| NIce quiet exhaust...finally!! [message #84097] |
Tue, 11 May 2010 14:57  |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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Some of you know that I.ve been struggling with a rather noisy exhaust. I've expressed my sediments several times relative to loud Motorcycles, cars, pick-ups. The exhaust system on the coach when I bought it was a factory stock system with bloated mufflers, and rusty pipes. I replaced it with a muffler system that had a single Flowmaster 70 series in the rear. For what ever reason, the Cadillac engine has a certain resonance that allow for a strong rap at certain engine RPM/load conditions. It came through to a fairly minor degree with the 70 Flowmaster, and while irritating to me, not enough so that I was motivated enough to change it. The issue was forced on me two summers ago while traveling in Utah when a failed distributor provided for backfires that actually loosened the baffles in the muffler and made for an annoying rattle. I replaced the Flowmaster 70 with a Spin-tech that "they" said was their quietest performance muffler, and headed to the Montgomery rally. To my disappointment it was VERY LOUD. After talking some about the new "Round" Flowmaster and how it was quieter than the Flowmaster 70, I purchased one and installed it. While quieter than the Spin-tech, it was still very loud, so I added a 3" resonator in the pipe were the system takes a turn and heads out to the right side frame rail. That took some of the rap away, but still louder than the old Flowmaster70. My final solution is a system that I am happy with. It is a 70 series Flowmaster with the resonator after the "Y". A nice idle rumble with quiet exhaust at all throttle/rpm ranges. Ever so slightly louder than a stock system.
I know that that there are many running the single exhaust system that Jimmy sells and I've heard them...sound nice. But I believe now that there is something about the Cad 500, and that length of exhaust that makes for a unpleasant rap out the exhaust. In any case....now I'm happy...low restriction.....and shhhhhhhh....quiet.....
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| Re: NIce quiet exhaust...finally!! [message #84115 is a reply to message #84097] |
Tue, 11 May 2010 16:32  |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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Interesting I was wondering if I shoulda got one of the new round mufflers instead of the 70.
Which resonator did you get?
Mines not in yet, maybe I should just do it ...
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: NIce quiet exhaust...finally!! [message #84125 is a reply to message #84097] |
Tue, 11 May 2010 17:51 |
djeffers
Messages: 219
Registered: June 2004
Karma: 2
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Senior Member |
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We have a very quite exhaust system with our 507 Cadillac engine (.010 oversize bore).
The down pipes from the Cad engine manifolds are of course newly made when the engine was installed. The mufflers went bad five years ago. I replaced them with two 36 inch long 2 1/2" i.d. inch glass pack mufflers bought from J C Whitney.
The mufflers turned out to be high quality mufflers from a manufacturer in Minn. They also turned out to be 36 inches long on the body plus the extra length for the inlet and outlet pipes. That hardly ever happens. Most glass packs I've bought were measured pipe tip to pipe tip and these proved to be a little tight in fit.
Anyway, it took a little hack sawing and welding of the "Y" where the two muffler outlets merge to get it all in between the forward and rearward cross members.
From there on out it is still the original '78 GMC system as when delived new from the General. However, I did just replace the outlet bend at the rear with a new one from Cinnabar. I had backed the end of the exhaust pipe into a small dirt bank a couple of years ago.
While at it I saw the aluminum/foam under floor insulation was sagging badly from the exhaust heat. As a tempory fix I got some 1 inch aluminum angle at Lowe's and cut it to length with a lip at each end to wedge in between the aluminum straps across the floor of the coach to hold the insulation up.
The foam under the light weight aluminum made some funny crunching noises as I jacked it up with a small bottle jack and 2 x 4, but the fix has held well for five years now and still looks good. We recommend it as a way to hold the sagging aluminum/foam under floor insulation up.
The coach is still very quite, sounds good at the exhaust outlet, is very quite inside and runs well; and it will run fast.
Don & Susan Jeffers
78 Eleganza II
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