[quote=from [url]www.mr2oc.com][/url]
Originally Posted by dsf3g
A quick question to those in the know (Ricky B? ATS?).
What are the negative effects of running, say 15 psi of boost on the stock ECU? I understand that the USDM 2nd Gen 3SGTE ECU has no fuel maps beyond 12psi, and that the ECU just dumps a lot of fuel into the engine at that point to avoid lean running and detonation.
Not correct. If you look at any 3sgte dyno chart with an A/F trace, it is obvious that the ECU makes a smooth, curvilinear transition from stoich at normal cruise conditions, to about 10.5-11:1 as boost climbs to 15 or more, and RPM increases. There is no sudden transition at 12 psi (or any other point) where the ECU "dumps fuel".
And the OEM fuel system, as well as the ECU programming, is fully capable of delivering an adequate, albeit somewhat rich, fuel supply for a CT26 equipped 3sgte.
BTW, I ran 15 psi on an otherwise stock '91T for about 6 years troublefree. Many others have safely run 15 psi with no other mods for long periods of time.
bill
http://www.mr2oc.com/showthread.php?...t=running+Rich
".....The stock ECU runs the engine excessively rich..... "
^^Taken from celicatech.com
http://www.celicatech.com/forums/sho...jump+fuel+pump
Stock 3sgte engines run rich to begin with. You can ask anyone who has a swaped 3sgte, and is running the 3sgte fuel pump.
If this wasn't an issue then people wouldn't start with 2 1/2" and then decide to go 3" straight back.
Taken from Nissan Performance Mag.com
You need to have the lowest backpressure possible to produce the maximum power by keeping pumping losses low. Too big of an exhaust pipe causes power loss, especially low-end torque. This is because a big pipe has less exhaust stream velocity than a smaller pipe. Velocity is essential to get the best scavenging (or sucking) effect from tuned headers, which we will discuss in more detail later in a future installment. To simplify things, if the exhaust gas flow is kept high with good velocity, a vacuum can develop behind the closed exhaust valve allowing even better scavenging when the exhaust valve opens on the next exhaust cycle. Good scavenging is even more critical on valve overlap, the part of the 4-stroke cycle where both the intake and exhaust valves are open, especially with longer duration performance camshafts.
If the exhaust pipe is too large, the flow will be sluggish with low velocity and the scavenging will not be good. Remember that a good exhaust has low backpressure and high velocity. The only possible exceptions to this rule are for turbocharged or nitrous motors. It is almost impossible to put too big of an exhaust past a turbocharger as a turbo depends a lot on the pressure differential across its turbine to get power recovery efficiency. A turbo engine can have an exhaust gas volume about 1.5-2 times more than an equivalent displacement naturally aspirated motor. NOS motors also have a pretty high exhaust volume and require a bigger exhaust if they are to be optimized for NOS operation.
The stock exhaust system on most modern rice rockets is often so well designed nowadays that just switching to a high performance cat back exhaust often does not allow for huge gains of power. With the exception of turbo cars, you can usually expect only about a 2-10 hp at the wheels difference on a stock car. The power gain will usually be the greatest from just below the torque peak to the tach’s redline. On cars that are modified with headers, intakes, cams, headwork, etc., you can expect bigger gains with the addition of a cat back exhaust due to the higher flow volume that these mods produce.
As turbo cars are very sensitive to back pressure, you can expect much larger gains with them, especially if the boost is turned up. A free flowing exhaust usually allows the turbo to spool faster also. A turbo car usually gains from 8-30 hp at the wheels depending on how bad the factory exhaust was and how high the boost is turned up over stock.
Taken from NissanPerformanceMag.com
http://www.nissanperformancemag.com/...fthenerds2.php
Now tell me why someone with a 3sgte is not running a 4" or a 3 1/2" exaust, can you tell me why you wouldn't wanna run something that big on a stock setup?