Porting Exhaust Manifolds...Question

tbirdman

Registered User
I'm swapping in a 95 SC engine into my 92 SC. I've sent the exhaust manifolds from the 95 engine to a guy in New Jersey who ports heads and exhaust manifolds. This is the first set of SC manifolds he will be doing, and he has a question. He wants to know the I.D. of the tube the bottom of the manifolds bolts up to, so that he can know how much to open up the bottom of the manifolds. Sorry about the lack of SC knowledge.

Thanks in advance for any help.
 
I'm guessing you examined the manifolds before you sent them off.
There is a lip about 1/8" thick extending about 1" into the collector all the way around, and it is squared off in the back (bad for flow).
All that needs to be done is to remove this elevated ridge so that the diameter at the bottom matches that of the rest of the collector. It will be very obvious once he looks at it.

2 1/4" exhaust pipes (downtubes) are the largest that can be reliably fastened to the stock manifolds, with or without porting them. You don't need any larger unless building something rare. The stock are 1 7/8" I believe.
You should plan to replace at least the stock downtubes and cats with 2 1/4" pipes and high flow cats to realize any gains from porting the manifolds.

Cheers
Bob
 
search and you will find some info, perhaps not exactly what you need but it should help... in particular posts from former member tbird88

http://www.sccoa.com/forums/showthread.php?s=&threadid=15964&highlight=porting+manifolds
http://www.sccoa.com/forums/showthread.php?s=&threadid=15964&highlight=porting+manifolds
http://www.sccoa.com/forums/showthread.php?s=&threadid=15211&highlight=porting+manifolds

Note that you will not want to do hardly any changes to the exhaust ports on the manifolds. They don not need to be made bigger. Just muck with the collector.
 
Thanks for the info, I do appreciate it. I will forward this on to him. I have done some searches through the forums for porting the exhaust manifolds, just never really found what the I.D. of the stock downtubes was, and I wanted to make sure I had the information he needs. The other info will be a big help also. At some point, I will go with the 2 1/4" downtubes into a new exhaust setup, but I'm not up to that point yet. Doing the engine work now.
 
inside diameter of stock down tubes at the outlet of the collector is 1-5/8". Not good at all. good luck with the work. I'd tell the guy to do as much as he can. I believe Tbird88 was able to get quite a way in the collector to make it a nice straight shot. Depends on the tools you have.
 
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