Exhaust leak affecting performance?

BabyBlueChevrolet · May 3, 2023

So I crawled under my ‘73 today to try and get to the bottom of why its running crappy. I was hearing a ticking or popping sound and so I stuck my hand around the exhaust flange and felt exhaust coming out, then I looked at the lower portion of the exhaust pipe and saw a huge hole in it. My question is, could this really have that big of an impact on engine performance? The engine dies on cold starts, when it warms up in can idle but it does it rough. And when i drop it into gear it’ll die. And when i give it gas itll sputter and die, unless its already up to speed on the freeway then it’ll run fine mostly.

Grit dog · May 3, 2023

No.
Not in the sense you’re asking.
I’ve drove enough vehicles back in the day with rotted out half patched together exhausts to say with confidence…lol.

Could be any number of engine issues causing it to run poorly.

SquareRoot · May 3, 2023

^^^^^
Just fyi, if this had EFI it would be a different story. A pinhole in the exhaust with an EFI causes big performance problems. It's been a learning experience for me.

75gmck25 · May 3, 2023

Just to ad a little detail, EFI is affected by an exhaust leak because it can change the O2 sensor readings. Feedback from the front O2 sensor tells the computer how rich the mixture is, and it’s used by the computer to determine the optimum mixture.

85K304SPD · May 3, 2023

Probably just an indicator of the overall condition of the vehicle. It all works together. Tune it up, clean up the carburetor, fix all the vacuum leaks, fix the exhaust, and go from there.

Scott91370 · May 3, 2023

I would guess a vacuum leak.

Grit dog · May 3, 2023

85K304SPD said:
Probably just an indicator of the overall condition of the vehicle. It all works together. Tune it up, clean up the carburetor, fix all the vacuum leaks, fix the exhaust, and go from there.

Basically could be anything but an exhaust leak.

BabyBlueChevrolet · May 3, 2023

Thats what i figured, theres no o2 sensors or cats on it. Im gonna pull the plugs and test compression first. It has new spark plugs supposedly from the previous owner but they look cheap. I put new wires and air filter on. I was trying to order a carb rebuild kit for the 2 barrel rochester i have but im not sure if its gonna fit. The numbers stamped on the side are 7031714. Does anyone know of a carb rebuild kit that will work for this?

squaredeal91 · May 3, 2023

Check your vacuum advance unit as well.

BabyBlueChevrolet · May 3, 2023

squaredeal91 said:
Check your vacuum advance unit as well.

You know how to test it?

Ricko1966 · May 4, 2023

BabyBlueChevrolet said:
You know how to test it?

Easy there is more than one way,but an easy one and you get a cheap tool for checking other vacuum servos. Go to the dollar store and get a meat marinating syringe. Pull the hose off the advance can and plug the hose,stick another piece of hose on it,go and get the big meat marinating syringe plug it into the hose thats on the distributor now.Start the engine at idle pull on the syringe,your idle should speed up,push it in the idle will slow down. Bonus you can use it to see how much vacuum advance the can has in it,for setting up distributors,you can check choke pull offs,bleed brakes all kinds of cool stuff.

Wonder Bob · May 10, 2023

Yes. An exhaust leak can have an affect on vehicle performance. I had a cracked manifold an all sorts of minor issues. Nothing dramatic but really annoying. There are pressure waves traveling back and forth through the exhaust system. You can write whole books on all of the factors that play into this. For example, Insufficient back pressure can cause you to run lean. I don't know if the fuel air mixture is actually being sucked out of the cylinder or not but low back pressure can basically have the same effect. Not sure how sensitive a 454 is. On the old Pontiacs you could run larger headers on a 400 than a 455. Counterintuitive but proven through dyno testing. Bottom line - Exhaust leak may not be the only problem but it can certainly contribute.

Ricko1966 · May 10, 2023

Wonder Bob said:
Yes. An exhaust leak can have an affect on vehicle performance. I had a cracked manifold an all sorts of minor issues. Nothing dramatic but really annoying. There are pressure waves traveling back and forth through the exhaust system. You can write whole books on all of the factors that play into this. For example, Insufficient back pressure can cause you to run lean. I don't know if the fuel air mixture is actually being sucked out of the cylinder or not but low back pressure can basically have the same effect. Not sure how sensitive a 454 is. On the old Pontiacs you could run larger headers on a 400 than a 455. Counterintuitive but proven through dyno testing. Bottom line - Exhaust leak may not be the only problem but it can certainly contribute.

I'll put open headers upside down like a boat,no hood on my 75 and scream it up and down my street. An exhaust leak is not causing his problems.

Exhaust leak affecting performance?

BabyBlueChevrolet

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Grit dog

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