Exhaust doughnut

[PlayingWithTBI]

Hell, just get some shorty headers, they use a ball joint instead. YMMV

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[udidwht]

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Drivers side donut

You can see it was burning thru on the manifold side of gasket as opposed to the pipe side. Passenger side was great (this time). The manifold is nice and flat and clean. These gaskets when I installed them in Bakersfield had a lose fit to them when put up into the manifold. The new ones I had bought (same Fel-Pro) had a much snugger fit into the manifold. Enough that I had to carefully tap them into place (would not go into place with finger/hand strength. Not entirely sure if this would have caused it given he passenger side was great. The burned gasket had ~ 1070 miles on it.

 

[udidwht]

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Drivers side donut

 

[Schurkey]

used plenty of copper seize.

Lots of copper seize.

ANTI-seize.

Are you putting the anti-seize on the donut? It goes on the threaded studs only.

You have the right donuts with the inserts.

He has the metal inserts. Jury's still out on whether he's got the right donuts.

This particular manifold the donut sits in the manifold steel ring end first with gasket facing down towards pipe. I'll get some pics of it installed.

Saw the picture of the assembly. I want to see how the manifold outlet is machined, and what the NEW donut looks like. What is the part number of the new donut?

I had used Fel-pro donuts. Once I had the pipe down the passenger side donut looked great. The drives had about a third burned thru. But the burned area was not on the pipe side it was the outer edge near the manifold. When I installed them in Bakersfield I had noticed they fit rather loose. I had to use a smear of copper paste to hold it in place. I'll post some pics of the donut.

Copper anti-seize amounts to powdered copper in a grease carrier. The copper acts like a billion ball-bearings, but it's common for the grease carrier to burn away. This is not a fault of the anti-seize; the grease isn't what stops the seizing.

Stop contaminating the donuts by applying burnable grease to them.

I'm beginning to think it's crap parts. Anyone know the part number from GM? Or how about some pics comparing the GM vs 3rd party brand?

I want to know if you're buying the right donuts. There's more than one shape, and there's various sizes. Some have a double-taper, some are flat on one end with a taper on the other end.

The donuts have to fit the parts they're sealing.

 

[udidwht]

1. Anti seize is on stud threads, nut threads and pipe tri-flange bore only.

2. Donuts come with metal inserts.

3. Fel-Pro gasket 60584

4. The copper paste was only used on the metal insert that sticks up into manifold to hold it up in place. Only enough to do the job. No paste used on gasket itself.

5. The donuts used are what is called for for a 1994 GM P-40 chassis. They are flat on the manifold side and taper on the pipe side.

The gaskets used were the same part number as prior. I had kept the package from the previous ones. The current ones did fit more snugger than the previous ones. No use of copper RTV to hold up. Pipe surfaces were very clean as was the manifold side. Clean and flat.

 

[Schurkey]

1. Anti seize is on stud threads, nut threads and pipe tri-flange bore only.

What is a "tri-flange"?

3. Fel-Pro gasket 60584

I'll look those up.

4. The copper paste was only used on the metal insert that sticks up into manifold to hold it up in place. Only enough to do the job. No paste used on gasket itself.

Better to tap the metal with a small hammer to distort it a little, for added friction, than to stick it in place with grease.
(Anti-seize)

5. The donuts used are what is called for for a 1994 GM P-40 chassis. They are flat on the manifold side and taper on the pipe side.

And is that how the manifolds are machined?

 

[udidwht]

1. The (3) bolt flange that slides up the pipe (tri = 3)

2. Did not attempt tapping since I did not wish to damage the gasket itself.

3. The manifolds are GM OEM.

 

[Schurkey]

2. Did not attempt tapping since I did not wish to damage the gasket itself.

Your current process is to install grease above the donut, which melts and drools down onto the donut, which then burns from the heat of exhaust.

Gotta do something different.

3. The manifolds are GM OEM.

But are they machined properly for the donut you're using. Post photo(s) of the manifold outlet.

I tried finding on-line photos of the gasket, but all I see are views from above. Nothing from the side showing the taper.

 

[udidwht]

These are what I used (same part#) best pics.

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[udidwht]

Update:

Just finished my annual summer trip (3.5 weeks( from Renton, Wa. to HB, Ca. I installed the donuts back in 7/11/22 74,087. After the return home I'm now at 78,1XX and the donuts are holding up very well. My thought as too why they are now and not previously...

I believe the cleaning of the radiator tube fins (exterior) played a major role in allowing the engine to run cooler. Using my phone app (ALDL) I was seeing average running temps on the flats of 202F - 207F (mostly 204-205F) This was in 90+F ambient temps. The dash gauge shows half a needle-full needle width to the right of 210 mark (not very accurate compared to the CTS reading via the phone app). On my previous trip (last year) prior to the AC condenser/oil cooler replacement and radiator exterior cleaning I was seeing at min a 10-12 degree increase of average temps on the flats same ambient temps. Being a TBI OBD-1 the engine temp will play a role in AFR adjustment/s during engine run time. This would also increase the temps on grade pulls.

With the radiator exterior clean the dash gauge needle on a grade pull now goes only 2/3rd into the bar to the right of 210 mark. Clutch fan is roaring at this point. Recovers quickly at crest and descent.