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Discussion Starter #1
Hi guys,
I was wondering how much extra boost can the stock turbo push without going over its efficiency and without maxing out the injectors, on an stock setup? This is with no other mods than an electronic boost controller. How much extra h/p can be achived by just raising the boost say to 16 or 17 psi?

Thanks in advance.
-d
 

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i have heard of people boosting 16ish psi on stock setup with no problems, not sure about actual hp numbers. hope this helps a little.

Kyle R
 

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APS info on 04STI

Someone who has detaldash or some sort of tool to measure injector duty cycle should provide us info. God, perhaps?

The above URL states that stock injectors are rated @ 480 max flow.. In 02 WRX, running 16.5 psi I saw stock injector DC running up to 96% with UTEC. I am not sure what it would be with 04 STI at 16 psi with stock injectors.

Bottom line is I would seek for safe max boost level with proper AFR around 11:0 to 1 in open loop.

Can someone provide info? Any tuners?

Thanks,

Dan from PA.
 

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I can run about 16.9-17.0 lbs of boost with a greddy E-01 BC, but I don't normally. I haven't tried to turn it up more than that, because I have seen people destroy their turbos by turning them up too high.
 

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Discussion Starter #6
I could run 16 psi on my WRX all day without any problems, so that's why I figured that on the STi it would be safe to run a bit more, due to bigger turbo and injectors. I wouldn't do over 20psi anyway :)

-d
 

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15-15.5 PSI is max if you just have boost controller. With tuning I can take it up to 16.5 PSI max. 17 PSI no way not without race fuel.
 

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Discussion Starter #8
Is this due to the injectors maxing out?
 

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I have seen 16.9-17.0 for sure without fuel cut. I think Guru is saying its not a good idea to run it that high, but I don't get fuel cut when I tried it. I have been told to go no higher than 15 psi to protect the turbo. Don't know for sure though...
 

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mkewrx said:
Is this due to the injectors maxing out?
No. And a/f, nor fuel cut, are an issue (until you raise boost significantly). It's a timing issue.

STIs have extremely advanced timing; the extra air (from increasing boost) will cause the conbustion process to speed up and produce timing knock/ping. (Yes, the very problem that warranted the ECU reflashes last year.)
 

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Stikya said:
mkewrx said:
Is this due to the injectors maxing out?
No. And a/f, nor fuel cut, are an issue (until you raise boost significantly). It's a timing issue.

STIs have extremely advanced timing; the extra air (from increasing boost) will cause the conbustion process to speed up and produce timing knock/ping. (Yes, the very problem that warranted the ECU reflashes last year.)
It certainly appears to be at least partially related to boost. I wouldn't touch boost, fuel, etc. on the engine/ECM without monitoring for knock at the very least.

-st
 

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Over heating issues?

Guru said:
15-15.5 PSI is max if you just have boost controller. With tuning I can take it up to 16.5 PSI max. 17 PSI no way not without race fuel.
Just to reinforce what Dan is saying - the TurboXS STi ran 16 PSI bone stock and pinged like a madman.

Linky:

http://www.turboxs.com/TXS TECH STI 1.htm

Perhaps the issue all along is the crazy advance the STi runs coupled with variances in the wastegate size on the VF39? Hmmmmm....more speculation. We need feedback from the companies that are cracking the ECM.

-st
 

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I did 18.3psi on my car. I got Invidia downpipe, Tanabe cat back setup and intake only. My HKS EVC V shown 18.3psi (with 91 fuel). But I don't do this as normal. I keep 14 to 15 for daily driving.
 

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port-n-polish turbo in new england area?

Just to reinforce what Dan is saying - the TurboXS STi ran 16 PSI bone stock and pinged like a madman.
We do have to keep in mind, that the TXS ping was pre-STI ECM reflashes (that became standard issue around October).

So, most of us have cars that run slightly retarded timing (atleast at certain RPMs) from the ping-happy STIs. This could allow us to run slightly higher boost safely. Maybe! The only sure thing is...

everyones car is going to run differently. There is no 1 max. psi number for all.

I've personally hit 17+ w/ no audible knock, but that doesn't mean it didn't knock and that doesn't mean I should set my boost level there.

Bottom line: up to 15.5 is safe for everyone's stock ECM. Some will be able to run higher w/ no problems, but will be doing so at the risk of knocking. (Keep in mind the beginnings of knock can be inaudible/masked by engine noise.)

IMO, an extra 15-25whp (from an extra psi or two) is not worth the potential of systematically destroying your engine.
 

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What exactly is knock/pinging, and why does turning the turbo up cause this? I have heard the term lots, but don't really know what it is. I do know that when I run 16-17 psi, I can't hear any strange noise resembling "knocking".
 

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Davidsk5018 said:
What exactly is knock/pinging, and why does turning the turbo up cause this? I have heard the term lots, but don't really know what it is. I do know that when I run 16-17 psi, I can't hear any strange noise resembling "knocking".
http://zhome.com/ZCMnL/PICS/detonation/detonation.html

(In our case) Simply put... knock/detionation can occur because the increased air (from adding boost) will raise engine temps and cause the a/f burn to occur prematurely (for our advanced timing). Basically, the piston is being forced up while it is trying to come down. This is what causes the vibration, and results in the timing knock/preignition.

The most common solutions are:
1) Don't raise boost
2) decrease timing (ECU)
3) raise boost anyway and hope your timing curve is different (retarded) enough that it doesn't cause knock in your car.
EDIT:
4) Or use alternative means to cooling down your burn, although all have their potential negative side effects: lower gap/cooler plugs or add a coolant ( http://www.aquamist.co.uk ) to the mixture.
 

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It seems as though a front mount intercooler would help the air cool down more to prevent early combustion. I think it would still be necessary to get the ECU remapped to change the timing though. Thoughts?

I had no idea that knock can be so bad for my car. Thanks for the great link. I will defintely keep the psi around 15.
 

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Davidsk5018 said:
It seems as though a front mount intercooler would help the air cool down more to prevent early combustion. Thoughts?
If you cool the air, before it goes back into the engine, you are going to be creating denser air. And denser air (= more air volume) will increase the temperature of combustion. So, the effect of it being cooler (to slow the burn) will be more than offset by the fact that you pulled in more air (which will increase the burn).

Take nitrous as an extreme example-it's just really cold air. But, because it's cold, it's very dense. So, it actually increases the temperature of the burn significantly. So, not only is additional fuel needed to offset the additional air, but also colder plugs w/ lower gap, because the burn is so hot. Any cooling effect is far outweighed by the fact that a greater air volume is present.

The trick is to intake the same volume of air, but have the mixture burn cooler. Using race fuel would slightly help. But, not enough to raise boost much - it becomes a benefit-to-cost loser.

The safest and simplist bet is to wait for an ECU and let it control timing and boost, so that timing can be retarded and boost added safely.
 
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