Max boost on a VF11 setup.

[robertpaige]

So i'm wondering this;

Last night I put in a new MBC from a friend, and I just guessed the amount and took off with the car. Well it was set at 15psi according to my gauge, I didn't bother to pull over and change it though. The car felt AWESOME! It actually pulled how I wanted it to. But what i'm wondering is can this harm anything? I don't care about the turbo because I'm doing a TD04 soon anyways, but I want to make sure other things are okay. My setup is STOCK besides the 3" turbo back exhaust, 06' intercooler, HKS FCD, a cold air intake setup with NGK plugs/wires. Can 15psi break my car? I have stock injectors and stock fuel pump, and the jecs metal maf with access to a plastic one if needed.

All thoughts appreciated

[Someperson]

Possibly, you're running a stock ecu w/out a piggyback correct?

[Alphius]

You won't have proper fuel or timing and are at an increased risk of breaking your engine due to that fact.

Just turn it down to 12 and be safe.

[Someperson]

i'd say 10 at most, w/ the afr screwey you'll have detonation

[robertpaige]

Yeah I am on stock ECU and no piggyback. What if I throw some 440 grey tops in? I also put the JECS plastic MAF in today.

[Someperson]

you will still need some ecu mods to control the 440s properly

[robertpaige]

Gotcha, some reason I thought stock ECU would handle 440's alright, you'd just run rich?

If I put the plastic JECS MAF on, would that make me run lean? i've read different things about it and was wondering.

[randomiam]

The JECS MAF is not compatible with our stock ecu, it will run lean and you do not want that.

The stock ecu can handle 440s but its not really ideal. It runs a little richer and in doing so provides a little more safety margin when boosting higher.

I'd skip the 440s and get a wideband so you know whats going on while you tweak this stuff..

[robertpaige]

But I do want to put it on when I get some type of EM due to the fact that these handle higher boost levels over the metal maf, correct?

And I need to buy a wideband soon.

I'm still trying to figure out what route of EM I want to go..

[Alphius]

I post this whenever someone asks about power on these cars. It's a solid, reliable, fairly cheap setup for what you get. There's not much else you can do that will get you to this power level with the same amount of safety for your engine.

The 440s will run on a stock ECU, but they will be terribly, terribly rich and waste fuel and in general cause many problems. If you get a RobTune you can use them, but won't be as good as the newer STi injectors I recommend below.

Best setup for cheap, reliable power on one of these cars (I post this whenever someone asks about power upgrades):
RobTuned EJ20G ECU
STi 550cc injectors
JECS (green label plastic) MAF
VF39 or TD05-16g turbo
06-07 WRX intercooler w/recirc BPV
Manual Boost Controller at 17psi
Free-flowing exhaust
Stock intake with de-snorkel and coffee cup mod

[Legacy777]

My two cents.....as long as your AFR's are good and you don't max your MAF out, you can run whatever boost you want. Depending on modifications that may be 12 psi, 14 psi, or 15 psi.

10-12 psi should be fine. I'd suggest getting the wideband setup so you can monifor AFR's and your AFR's are good, you can probably bump the boost up a little bit. However, the vf11 probably won't feel or give you much more air (more volume) at higher boost pressures.

[Alphius]

The problem is that the metal MAF will be maxed out over about 12psi with a VF11, at which point your fueling goes to crap and your timing will not be accurate.

Even with good AFR you can still break things with too high of timing, high IATs, or high EGTs. AFR isn't everything when it comes to tuning or running an engine properly.

[SILINC3R]

I would be afraid of the increased temps without an intercooler.

[James614]

If you have the plastic MAF and 440s already, along with an inter cooler and exhaust, just get a robtune and you'll be set for what you're trying to do with proper timing and fueling, and much more power than forcing it to run on he stock ECU.

[Legacy777]

The problem is that the metal MAF will be maxed out over about 12psi with a VF11, at which point your fueling goes to crap and your timing will not be accurate.

Even with good AFR you can still break things with too high of timing, high IATs, or high EGTs. AFR isn't everything when it comes to tuning or running an engine properly.

I guess I should have clarified that when the MAF maxes out that the AFR's usually drop into the low 10's, and if you're seeing that with the wideband, boost needs to be backed off.

I don't really see how timing is going to be affected. At the higher load ranges, the timing doesn't change much, so I don't think that's going to be a big issue.

[robertpaige]

Alphius, thank you for that. That's exactly what i'm aiming for, for now.


SILINC3R, I am intercooled, both my OP and sig state that!

[Alphius]

I guess I should have clarified that when the MAF maxes out that the AFR's usually drop into the low 10's, and if you're seeing that with the wideband, boost needs to be backed off.

I don't really see how timing is going to be affected. At the higher load ranges, the timing doesn't change much, so I don't think that's going to be a big issue.

OK, makes sense on the AFR/wideband then. I am with you there.

Maybe I am a little too wary of appropriate timeing, but timing needs to reduce with boost and load and if the ECU cannot measure load above a certain point timing will not be reduced appropriately. I don't like depending on the knock sensor to bring the timing down when necessary, and with the Subaru ECU doing so impacts the entire timing table not just the points at which knock occurs.

[Legacy777]

Without seeing what a stock timing table looks like, I can't say for sure, but it would probably be ok. I agree that timing should be pulled as boost/load increases, and unless you go super crazy with the boost, the timing values at the "max load" position will be what is used. This isn't ideal, but again I don't think it is going to be your biggest issue.

[Alphius]

I think we agree here Josh. Regardless, he shouldn't do it.

[Legacy777]

Agreed