Porting quad4 exaust

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Porting quad4 exaust

Postby Guest » Tue Mar 19, 2002 11:47 pm

i want more flow out of my quad's exhaust.  I have a 94 quad4 z26 and it is 10 hp less due to exhaust restrictions.  I know one major restriction is the downpipe.  I plan on getting a 2.5" downpipe as well as the rest of the exaust.
Now for my porting question.  should the exhaust ports on the head be opened up more, or should the manifold be opened opened up only.  Would it be bad to open up the ports on the head?


Porting quad4 exaust

Postby Guest » Wed Mar 20, 2002 5:26 pm

I'm not certain (ask Rex for more info), but I believe you do NOT want to touch the exhaust ports on a Quad, even one with the 753 head like you have. You DO want to open up the manifold, and enlarge the downpipe to either 2.25in or 2.5in as well as add a high flow cat and a good cat-back exhaust (mandrel bent) with a straight through muffler (like an Ultraflow or Borla) for best performance. If I remember correctly, even if you do touch up the exhaust ports, leave the floor alone and only enlarge the sides and top.

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Porting quad4 exaust

Postby NVMYGTZ » Wed Mar 20, 2002 6:08 pm

From 93+ they used  a small exhaust manifold and down pipe.
You will want a Pre 93 manifold and downpipe. The 93+ down pipe will not fit the earler style.

Yes if you do work head you will want to raise the roof of the Exh. port up about .25 to the gasket line of a 086 gasket(yea there diffrent) Also blend in the valves. The Exhaust valves can also benifit from a back cut of around 23deg

I'd say check out my site but my server is down.

93 GTZ Q4<-- Just a few mods =^P
92 GTZ Q4<-- A few less than above
91 GTZ Q4<-- Euro-spec *Black*
69 Chevelle 396SS


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