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1981 Cadillac Deville
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19 Posts
Discussion Starter #1
Been restoring this 81 for a few mounts now, thought I would start a Thread to aid in my restoration questions. I will be soon posting a driving video including a visual of the V8-6-4 on the Sentinel. The car tops 20mpg ( I only go about 60 and where I live in SD there is no city traffic). Most Reliable system I have ever driven with, and 6 is only noticeable on hills or under 45 mpg. Now its CAT clogged, and am questioning if it would have enough backpressure with it punched, or will I have to put another muffler on it until I can afford true duals.
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(pictures are from the dealer, will have new ones later)
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,737 Posts
If you only drive 60 then duals will NEVER pay for themselves! Dual exhaust can? raise horsepower but you'll never benefit from it.
 

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1980 FBC
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980 Posts
A large single exhaust woke up my all factory engine parts 500 powered 1980.

A 368 might see some performance improvement if you also hiked the fuel pressure in the throttle body.

BTW, some of us would be interested in fuel calculator mileage verses topping the tank and figuring it out the old fashioned way.
 

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2003 deville
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604 Posts
You can try using a h-pipe or x between the duals, h keeps more back pressure for low end x is more for some pressure low end but mainly for balancing between the pipes and more flow more useful for higher reving engines or consistant high speed driving. I had true duals on a 4.6 98 Town car no crossover pipe, it ran fine but less low end power and sounded like a small block muscle car than a 98 Lincoln. Ended up with a stainless h setup and borla tips still throaty but more like a modern mustang.
 

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1981 Cadillac Deville
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19 Posts
Discussion Starter #7
Thanks for all the replies! Put it on my lift for the first time yesterday, cut out the CAT, and found I have the optional POSI rear end.

PS I only drive 60 due to the fact I live in South Dakota and all the main roads are 55mph. The problem is All the interstates are set at 80mph, along with that I would like to pull a small boat.

Next month I will likely bend in some duals, but for now I gotta touch up the paint and replace the fillers. Soon I might go up to Minnesota and buy a nicer set of bumpers.

ALSO, looking into installing the Guidematic headlight system, if anyone has any information.
 
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