71 350/270hp 2" manifolds where donut gasket mounts over extension.
extension fits inside of pipes with donut over outside. The inside diameter of extension is 1 5/8" this seems restrictive. the extension does not seem to add any length looks more like a liner to prevent blow out of the donut gasket. I would like to get ride of the extension so exhaust pipe would be closer to 2". Any reason not to or is there another way around it?
thanks Chris

Chris,

Which side are you talking about? On my '70 350/300hp with 2" manifolds the left side pipe connects directly to the manifold with the donut in between. On the right side the heat riser assembly is sandwiched between the pipe and the mainfold with a gasket on the top side of the heat riser and a donut on the other. Don't know how different the '70 and '71 are in that regard.

These extension are on both sides and slice into exhaust pipes. these extension are about 3" long .they look like an adapter to fit two different pipes together. the bottom has a 1 5/8 I.D. and the top has a 2" O.D. with a slight lip at top. The donut slides on fron the bottom with the lip at top stopping it. then the whole unit is slide into the exhaust pipe stopping flush with top of exhaust pipe. Looking like just a donut gasket there. They add no length to pipe I really have no idea what they do except restrict exhaust at that point. Only thing I could think of was to prevent blow out of donut. These came on this car and i have scene them in corvette world parts magazine in exhaust section with no explanation as to purpose. I'am going to try it without them and see what happens.

I looked in 7 different parts catalogs that I have - 3 of them show the extension you have as part of the exhaust system, the other 4 don't mention them. My AIM shows one on the left side, but the right side isn't expanded to show what's inside. They were not present in my exhaust system before I replaced the system from the manifolds back so I put everything back together without them. Don't know what their purpose would be, other than to help retain the donut integrity like you mentioned and/or to increase back pressure in the exhaust system by constricting the pipe size. Anyone else have some thoughts?


Jim O.

update: A older guy that built exhaust systems back in the day told me the old machines used to be able to bend the pipe over at the top 180 degrees then back down the pipe a bit turning up a 45 degree angle and stopping leaving a nipple of sorts for the donut to slide over and seat. The protruding nipple would extend a 1/2" or so past the top of the donut. When installed the nipple would slide up into the manifold 1/4 to 1/2 " when the donut was seated . This would keep exhaust gases from burning through donut. these bending machines are not useful in todays type systems so exhaust makers have gone to extensions to create the heat shield/liner. some are straight and pressed into pipes for a tight fit or like mine an adapter for two different pipe sizes only that mine does not reach up into the manifold. This sounds like the best reasoning i've heard so far. Looking into the under side of my exhaust manifold i can see a recessed area where the nipple on the pipe would fit. I'am going to get a straight 2" OD pipe and cut to fit a new heatshield /liner for mine getting me back to a truer 2" exhaust.

thanks for your help here Chris

Sounds reasonable. Something to put in the back pocket for the next time I have the pipes apart.

Thanks for the update.


Jim O.

try to show my car image

Your Forum Signature should look like this (but replace the "?" marks with "|" - vertical bar symbol):

Chris
?IMG? http://www.c3vetteregistry.com/member_uploads/904/1971.jpg ?/IMG?

You might want to resize your pics and shrink them down some. Great looking ride you've got though! Like the wheels ALOT. What brand are they?


Jim O.

Gonna try again, They are Rocket Mags They were on the car when I got it , the fella said he bought them back in 1978 same as the Goodyears on there

Hey Chris,

If you're still having trouble with getting a pic into your signature there are a couple of others having the same problem. Check out the postings in the General Discussion forum.

Jim O.