Need your input on bypass pipes

[Kevfra]

For those of you not living in California allow me to explain something about our smog test. The test equipment is connected via modem to a State of California computer such that all readings during a test are sent to this computer. This was an evolution in the smog test saga, and was designed to avoid fraud. In the past it would be common to slip a guy twenty bucks and he would make sure you pass the test, or he would enter your VIN info and then tailpipe a known clean car, rather than your nasty beast.

Now the emission stats are in the CA computer and it is pretty savvy as to what kind of readings to expect from what type of car. So if you are running a big V8 ford and the computer sees readings appropriate for a Pinto – flares are going to go off. And more important – you don’t get do-overs. The State knows you just failed, and now you have to fix your car before you can test again. Yes – it’s all spelled $$$ more than spelled clean air. Ask me about the custom engine I’m getting approved right now, regardless of emissions…

However there is something called a ‘dry board’. This is where they tailpipe you but not connected to Big Brother. It’s a chance to see your readings before a true test. Generally we don’t do this because it runs about fifty bucks, and so we just go with the test and mostly pass. But if you’ve been fussing with your car in some fashion…a dry board is a good thing to do.

I have the four cat exhaust on my 3.2 and want to install the bypass pipes to replace the second set of cats. No headers, and leaving the first cats intact. No O2 sensors on the rear cats, so this is simply going to have an effect on the emissions…but what effect? My engine is clean and just passed its regular smog test nicely, so now is a good time to do a mod and go for the dry board to see if this is going to hang me up next time I do the real thing.

So I’m going to install the bypass pipes (test pipes) and then run a dry smog check to look at my readings. I will know if the elimination of the second cats increased my emissions, and by how much, and if over the limits. If under the limits I might be able to keep the pipes on the car, as they never seem to do a visual check. If over the limits…well then I know for sure I have to make things right before I exhale in Arnold’s face two years from now.

I’ll post my results for your reference. Meanwhile I need some pipes! What do you folks recommend as a good set, reasonably priced, for an ’01 S ?

[Tool Pants]

I know a little bit, for a lay person.

http://www.renntech.org/forums/index.php?s...983&hl=smog

In the olden days the car sat still on the parking lot. Wheels never turned during the test.

Then the dyno thing came out. Before your rear tires rest in the dyno rollers, there is a bar in the front of the rollers. When you drive the car onto the rollers the tires push down on the bar which is a weight scale.

If you look at some recent smog inspection reports there is a line item for the test weight of the vehicle.

So if you tell the smog machine you have a 2,000 pound Elise for testing, but a 3,000 pound vehicle such as a Boxster just drove up on the rollers, you got a problem with Arnold.

Then if something went wrong during the test, such as the mechanic could not hold a steady speed during the test, then you backed the car off the rollers and started all over again. Why? Because to restart the test the vehicle needs to be weighed all over again.

The speed that needs to be held for the test is 15 mph and then again at 25 mph. This is not hard to do with a manual transmission. Problem is some vehicles have an automatic transmission and if it shifts to the next higher gear during the test the rpms drop or the speed changes, which means you cannot compete the test. Then you need to restart the test, and back the car off the rollers.

[heyjae]

My guess is that you'll pass just fine. I passed just fine with just my factory secondary cats. The primary cats/manifold were replaced with headers some time ago. In fact, the numbers this time around were better than 2 years ago when I first installed the headers. However, I just installed headers with 200 cell primary cats and got rid of my secondary cats with a bypass pipe (I did this because I wanted to get less restrictive sport cats and for my needs this was the most cost effective way of doing it). I recommend that you do the opposite of what you intended and install headers and relocate the o2 sensors rearward instead. You'll still get more sound, albeit a modest increase, but more power as well. The factory manifold is very restrictive.

But if you want to go the secondary bypass route, I got the Fabspeed bypass which appears very well made, but it is expensive. I wasn't able to locate a cheaper one and didn't have time to look too deeply, although they must exist. Worst case, a muffler shop could probably make one pretty cheap, although it most likely wouldn't be mandrel bent.

Tool Pants,

Following up from our last exchange about readiness codes. Obviously I managed to get the readiness codes set and was able to do in one drive... well 7 out of 8 anyway, which is good enough to pass. I started the car and turned on the defrosters on max and let the car idle for 2 minutes after letting it cool overnight. Then I drove it at 30-35 mph for about 5-10 minutes with minimal stops, rpm below 3000 and the AC on. Then I sped up and drove for another 20-25 minutes at about 45 mph. Again with minimal stops, rpm below 3000 and the AC on. One by one the codes were set except for the secondary air injection. I'm guessing that one takes a couple starts with a cold engine to be set. The speed was actually dictated by the speed limits on my route, so it all may be a coincidence, but it seemed to be the right combination to quickly get the readiness codes set.