64 Exhaust component questions

[Ed S.]

Just purchased an N11, 2 1/2 inch aluminum treated exhaust system from Corvette Central for my 64 convert (L76 & 4 speed). Need advice on a few issues - have searched old threads, nothing current and old opinions vary.

Package from CC came with fiber (non metallic) donuts and extensions. The system I removed from my car was an after market repro - manufacturer or origin unknown - installed by a previous owner. Donuts on the car that I removed were metal (magnetic) and in good condition - there were no extension tubes.

Should I use the CC provided fiber donuts with extensions or, metal donuts without extensions, or metal donuts with extensions?

Flange question. Flanges removed from car are in good condition - surface rust only, easily cleaned up. There are no markings or part #s on the flanges. Previous owner used original parts when ever possible - these could be original. These flanges are 1/4 inch thick. Flanges supplied by CC are identical in shape to those I removed from car except they are 11/32 inches thick. Two pics are included - old used flange on bottom - new CC flange on top. Which, if either are "correct". If neither are correct - can you recommend a source for correct flanges.

Last question - nuts to secure exhaust pipe to manifold. Old discussions (6 years or more) in this forum state that no vendor carries "correct" nuts. What is the current thinking on this? Do any vendors carry a good repro nut? Paragon has a set and they say these are a "must" if the car is going to be judged. Recommendations please.

Thanks for your recommendations.

[Joe L.]

Re: 64 Exhaust component questions

Just purchased an N11, 2 1/2 inch aluminum treated exhaust system from Corvette Central for my 64 convert (L76 & 4 speed). Need advice on a few issues - have searched old threads, nothing current and old opinions vary.

Package from CC came with fiber (non metallic) donuts and extensions. The system I removed from my car was an after market repro - manufacturer or origin unknown - installed by a previous owner. Donuts on the car that I removed were metal (magnetic) and in good condition - there were no extension tubes.

Should I use the CC provided fiber donuts with extensions or, metal donuts without extensions, or metal donuts with extensions?

Flange question. Flanges removed from car are in good condition - surface rust only, easily cleaned up. There are no markings or part #s on the flanges. Previous owner used original parts when ever possible - these could be original. These flanges are 1/4 inch thick. Flanges supplied by CC are identical in shape to those I removed from car except they are 11/32 inches thick. Two pics are included - old used flange on bottom - new CC flange on top. Which, if either are "correct". If neither are correct - can you recommend a source for correct flanges.

Last question - nuts to secure exhaust pipe to manifold. Old discussions (6 years or more) in this forum state that no vendor carries "correct" nuts. What is the current thinking on this? Do any vendors carry a good repro nut? Paragon has a set and they say these are a "must" if the car is going to be judged. Recommendations please.

Thanks for your recommendations.

Ed------


The GM exhaust pipe flanges were stamped steel with raised edges, not "flat" like these.

The original exhaust pipe packing (donut) was a fibrous material heavily laden with asbestos. Some of these had a thin aluminum shield on one side but I do not think any of those used in PRODUCTION did. The sintered iron variety were primarily used in trucks. However, this is the only type I recommend for use on Corvettes and I use them exclusively.

As far as the extensions go, many replacement forward exhaust pipes have the extensions "built in". In that case, no separate extension is necessary (or, could even be used). If the forward pipes do not have the built in extensions, then you should use the separate extensions as were originally used.

[Ed S.]

Re: 64 Exhaust component questions

Joe,
Thank you for the quick reply and for sharing your extensive knowledge. I'll definitely reuse my sintered iron donuts. Do you, or anyone have a recommended source for a correct looking flange and nuts that secure the exhaust pipe / flange to the manifold? When you say "stamped steel with curved edges I assume the one in the attached pic is what you mean. This one is being sold on E-bay for about $6.00. Not suggesting it is "correct" - just similar to your description. Thanks again.

[Ed S.]

Re: 64 Exhaust component questions

After further investigation it appears that the stamped steel flange, similar to the one in the pic (in my previous post) was only used with the 2 inch exhaust system, while the solid metal cast type flange (as in my original picture) was used on 2.5 inch systems on SB engines. Part #, as the the AIM, for the 2.5 inch flange is 3850231. Which brings me back to my original question - which of the two in my original pic might be correct? The rusted one I took off the car is about 1/4 inch thick, the silver colored one (provided by CC) is closer to 11/32 inches thick. I can't find dimension for the GM part anywhere? Can someone with a known original flange kindly post the thickness - as best you can determine. Thanks again.

[Joe L.]

Re: 64 Exhaust component questions

After further investigation it appears that the stamped steel flange, similar to the one in the pic (in my previous post) was only used with the 2 inch exhaust system, while the solid metal cast type flange (as in my original picture) was used on 2.5 inch systems on SB engines. Part #, as the the AIM, for the 2.5 inch flange is 3850231. Which brings me back to my original question - which of the two in my original pic might be correct? The rusted one I took off the car is about 1/4 inch thick, the silver colored one (provided by CC) is closer to 11/32 inches thick. I can't find dimension for the GM part anywhere? Can someone with a known original flange kindly post the thickness - as best you can determine. Thanks again.

Ed-------


Yes, the photo you posted is the configuration I was describing and, yes, the 63-67 flange for 2-1/2" systems was GM #3850231. However, the 63-82 for 2" systems and the 68-74 for 2-1/2" systems was the style I described. It's very possible the 63-67 2-1/2" style did use the flat type. I've only seen these on replacement systems. I have no other knowledge of them, though, so I can't tell you which of the two you pictured is correct.

[Ed S.]

Re: 64 Exhaust component questions

Thanks again Joe. I am not reasonably confident that the correct flange for a 64 SHP 2.5 inch exhaust is the solid metal version. I just know know what the dimensions of an original are. Hopefully some one that has a known original will respond with data that I can use to identify a correct flange.

[Jim D.]

Re: 64 Exhaust component questions

On both my 65's with 2 1/2" exhaust, 1 small block and 1 big block, the flanges are the flat solid type and approx. 3/8" thick. The 65 A.I.M states they are #3850231. I hope this helps.

[Ed S.]

Re: 64 Exhaust component questions

Jim,
Thanks for taking the time to measure your flanges. Yes, it does help. I measured the thickness of mine with a digital caliper. The one I got from CC is exactly 3/8 of an inch thick - and, one side of the inner circumference is tapered some to enhance seating against the flared exhaust pipe. The one I took off my car is 5/16 of an inch thick and it is not tapered, it can go on either way. I'm going with the CC supplied 3/8 inch thick flange - it appears to be a better match to an original. Thanks again.