Big Boyz Head Porting  

 

Something that can be easily overlooked when building a performance V-twin, the exhaust gaskets. The stock exhaust gaskets have a lot of "crush" in them. They tend to crush down and block the exhaust port. After spending hundreds or even thousands on the heads, installing the stock exhaust gaskets can take away a lot of the performance gain.

We include a set of SE performance exhaust gaskets (or equivalent) with the heads to make sure that the right ones are used. HD part# 17048-98

I took a picture of a stock exhaust gasket used in a ported head to show what I was talking about.

The part of the gasket between the Yellow line and the Blue line is the "shelf" where the gasket sits.

The part of the gasket between the Yellow line and the Red line overlaps into the port, partially blocking it. You can see the clearly defined line of Carbon from the exhaust gasses. Also note how irregular the inside of the gasket is. That is the part that gets "Crushed" into the port.



Here is a picture of a performance exhaust gasket after being used. It is a good comparison to the stock exhaust gaskets above. It is easy to see that there is no carbon line like the stock gasket. It is a good representation of how little it blocks the port compared to the stock gasket.




As a side note, if the stock gaskets are used PROPERLY, they won't block the port. The keyword here is PROPERLY. It is very easy to over tighten the exhaust and crush the gasket. This is where the problem lies. Nearly all the heads we receive still have the old exhaust gasket still in the port. This allows us to inspect many of them. Not all are crushed into the ports but we even see Brand NEW take offs come in with crushed exhaust gaskets right from the factory.

Using the performance gaskets can be tricky as well. Since there is less gasket material it can be harder to get a good seal sometimes. It may require adjusting the exhaust fitment a couple times to get it right but they won't crush into the port.

Both the exhaust gaskets in the pictures above started out the same width. The Performance gasket and the stock gaskets are the same width but the stock gaskets are taller and that is what allows them to crush so much.


Here is a perfect example of the stock exhaust gaskets crushing into the port.

In the first picture you can see the port from the inside showing what the exhaust gases are running into (red arrows).



Between the red arrows in this picture you can see the port wall and the shelf that the gasket sits on. The yellow arrows are showing where the gasket extends into the port, blocking it.



The 2 read arrows in this picture show where the exhaust gasket starts protrude into the port area. The red line is the total distance that the exhaust gasket is in the port, note more than 50% of the way around. The yellow line shows where the exhaust pipe was crushed into the gasket, note the relation to the red line.



This is the exhaust gasket after it was removed. Between the yellow arrows you can see the carbon line clearly showing how much of the gasket was in the port.





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