Exhaust manifold gasket placement

[Terry M.]

Re: Exhaust manifold gasket placement

I agree about the heat transfer relative to gaskets being an issue. With the Gen II LT1 exhaust manifold cracking, and fastener sheering is a major issue. I never considered that the gasket might have something to do with that.

TIme to scratch my head some more.

[Bill C.]

Re: Exhaust manifold gasket placement

The point about heat transfer is very interesting. I often check my exhaust manifold temps after a drive and b4 shutdown (63 L-76), and usually see about 525 to 560 degrees above the outlets. The R.H. side always seems to be running hotter than the L.H., with or without the heat riser butterfly wired open. I don't know what I am looking for or what they should be, other than I was looking for any changes or trends while I was making carburetor changes during my percolation problems this past summer.

Does anyone have any spec data or theories on what these temps should be and, if extreme or out of line, what could the cause be, etc.

Hope this isn't deviating too far off the subject of the thread.

Stu Fox

Stu,

Have to check my notes but as a general rule I find with a correctly tuned sb engine and no gaskets using the IR temps should be in the 500 degree range, some as low as 475! Really depends on the engine setup.
But, I find that if I do take a reading on an engine with gaskets and then remove them, check clearances and fit and reinstall without the gaskets I am not surprised to see them run 150 - 200 degrees cooler. Substantial when you think of the mass involved and the heat it throws!

The IRT is one of the best tools in my box!!

Here's something of interest.
Did you ever wounder why ya just could not keep gaskets on headers? Its because they got so hot, that caused LOTS of movement! Warped flanges, etc. and that of course allowed the gaskets to "breath" and blow.
Same holds true in the following: Stand next to a car with headers or a multi piece poorly fitting exhaust system (include the manifolds with gaskets here) after its fully heated , preferably after a hard run and turn it off.

Now listen to the "tink-tink-tink" coming from the system as it cools off, know what that noise is? Movement! Yes, I know all about the engineers that are going to holler about dissimilar metals and heat expansion blah blah, but, movement none the less, the hotter the system was, the more movement.

Now stand next to one of our old dogs with the manifolds correctly installed with no gaskets and fitting properly and do the same thing (this assumes a well fitted quality exhaust system) and tell me what you hear. (Oh, now we have two SIMILAR metals mated together, cast iron head and cast iron manifold)

Nothing!
Great! The parts are not searching for equilibrium! Tey never got that hot, the heat was absorbed by the head and dissapated into the cooling system.
Try it, I guarantee you will be amazed at the drop in under hood temps!

Use your IRT if ya have one and prove it to yourself, I have been thru this exercise many times. If you do not have an IRT, you can always carefully use the low tech testing device we all have, the back off your hand.
You will feel a substantial difference!

Needless to say this all applies to Big Blocks also!
Bill

[Bill C.]

Re: Exhaust manifold gasket placement

I agree about the heat transfer relative to gaskets being an issue. With the Gen II LT1 exhaust manifold cracking, and fastener sheering is a major issue. I never considered that the gasket might have something to do with that.

TIme to scratch my head some more.

Terry,
Don't scratch to hard, leads to rapid hair loss, trust me!
I am not familiar with the later motors at all, I stick with the low tech dinosaurs. But I do know any type of thermal barrier (gasket) placed between an exhaust manifold of any type and the head will allow that manifold to reach whatever temps the escaping exhaust gases reach, and then cool off, cycling minimally during load and cruise or running at all and shut down, this would be more of of problem in colder climates. Thats an awful lot of expansion cycles! Can you associate these problems geographically? Have a peek at the response I just left Stu above.
Bill

[Timothy B.]

Re: Exhaust manifold gasket placement

Learn something new every day, it makes sence to me. Thanks for the info.

[Terry M.]

Re: Exhaust manifold gasket placement

Bill,
My 1965 Impala, when new creaked, when cooling off after a good run. My 1970 LT1 did the same, and so does my 2008 Z06. I don't know what parameters you want to look to, but there are not too many similarities between the 2008 and the other two.

I do think we are on to something with the higher temperature of the exhaust manifolds when gaskets are used. Next time I have the exhaust off the Gen II LT1s I'll try leaving the gaskets out and see what happens.

[Bill C.]

Re: Exhaust manifold gasket placement

Great
Let us know the outcome!

[Terry M.]

Re: Exhaust manifold gasket placement

Terry,
Don't scratch to hard, leads to rapid hair loss, trust me!
I am not familiar with the later motors at all, I stick with the low tech dinosaurs. But I do know any type of thermal barrier (gasket) placed between an exhaust manifold of any type and the head will allow that manifold to reach whatever temps the escaping exhaust gases reach, and then cool off, cycling minimally during load and cruise or running at all and shut down, this would be more of of problem in colder climates. Thats an awful lot of expansion cycles! Can you associate these problems geographically? Have a peek at the response I just left Stu above.
Bill

If I could figure out how to lose only the gray hairs, losing some would be OK. I still have plenty.

The exhaust issues in B-bodies are generally supposed to be associated with police vehicles -- according to GM. Empirical evidence indicates all B-bodies are subject to either fastener failure or manifold cracking, or both. It is routine for us to change the grade 5 fasteners for grade 8, and that eliminates the fastener failure.

It is thought that the thin-wall casting leads to the manifold cracking, combined with the high temperatures of law enforcement service. Many Gen II LT1 owners comment on glowing manifolds at night, so there is no doubt elevated temperatures could be a factor. There seems to be no geographic factor. It happens to all of us sooner or later. Of course many of us put major miles on our cars. Both of mine are approaching 200K, and some in taxi service exceed half a million miles. These things are built like tanks (of course some would say they look like tanks also), and routine maintenance will keep them running for quite a while. They also happen to be the last old-school rear wheel drive sedans, and can be made to handle reasonably well. They jump curbs just fine also.