Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

[Gary B.]

At the connection between the exhaust manifold and the exhaust pipe, what surface is critical for providing a leak-proof seal to exhaust gasses? Is it the flat surface of the exhaust manifold that is more or less parallel to the ground? Or is it the 45 deg beveled surface inside the exhaust manifold outlet? How important is it for that 45 deg surface to be smooth and residue free? I purchased GM sintered donuts, which I know where not used on the production line, but will those sintered donuts provide some additional help in sealing that junction?


Gary

[Joe L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

At the connection between the exhaust manifold and the exhaust pipe, what surface is critical for providing a leak-proof seal to exhaust gasses? Is it the flat surface of the exhaust manifold that is more or less parallel to the ground? Or is it the 45 deg beveled surface inside the exhaust manifold outlet? How important is it for that 45 deg surface to be smooth and residue free? I purchased GM sintered donuts, which I know where not used on the production line, but will those sintered donuts provide some additional help in sealing that junction?


Gary

Gary------


The 45 degree surfaces are the important ones. The flat surfaces are irrelevant (except the flat surfaces between the heat riser and manifold).

The45 degree surfaces need to be as clean as possible, especially when using the sintered iron packings as these packings have very little conformability. The real benefit of the sintered iron packings is long-term leak free performance. I will only use the sintered iron packings.

[Gary B.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Joe,

Is there a recommended way to freshen up that 45 deg beveled surface?

Gary

[Joe L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Joe,

Is there a recommended way to freshen up that 45 deg beveled surface?

Gary

Gary------


If the surface is not perfectly smooth I would use sandpaper to smooth it out being careful to not remove more material than necessary.

[David C.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Are you also using the exhaust donut alignment sleeves with the donut?

[Gary B.]

[Joe L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

David,

No, I don’t have the alignment sleeve. Is the sleeve essential when using the donut? Will the presence of the sleeve result in a judging deduct?

Gary

Gary------


The sleeve (extension in GM parlance) was used originally although it is indiscernible when installed. It should definitely be used. It has several benefits including centering the packing and reducing the possibility of exhaust leaks.

Some aftermarket exhaust pipes have the sleeves built in. No separate sleeve is used in this case.

[Gary B.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

My plans are to buy the N11 welded system from Corvette Central. Does anyone know if those pipes have the sleeve built in?

Gary

[Joe L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

My plans are to buy the N11 welded system from Corvette Central. Does anyone know if those pipes have the sleeve built in?

Gary

Gary------


The CC systems do not have the built-in sleeves. However, I believe the separate sleeves are supplied with the complete systems.

[Mike M.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

the sleeves are supplied with corvette centrals systems. I've been using stainless steel donuts for years without leaks or deterioration common with the asbestos or sintered iron donut packings. the stainless donuts are getting more difficult to acquire. mike

[Gary B.]

[Patrick H.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Gary,

Most machine shops will do this.

I have them remove the studs, and then machine the block side of the manifold as well as the heat riser side. Note that the heat riser side is a bit at an angle, not perfectly square to the block surface. Make sure you explain what you want, that you only want them trued at the same angle they're at currently.

Then replace the studs.

[Jim L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

I have a follow-up question. My driver’s side exhaust manifold has a relatively wide 45-deg bevel to accept the sintered donut. By contrast, the passenger’s side exhaust manifold has a much smaller bevel. But then I realized the passenger side manifold outlet mates up to the heat riser. The heat riser has a bevel for the sintered donut only on the bottom, outlet side. The top side of the heat riser is perfectly flat. Which means the lower surface of the RH exhaust manifold must be perfectly flat to obtain a leak-proof seal. Is there a recommended method to refurbish the outlet surface of the RH manifold to make it flat and smooth?

Gary

There is a flat gasket which goes between the heat riser and the RH manifold. You don't need to worry about getting the mating surfaces perfectly flat.

[Gary B.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Jim,

Ahhh! Do you happen to know a part number and vendor for that gasket? Amazon?

Gary

[Jim L.]

Re: Exhaust manifold to exhaust pipe connection; how to get a leak-proof connection

Gary,

If I was in the hunt for one, my first stop would be at NAPA. I don't know a part number, though. sorry.

Jim

Edit: NAPA web page shows Fel Pro FPG9097 and FPG60083. I suspect the difference in them is whether they fit a 2" exhaust or 2-1/2" exhaust.