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Discussion Starter · #1 ·
Just want to make sure I'm understanding the dangers of increasing boost. On a bone-stock engine, turbos, injectors, etc., raising the boost over 15psi will leave the injectors unable to inject enough fuel, making the mixture lean and prone to pre-detonation, right? Then if my Autometer A/F guage ever shows lean at high boost, I've got a problem. If it stays in stoichiometric or rich, I'm good, right?

(I do have a boost guage as well, but it's autometer and I guess it might not be all that accurate)

When idling, it will bounce lean to rich? On high throttle, it will be rich? Why is that, btw, wouldn't you want to be at stoichiometric ratio as much as possible?

thanks!
 

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Thats correct about the 15 psi on stock fuel. Do not only trust the autometer A/F because I am assuming its connected to your stock o2 sensor. ( not a wide band o2) At idle, you engine will automatically fluchuate between lean and rich A/F.
 

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Discussion Starter · #3 ·
yeah, stock O2 sensor. I know the A/F gauge won't be too accurate, but I mostly got it to have the peace of mind that I'm not overboosting rather, not planning on doing too much fine tuning with that thing. I wonder if I should get an EGT gauge too.

Does anyone know what voltage range the EGT sensor produce? I figure I already bought one fancy led voltmeter thingy (A/F), maybe I can put an input switch and have it double as EGT gauge?
 

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Vr-4 Evr
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they say never boost past 17lbs or you'll lean on stock fuel....i've been bosting 18bs on stock everything and 93 octane for 2 years and i street race a shit load. Car running the same way. Im not saying to do it though.
 

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I was under the impression that the fuel pump was the problem when overboosting on stock 9bs, not providing constant fuel pressure to the injectors. Injectors were big enough to handle fuel requirements of the turbos. I never had a problem running 15psi on the stock fuel system. Still do now with 13Gs. The 9bs can't hold it to redline so injectors can usually handle the load.

Lord Warlock
 

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peopleofwalmart.com
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One correction:
Your air fuel ratio can be rich and your engine still knock like mad.
This is do to heat.
Stock turbos make a lot of heat when ran over stock boost.
That heat if not cooled by the intercoolers (dirty, oil inside, hot ambient temp.) will heat up the combustion chamber until hot spots are created.
Then these hot spots will pre-ignite the fuel-air mix and blow-up, combust, before the proper time.
This is knock and will blow up pistons, rods, wrist pins.
Something will give.
You should datalog when setting your boost and look for knock.
Also look for timing retard.
I have seen turbo cars gain mad amounts of horspower by turning down the boost which lets the engine advance the timing!!
If you don't datalog, set it at 15psi like so many people have tested and found out the hard way:D

p.s. This is why I can't believe Mitsu didn't put in 13Gs and turn the boost down to say 6 psi (comparable to what Toyota did with the Supra).

p.s.s There are people on this board working on a cheap datalogger with A/F and EGT inputs!!!!!
 

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Hellfire Master
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If you want to get by the stock injectors the cheap and easy way, just get a nasty fuel pump and an adjustable FPR. Crank up fuel pressure and thus you will be jetting in more fuel to combat the lean condition. Not sure if this will have any adverse effects on the stock injectors or not (I would probably imagine so).

devilmanVISA
 

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fuel

yes the stock injectors flow pretty good so with a larger fuel pump and FPR you could make a great improvement in your fuel system.
 

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Ninja Performance
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Be careful

The AF Gauge is not acurate at WOT unless the WOT mod has ben done to it. Which most have not done.

over 14.6 supposedly you are running risk

EGTs and Knock need to be monitored. As mentioned already, you can have knock even massive knock with good O2s...

And remember:

The highest EGTs occur at Stoich and EGT temps Drops going away from Stoich both going to rich and going to Lean

Be careful. Boosting 17psi one stock with 550cc inj I cracked two pistons and blew the head......No EGT or Logger....New motor 4K on it.
 

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WOT mod

What is the WOT mod for an AF gauge? Does it work with the AF gauge that comes with an ARC2?
 
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