I'm no mechanic, but for some reason it seems to me that the following question has merit: if I install a cold air intake and a highflow exhaust, including a high-flow cat, but not headers, then I will seriously lean-out my mixture and create more performance problems than I solve - right? I am trying improve throttle response and milk out additional road mileage from my '93 4Runner 3.0 w/MT, but I am concerned that running a bunch of air through an engine that is probably already too lean with emissions will do much of anything postitive. Any thoughts/ideas/facts will be appreciated. Thanks.

 

Your ECU should compensate for the increased airflow. Start with intake and exhaust; a high-flow cat will only be beneficial if your stock cat is clogged. You can add the cat later anyway.

 

thats correct the ecu should take care of it unless you dump a ton of air into it. as it gets leaner the 02 sensor will read that, and more fuel will be dumped into the engine

 

Cool! I was hoping that the ECU would function this way, but I didn't know. What little I do know applies to bikes, and I know it is typically best to re-map an ECU if you make big changes in airflow. As for the CAT, my thought is that if I am going to a 2.5" exhaust, that the more restrictive OEM CAT would tend to defeat the purpose of the free flowing cat-back. Am I just way off? Thanks, again.

 

the cat shouldn't make much of a difference as long as it isnt clogged, but i had trouble getting my header to properly mate up with it as the holes were differently sized, and the gasket wouldn't properly seal it.

Its correct that you will have to make major modifications if you bring in too much air, but you'd have to bring in a lot of air beyond what an intake and exhaust will do.

 

and I'm not sure about 2.5 inch exhaust, that may be slightly to big and you'll lose some backpressure, which in turn causes the exhaust gas to slow down, giving it a chance to expand and get cooler, and heavier, and even slower, which means it has MORE time to expand and cool, which means your engine is working harder to push that exhaust out, whereas with a slightly more restrictive exhaust the exhaust will pulse and pull itself out while it is being pushed by the new gas coming out of the engine....

you might thnk about fluid dynamics and cooling gas properties, and stick with 2.25 inch exhaust piping.

 

when was the o2 replaced?

if it has more than 80K on it replace it

 

I've had great success with headers w/2.5 exhaust with almost zero backpressure (2 race mufflers), ram air intake, and leaning out the air fuel mixture. The ecu compensates the extra air at cruise (closed-loop) but once you pass a certain threshold with the throttle position your ecu ignores the O2 sensor, and runs off of your AFM (open-loop). Although I wouldn't recommend playing with your air/fuel ratio without a wideband O2 sensor.

Uncorking your engine with the intake and exhaust will undoubtedly give you better throttle response and improved mileage. EGR bypass will also give you better throttle response but that's not recommended for pollution controlled motor vehicles as it's illegal.

3vze's run very rich in their stock configuration.

 

how is the dual exhaust? I've been thinking about cutting off my single 2.25" flowmaster 40 and going dual but people tell me it will suck for wheeling..

 

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These mods you can see here (isr and extractors) give good throttle responce, i also run a few degrees of advance in the dizzy, this makes a good improvement to! (with 98 fuel)

 

The dual exhaust setup would probably be equivalent to my single 2.5" in terms of flow w/cats and mufflers, great on the road, for wheeling purposes the jury is out as I haven't gone wheeling for a very long time. You may see a decrease in low end torque, shouldn't be significant enough to make a huge impact on your wheeling but I can't speak from experience on this issue, so perhaps the others are correct in their statements.