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Based on the sequence, whatever it is, I believe the first step in trying to optimize exhaust flow is to make the pipes the right lengths to avoid collisions - i.e., two exhaust pulses trying to squeeze into the same spot at the same time.
If the firing cylinders would alternate between banks (they do not on this engine, e.g., 5-7 and 8-4), then equal length pipes does this pretty simply, avoiding collisions at all RPM.
Based on what the exhaust manifolds look like, does it seem like they tried to do this? I have not looked carefully at all. Just interested.
Removing post-catalytic converter probe from exhaust stream
Originally Posted by YODAONE
Am not replacing the stock exhaust system but am planning a few modifications.
LS430 has a better exhaust layout (from exhaust manifolds back) Perhaps components could be configured for the LS400.
Next project will be to eliminate the sharp transition and oxygen sensor blockage on Y-pipe.
The post catalytic converter oxygen sensor probe is a significant blockage in exhaust stream. This sensor serves only to monitor when catalyst levels fall below certain efficiency. Spark plug anti-fouling spacers could solve this.
The 1990-2000 LS400's employs right and left bank post catalytic converter (downstream) oxygen sensors which monitor whether catalytic converters are functioning, but does not actually influence or serve in engine management capacity.
1995-2000 LS400 post-catalytic oxygen (downstream) sensor. Right and left bank sensor probes extend into the narrow neck of the front Y-pipe creating turbulence and blockage.
To experiment, acquired Dorman # 42009 from Autozoned. This is not tapered version, so it correctly mates with Y-Pipe oxygen sensor bungs and 02 sensor. Will extract one of the post catalytic converter oxygen sensors ("downstream") to ascertain if additional machining is required or if another type of spacer required. Goal is not to eliminate downstream sensor function (only monitors catalytic converter) but move it from further interference with y-pipe exhause stream.
Unsure what improvement will obtain, and will not be performing before/after dyno testing, but indicators suggest increased performance and, or, efficiency.
Oxygen Sensor spacers were bored out to accept the oxygen sensor probes. Installed without incident. There appears adequate clearance around the sensor wire lead end.
Downstream/post catalytic converter oxygen sensor spacer is bored out to 1/2" to allow clearance for sensor probe. Rear oxygen sensor installed into modified spacer. Notice probe does not extend past end of spacer, so no interference with exhaust flow. Image depicts oxygen sensor probe inside extender...just enough clearance for expansion and gas circulation. On LS400, downstream oxygen sensors do not instruct ECU on adjusting air/fuel mixture. Their primary purpose is to signal when converters are operating below set thresholds.ie; when they are failing.. Downstream oxygen sensor and extender installed. Clearance appears adequate...PB Blaster applied several times over a week to insure the sensor would loosen. Another angle. OEM oxygen sensor cable is fine with extender
Am not running before/after dyno testing, but a significant blockage is removed.
Best guesstimate is probe represents 10% restriction....and this is without considering turbulent airflow..
Perhaps someone wishes to do the math.
In any event, it is a budgetary plug-and-play proposition without modifying the exhaust pipes.
11-25-19, 06:58 AM
