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Quiz.....what are these?

There are some factory y-pipes that had a longer pipe on the passenger side with a flat flange,so did the exhaust manifold,so no donut gasket was needed,a thin flat gasket was used instead..

Some years did use 2 donut gaskets,others only one...

I had a '75 2wd K5 and the exhaust manifolds on the 307 V8 I put in it from a '71 K10 Suburban were rotted thin and had cracked--a friend had a 4x4 K5 around 1978 vintage,he ditched the stock manifolds in favor of headers,so he gave them to me..
When I went to bolt up the original y-pipe,that fit fine on the 307's manifolds,I had a problem--his manifolds had a cast in "donut" made to the manifold,and my y-pipe was now too long ,even if I ditched the heat riser..

I ended up ordering 3 different y pipes from various years in the mid 70's before I got the "right" one that had the longer pipe and a tapered opening to allow it to mate properly with the manifold ,without using the heat riser...it was a pain,the Walker exhaust catalog showed the "right" pipe using donut gaskets on both sides,but it was "wrong"...

I should have just made my own "custom" dual exhaust front pipes,but I'd have had to buy another muffler and all the pipes for the drivers side..truck already had a practically new single exhaust on it and I didn't feel like spending much on it or doing the labor..
 
76zimmer said:
can you hook up your exhaust head pipe without the heat riser valve in between them?
Click to expand...
Only way to do that would be to get a spacer the same thickness. I don't really understand the purpose of this thing. I've read these posts stating that the valve is there to re-route the hot air, but there is no where for the hot air to go. If this valve is closed, it simply blocks the exhaust. My only thought is that by blocking it, it backs up into the smog pump. But that doesn't make much sense. There is no "alternate passageway" for the exhaust to travel. Other than the air lines plugged into the top of each exhaust port that go to the smog pump. Wish I was in another state so I could get rid of all this crap!
 
Thanks everyone for your help. Sounds like perhaps the best plan is to "modify" the valve to make sure it's not blocking the exhaust. And I guess the reality is......who cares why it's there, since I'm fixing it anyway. I'll just make sure it appears intact when it's all bolted up.
 
There is a passageway in the cylinder heads (see the one in the middle?):
ccrp_9903_18_o%2B305_chevy_small_block_engine_build%2B305_cylinder_head_option.jpg


Never thought about it that much before, but with the valve closed, that forces exhaust back through that passage, into the intake, under the carb, which heats it up faster, and keeps it warm in the case of icing. Since the Y-pipe merges after the valve, it's not a complete exhaust restriction when it's closed, you just have very little exhaust going out that side of the engine when the valve is closed.
 
Some intake gaket sets also come with metal block off plates that are either "closed" or just have a small hole in them,that blocks or limits the hot exhaust flow under the intake in that center port,in the case of vehicles that are emission exempt or in heavy duty trucks,hi performance, that dont need the carb to be heated up,you use those--if it has a heat riser and you want it functional,you leave those metal block offs out..
 
dyeager535 said:
There is a passageway in the cylinder heads (see the one in the middle?):
ccrp_9903_18_o%2B305_chevy_small_block_engine_build%2B305_cylinder_head_option.jpg


Never thought about it that much before, but with the valve closed, that forces exhaust back through that passage, into the intake, under the carb, which heats it up faster, and keeps it warm in the case of icing. Since the Y-pipe merges after the valve, it's not a complete exhaust restriction when it's closed, you just have very little exhaust going out that side of the engine when the valve is closed.
Click to expand...
OK, that makes sense.....thanks, I finally understand. I thought I was supposed to be looking for something on the outside. Thanks!
 
diesel4me said:
Some intake gaket sets also come with metal block off plates that are either "closed" or just have a small hole in them,that blocks or limits the hot exhaust flow under the intake in that center port,in the case of vehicles that are emission exempt or in heavy duty trucks,hi performance, that dont need the carb to be heated up,you use those--if it has a heat riser and you want it functional,you leave those metal block offs out..
Click to expand...

And it would be a bad idea to block them off, but leave the heat riser in place!

I suspect working correctly pressure will force the valve open, but it wouldn't help, that's for sure.
 
The metal gaskets are just aluminum I think--seen a few that melted when someone left the heat riser in and hooked up before,and used the "block off" gaskets!..guess they figured someone would do that!..
 
thought the OP was my auto shop teacher back from the dead..checking to see if I retained anything
 
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