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Old 03-12-2004, 09:37 AM   #1
Scooby Specialist
Member#: 12737
Join Date: Nov 2001
Location: Bean-Town
MY02 wagon 325/300

Default Can you explain tunning/spool relationship?

I have read on several posts that to no small part the spooling charecteristics of a turbo are dependent on engine managment tuning. Can someone please elucidate this stetement for me (and other I am sure).

My understanding was thet the quickness of the spool is determined by the differences in the compressor and exhaust wheel size/housings of a turbo. The exhaust side is in a sence a "motor" of the turbo and the compressor side is the "wheel" of the turbo. 'The motor spins the wheels'. So as long as the "wheels" are not too big the motor can rev up quickly. Similarly as long as the 'motor' is not too big the exhaust gases will spool it faster etc..

Will changing fuel/timing maps actually produce more gas to spin the turbine earlier?

What am I not understanding?
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Old 03-12-2004, 10:36 AM   #2
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2002 WRX chassis...


Turbos spool from energy.

Heat is a form of energy.

More heat, more energy.

Exhaust gases have heat.

Exhaust gas heat is tunable.
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Old 03-12-2004, 10:39 AM   #3
Jon [in CT]
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02 WRX Sedan


The ratio of the pressure at the turbine inlet to the pressure at the turbine outlet determines how fast any particular constant pressure turbocharger will spool up. Raising the exhaust gas temperature (EGT) will increase that pressure ratio.

The A/F ratio which produces the highest EGT is the fuel's stoichiometric A/F ratio.

EGT rises as spark advance is retarded.

A misfire will send fuel into the exhaust which then burns in the exhaust pipe, raising EGT.
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Old 03-12-2004, 02:21 PM   #4
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Ok, that makes sence. Thank you both

So, a tuner's objective is to find that zone between lean A/F(high EGT's) and non-detonating conditions - correct?

Why does retarding timing increase EGT's? (unless of course its because since the spark is initiated later in the cycle which in turn leaves less time for the entire fuel mixture to combust, leading to some amount of this unburnt fuel exiting into the exhaust path where it continues to burn leading t highr EGT's - am I even close?)


But this seems to say the opposite


"Other goals, like minimizing emissions, take priority when maximum power is not required. For instance, by retarding the spark timing (moving the spark closer to the top of the compression stroke), maximum cylinder pressures and temperatures can be reduced. Retarding the timing may also eliminate knocking.."

Last edited by savka; 03-12-2004 at 02:27 PM.
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Old 03-12-2004, 02:23 PM   #5
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2002 PSM WRX (Sold)
2009 BMW X5


Right on spot.
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