What exactly is involved in porting the heads and does it change the compression?

 

Here's an overview:

The ideal cylinder head setup would be to have straight and direct ports so the porting and smoothing of the ports is important. Increasing volume and velocity is the major goal of these two...mainly to clean-up the poor quality of the stock castings. This is where flow bench testing comes into play. Larger valves can be incorporated to allow for more flow as well but you want to keep the valve weight down as much as possible. Valve size is very dependent on cylinder bore size. Port matching is also important to remove any turbulence that may occur between the intake manifold, headers and heads. A good 3+ angle valve job is also important for proper seal/compression. Milling or decking the heads is a good idea to remove any warpage and/or increase compression. Combustion chamber and valve sizes should match the bore size...chamber size will effect compression ratio as well. Balancing all of these variable is what makes for a good set of heads.
-----------------------------------

Each tuner has their own exact formulas for their ported heads. You should check out MTI's site for their breakdown of what they do for their Stage 1-3 cylinder heads...nice pics too. Here's a link: http://www.motorsporttech.com/c5_engine01.asp

:cheers:

 

"Porting"- shapes the intake and exhaust "ports" (or runners) in order to maximize port flow and velocity for a given application. Compression is not changed with "porting" as the combustion chamber is not changed. When developing a set of heads ,for a particular application, you might reshape/size the combustion chamber to increase or decrease compression.
Her is a good article on porting smallblock chevy heads. Doesn't specifically apply to an LS1/6 but does in general.
http://www.chevyhiperformance.com/techarticles/95518/ Hope this helps!! :yesnod: :steering:
joel (Bink) :cheers:


I type too slow! In the time it took me to put this together C5CEMO provided his excellent response :thumbs:


[Modified by binksZ06, 9:25 PM 5/23/2003]

 

Thanks guys. Great links to general info sites. The pictures explain alot. How poor is the cast porting on the stock LS1 heads? Is it really that bad or can every stock head benefit from some degree of porting? After you port the heads and add a cam and headers, do emissions go way up? Will this thing pass smog testing in CA? :chevy

 

Any stock head can benefit from some degree of porting provided it fits with the overall package. :thumbs: