1974 Exhaust resonators (perhaps a little help from Joe Lucia)

[Harris B.]

Trying to get a few items on my new-to-me 1974 convertible 454 4-speed. I would really like to get the exhaust pipes with the resonators (which I think was a 1974 only item). I found a left and right exhaust pipe with part numbers 340822 (for the RH side) and 340825 (for the LH side). I fear that one or both of these are for an automatic transmission, not the 4-speed manual transmission. Are these the correct parts for my 1974? Joe Lucia can you weigh in on this?

[Joe L.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Trying to get a few items on my new-to-me 1974 convertible 454 4-speed. I would really like to get the exhaust pipes with the resonators (which I think was a 1974 only item). I found a left and right exhaust pipe with part numbers 340822 (for the RH side) and 340825 (for the LH side). I fear that one or both of these are for an automatic transmission, not the 4-speed manual transmission. Are these the correct parts for my 1974? Joe Lucia can you weigh in on this?

Harris------


Yes, these resonators with pipe are applicable only to the 1974 model year.

The GM #340825 is applicable to 1974 LS-4 LEFT SIDE with either 4 speed or THM400. It was discontinued without supercession in July, 1985.

However, the GM #340822 is applicable to 1974 L-48 RIGHT SIDE with 4 speed. It was discontinued without supercession in November, 1984

The RIGHT SIDE resonator with pipe for 1974 LS-4 is GM #340826. It was discontinued without supercession in September, 1984.

[Harris B.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Joe, I truly appreciate your response. I'll probably buy the 340825 and continue my search for the RH side (now that I have the correct part number thanks to you).

[James G.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

There were a NOS pair on ebay 6 months ago, each side was a different seller for the 6 months or so I watched them from the end of 2022-beginning of 2023 until I dropped the consideration of buying a 74 L82 4 spd. The 74 L82 also uses the 2-1/2" exhaust which IIRC also came with the resonator.

Another option: I have seen bullet shaped resonators in many lengths and pipe fit ups - so You may be able to find a resonators and weld them into the correct postion on a pair of reproduction pipes.


FWIW The L48 uses a 2" exhaust from manifold all the way out.

[Joe L.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Joe, I truly appreciate your response. I'll probably buy the 340825 and continue my search for the RH side (now that I have the correct part number thanks to you).

Harris----

By the way, the 1974 L-82 uses the exact same resonator/pipes as the LS-4.

[Doug C.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Does anyone know why resonators were added in 74?

[Tom R.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Does anyone know why resonators were added in 74?

I believe they were precursors to the 1975 catalytic converter. Initially, there was thought, b engineers, that two of the pancake style 75 cat converter would be needed. But then testing showed that one was sufficiently efficient to complete combustion and reduce oxides of nitrogen.

[Vince C.]

Re: 1974 Exhaust resonators (perhaps a little help from Joe Lucia)

Hi Harris!

Congratulations on the new addition to your garage! Great original low mile example! Good luck my friend!

Regards,
Vince