How much boost before I need larger injectors?

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 5:09 pm

So... If I had a Boost Guage, FCD, MBC, '06 FXT TMIC, and say a VF-12...

And of course a 3" TBE...

How much boost can I run before I run out of fuel... 14? 16?

And which injectors would I need to say run... 16? And what rails would I need with said injectors...

OH and when to upgrade fuel pump?

Thanks guys

Arctic Assassian · Post by **Arctic Assassian** » Tue Feb 05, 2008 5:44 pm

Well, The only way to really know, is check your injector duty cycle. You should be right at the limit with 14.
I would reccomend the yellowtops out of the wrk for starters, with 92-94 na legacy rails.
If you ever decide to go even bigger, you can mod the yellowtops out to 1000 cc.
fuel pump now.

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 5:58 pm

Now... With the WRX injectors would I need more EM?

vrg3 · Post by **vrg3** » Tue Feb 05, 2008 6:01 pm

Upgrade the fuel pump right away. Your pump has got to be tired by now, and increased boost makes it work harder because it needs to produce more pressure against the boost.

You don't size injectors by boost pressure, though; you size them by power. A simple rule of thumb for a turbo 4-cylinder is that your injectors' flow in cc/min needs to be about double your engine's output in horsepower, plus a little extra safety margin; that's based on generally-accepted values of 0.65 lb/hr/hp for BSFC and a maximum duty cycle of 85%.

I would guess that your stock fuel system would be maxed out with a VF12 at 9 psi, a Forester intercooler, and a 3" turbo-back exhaust.

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 6:24 pm

Cool, thanks...

Walbro 255lph right? On the top of the list... After Suspension and Brakes of course.

How many cc/min are WRX yellowtops?

And can the stock ECU control those?

vrg3 · Post by **vrg3** » Tue Feb 05, 2008 7:22 pm

A Walbro 255-liter-per-hour pump should do, yes. I myself am using a stock fuel pump from a 4th-generation Toyota Supra Turbo. It is supposedly similar in capability to the Walbro, but built by Denso to Toyota's reliability standards. I also like having Toyota parts on my Subaru.

The yellow top injectors you're thinking of are the new-age STi ones? From what I hear, they flow about 550 cc/min. That's at the STi's stock fuel pressure, though, which is higher than ours. At our fuel pressure they'd flow about 500 cc/min. They fit right into 92-94 NA fuel rails, which bolt right up to an EJ22T.

The stock ECU cannot adequately control any injectors other than the stock ones.

I am running my stock injectors and stock ECU. My fuel system upgrades consist of the aforementioned pump and a Vortech RRFPR with an adjustable bleed valve to control the amount of fuel pressure rise. If you want a simple solution, I highly recommend this one.

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 8:38 pm

How much do the stock injectors flow?

And the yellow tops reffered to, I believe, were stock WRX ones...

So does that bleed valve allow more flow with the stock injectors? Sorry for bein a tard, but I dont know that much about the fuel system...

asc_up · Post by **asc_up** » Tue Feb 05, 2008 8:41 pm

Vikash - couldn't he run the EJ20G injectors? The flow 440cc's. I've read that the ECU can flow a maximum of 444cc's and the 440's are literally right under that limit...

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 8:43 pm

I know Devan (livestrong) is running 440s and I think he has the stock ecu...

asc_up · Post by **asc_up** » Tue Feb 05, 2008 8:48 pm

Jake (Jake15) runs 440's on the stock ECU. He said that he runs rich sometimes, but otherwise it sounds fine.

dropdfocus · Post by **dropdfocus** » Tue Feb 05, 2008 9:03 pm

Ok, I'll throw my $.02 worth in on the matter. If you're gonna do this, do it right. Back pedaling is a dumb thing to do (trust me on this!)...

It is very worth while to use 550cc STi yellow tops (WRX uses top feed & you'd need to change out your fuel rails to mate up correctly) with the ]TurboXS Dtec fuel controller for fuel management & also a rising rate fuel pressure reg. To install these injectors, you will need N/A fuel rails (easier to track down & much cheaper than WRX parts).

As for the JDM 440cc WRX grey injectors (Jap. used side feed on the 1st Gen WRX), you can cheat with using the stock ECU, but you have no control over the management of the air/fuel ratio.

Also, with Vikash's statement on injector duty cycle, you should not pass 85% or you will run into the possibility of burning out an injector (if not all of them). Using the Walbro 255 is a good idea, but you can also utilize the STi fuel pump too. Many guys are selling them for $20-$40 on NASIOC since they swapped to the Walbro.

smh0101 · Post by **smh0101** » Tue Feb 05, 2008 9:16 pm

Do I get a High Pressure Walbro? Or an OEM replacement?

Jason - That sounds like a good chunk of change...

My goal is about 230hp...

What will I need to do this? I mean in terms of fuel stuff...

dropdfocus · Post by **dropdfocus** » Tue Feb 05, 2008 9:32 pm

Well, if cheap is your route, then here ya go:
JDM 440cc grey injectors - $ really depends on who's selling them
- from EJ20G or EJ20K
N/A fuel rails - $20 average price
- (EJ22 1st or 2nd Gen Legacy or EJ25 from Legacy GT)
STi stock fuel pump - $40 average price
-----------------------------------------
This would get you started.

