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View Full Version : How come no gasket matching exhaust manifolds



Dirk SC
03-21-2006, 12:42 AM
Pretty much as the title states. Why is this bad and how would you see a gain from not doing it?

Ddubb
03-21-2006, 02:04 AM
Well for one, our cars dont use exhaust manifold gaskets.

The Mis-alignment of the exhaust manifold to the cylinder head exhaust port forms a reversion dam that keeps the exhaust gases from re-entering the combustion chamber as the exhaust pressure pulses vary.

When you do port work, there are four areas to look at to see if restricting material needs to be removed - The valve pocket, short side radius, valve bowl, and the intake ports.

- Dan

68COUGAR
03-21-2006, 02:08 AM
Why is this bad and how would you see a gain from not doing it?
Wow, you're opening up a can of worms here!!!!!!

The whole idea of Exhaust Performance, is to increase FLOW. Exhaust FLOW, starts with the piston shape, continues to the exhause valve, through the head, to the exhaust maniflod/header, & to points beyond.

ANY Thing that you can do to increase exhaust FLOW is GOOD.

Exhaust Port Matched gaskets? I guess that would have to depend on YOUR Exhaust Port Diamentions? Do SC's even use Exhaust gaskets? It's been so long I can't remember.

68COUGAR

Randy N Connie
03-21-2006, 11:12 AM
I havent tried this yet,but have on other type motors.

Port match the exhaust to header flange.And the use a stepped header
to reduce exhaust revertion.

I have raised the short side radius & port roof around the valve guide.
& plan to raise the exhaust flange roof.Then I would like to
try and build a raised with longer radius stepped header. If I ever
get around to building the headers, I will know if it is an improvment
or not.It should be. I been working on this in my spare time for two
years. Hope to get-r-done this year.

Randy

CMac89
03-21-2006, 02:50 PM
The flange of the exhaust manifolds are already bigger than the actual exhaust port so there's no need to.

S_Mazza
03-21-2006, 05:44 PM
About the gaskets - some (probably most) Thunderbirds came without exhaust gaskets. But if you pull the manifolds off, it's a very good idea to use gaskets. I think most upper engine gasket kits come with them (the puffy metal kind).

Wzenheimer
03-21-2006, 05:58 PM
I have raised the short side radius & port roof around the valve guide.
& plan to raise the exhaust flange roof.Then I would like to
try and build a raised with longer radius stepped header.
Randy

The short side radius being raised is the biggest gain I have seen. I would agree Randy that a raised stepped header would also improve flow. Just not sure if there is room between the head and the shock tower.

Chris

Dirk SC
03-21-2006, 08:42 PM
good to know. Thanks.

scbird1
03-21-2006, 11:59 PM
Let me tell you about my mistake. If your not sure what your doing, dont touch the exhaust ports. Before I understood these motors I went to town on a set of heads I had laying around. Made the ports a lot bigger to match the exhaust manifolds and open up the bowels. Well I bolted them to a stock rebuilt engine. From a standing start my NA 3.8 would take this car but at 5000k it pulled a little better then stock. After a head swap it had all that fun loving TQ that makes it a SC. I did play with the intakes as well. Grinding, sanding and polishing for hours:o You live and learn. Leave it to the pro`s;)

XR7Kurt
03-22-2006, 12:55 AM
But if you pull the manifolds off, it's a very good idea to use gaskets.
Just curious,why?

Kurt

S_Mazza
03-22-2006, 02:41 PM
Because they can warp a good bit over time. Once you take them off, it can be really hard to get them to sit flat, or even line up the bolt holes! So it's good to use a gasket there to make sure they seal evenly.

(Also, there is a certain bolt location on each exhaust manifold designated as a "pilot" which you should install first. Then slot the other holes to fit the head if necessary.)

Randy N Connie
03-23-2006, 09:03 AM
If your header flange is warped.Most machine shops can lap the header flange
back to being true flat surface.

The machine used to lap header flanges looks like a spinning flat wheel that you would use to make clay pots on.

The wheel, a lapping plate spins,and you just hold the header flange down on the lap plate by hand.And move the header around in a swirl motion on top of the lap plate. You lap the header flange until the header flange surface is a consistant shiny color all the way across its surface.It take about 2 to 5
minutes to true a header flange surface.

Randy

David Neibert
03-23-2006, 09:45 AM
I use the felpro gaskets and a thin coating of copper RTV on my headers.

David

Randy N Connie
03-23-2006, 11:07 AM
Like David N. I use the aluminum faced Fel-Pro gasket.

But with the aluminum face Fel-Pro gasket being between the
steel header and the aluminum head.The gasket stops
electroalicess(sp) that happins when steel is mated to
aluminum,and slows the aluminum from getting pitted bad
over the years of use.

Randing

S_Mazza
03-23-2006, 02:33 PM
electrolysis

Slysc
03-23-2006, 10:40 PM
The throat of the exhaust bowl is a big choking point of the exhaust flow. The exits near the gasket are already much larger than the throat already. Flow is greatly improved by equalizing the velocity of the exhaust exiting the port. If the velocity is high through the throat and then slows greatly as it exits because you have opened up the port near the gasket, then it causes the flow to tumble and that actually increases restriction. The best flow is acheived when you open up the bowl and the throat and then weld up the exit to match the cross sectional area of the bowl and the throat. That will keep the velocity constant and linear which will increase the flow numbers.