cutlassconvertee

Hi everyone,

One of the first projects under the hood of my 72 convertible was to fix some exhaust leaks, so I set out to install exhaust gaskets. Oh my God, what a pain to get the rusted bolts out! Finally did it and got the driver's side replaced. Unfortunatley, the passenger's side fell apart as soon as I pulled out the front bolt. So, now I have to replace the passenger's side manifold.

My question is:

- Why does the passenger's side have 2 exit flanges?
- The middle one had a fairly rusted cap inside that I had to remove to pull the manifold out. Do I need to install a doughnut gasket in that flange too?

Thanks,
Dale

MDchanic

Assuming that you have a car with dual exhausts, the front outlet on the passenger side is the inlet for the pipe from the driver's side manifold on cars with single exhaust.
The normal driver's side manifold has an outlet that goes straight down in the middle, and the pipe goes from there to the passenger side manifold, while the dual exhaust driver's manifold has an outlet that goes toward the back of the car.

The Olds exhaust manifolds don't use exhaust doughnuts or any other type of gasket.
If you're using them, how on earth did you get them on?

- Eric

Allan R

Dale,
Just to add a bit to Eric's post. Sounds like you have a 72 vert with a 350 in it. Oldsmobile never made a true dual exhaust system for the 350; even for the cars with the N10 dual exhaust option. So what you're seeing is the crossover pipe inlet that's been blocked off. That's typically how the factory did 350 duals on these cars. If the car had come with a 455 and dual exhaust? Different story. Olds did make a true dual exhaust manifold for that engine.

If you're interested in a reproduction dual exhaust that mimicks the 455 one? check out Thornton's. The developed a 350 dual system that Olds never did. Have a look:
http://www.ebay.ca/itm/Oldsmobile-Cu...#ht_564wt_1257 Dewel92 is a seller for their on line store. Some of the members on this site who have seen these in person have mixed feelings about the design and quality. About all I can say on it.

cutlassconvertee

Eric,

Thanks for the info. I had never seen a manifold like that. I haven't installed the doughut gaskets yet. I only have the driver's side exhaust manifold gasket installed so far. I am going to have to replace the passenger's side.

The guy at the local parts store(s) said that there was a doughnut in the flange where the pipes bolt up to the manifold, so I bought 2 of them.

So, I am not supposed to install the doughnuts?

Thanks,
Dale

cutlassconvertee

Hi Allan,

Yes, I have a 350. I would love to upgrade the exhaust manifolds, but right now I have too many other issues that need to be addressed first. I wanted a fixer-upper.....well, I got one!

I thought about just buying a set of headers and going that route, but headers can be a head ache themselves sometimes. I don't know about the cutlass, but they were a chore on my 69 chevelle.

Thanks,
Dale

joe_padavano

I'll clarify a little more. The N10 option was absolutely a true dual exhaust system - there were two different pipes, one connected to each manifold. What Allan is trying to say is that Olds never made dedicated dual exhaust manifolds for the small block. All RWD Olds small blocks use manifolds designed to accommodate a crossover for the single exhaust option. This extra port was capped from the factory for dual exhaust cars. Even the W-31s used this configuration. No, you cannot install the BBO W/Z manifolds on a small block. You will not be able to install donuts on these manifolds. Olds used a metal-to-metal seal and the manifolds are not designed nor machined to accept donut seals.

cutlassconvertee

Thanks Joe,

Both Pep Boys and Kragen said their computers showed a doughnut gasket.

Appreciate the info.

Dale

joe_padavano

Not the first example of a vendor's catalog being wrong. I suspect that both stores use the same vendor for exhaust parts. The only Olds manifold I'm aware of that uses donuts is on the 307.

Eightupman

I beleive the 403 uses a flange donut as well.

If you are looking for a set of 350 manifolds in the true dual exhaust configuration, Thornton Reproductions makes a stock appearing dual exhaust manifold for the aftermarket.

Its really simple to make a "plug" for that crossover port. Just need a flange, a lenth of flanged pipe from the parts store and a welder.

OR if you are looking for a stock manifold, there are several guys that have a stock cast passenger side manifold... including me

John

Olds442redberet

I have the same issue with my passenger side exhaust manifold. It fell apart as I was taking it off the motor last week. I bought a used one off Ebay and paid a pretty penny for it. Let me tell you, I was quite surprise to find out just how expensive Oldsmobile stuff can be. At least the seller bead blasted it and painted it cast prior to posting the add.
I also just bought a set of Thornton manifolds. I got them off Ebay as well. I haven't seen them yet (just pictures) so I don't know how they're going to work, but based off an earlier thread posted on this site, I have confidence that they'll be just fine. I ended up paying just a little bit more for the pair of used Thorntons than I did for the single stock exhaust manifold. I plan on running the stock replacement for a month or so before changing out the entire exhaust for 2" pipes, the Thorntons and a pair of Flowmasters.
Oh, by the way, I have a 442 with a non-original Olds 350. So all of this work will be replaced after I find a good replacement 455.


Good luck with your repairs.

Octania

Every gasket kit I ever bought came with donuts. I wondered why. My experience was mainly with 64-72 A-bodies. I ended up donating a big lot of them to the local NAPA store years ago.

Turns out, B, C, and E-bodies tended to use donuts. Sometimes, the same manifold casting is cut with a tapered seat for donutless A-body uses, or with a recess for a donut for B/C body applications. To wit, here's one of each type #4 RH manifiold:

http://www.ebay.com/itm/1965-72-OLDS...item3f1fa78192

http://www.ebay.com/itm/1965-67-OLDS...item3f1fa71f0c

Olds442redberet

Well, the Thornton exhaust manifolds arrived. They look really nice, but upon closer inspection, things didn't look so great after all. It is obvious, looking at the flat mounting surface they weren't going to mount flush. The mounting surface is quite rough and using a true straight edge I found two high spots. These are probably the infamous one bad casting of the bunch, but I expected as much since they were being sold after only limited use. I was thinking there was a reason the seller didn't want them anymore.
I took them into the local machine shop and had them surfaced today, in order to ensure a true flat mounting surface. The machinist informed me there was no way they would have held a gasket. Pretty much what I thought. I figure, with the machine work properly done, they'll work now.

Positives: They look cleaner than the originals, they do not have the blocked crossover outlet, and since they are cast iron they have a stock appearance with cooler under hood temperatures.

Total cost:
Manifolds purchased off Ebay $201.93 ($299.00 from the manufacturer)
Shipping $20.00
Machine work $40.00
Studs $8.00
Manifold bolts (stainless) $17.00

Total $286.00

I'll keep everyone posted on how easy they install and how well they hold up over time.

XTREMEGSXR

I have a 70 cutlass with 350. If I'm using headers do I have to worry about this?

Olds442redberet

If you are not experiencing problems don't worry about it. Like the old saying goes, "if it isn't broke, don't fix it".