djcrook73

hi all, i saw a similar thread, but have to ask anyway.. after replacing some of my original exhaust, (muffler and straight pipe bypass for the huge cat) i realized that the pipes are super thin from the inside out and i have to replace them, so duals it will be as it feels like the 455 is breathing through a straw as it is! i saw a block off plate for the pass manifold second outlet supossedly for the early 70s cars to go with duals. would that work or do i need early manifolds to do it right? thanks for any insight!

rocketraider

If you're gonna ditch the cat, get a set of W-Z exhaust manifolds and a trans crossmember from a 71-74 fullsize GM car. Then get your muffler guy to bend them per 71-74 Ninety Eight dual exhaust program cards. You'll then have full dual exhaust using the factory components. Go ahead and install a new transmission mount while you're into it, since it has to come loose anyway.

You can do it by blanking off the crossover on the RH manifold and not changing the crossmember, but the LH pipe will be all up in the starter and suspension and it will have to pass underneath the crossmember. The 71-74 piece will have dual humps for exhaust to route thru.

Allan R

In 76, the 455 wasn't really putting out big hp numbers anyway. The car weighs pretty close to 2 1/2 tons. They never had duals from the factory on those cars. raider is giving you good info.

You do know that duals will be quite a bit louder than what you're used to, and may not increase the performance of the engine any great amount?

coppercutlass

I did duals on my dad"s olds powerd 77 pontiac bonneville using the exhaust system off a 94-96 impala ss. I used the original 350 olds manifolds with the cross over capped off. The only hard work was making my own down pipes and it wasnt very hard . I nothced the cross member took it to my buddies welding shop and the welded plates in cost 25 bucks.

lsutigers93

Been wondering about going about doing this...sound like a noob but what are "W-Z" manifolds? Is my '72 Ninety Eight with single exhaust already equipped for duals or do I need to swap manifolds as well?

Allan R

W Z exhaust manifolds are the ones that Olds made for the higher performance engines with true dual exhausts. These will fit 400/455 engines. Just run your exhaust straight back. You replace your stock exhausts with them.
In this pic you can see the W and Z cast into the manifolds. If you want new repros, you can buy them from Thorntons for around 299

djcrook73

thanks for the very useful info on the exhaust swap info. i will go with the wz manifolds and swap the crossmember with a set of quiet mufflers as im not wanting a poseur sound but feel it will benefit slightly from the better breathing. it has 60k original on it and seems to be untouched.( vacuum lines, wires and such) so its also up for a full tune up and carb rebuild as spraying brake cleaner around the outside of the carb made it idle up indicating vacuum leakage around the gaskets and possibly primary throttle shaft. i think everything together will smooth her out and wake her up a little. and i just like the symmetry of dual pipes out the rear of a classic!

djcrook73

hey coppercutlass, did the duals help the car at all?

coppercutlass

I used thrush turbo mufflers on my dads car with 2.25 exhaust. It sounded good at idle had a nice rumble as it has a very mild cam and quiet while cruising plus at 25 bucks a muffler not bad .

coppercutlass

yes the duals helped alot. The engine that went into my dad's car was one of my old engines that ran high 13's. I had headers he wanted manifolds so we put them on., but anytime you can un restrict an exhaust it's a major improvement.

rocketraider

The W-Z manifolds were factory installation on 1971-74 Delta 88 and Ninety Eight with 455 dual exhaust, as well as the A-body performance cars.

I put duals on my Regency but in order to remain legal here in the Communistwealth of Vajenya, I had to keep the cat. The exhaust goes thru the cat and then splits aft of the crossmember. Not the most efficient dual exhaust system but I could tell some difference in the butt dyno. Fuel mileage picked up a bit, nothing fantastic.

I had the muffler shop run aluminized pipe out the back with angle-cut turndowns just barely visible under the rear bumper. Looks like a factory install and appropriate for a Ninety Eight.

djcrook73

raider that sounds like the way i wanted the pipes to exit to a T. just enough to know they are there and with a factory look. if any of you have a line on the proper crossmember, drop me a line. im sure im probably best off going for the repro manifolds,as opposed to trying to locate a used set .

stressed1

Forget the "W Z" manifolds and just run headers. Will breathe far batter, and you could run 3" exhaust from a 3.5" collector.