I have a 68 GMC with a 292, split exhaust manifold. I would like to have a reasonably quiet dual exhaust. I've talked to three local muffler shops and they all recommend Flowmaster mufflers or something similar. I had some Flowmaster clones on a V8 dual exhaust once and it wasn't bad but I'm expecting the 6 to be louder. I don't mind a little rumble out the back but I don't want it obnoxiously loud and I want the cab to be as quiet as possible. I can only afford to do this once so I'd like to hear any recommendations and what has worked for other folks. Thanks.
'64 swb stepside (gone) '57 1 ton '53 phone truck '59 swb '46 1 1/2 ton '68 swb gmc
I have a 261 with Fenton headers and 2 inch pipes all the way to the rear bumper. Have thrush turbo mufflers right before the rear end, they are not loud, but do have a nice rumble when you wind the engine up. If I remember they were about $30.00 each at pep boys,8yrs ago.
The mufflers used on the 1970's Cadillacs have 2 1/2" diameter pipes, in and out. I've used them on numerous vehicles. ONE muffler is designed to handle the exhaust volume of a 500 cubic inch engine. If you want free-flowing AND quiet, that's the way to go, particularly if you choose to run two of them for the visual effect of having twin pipes sticking out under the bumper. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
When I added a true split manifold and dual exhaust to my 235 I went looking for a set of quiet mufflers. I thought I wanted two long, stock type mufflers. I let my trusted parts counter guy pick them. He chose a pair of DynaMax Ultra Flo mufflers. I was scared when I saw they were straight through glass packs. My fears went away when I started the car for the first time after installing them. They have a really nice and quiet rumble at idle. I had to get out of the car and walk to the back to even hear them. They are also very quiet at highway speed. If it wasn't for the rap of the split manifold I wouldn't even notice them. They are perfect.
Fenton headers, 2" dia pipe 16" long resonators under cab, dymomax turbo mufflers. Slight drone at highway. Awesome deep idle and mid throttle and a deep tone with heavy throttle with a bit of rasp.
Those mufflers sound great. I'm surprised they are DynaMax, though. My DynaMax mufflers seem much quieter in the cabin than yours. Do you have side pipes or do the pipes go out the back? Maybe is the difference in the models.
I personally find Flowmaster mufflers obnoxiously loud. But whatever mufflers you choose I would suggest researching the benefits of an "H" or "X" balance pipe. They are very simple to add using a hole saw to form the fish mouth ends of the "H" balance tube and to open the exhaust pipes where the "H" joins them. An "X" can be very easily made from over the counter "U" bends. Fabricating exhaust systems is really simple and exhaust tubing welds very nicely with oxy-acetylenme, stick or mig. Some modest power gains are attributed to "H" and "X" pipes. I don't know about that but an "H" pipe definitely makes the exhaust noticeably quieter.
Rube Goldberg pipe configurations allegedly work on V8's- - - -but after hundreds of hours of dyno testing I've never been able to record a measureable difference. On stovebolts they just give you more pipe to rust out. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
I first read about the "H" pipe concept on the 1960s in one of the hot rod publications, maybe Hot Rod Magazine. It explained that Mopar engineers had discovered small performance gains as well as quieter exhaust.
Occasionally this subject also comes up on the Performance portion of the Chevy Talk forum. The moderator there "Grumpy Vette" has posted a lot of information on the details of "H" and "X" pipe construction and their placement in the exhaust system. If I remember correctly he also posted details of actual measured performance gains.
In the summer of 1967, when I was a college kid, I worked at Doug's Headers tig welding. Since then I've been really interested in exhaust system design and I've followed the balance tube and other exhaust related inventions with interest. To most of us it's fun to learn new things.
