is usually the one to have problems. I wish I could find the website of the company selling them.

well if you had your injectors flowed you could install them to where the best flowing one went in the #3 and so on to the richest.

wouldn't a fuel pump and fail rails be a good way to go? :D

Agree here all the way. if all your adding is a DP and a high flow cat you will be fine. for that added safty and to keep your mind at ease just do the parallel fuel rail mod. quick easy and done with it..and the fuel pump will not hurt either. no need to up the injector size or do a reflash..YET!
the only real time you should up your injectors is when you are doing a turbo swap, an injector upgrade and ecu reflash or getting an SAFC is what they ref. to as supporting mods.

Wow! You guys pretty much covered it all....


I love lamp.

and here comes MattR too intoxicate us off topic :lol: :lol:


Pump Group Buy? Install Day? hehehe

ok back on topic! 8)

Seriously though, I would love to get a more definate answer on this subject, I suppose the main question is not which mods to go with, it's in which order to get them. Whether or not the fuel pump is the starting point, I'm not sure. It couldn;t hurt.

1. Fuel Pump
2. Fuel Rails
3. Injectors
4. Intercooler
5. Turbo
6. Dyno Tuning

wow thats a lot of steps :lol:

there has been tons of threads and discussions on the idea that fuel rails may not be needed. I do not know about STi's, but a ton of WRX owners are upgrading without the addition of fuel rails.

Based on all the reading I do at work all day ;) if/when I get an STi the mod path will be:

Step 1: Turboback + custom dyno tune

Step 2: Fuel Pump + injectors + turbo + custom dyno tune

I believe that the STi topmount intercooler is as good as any out there. I would only replace it if I was going to go to a frontmount intercooler. Higher lag but more power potential and no more heatsoak worries. Also, I believe that upgrading fuel rails is overrated, but then again I only have 8 hours a day to do research ;)

Powerwise I don't think it is worth going beyond those 2 steps unles you are going for an all out built block == $$

Honestly a custom suspension setup will make more difference on the track.

I ate a red candle!

actually that mod BAN and I were talking about isn't a rail replacement its just changing the way each rail gets fuel.

Exactly. It's not a good idea to do engine mods one step at a time. As you chenge one system, you need to make sure it still works as a cohesive whole.