1978 seville

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5.0 and 5.7 Discussion, 1978 seville in Cadillac Engine Discussion; Hi I have a 78 seville with the 350ci olds fuel injection engine. I would like to replace the single ...
  1. #1
    coatongo is offline Cadillac Owners Member
    Automobile(s): 1978 Seville sedan
    Join Date
    Apr 2010

    Cool 1978 seville

    Hi I have a 78 seville with the 350ci olds fuel injection engine. I would like to replace the single exit exhaust with a dual one. does anyone know which Olds model I could use the manifolds from to get rid of the cross over pipe from left to right manifold?


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  3. #2
    lovemycadillac's Avatar
    lovemycadillac is offline Cadillac Owners Member
    Automobile(s): 1988 Superior Hearse, 1990 Sedan deVille, 2001 ESC
    Join Date
    Oct 2008
    Water Winter Wonderland

    Re: 1978 seville

    I once had a 1979 Oldsmobile Ninety Eight that I put duals on. It had the 350 Olds R code engine, and was not fuel injected. The shop that I had put the pipes on plugged one of the outlets on the passenger side exhaust manifold to eliminate the need to change to a new manifold.

    I don't know if your fuel injected engine is like this, but mine had a positive back pressure EGR valve, which means that back pressure is required along with vacuum for the valve to work properly.

    The car ran and sounded great with the duals, but the EGR valve did not operate because the back pressure was very low. It ran hot, smelled hot, and there was lots of spark knock. I had no idea about the EGR valve and spent lots of time trying to figure out what the problem was.

    I eventually figured out what the problem was, and put on a universal EGR valve that was adjustable, and did not require back pressure to operate. The car still never ran as good as it did when the original exhaust system was on there.

    I'm not trying to discourage you from wanting to put duals on, but maybe my experience will prevent some frustration on your part if you are able to check out the EGR first.

  4. #3
    cadillac_al is offline Cadillac Owners Connoisseur
    Automobile(s): Cadillac 78 Seville, 78 Coupe de Ville, 92 Sedan de Ville
    Join Date
    Feb 2007

    Re: 1978 seville

    Hey Seville brother, There was a block off plate made for that manifold but I'm quite sure it has to be discontinued now. They were used on the 79 Seville and Chevy pickups with the Olds diesel engine. Most muffler shops can block it off their own way. You could also run a transverse muffler from a Camaro Z28 and it will give you two tailpipes to balance the rear of the car. I've never heard of that positive back pressure EGR stuff but I never ran EGR on any of my 70's cars. I'm positive Cadillac didn't change the EGR or computer on the 79 Seville to accommodate the duals.

  5. #4
    coatongo is offline Cadillac Owners Member
    Automobile(s): 1978 Seville sedan
    Join Date
    Apr 2010
    Thread Starter

    Thumbs up Re: 1978 seville

    Thanks to both you guys for your help! i now have a couple of options for my pipes.

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