Any difference between 996 3.4L mufflers (MY99 6-speed vs. MY01 Tiptro

[John in Norcal]

I recently modified my old MY99 6-speed 996 3.4L mufflers (P/Ns 996 111 122 56; 996 111 121 56) for better sound and installed them on my current MY01 Tiptronic 996. I got an improved exhaust note but now when my 01 is stopped at a light with the Tiptronic in 'Drive', I have a unwanted vibration/rough idle in the car. The vibration goes away when the car is moving or if I put the Tip in 'P' or 'N' but when the car is in gear (D or R) and stopped, the vibration is there. I did not have this unwanted vibration when I still had my stock MY01 mufflers (P/Ns 996 111 131 54; 996 111 132 54) on the car. I noticed that the MY01 Tip and MY99 6spd mufflers have different part numbers though the mufflers looked the same on the outside. Does anyone know if there are internal differences between the two sets of mufflers and that maybe by putting my old MY99 mufflers on my MY01 it may be causing this unwanted vibration? TIA for any helpful advice!

[Loren]

Sorry, I can't find anything on what the differences are.

[1999Porsche911]

I run mufflers from an 2003 C4S on my 99 C2 and they fit perfectly. You just have to use the 99 mounting brackets.

Edited November 25, 2008 by 1999Porsche911

[John in Norcal]

Sorry, I can't find anything on what the differences are.

Thanks for checking.

[John in Norcal]

I run mufflers from an 2003 C4S on my 99 C2 and they fit perfectly. You just have to use the 99 mounting brackets.

I believe 99 and 01 mufflers use the same hangers so I have no fitment problem. I'm just curious if the mufflers for 99 6speed cars are different than 01 Tip cars because the part numbers are different.

Edited November 26, 2008 by John in Norcal

[Loren]

Yes, the part numbers are different for 3.4 liter Tips and 6-speeds but not for 3.6 liter cars.

I have not been able to find any information why.

[John in Norcal]

Yes, the part numbers are different for 3.4 liter Tips and 6-speeds but not for 3.6 liter cars.

I have not been able to find any information why.

I may try to put the stock Tip mufflers back on to see if the vibration goes away. That'll at least determine if the muffler swap is causing it.

[wvicary]

If you have no clearance issues with the new exhaust I would check the engine/transaxle mounts.

[John in Norcal]

Yesterday I removed the modified MY99 6spd mufflers and put the stock MY01 Tip mufflers back on and the vibration went away. While the mufflers were off, I saw that the MY01 Tip mufflers had the accordian inlet pipes while the MY99 mufflers had the smooth inlet pipes. Maybe that minor difference prevents the vibration while Tip cars are at a stop and in gear. Now I'm curious if I upgrade to aftermarket mufflers if I'm going to have the same vibration issue on my Tip 996.

To Tiptronic 996 owners with aftermarket exhaust, do you have any vibration in the car when the car is at a stop and in gear?

[slbates]

John,

I think you may have had an adjustment issue. My 99 came with the accordian style pipes you mention before they failed due to age. I do not believe your problem was related to smooth vs. accordian. As 1999 said above, the newer mufflers fit just fine on a 996 Tip. As he mentioned, the mounting bracket is slightly different on the earlier cars, so just use your old ones to avoid alignment issues. The GHL's fitting perfectly fine on the Tip cars with no issues.

[John in Norcal]

John,

I think you may have had an adjustment issue. My 99 came with the accordian style pipes you mention before they failed due to age. I do not believe your problem was related to smooth vs. accordian. As 1999 said above, the newer mufflers fit just fine on a 996 Tip. As he mentioned, the mounting bracket is slightly different on the earlier cars, so just use your old ones to avoid alignment issues. The GHL's fitting perfectly fine on the Tip cars with no issues.

We used the original 01 mounting brackets from my current 01 996 when we installed the modified 99 mufflers. Are you saying that I should have used the old 99 mounting brackets instead?