I Removed My Soup Can Cat

So I removed my rear cat and made up a pipe to replace it. I flared the end that goes onto the head pipe and cut factory style slits into it. Performance wise I didn't see a big difference but the bike was definitely louder. Currently I'm using a stock muffler with 7/8" holes drilled in the baffles. I was amazed how heavy the stock muffler is.

I do have a question. If I put performance mufflers on do I have to remap the fuel delivery on an '08. The bike uses an O2 sensor so can't it make the proper adjustments?

I'll try to get a sound track and pictures done later.

Ruggybuggy said:

If I put performance mufflers on do I have to remap the fuel delivery on an '08. The bike uses an O2 sensor so can't it make the proper adjustments?

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The quick answer is NO. I ran Leo Vince without doing any other mods and bike ran absolutely perfectly.

However, if you want to get full benefit of aftermarket pipe, it would probably work much better with high flow filter and proper fuel tuning.

Erci said:

The quick answer is NO. I ran Leo Vince without doing any other mods and bike ran absolutely perfectly.

However, if you want to get full benefit of aftermarket pipe, it would probably work much better with high flow filter and proper fuel tuning.

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I was also considering doing the air box mod but what do you mean by fuel tuning. Are you referring to a controller?

Ruggybuggy said:

I was also considering doing the air box mod but what do you mean by fuel tuning. Are you referring to a controller?

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There's power commander, but the best gains should come from dyno-tuning.

Erci said:

There's power commander, but the best gains should come from dyno-tuning.

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No dyno available in my area. What's confusing to me, if the bike has an O2 sensor why can't the ECM control the fuel to keep it into the proper air/fuel ratio? Why the power commander?

Your o2 s reads the exhaust if it's to rich it tells the computer to lean out if it's to lean it tells the computer to add fuel the secondary o2s reads if the cat is doing its job by burning up the extra fuel so base on the readings the ECM optimizes the fuel etc.... By changing anything to much the computer can't go outside of it's parameters, I'll let you do the math

Gelvatron said:

Your o2 s reads the exhaust if it's to rich it tells the computer to lean out if it's to lean it tells the computer to add fuel the secondary o2s reads if the cat is doing its job by burning up the extra fuel so base on the readings the ECM optimizes the fuel etc.... By changing anything to much the computer can't go outside of it's parameters, I'll let you do the math

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Our S2s only have one o2 sensor.
Header ->PreCats ->O2 ->CAT ->Tail and muff

Performance wise I didn't see a big difference

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Did you loose low end torque?

fazil said:

Did you loose low end torque?

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Hard to tell, but now that you mention it maybe a touch. So I guess the question is if you install a free flowing exhaust with a cat eliminator are you going to need a controller? For the people who did this was a controller necessary for a performance gain? Did you verify by dino tuning?

I saw a cat eliminator pipe on Ebay and did wonder what the effect would be - louder exhaust? poor fueling without a power commander? MOT failure next year?

Sounds like there is no real advantage to taking the CAT out

dolau said:

I saw a cat eliminator pipe on Ebay and did wonder what the effect would be - louder exhaust? poor fueling without a power commander? MOT failure next year?

Sounds like there is no real advantage to taking the CAT out

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I wouldn't say that. I found no difference in fuel economy and with a drilled stock exhaust and cat removed noticed the engine did rev to redline quicker with some notice in performance.

Ruggybuggy said:

So I removed my rear cat and made up a pipe to replace it. I flared the end that goes onto the head pipe and cut factory style slits into it. Performance wise I didn't see a big difference but the bike was definitely louder. Currently I'm using a stock muffler with 7/8" holes drilled in the baffles. I was amazed how heavy the stock muffler is.

I do have a question. If I put performance mufflers on do I have to remap the fuel delivery on an '08. The bike uses an O2 sensor so can't it make the proper adjustments?

I'll try to get a sound track and pictures done later.

Click to expand...

I'll give you some info about engine mapping, which I hope will help you out, please ask if you have any questions.


Having changed/modified a component, to achieve optimum performance re-mapping would be necessary. However, the change in air/fuel ratio from, for example, changing an exhaust is very unlikely to affect the air/fuel ratio enough to put the engine in immediate danger.

In fact, a modification affecting the breathing of an engine is likely to improve volumetric efficiency within a certain engine speed range, and reduce it within another. This would affect the air/fuel ratio within these ranges, effectively leaning the mixture in the range seeing improved volumetric efficiency, and richening in the range seeing lowered volumetric efficiency.

I haven't seen any confirmed numbers for when the FZ6 runs in closed loop mode, however I have seen figures of under 40% throttle, and below 6000 RPM being thrown around. This means that the ECU uses the lambda sensor signal to try and achieve a target air/fuel ratio when both these conditions are met, however the ECU then switches to open loop mode, using a pre-set map, when one or both of these conditions are not met.


Hope this helps, again please ask if you have any questions. :thumbup:

Yamahaboyz

Some other reading that's been posted here. http://www.600riders.com/forum/garage-mechanical-help/34007-exhaust-backpressure-fact-fiction.html

Nothing will beat a treadmill and a sniffer to tell you what it's actually doing.