Will Adding A Muffler Require A Retune?

[jonathon]

Hey all - I've got the gtr tuned with nistune, however I'm looking at adding another high flow muffler to reduce some noise (and adding a cat converter) would I need to get it retuned? Does nistune retain some ability to alter settings on the go?

[AngryRB]

might be worth a quick power run to check if the new muffler and cat have caused some restriction and

need some timing taken out of the tune, but if the tune was not on the knife edge it will probably be

ok.

[Badgaz]

you shouldn't need to change the tune....but if you are a perfectionist you might.... restriction on the exhaust side can increase back pressure and increase cylinder temps,... i wouldn't worry so long as you aren't impeading flow.

[Dose Pipe Sutututu]

thus increasing cylinder pressure

but if the muffler is 100% straight through, i.e. no weird step downs or weird bends inside then don't worry too much

[butterfly effect]

It all depends on the flow rate of the original muffler compared to that of the replacement. I f there is a substantial difference then the answer is yes.

[32rrr]

No. Wont make a difference.

[joeyjoejoejuniorshabadoo]

depends on how much it impedes the flow...

I tuned my car with a completely f**ked pod filter and then when I put a new one on (same model exactly) we threw it on the dyno just for the hell of it and the afr's were out by 2

[scotty nm35]

I change the muffler constantly on the road, as I use a Varex muffler. Going to a more restrictive muffler shouldn't change the tune that much, but any muffler that flows better will improve the airflow through the engine, possibly making it run leaner which is more of an issue.

If you are running petrol, running a little lean would be bad and possibly cause det. If you are tuned for ethanol, it would likely make bugger all difference.

[Badgaz]

I change the muffler constantly on the road, as I use a Varex muffler. Going to a more restrictive muffler shouldn't change the tune that much, but any muffler that flows better will improve the airflow through the engine, possibly making it run leaner which is more of an issue.

If you are running petrol, running a little lean would be bad and possibly cause det. If you are tuned for ethanol, it would likely make bugger all difference.

why would getting better flow out the exhaust cause a lean condition?

[Ben C34]

Because it changes how the engine breathes.

[scotty nm35]

Depends how it's tuned really, but more exhaust flow requires more fuel, so why wouldn't it?

[Badgaz]

i would've thought it would just make what you've burnt get out faster and reduce heat therefore detonation...but not change afr's.

[scotty nm35]

It's called Air/Fuel ratio for a reason. If you flow more air you need more fuel obviously.

[Badgaz]

yes so if you turn your boost up then sure...but making an exhaust evacuate those burnt hydrocarbons better doesn't change those hydrocarbons....right....so yes it does mean you can add more fuel to your tune and make a bigger bang.

[scotty nm35]

Less exhaust restriction makes it easier to get the exhaust out, making the manifold pressure lower, meaning more boost and better engine flow with no other changes.

If your AFM was out of resolution then it would definitely run lean, as there are no higher cells tuned to add fuel. I would be getting a retune just to make sure. There can be a huge change in engine flow due to simple exhaust changes. Other reasons for running lean could include running out of fuel flow for the extra airflow, even if the tune is compensated.

[Badgaz]

ok...my brain hurts lol...i don't think i was relating the pressure drop across the cylinder head i was treating it as intake vs exhaust and not really understanding the direct relationship....i understand now thanks

[ido09s]

What would you prefer, to waste $50 on a few dyno runs or find out the engine needs a rebuild?

I would always have it checked just in case. No two cars are ever the same

[joeyjoejoejuniorshabadoo]

^ this