Engineer

I have a Mercruiser 350 with the catalyst system on it. I am wanting a bit more power and was thinking of pulling the cats and maybe putting headers on it. Has anyone worked with this system yet? I don't want to make a mess of the system by pulling stuff apart before I know what I am doing.

stevesxm

I] I don't want to make a mess of the system by pulling stuff apart before I know what I am doing.[/
well... THIS puts you in a 1/2 of 1 % minority of people here...

before you do anything, get the FACTORY workshop manual .
have a quick look at where they put the lambda sensor if it has one... if it is before the cat , i would suggest you can dump them with no issue... if they are after then you are going to have to think how to make that signal correct without the cat. study the worksop manual pretty throughly and that will have a detailed explanation of the sensor array and operation and essentially tell you straight away if taking them off will screw you up. on the cars it was directly dependant on where the lambda sensor was...

Engineer

The system has one sensor before each cat and one after each cat! The wires go back to the engine computer. A buddy has an 8.1 cat engine and his is set up the same way. He ran with the sensors disconnected and it threw fault codes! This is why I am asking.

Drivehard

If this is like an automotive setup...

THe sensor BEFORE the cat (between engine and cat) is the primary O2 sensor that does the work of telling the ECM what the air/fuel ratio is. This sensor you do not want to mess with.

The sensor AFTER (between cat and water) is there only to monitor the function of the catalyst. If you disconnect this, it will send an error code. If you pull the cat, it WILL send an error code. There are two options though to still be able to remove the cat and trick the computer. Both of these options have tons of history out there if you do a little searching.

#1 - use a spark plug non-fouler spacer to space the sensor further out of the exhaust stream. This will trick the sensor to send an incorrect reading that will tell the computer that the cat is still there and functioning. Here is a decent "how to"
http://www.audizine.com/forum/showth...-High-Flow-Cat

#2 - using radio shack components, build a sensor emulator that tricks the computer into thinking it is getting the correct reading. This will take a little more technical know-how and reasearch, but can also easily be done.

The third option is to pull the cat, and just live with the light. It should not effect fueling or performance...but simply tell you that the cat is missing (which you obviously know duh!)

CigDaze

I'm not sure how far along things have progressed with these systems, but what we'd do in the past with cat-delete systems is to replace the after-cat sensor with an appropriately-sized resistor which tricks the computer into thinking all is well.

You have to measure the current flow through the sensor circuit with an ammeter and do a little math to determine the resistance of the sensor when it's providing the correct reading under normal operation. From that measurement you can calculate the resistance using [R=V/I]. Replace the sensor with the desired resistor and you should be all set.

Griff

Changing the exhaust will not give you any signifcant power gains. Maybe 1-2mph at most.

stevesxm

thats true griff for sure as long as they are working but they make a lot of heat and when they foul at all its a bad deal and expensive... i would try to get rid of them just to make a cleaner cooler fractionally better flowing system if it can be done without screwing up the sensor inputs.

stevesxm

well... as mentioned accurately above, if it has after cat sensors you need to determine what that signal is and replicate it... sometimes ( again as noted accurately above) it is a matter of a resistor to put the reference voltage where it needs to be... but the factory manual will tell you this in the diagnostics for the sensor.

Engineer

I like the Radio Shack option from above, but I am not an electrical guy. There must be something out there. Catalysts have been around for too long for there not to be!

HaxbySpeed

The amount of time it saves you might be worth the extra $$..

http://www.cpperformance.com/p-16709...-computer.aspx