As for my setup:
Walbro 255 - $45 (used)
TurboXS Dtec fuel controller - $300 (used)
- w/ GameBoy Advance
TurboXS analog/digital aux. signal input - $30 (new)
STi 550cc yellow top injectors $185 (used)
N/A fuel rails - $ freebie
PLX Devices wideband air/fuel ratio controller - $182 (new)
Vortec RRFPR - $119 (new)
-------------------------------------
Total Price: $861
Not running lean & tanking a motor - PRICELESS!!!

vrg3 · Post by **vrg3** » Tue Feb 05, 2008 10:25 pm

The stock injectors flow about 370 cc/min. And like Jason says, the yellow-tops are stock STi injectors, not WRX injectors.

The ECU's fuel trims can range up to plus or minus 20%, so you might find that if everything else is in perfect alignment you can get good results with 440 cc/min injectors which are pretty close to 20% bigger than stock. Would I recommend it? Nope. But that's just me.

If you're not using a rising-rate fuel pressure regulator and running less than about 20 psi of boost, the regular Walbro pump should do okay. It's just that above about 60 psi its flow starts to drop off. But I'd suggest getting the high-pressure one just in case.

The bleed valve on my RRFPR is in the boost line. It lets me reduce the amount of extra fuel thrown in because of the RRFPR. I put it in because otherwise I'd have way too much fuel. Try searching for posts by me where I explain about FPRs and RRFPRs to learn more about how that works.

The DTEC does give you more control over fueling than a single knob on the bleeder, but it also introduces a new source of trouble: spark timing. Because the DTEC messes with the MAF sensor signal, it messes with the ECU's load calculations. Minimum spark advance at light load is way higher than the maximum permissible advance at high boost.

If you do decide to go with STi injectors, PM me. I have a set I can sell.

dropdfocus · Post by **dropdfocus** » Tue Feb 05, 2008 10:46 pm

vrg3 wrote:If you do decide to go with STi injectors, PM me. I have a set I can sell.

Well that sucks...

I just picked mine up like a week ago after I sold the aftermarket 550cc injectors to Douglas Vincent. I would have given my money to you if I had known ahead of time.

As for the timing issue, that is something that sucks about the OBD I cars. This is why I plan on purchasing the Perfect Power 6 eventually to take the place of my TurboXS Dtec. This is what I was talking about with back pedaling... If I had done more research, I would have just saved up a bit more & spent the extra cash on the PP6 instead.

vrg3 · Post by **vrg3** » Tue Feb 05, 2008 11:08 pm

D'oh. Opportunity missed.

Yeah, it's hard to draw the line between doing something reasonable now and having it set up to do the Right Thing when you have the money. I got lucky and got my RRFPR used for only $40, so if I ever decide to do anything differently I'm only out that small amount. The high-output pump was a necessity regardless.

BXSS · Post by **BXSS** » Wed Feb 06, 2008 2:43 pm

vrg-3
What plate/ratio are you using on the FMU?
FMU's are always in demand for ghetto-turbo conversions in my neck of the woods, I think you would be able to get your $40 with no probs.

To the original poster I'm also using 440's on a stock ECU with decent results, but I did lower the base fuel pressure down a smidge.
A low ratio FMU (2 or 3:1) + stock injectors would be interesting to try & should work well.

The Denso fuel pump from the twin-turbo Supra actually flows slightly more than a Walbro 255, but costs like 3x as much money if one were purchased new. The RX7 TT pumps also flow alot of fuel but are pricey.

Spend $100 & get a Walbro 255hp/hv pump new.

vrg3 · Post by **vrg3** » Wed Feb 06, 2008 4:58 pm

I don't know what the rise ratio is on my FMU. It's effectively very low, though, because I'm bleeding most of the boost signal away from it.

I'm pretty much doing what you describe -- an effectively low ratio FMU with stock injectors. It does work well for me.

BXSS · Post by **BXSS** » Wed Feb 06, 2008 5:04 pm

I see Adjustable FPRs with a 1.7:1 rise rate (instead of the normal 1:1 rise) advertised in car mags I get from England & Australia.

I wish there was something like that available here, the closest thing that comes to mind is the Vortech Super FMU but those suckers are pricey (cost about the same as an Aeromotive FPR+a Vortech FMU).

vrg3 · Post by **vrg3** » Wed Feb 06, 2008 5:07 pm

Why? The bleed valve approach works quite well, costs only a couple of bucks, and is adjustable.

BXSS · Post by **BXSS** » Wed Feb 06, 2008 5:17 pm

It basically kills 2 birds with 1 stone for folks who want to change base fuel pressure & have a slightly higher than 1:1 rise with boost for the cost of just the FPR.

The FMU will do the same job for folks on the stock FPR which is probably 97.5% of the folks here.

vrg3 · Post by **vrg3** » Wed Feb 06, 2008 5:22 pm

Ah, gotcha. I missed the part about adjusting base pressure.

smh0101 · Post by **smh0101** » Wed Feb 06, 2008 5:33 pm

And I am officially lost...

vrg3 · Post by **vrg3** » Wed Feb 06, 2008 5:34 pm

Lost?

smh0101 · Post by **smh0101** » Wed Feb 06, 2008 5:37 pm

Yea... FMU's FPR's and ratios and stuff...

Oh look all this just flew over spencers head like a Boeing 747! lol

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How much boost before I need larger injectors?

How much boost before I need larger injectors?