Jasonb86

Hi all, as I make progress in the restoration of my '70 L46 Coupe, I was able to get the exhaust together and installed. I went with a 2.5" setup coming from ceramic coated headers, an x-pipe after the transmission crossmember, and Dynomax VT mufflers. For those not familiar with them, they purport to eliminate drone and have a valve that opens up under WOT to give you the best of both worlds - sound when you need it, relative peace when you don't.

However, after installing them, I'm glad they come with a satisfaction guarantee. I bought them from Advance Auto on sale and have probably about $90 into both of them. Which is good for Dynomax as they'll be buying them back from me, plus $50 of installation credit so I can install a new set. The sound at idle is ok, there's still some drone at higher RPMs, but the real problem is the clanking. The valves in both mufflers open and close incessantly, a problem I was assured was solved for these newer editions.

Not so. Here's a video of the exhaust sound, complete with roller-coaster/mack truck like clanking.

http://s116.beta.photobucket.com/use...bbe57.mp4.html

I'm not in a hurry to get them off and it's not noticeable while driving. However, as soon as I can order in another set of mufflers, these mechanical monsters will be going back to Dynomax. Save yourself the trouble and pass on these. Maybe others have a different experience with them and I'd be happy to hear it. I wish I did! The premise was very appealing, it just didn't deliver.

zwede

Which PN did you get? I installed a pair of 17156's just a few weeks ago on my '71 and love them! No drone at all, and sound great.

I started it up after only installing one muffler, with a Borla muffler on the other pipe, and did have loud clanking whenever I let off the throttle. But after installing the second muffler there has been no clanking.

racegofast

Whats wrong with drone as you call it. I want to hear my engine sing.....

Jasonb86

I installed the same 17156. I wonder why there would be such inconsistencies? As you can tell from the video mine are constantly opening and closing. Where did you buy yours from?

MelWff

I have them installed on a Pontiac GTO and have no clanking. Bought them from Summit Racing. Any chance they were old stock that Advance was trying to get rid of? Contact Dynomax and see if there is a serial number on them that would indicate how old they are.

zwede

Got them from Amazon. If you got two of them for less than $100 I suspect they were very old. The early ones had clanking issues, there was a design change to fix it.

7t2vette

Holy christ that is an awful noise!!!!!!

Jasonb86

Advance had them listed for $95 or so each, I used coupon codes, ordered them individually, and ordering them with oil (which doesn't discount and is returnable) to get them that cheap. I would consider going with another vendor to get them, but if I went through the hassle to get another set installed and they did the same thing I'd be pretty upset...

zwede

I can shoot a video of mine if you think it would help?

Jasonb86

Other than the clanking noise, does yours sound similar? Do you have a crossover pipe (h or x?)

Shark Racer

FWIW they have different versions of the mufflers for different backpressure. If you have a mismatch, you run the risk of them always being open or opening too easily. Zwede's car is a mildly worked 454, that will have very different exhaust characteristics from your L46.

zwede

No speakers at work. I'll listen to it when I get home.

I have headers and an X-pipe.

Kacyc3

Put a set on my friends Malibu with 3 in exhaust, the drone is almost completely gone. When I redo the exhaust on my vette it will be getting them.