C3 exhaust spacer function

[Jeff M.]

On my 71 big block, they have a spacer on the drivers side where the exhaust meets the manifold, what was the reason for it and any issues removing it? The right side has the heat riser and does not use it. I am thinking maybe it has something to do with the torque of the motor pulling up when the car is accelerated?

[Alan S.]

Re: C3 exhaust spacer function

Hi Jeff,
Your question made me take a look at the 71 AIM.
The info in the LS-6 option pages indicates that the exhaust studs on the right side are to be torqued to a dimension of 2.87", while the studs on the left side should have a dimension of 1.75".
Does that dimension difference correspond with what you're seeing? I don't see any mention of a spacer on the left side, just the heat riser on the right side.
Regards,
Alan

[Jeff M.]

Re: C3 exhaust spacer function

The spacer I am referring to goes inside the pipe and is also called a stiffener, it is made out of exhaust tubing and fits inside. I looked in the archives and see that Joe Lucia would not go without them, and also says to buy the steel exhaust donuts #3767556 does any body know if gm still sells them

[Doug F.]

Re: C3 exhaust spacer function

it keeps the donut in place and maybe acts as a shield from hot exhaust gasses, the earlier pipe had them built in, but i guess it was cheaper to make it as a separate part, i suppose you could do without, but why, those engineers were pretty smart fellows for the most part

[Joe L.]

Re: C3 exhaust spacer function

The spacer I am referring to goes inside the pipe and is also called a stiffener, it is made out of exhaust tubing and fits inside. I looked in the archives and see that Joe Lucia would not go without them, and also says to buy the steel exhaust donuts #3767556 does any body know if gm still sells them

Jeff-----


The part is not a spacer; it is called an EXTENSION. The GM piece for 2-1/2" pipes is GM #3890689 but it was discontinued without supercession in March, 2003. However, you can purchase these in most auto parts stores for a very low price. If the exhaust pipes or the packing do not have integral extensions (some soft packings do have integral extensions), then I absolutely recommend the use of the separate extensions.

The sintered iron packing is GM #3768711 and is still available.

[Jeff M.]

Re: C3 exhaust spacer function

Joe, thanks for the info, I am having a custom mandrel bent exhaust done next week and will be taking off the right side heat riser valve when the new system is installed. I would think they have to cause some type of restriction and would like to not use them and just use the iron rings, what do you think? Why did gm only use them on the drivers side?

[John H.]

Re: C3 exhaust spacer function

Joe, thanks for the info, I am having a custom mandrel bent exhaust done next week and will be taking off the right side heat riser valve when the new system is installed. I would think they have to cause some type of restriction and would like to not use them and just use the iron rings, what do you think? Why did gm only use them on the drivers side?

Jeff -

Either the loose extension or an integral one in the exhaust pipe is absolutely required on both sides; it supports the I.D. of the donut and keeps the donut from collapsing/disintegrating.

[Joe L.]

Re: C3 exhaust spacer function

Joe, thanks for the info, I am having a custom mandrel bent exhaust done next week and will be taking off the right side heat riser valve when the new system is installed. I would think they have to cause some type of restriction and would like to not use them and just use the iron rings, what do you think? Why did gm only use them on the drivers side?

Jeff-----


The extensions were used on BOTH sides, not just the left side. On both sides, the extensions slip into the throat of of forward exhaust pipe.

You can eliminate the heat riser and install a spacer instead. However, cold engine warm-up might be slightly impaired and choke operation will be significantly impaired. You might just want to disconnect the choke.