Effects of unbalanced exhaust?

[newyorkin]

If the passenger side of the y-pipe rotted out, but the drivers' side were fine, would this unbalanced backpressure eventually damage the heads/valves/cam?

This is on an '85 K20 that has a vaccuum heat riser on the passenger side manifold.
My guess would be that it shouldn't cause any permanent damage, since the heat riser should cause fairly dramatic unbalanced backpressure at the worst time, when the motor's cold, also.
But... I suppose I could also see the theory of long term damage having some validity.

So... real-world thoughts on it?

 

[kennyw]

I think as long as the exhaust manifold is still there it won't hurt anything. I've been told not to run without manifolds or you can burn your valves though.

 

[Blue85]

Since it is a Y-pipe, it ties the two banks together. A hole anywhere will drop the pressure on both sides. Granted, the side with the hole will be lower.

I don't think it will hurt the engine. I would be more worried about melting/burning stuff.

 

[newyorkin]

Yeah, both sides will definately be way off, but the pass side looks like a cheese grater much closer to the top, so the drivers side is going to have higher psi from being contained to that point at least.

I'm trying to sell the truck, and a guy told me he thinks the cam is shot because of the exhaust problems. I've heard of flex plates cracking with exhaust leaks, but not ever internal damage. Not that it can't happen, I've just never heard of it.

 

[kennyw]

If the cam is damaged it has nothing to do with the exhaust. GM small blocks are notorious for having flat cam's though. Just poor material quality in the stock cam.

How do you crack a flexplate with an exhaust leak?

 

[toomany]

How do you crack a flexplate with an exhaust leak?

The might sound the same...other than that I don't see anyway it would happen. Would open manifolds cause it to fall appart?

I cracked/broke the flex plate in my K20, didn't make any noise. Only reason I knew I had a problem was the starter wasn't meshing with the teeth on it. Pulled the trans out and about half of the plate fell on the ground, the other half was still on the crank.

 

[dyeager535]

Not going to hurt anything.

I think everyone has heard the burned valve theory, never seen it actually tested. I've talked with an engineer who was heavily involved in engine design, theory, etc., including 4 strokes, and he said the burned valve due to insufficient exhuast was a myth.

Everyones heard why it supposedly will happen, AFAIK it's never been proven in a controlled environment. Way too many variables for someone outside of a testing facility to be able to positively say a valve problem was or was not caused by this.

Since your guy is talking about camshafts, he's gotten his second hand stories wrong. Comments/thinking like this are exactly why, without absolute proof, these sort of automotive ideas are impossible to believe.

 

[throttleissues]

Just "fix" the leak with a beer can and bailing wire. I saw that around here somewhere.

 

[kennyw]

Just "fix" the leak with a beer can and bailing wire. I saw that around here somewhere.

Have you seen a Midwest/Eastcoast swiss cheese truck in person yet? It would take a lot of beer cans to cover anything up on those things. He would be left passed out on the garage floor after drinking that much and forget about the guy he was going to sell it too

 

[dyeager535]

Just "fix" the leak with a beer can and bailing wire. I saw that around here somewhere.

Hey, I resemble that remark!

Tried that when I was quite a bit younger, as a fix for a Dodge, what I now believe was an EGR tube. The piece of can I used melted through in pretty short order lol. Learn something new every day: Aluminums melting point is below the exhaust temp of a Dodge's EGR.

 

[newyorkin]

The flex plate thing always boggled me, too. But, I'd heard it for a while, then when I ws working in a shop years ago, a kid came in looking for a flex plate.
The counter guy said, "do you have an exhaust leak?"
"Yeah"
"Fix that first, or you'll crack another plate."

I'm sure it could've been the myth plus coincidence that the kid had an exhaust leak, though.

Dyeager, thanks for the info, I trust your opinion and I'm glad it agrees with what I think...


I did 7 root beer cans with exhaust putty, and two rolls of muffler tape on this thing one night at work months ago. The drive home that night was GREAT, and the truck regained a lot of power.
Unfortunately, it all melted or fell off within 2 or 3 drives... And I only drove the truck once a week then...

I have new exhaust I will include with the truck, too. This guy's apparently trying to drive my price down saying it needs major engine work. Nothing wrong with that, really, I guess.
But...I'm selling it with a spare engine, so that is kind of a bad way to try driving the price down.

Thanks for the replies all!

 

[jonrpick]

Not going to hurt anything.

I think everyone has heard the burned valve theory, never seen it actually tested. I've talked with an engineer who was heavily involved in engine design, theory, etc., including 4 strokes, and he said the burned valve due to insufficient exhuast was a myth.

Everyones heard why it supposedly will happen, AFAIK it's never been proven in a controlled environment. Way too many variables for someone outside of a testing facility to be able to positively say a valve problem was or was not caused by this.

Since your guy is talking about camshafts, he's gotten his second hand stories wrong. Comments/thinking like this are exactly why, without absolute proof, these sort of automotive ideas are impossible to believe.

I've read about the burned valve deal... It's caused by an engine that's running too lean, but is otherwise kept in check with excessive exhaust back pressure. As the back pressure keeps the exhaust from being fully expelled, the fuel/air charge is contaminated, and therefore (exactly as in the case of an EGR valve) the result is lowered combustion chamber temperatures.

Remove the restriction, the fuel and air burn hotter, combustion chamber temps shoot up, and valves can get burned.

Usually the burned valve theory is totally mis-explained, or not explained at all, and is right up there with other good ones like "some back pressure is a good thing".

This just made me think of something... new thread coming.

 

[dyeager535]

So not to go further off topic, but valve burning may be compounded by lack of exhaust, but not a cause. I can buy that.

 

[jonrpick]

So not to go further off topic, but valve burning may be compounded by lack of exhaust, but not a cause. I can buy that.

Yep... and not completely off topic. IIRC, this is decades old info that was "learned" when people started pulling emissions equipment off of older, carb'd cars back in the 70's. In their shadetree search for power, they ended up causing damage to the detuned, SMOG-compliant motors.

The motors were running leaning, but the restrictive exhaust was, again IIRC, the bandaid that held the thing together.

 

[BILTIT]

As said above, running without exhaust causes the motor to expell unburnt gases more efficiently which in turn causes the motor to run leaner=hotter temps.

This is seen alot at the dragstrip when running open headers, the carb needs to be fattened up to compensate.

 

[dyeager535]

Well designed exhaust (headers for instance) pulls exhaust out. An exhaust leak (or none) counters that function. Any exhaust restriction past the exhaust valve increases backpressure and would certainly require adding fuel when removed.

More air/fuel in, more air/fuel out.

 

[throttleissues]

I did 7 root beer cans with exhaust putty, and two rolls of muffler tape on this thing one night at work months ago. The drive home that night was GREAT, and the truck regained a lot of power.
Unfortunately, it all melted or fell off within 2 or 3 drives... And I only drove the truck once a week then...

Oh crap, I was just kiddin' ya, but that's funny!